1//===- InstrRefBasedImpl.cpp - Tracking Debug Value MIs -------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8/// \file InstrRefBasedImpl.cpp
9///
10/// This is a separate implementation of LiveDebugValues, see
11/// LiveDebugValues.cpp and VarLocBasedImpl.cpp for more information.
12///
13/// This pass propagates variable locations between basic blocks, resolving
14/// control flow conflicts between them. The problem is SSA construction, where
15/// each debug instruction assigns the *value* that a variable has, and every
16/// instruction where the variable is in scope uses that variable. The resulting
17/// map of instruction-to-value is then translated into a register (or spill)
18/// location for each variable over each instruction.
19///
20/// The primary difference from normal SSA construction is that we cannot
21/// _create_ PHI values that contain variable values. CodeGen has already
22/// completed, and we can't alter it just to make debug-info complete. Thus:
23/// we can identify function positions where we would like a PHI value for a
24/// variable, but must search the MachineFunction to see whether such a PHI is
25/// available. If no such PHI exists, the variable location must be dropped.
26///
27/// To achieve this, we perform two kinds of analysis. First, we identify
28/// every value defined by every instruction (ignoring those that only move
29/// another value), then re-compute an SSA-form representation of the
30/// MachineFunction, using value propagation to eliminate any un-necessary
31/// PHI values. This gives us a map of every value computed in the function,
32/// and its location within the register file / stack.
33///
34/// Secondly, for each variable we perform the same analysis, where each debug
35/// instruction is considered a def, and every instruction where the variable
36/// is in lexical scope as a use. Value propagation is used again to eliminate
37/// any un-necessary PHIs. This gives us a map of each variable to the value
38/// it should have in a block.
39///
40/// Once both are complete, we have two maps for each block:
41/// * Variables to the values they should have,
42/// * Values to the register / spill slot they are located in.
43/// After which we can marry-up variable values with a location, and emit
44/// DBG_VALUE instructions specifying those locations. Variable locations may
45/// be dropped in this process due to the desired variable value not being
46/// resident in any machine location, or because there is no PHI value in any
47/// location that accurately represents the desired value. The building of
48/// location lists for each block is left to DbgEntityHistoryCalculator.
49///
50/// This pass is kept efficient because the size of the first SSA problem
51/// is proportional to the working-set size of the function, which the compiler
52/// tries to keep small. (It's also proportional to the number of blocks).
53/// Additionally, we repeatedly perform the second SSA problem analysis with
54/// only the variables and blocks in a single lexical scope, exploiting their
55/// locality.
56///
57/// ### Terminology
58///
59/// A machine location is a register or spill slot, a value is something that's
60/// defined by an instruction or PHI node, while a variable value is the value
61/// assigned to a variable. A variable location is a machine location, that must
62/// contain the appropriate variable value. A value that is a PHI node is
63/// occasionally called an mphi.
64///
65/// The first SSA problem is the "machine value location" problem,
66/// because we're determining which machine locations contain which values.
67/// The "locations" are constant: what's unknown is what value they contain.
68///
69/// The second SSA problem (the one for variables) is the "variable value
70/// problem", because it's determining what values a variable has, rather than
71/// what location those values are placed in.
72///
73/// TODO:
74/// Overlapping fragments
75/// Entry values
76/// Add back DEBUG statements for debugging this
77/// Collect statistics
78///
79//===----------------------------------------------------------------------===//
80
81#include "llvm/ADT/DenseMap.h"
82#include "llvm/ADT/PostOrderIterator.h"
83#include "llvm/ADT/STLExtras.h"
84#include "llvm/ADT/SmallPtrSet.h"
85#include "llvm/ADT/SmallSet.h"
86#include "llvm/ADT/SmallVector.h"
87#include "llvm/BinaryFormat/Dwarf.h"
88#include "llvm/CodeGen/LexicalScopes.h"
89#include "llvm/CodeGen/MachineBasicBlock.h"
90#include "llvm/CodeGen/MachineDominators.h"
91#include "llvm/CodeGen/MachineFrameInfo.h"
92#include "llvm/CodeGen/MachineFunction.h"
93#include "llvm/CodeGen/MachineInstr.h"
94#include "llvm/CodeGen/MachineInstrBuilder.h"
95#include "llvm/CodeGen/MachineInstrBundle.h"
96#include "llvm/CodeGen/MachineMemOperand.h"
97#include "llvm/CodeGen/MachineOperand.h"
98#include "llvm/CodeGen/PseudoSourceValue.h"
99#include "llvm/CodeGen/TargetFrameLowering.h"
100#include "llvm/CodeGen/TargetInstrInfo.h"
101#include "llvm/CodeGen/TargetLowering.h"
102#include "llvm/CodeGen/TargetRegisterInfo.h"
103#include "llvm/CodeGen/TargetSubtargetInfo.h"
104#include "llvm/Config/llvm-config.h"
105#include "llvm/IR/DebugInfoMetadata.h"
106#include "llvm/IR/DebugLoc.h"
107#include "llvm/IR/Function.h"
108#include "llvm/MC/MCRegisterInfo.h"
109#include "llvm/Support/Casting.h"
110#include "llvm/Support/Compiler.h"
111#include "llvm/Support/Debug.h"
112#include "llvm/Support/GenericIteratedDominanceFrontier.h"
113#include "llvm/Support/TypeSize.h"
114#include "llvm/Support/raw_ostream.h"
115#include "llvm/Target/TargetMachine.h"
116#include "llvm/Transforms/Utils/SSAUpdaterImpl.h"
117#include <algorithm>
118#include <cassert>
119#include <climits>
120#include <cstdint>
121#include <functional>
122#include <queue>
123#include <tuple>
124#include <utility>
125#include <vector>
126
127#include "InstrRefBasedImpl.h"
128#include "LiveDebugValues.h"
129#include <optional>
130
131using namespace llvm;
132using namespace LiveDebugValues;
133
134// SSAUpdaterImple sets DEBUG_TYPE, change it.
135#undef DEBUG_TYPE
136#define DEBUG_TYPE "livedebugvalues"
137
138// Act more like the VarLoc implementation, by propagating some locations too
139// far and ignoring some transfers.
140static cl::opt<bool> EmulateOldLDV("emulate-old-livedebugvalues", cl::Hidden,
141 cl::desc("Act like old LiveDebugValues did"),
142 cl::init(Val: false));
143
144// Limit for the maximum number of stack slots we should track, past which we
145// will ignore any spills. InstrRefBasedLDV gathers detailed information on all
146// stack slots which leads to high memory consumption, and in some scenarios
147// (such as asan with very many locals) the working set of the function can be
148// very large, causing many spills. In these scenarios, it is very unlikely that
149// the developer has hundreds of variables live at the same time that they're
150// carefully thinking about -- instead, they probably autogenerated the code.
151// When this happens, gracefully stop tracking excess spill slots, rather than
152// consuming all the developer's memory.
153static cl::opt<unsigned>
154 StackWorkingSetLimit("livedebugvalues-max-stack-slots", cl::Hidden,
155 cl::desc("livedebugvalues-stack-ws-limit"),
156 cl::init(Val: 250));
157
158DbgOpID DbgOpID::UndefID = DbgOpID(0xffffffff);
159
160/// Tracker for converting machine value locations and variable values into
161/// variable locations (the output of LiveDebugValues), recorded as DBG_VALUEs
162/// specifying block live-in locations and transfers within blocks.
163///
164/// Operating on a per-block basis, this class takes a (pre-loaded) MLocTracker
165/// and must be initialized with the set of variable values that are live-in to
166/// the block. The caller then repeatedly calls process(). TransferTracker picks
167/// out variable locations for the live-in variable values (if there _is_ a
168/// location) and creates the corresponding DBG_VALUEs. Then, as the block is
169/// stepped through, transfers of values between machine locations are
170/// identified and if profitable, a DBG_VALUE created.
171///
172/// This is where debug use-before-defs would be resolved: a variable with an
173/// unavailable value could materialize in the middle of a block, when the
174/// value becomes available. Or, we could detect clobbers and re-specify the
175/// variable in a backup location. (XXX these are unimplemented).
176class TransferTracker {
177public:
178 const TargetInstrInfo *TII;
179 const TargetLowering *TLI;
180 /// This machine location tracker is assumed to always contain the up-to-date
181 /// value mapping for all machine locations. TransferTracker only reads
182 /// information from it. (XXX make it const?)
183 MLocTracker *MTracker;
184 MachineFunction &MF;
185 const DebugVariableMap &DVMap;
186 bool ShouldEmitDebugEntryValues;
187
188 /// Record of all changes in variable locations at a block position. Awkwardly
189 /// we allow inserting either before or after the point: MBB != nullptr
190 /// indicates it's before, otherwise after.
191 struct Transfer {
192 MachineBasicBlock::instr_iterator Pos; /// Position to insert DBG_VALUes
193 MachineBasicBlock *MBB; /// non-null if we should insert after.
194 /// Vector of DBG_VALUEs to insert. Store with their DebugVariableID so that
195 /// they can be sorted into a stable order for emission at a later time.
196 SmallVector<std::pair<DebugVariableID, MachineInstr *>, 4> Insts;
197 };
198
199 /// Stores the resolved operands (machine locations and constants) and
200 /// qualifying meta-information needed to construct a concrete DBG_VALUE-like
201 /// instruction.
202 struct ResolvedDbgValue {
203 SmallVector<ResolvedDbgOp> Ops;
204 DbgValueProperties Properties;
205
206 ResolvedDbgValue(SmallVectorImpl<ResolvedDbgOp> &Ops,
207 DbgValueProperties Properties)
208 : Ops(Ops.begin(), Ops.end()), Properties(Properties) {}
209
210 /// Returns all the LocIdx values used in this struct, in the order in which
211 /// they appear as operands in the debug value; may contain duplicates.
212 auto loc_indices() const {
213 return map_range(
214 C: make_filter_range(
215 Range: Ops, Pred: [](const ResolvedDbgOp &Op) { return !Op.IsConst; }),
216 F: [](const ResolvedDbgOp &Op) { return Op.Loc; });
217 }
218 };
219
220 /// Collection of transfers (DBG_VALUEs) to be inserted.
221 SmallVector<Transfer, 32> Transfers;
222
223 /// Local cache of what-value-is-in-what-LocIdx. Used to identify differences
224 /// between TransferTrackers view of variable locations and MLocTrackers. For
225 /// example, MLocTracker observes all clobbers, but TransferTracker lazily
226 /// does not.
227 SmallVector<ValueIDNum, 32> VarLocs;
228
229 /// Map from LocIdxes to which DebugVariables are based that location.
230 /// Mantained while stepping through the block. Not accurate if
231 /// VarLocs[Idx] != MTracker->LocIdxToIDNum[Idx].
232 DenseMap<LocIdx, SmallSet<DebugVariableID, 4>> ActiveMLocs;
233
234 /// Map from DebugVariable to it's current location and qualifying meta
235 /// information. To be used in conjunction with ActiveMLocs to construct
236 /// enough information for the DBG_VALUEs for a particular LocIdx.
237 DenseMap<DebugVariableID, ResolvedDbgValue> ActiveVLocs;
238
239 /// Temporary cache of DBG_VALUEs to be entered into the Transfers collection.
240 SmallVector<std::pair<DebugVariableID, MachineInstr *>, 4> PendingDbgValues;
241
242 /// Record of a use-before-def: created when a value that's live-in to the
243 /// current block isn't available in any machine location, but it will be
244 /// defined in this block.
245 struct UseBeforeDef {
246 /// Value of this variable, def'd in block.
247 SmallVector<DbgOp> Values;
248 /// Identity of this variable.
249 DebugVariableID VarID;
250 /// Additional variable properties.
251 DbgValueProperties Properties;
252 UseBeforeDef(ArrayRef<DbgOp> Values, DebugVariableID VarID,
253 const DbgValueProperties &Properties)
254 : Values(Values), VarID(VarID), Properties(Properties) {}
255 };
256
257 /// Map from instruction index (within the block) to the set of UseBeforeDefs
258 /// that become defined at that instruction.
259 DenseMap<unsigned, SmallVector<UseBeforeDef, 1>> UseBeforeDefs;
260
261 /// The set of variables that are in UseBeforeDefs and can become a location
262 /// once the relevant value is defined. An element being erased from this
263 /// collection prevents the use-before-def materializing.
264 DenseSet<DebugVariableID> UseBeforeDefVariables;
265
266 const TargetRegisterInfo &TRI;
267 const BitVector &CalleeSavedRegs;
268
269 TransferTracker(const TargetInstrInfo *TII, MLocTracker *MTracker,
270 MachineFunction &MF, const DebugVariableMap &DVMap,
271 const TargetRegisterInfo &TRI,
272 const BitVector &CalleeSavedRegs,
273 bool ShouldEmitDebugEntryValues)
274 : TII(TII), MTracker(MTracker), MF(MF), DVMap(DVMap), TRI(TRI),
275 CalleeSavedRegs(CalleeSavedRegs) {
276 TLI = MF.getSubtarget().getTargetLowering();
277 this->ShouldEmitDebugEntryValues = ShouldEmitDebugEntryValues;
278 }
279
280 bool isCalleeSaved(LocIdx L) const {
281 unsigned Reg = MTracker->LocIdxToLocID[L];
282 if (Reg >= MTracker->NumRegs)
283 return false;
284 for (MCRegAliasIterator RAI(Reg, &TRI, true); RAI.isValid(); ++RAI)
285 if (CalleeSavedRegs.test(Idx: (*RAI).id()))
286 return true;
287 return false;
288 };
289
290 // An estimate of the expected lifespan of values at a machine location, with
291 // a greater value corresponding to a longer expected lifespan, i.e. spill
292 // slots generally live longer than callee-saved registers which generally
293 // live longer than non-callee-saved registers. The minimum value of 0
294 // corresponds to an illegal location that cannot have a "lifespan" at all.
295 enum class LocationQuality : unsigned char {
296 Illegal = 0,
297 Register,
298 CalleeSavedRegister,
299 SpillSlot,
300 Best = SpillSlot
301 };
302
303 class LocationAndQuality {
304 unsigned Location : 24;
305 unsigned Quality : 8;
306
307 public:
308 LocationAndQuality() : Location(0), Quality(0) {}
309 LocationAndQuality(LocIdx L, LocationQuality Q)
310 : Location(L.asU64()), Quality(static_cast<unsigned>(Q)) {}
311 LocIdx getLoc() const {
312 if (!Quality)
313 return LocIdx::MakeIllegalLoc();
314 return LocIdx(Location);
315 }
316 LocationQuality getQuality() const { return LocationQuality(Quality); }
317 bool isIllegal() const { return !Quality; }
318 bool isBest() const { return getQuality() == LocationQuality::Best; }
319 };
320
321 using ValueLocPair = std::pair<ValueIDNum, LocationAndQuality>;
322
323 static inline bool ValueToLocSort(const ValueLocPair &A,
324 const ValueLocPair &B) {
325 return A.first < B.first;
326 };
327
328 // Returns the LocationQuality for the location L iff the quality of L is
329 // is strictly greater than the provided minimum quality.
330 std::optional<LocationQuality>
331 getLocQualityIfBetter(LocIdx L, LocationQuality Min) const {
332 if (L.isIllegal())
333 return std::nullopt;
334 if (Min >= LocationQuality::SpillSlot)
335 return std::nullopt;
336 if (MTracker->isSpill(Idx: L))
337 return LocationQuality::SpillSlot;
338 if (Min >= LocationQuality::CalleeSavedRegister)
339 return std::nullopt;
340 if (isCalleeSaved(L))
341 return LocationQuality::CalleeSavedRegister;
342 if (Min >= LocationQuality::Register)
343 return std::nullopt;
344 return LocationQuality::Register;
345 }
346
347 /// For a variable \p Var with the live-in value \p Value, attempts to resolve
348 /// the DbgValue to a concrete DBG_VALUE, emitting that value and loading the
349 /// tracking information to track Var throughout the block.
350 /// \p ValueToLoc is a map containing the best known location for every
351 /// ValueIDNum that Value may use.
352 /// \p MBB is the basic block that we are loading the live-in value for.
353 /// \p DbgOpStore is the map containing the DbgOpID->DbgOp mapping needed to
354 /// determine the values used by Value.
355 void loadVarInloc(MachineBasicBlock &MBB, DbgOpIDMap &DbgOpStore,
356 const SmallVectorImpl<ValueLocPair> &ValueToLoc,
357 DebugVariableID VarID, DbgValue Value) {
358 SmallVector<DbgOp> DbgOps;
359 SmallVector<ResolvedDbgOp> ResolvedDbgOps;
360 bool IsValueValid = true;
361 unsigned LastUseBeforeDef = 0;
362 bool DbgLocAvailableAndIsEntryVal = false;
363
364 // If every value used by the incoming DbgValue is available at block
365 // entry, ResolvedDbgOps will contain the machine locations/constants for
366 // those values and will be used to emit a debug location.
367 // If one or more values are not yet available, but will all be defined in
368 // this block, then LastUseBeforeDef will track the instruction index in
369 // this BB at which the last of those values is defined, DbgOps will
370 // contain the values that we will emit when we reach that instruction.
371 // If one or more values are undef or not available throughout this block,
372 // and we can't recover as an entry value, we set IsValueValid=false and
373 // skip this variable.
374 for (DbgOpID ID : Value.getDbgOpIDs()) {
375 DbgOp Op = DbgOpStore.find(ID);
376 DbgOps.push_back(Elt: Op);
377 if (ID.isUndef()) {
378 IsValueValid = false;
379 break;
380 }
381 if (ID.isConst()) {
382 ResolvedDbgOps.push_back(Elt: Op.MO);
383 continue;
384 }
385
386 // Search for the desired ValueIDNum, to examine the best location found
387 // for it. Use an empty ValueLocPair to search for an entry in ValueToLoc.
388 const ValueIDNum &Num = Op.ID;
389 ValueLocPair Probe(Num, LocationAndQuality());
390 auto ValuesPreferredLoc =
391 llvm::lower_bound(Range: ValueToLoc, Value&: Probe, C: ValueToLocSort);
392
393 // There must be a legitimate entry found for Num.
394 assert(ValuesPreferredLoc != ValueToLoc.end() &&
395 ValuesPreferredLoc->first == Num);
396
397 if (ValuesPreferredLoc->second.isIllegal()) {
398 // If it's a def that occurs in this block, register it as a
399 // use-before-def to be resolved as we step through the block.
400 // Continue processing values so that we add any other UseBeforeDef
401 // entries needed for later.
402 if (Num.getBlock() == (unsigned)MBB.getNumber() && !Num.isPHI()) {
403 LastUseBeforeDef = std::max(a: LastUseBeforeDef,
404 b: static_cast<unsigned>(Num.getInst()));
405 continue;
406 }
407 recoverAsEntryValue(VarID, Prop: Value.Properties, Num);
408 IsValueValid = false;
409 break;
410 }
411
412 // Defer modifying ActiveVLocs until after we've confirmed we have a
413 // live range.
414 LocIdx M = ValuesPreferredLoc->second.getLoc();
415 ResolvedDbgOps.push_back(Elt: M);
416 if (Value.Properties.DIExpr->isEntryValue())
417 DbgLocAvailableAndIsEntryVal = true;
418 }
419
420 // If we cannot produce a valid value for the LiveIn value within this
421 // block, skip this variable.
422 if (!IsValueValid)
423 return;
424
425 // Add UseBeforeDef entry for the last value to be defined in this block.
426 if (LastUseBeforeDef) {
427 addUseBeforeDef(VarID, Properties: Value.Properties, DbgOps, Inst: LastUseBeforeDef);
428 return;
429 }
430
431 auto &[Var, DILoc] = DVMap.lookupDVID(ID: VarID);
432 PendingDbgValues.push_back(
433 Elt: std::make_pair(x&: VarID, y: &*MTracker->emitLoc(DbgOps: ResolvedDbgOps, Var, DILoc,
434 Properties: Value.Properties)));
435
436 // If the location is available at block entry and is an entry value, skip
437 // tracking and recording thr transfer.
438 if (DbgLocAvailableAndIsEntryVal)
439 return;
440
441 // The LiveIn value is available at block entry, begin tracking and record
442 // the transfer.
443 for (const ResolvedDbgOp &Op : ResolvedDbgOps)
444 if (!Op.IsConst)
445 ActiveMLocs[Op.Loc].insert(V: VarID);
446 auto NewValue = ResolvedDbgValue{ResolvedDbgOps, Value.Properties};
447 auto Result = ActiveVLocs.insert(KV: std::make_pair(x&: VarID, y&: NewValue));
448 if (!Result.second)
449 Result.first->second = NewValue;
450 }
451
452 /// Load object with live-in variable values. \p mlocs contains the live-in
453 /// values in each machine location, while \p vlocs the live-in variable
454 /// values. This method picks variable locations for the live-in variables,
455 /// creates DBG_VALUEs and puts them in #Transfers, then prepares the other
456 /// object fields to track variable locations as we step through the block.
457 /// FIXME: could just examine mloctracker instead of passing in \p mlocs?
458 void
459 loadInlocs(MachineBasicBlock &MBB, ValueTable &MLocs, DbgOpIDMap &DbgOpStore,
460 const SmallVectorImpl<std::pair<DebugVariableID, DbgValue>> &VLocs,
461 unsigned NumLocs) {
462 ActiveMLocs.clear();
463 ActiveVLocs.clear();
464 VarLocs.clear();
465 VarLocs.reserve(N: NumLocs);
466 UseBeforeDefs.clear();
467 UseBeforeDefVariables.clear();
468
469 // Mapping of the preferred locations for each value. Collected into this
470 // vector then sorted for easy searching.
471 SmallVector<ValueLocPair, 16> ValueToLoc;
472
473 // Initialized the preferred-location map with illegal locations, to be
474 // filled in later.
475 for (const auto &VLoc : VLocs)
476 if (VLoc.second.Kind == DbgValue::Def)
477 for (DbgOpID OpID : VLoc.second.getDbgOpIDs())
478 if (!OpID.ID.IsConst)
479 ValueToLoc.push_back(
480 Elt: {DbgOpStore.find(ID: OpID).ID, LocationAndQuality()});
481
482 llvm::sort(C&: ValueToLoc, Comp: ValueToLocSort);
483 ActiveMLocs.reserve(NumEntries: VLocs.size());
484 ActiveVLocs.reserve(NumEntries: VLocs.size());
485
486 // Produce a map of value numbers to the current machine locs they live
487 // in. When emulating VarLocBasedImpl, there should only be one
488 // location; when not, we get to pick.
489 for (auto Location : MTracker->locations()) {
490 LocIdx Idx = Location.Idx;
491 ValueIDNum &VNum = MLocs[Idx.asU64()];
492 if (VNum == ValueIDNum::EmptyValue)
493 continue;
494 VarLocs.push_back(Elt: VNum);
495
496 // Is there a variable that wants a location for this value? If not, skip.
497 ValueLocPair Probe(VNum, LocationAndQuality());
498 auto VIt = llvm::lower_bound(Range&: ValueToLoc, Value&: Probe, C: ValueToLocSort);
499 if (VIt == ValueToLoc.end() || VIt->first != VNum)
500 continue;
501
502 auto &Previous = VIt->second;
503 // If this is the first location with that value, pick it. Otherwise,
504 // consider whether it's a "longer term" location.
505 std::optional<LocationQuality> ReplacementQuality =
506 getLocQualityIfBetter(L: Idx, Min: Previous.getQuality());
507 if (ReplacementQuality)
508 Previous = LocationAndQuality(Idx, *ReplacementQuality);
509 }
510
511 // Now map variables to their picked LocIdxes.
512 for (const auto &Var : VLocs) {
513 loadVarInloc(MBB, DbgOpStore, ValueToLoc, VarID: Var.first, Value: Var.second);
514 }
515 flushDbgValues(Pos: MBB.begin(), MBB: &MBB);
516 }
517
518 /// Record that \p Var has value \p ID, a value that becomes available
519 /// later in the function.
520 void addUseBeforeDef(DebugVariableID VarID,
521 const DbgValueProperties &Properties,
522 const SmallVectorImpl<DbgOp> &DbgOps, unsigned Inst) {
523 UseBeforeDefs[Inst].emplace_back(Args: DbgOps, Args&: VarID, Args: Properties);
524 UseBeforeDefVariables.insert(V: VarID);
525 }
526
527 /// After the instruction at index \p Inst and position \p pos has been
528 /// processed, check whether it defines a variable value in a use-before-def.
529 /// If so, and the variable value hasn't changed since the start of the
530 /// block, create a DBG_VALUE.
531 void checkInstForNewValues(unsigned Inst, MachineBasicBlock::iterator pos) {
532 auto MIt = UseBeforeDefs.find(Val: Inst);
533 if (MIt == UseBeforeDefs.end())
534 return;
535
536 // Map of values to the locations that store them for every value used by
537 // the variables that may have become available.
538 SmallDenseMap<ValueIDNum, LocationAndQuality> ValueToLoc;
539
540 // Populate ValueToLoc with illegal default mappings for every value used by
541 // any UseBeforeDef variables for this instruction.
542 for (auto &Use : MIt->second) {
543 if (!UseBeforeDefVariables.count(V: Use.VarID))
544 continue;
545
546 for (DbgOp &Op : Use.Values) {
547 assert(!Op.isUndef() && "UseBeforeDef erroneously created for a "
548 "DbgValue with undef values.");
549 if (Op.IsConst)
550 continue;
551
552 ValueToLoc.insert(KV: {Op.ID, LocationAndQuality()});
553 }
554 }
555
556 // Exit early if we have no DbgValues to produce.
557 if (ValueToLoc.empty())
558 return;
559
560 // Determine the best location for each desired value.
561 for (auto Location : MTracker->locations()) {
562 LocIdx Idx = Location.Idx;
563 ValueIDNum &LocValueID = Location.Value;
564
565 // Is there a variable that wants a location for this value? If not, skip.
566 auto VIt = ValueToLoc.find(Val: LocValueID);
567 if (VIt == ValueToLoc.end())
568 continue;
569
570 auto &Previous = VIt->second;
571 // If this is the first location with that value, pick it. Otherwise,
572 // consider whether it's a "longer term" location.
573 std::optional<LocationQuality> ReplacementQuality =
574 getLocQualityIfBetter(L: Idx, Min: Previous.getQuality());
575 if (ReplacementQuality)
576 Previous = LocationAndQuality(Idx, *ReplacementQuality);
577 }
578
579 // Using the map of values to locations, produce a final set of values for
580 // this variable.
581 for (auto &Use : MIt->second) {
582 if (!UseBeforeDefVariables.count(V: Use.VarID))
583 continue;
584
585 SmallVector<ResolvedDbgOp> DbgOps;
586
587 for (DbgOp &Op : Use.Values) {
588 if (Op.IsConst) {
589 DbgOps.push_back(Elt: Op.MO);
590 continue;
591 }
592 LocIdx NewLoc = ValueToLoc.find(Val: Op.ID)->second.getLoc();
593 if (NewLoc.isIllegal())
594 break;
595 DbgOps.push_back(Elt: NewLoc);
596 }
597
598 // If at least one value used by this debug value is no longer available,
599 // i.e. one of the values was killed before we finished defining all of
600 // the values used by this variable, discard.
601 if (DbgOps.size() != Use.Values.size())
602 continue;
603
604 // Otherwise, we're good to go.
605 auto &[Var, DILoc] = DVMap.lookupDVID(ID: Use.VarID);
606 PendingDbgValues.push_back(Elt: std::make_pair(
607 x&: Use.VarID, y: MTracker->emitLoc(DbgOps, Var, DILoc, Properties: Use.Properties)));
608 }
609 flushDbgValues(Pos: pos, MBB: nullptr);
610 }
611
612 /// Helper to move created DBG_VALUEs into Transfers collection.
613 void flushDbgValues(MachineBasicBlock::iterator Pos, MachineBasicBlock *MBB) {
614 if (PendingDbgValues.size() == 0)
615 return;
616
617 // Pick out the instruction start position.
618 MachineBasicBlock::instr_iterator BundleStart;
619 if (MBB && Pos == MBB->begin())
620 BundleStart = MBB->instr_begin();
621 else
622 BundleStart = getBundleStart(I: Pos->getIterator());
623
624 Transfers.push_back(Elt: {.Pos: BundleStart, .MBB: MBB, .Insts: PendingDbgValues});
625 PendingDbgValues.clear();
626 }
627
628 bool isEntryValueVariable(const DebugVariable &Var,
629 const DIExpression *Expr) const {
630 if (!Var.getVariable()->isParameter())
631 return false;
632
633 if (Var.getInlinedAt())
634 return false;
635
636 if (Expr->getNumElements() > 0 && !Expr->isDeref())
637 return false;
638
639 return true;
640 }
641
642 bool isEntryValueValue(const ValueIDNum &Val) const {
643 // Must be in entry block (block number zero), and be a PHI / live-in value.
644 if (Val.getBlock() || !Val.isPHI())
645 return false;
646
647 // Entry values must enter in a register.
648 if (MTracker->isSpill(Idx: Val.getLoc()))
649 return false;
650
651 Register SP = TLI->getStackPointerRegisterToSaveRestore();
652 Register FP = TRI.getFrameRegister(MF);
653 Register Reg = MTracker->LocIdxToLocID[Val.getLoc()];
654 return Reg != SP && Reg != FP;
655 }
656
657 bool recoverAsEntryValue(DebugVariableID VarID,
658 const DbgValueProperties &Prop,
659 const ValueIDNum &Num) {
660 // Is this variable location a candidate to be an entry value. First,
661 // should we be trying this at all?
662 if (!ShouldEmitDebugEntryValues)
663 return false;
664
665 const DIExpression *DIExpr = Prop.DIExpr;
666
667 // We don't currently emit entry values for DBG_VALUE_LISTs.
668 if (Prop.IsVariadic) {
669 // If this debug value can be converted to be non-variadic, then do so;
670 // otherwise give up.
671 auto NonVariadicExpression =
672 DIExpression::convertToNonVariadicExpression(Expr: DIExpr);
673 if (!NonVariadicExpression)
674 return false;
675 DIExpr = *NonVariadicExpression;
676 }
677
678 auto &[Var, DILoc] = DVMap.lookupDVID(ID: VarID);
679
680 // If the expression is a DW_OP_entry_value, emit the variable location
681 // as-is.
682 if (DIExpr->isEntryValue()) {
683 Register Reg = MTracker->LocIdxToLocID[Num.getLoc()];
684 MachineOperand MO = MachineOperand::CreateReg(Reg, isDef: false);
685 PendingDbgValues.push_back(Elt: std::make_pair(
686 x&: VarID, y: &*emitMOLoc(MO, Var, Properties: {DIExpr, Prop.Indirect, false})));
687 return true;
688 }
689
690 // Is the variable appropriate for entry values (i.e., is a parameter).
691 if (!isEntryValueVariable(Var, Expr: DIExpr))
692 return false;
693
694 // Is the value assigned to this variable still the entry value?
695 if (!isEntryValueValue(Val: Num))
696 return false;
697
698 // Emit a variable location using an entry value expression.
699 DIExpression *NewExpr =
700 DIExpression::prepend(Expr: DIExpr, Flags: DIExpression::EntryValue);
701 Register Reg = MTracker->LocIdxToLocID[Num.getLoc()];
702 MachineOperand MO = MachineOperand::CreateReg(Reg, isDef: false);
703 PendingDbgValues.push_back(Elt: std::make_pair(
704 x&: VarID, y: &*emitMOLoc(MO, Var, Properties: {NewExpr, Prop.Indirect, false})));
705 return true;
706 }
707
708 /// Change a variable value after encountering a DBG_VALUE inside a block.
709 void redefVar(const MachineInstr &MI) {
710 DebugVariable Var(MI.getDebugVariable(), MI.getDebugExpression(),
711 MI.getDebugLoc()->getInlinedAt());
712 DbgValueProperties Properties(MI);
713 DebugVariableID VarID = DVMap.getDVID(Var);
714
715 // Ignore non-register locations, we don't transfer those.
716 if (MI.isUndefDebugValue() || MI.getDebugExpression()->isEntryValue() ||
717 all_of(Range: MI.debug_operands(),
718 P: [](const MachineOperand &MO) { return !MO.isReg(); })) {
719 auto It = ActiveVLocs.find(Val: VarID);
720 if (It != ActiveVLocs.end()) {
721 for (LocIdx Loc : It->second.loc_indices())
722 ActiveMLocs[Loc].erase(V: VarID);
723 ActiveVLocs.erase(I: It);
724 }
725 // Any use-before-defs no longer apply.
726 UseBeforeDefVariables.erase(V: VarID);
727 return;
728 }
729
730 SmallVector<ResolvedDbgOp> NewLocs;
731 for (const MachineOperand &MO : MI.debug_operands()) {
732 if (MO.isReg()) {
733 // Any undef regs have already been filtered out above.
734 Register Reg = MO.getReg();
735 LocIdx NewLoc = MTracker->getRegMLoc(R: Reg);
736 NewLocs.push_back(Elt: NewLoc);
737 } else {
738 NewLocs.push_back(Elt: MO);
739 }
740 }
741
742 redefVar(MI, Properties, NewLocs);
743 }
744
745 /// Handle a change in variable location within a block. Terminate the
746 /// variables current location, and record the value it now refers to, so
747 /// that we can detect location transfers later on.
748 void redefVar(const MachineInstr &MI, const DbgValueProperties &Properties,
749 SmallVectorImpl<ResolvedDbgOp> &NewLocs) {
750 DebugVariable Var(MI.getDebugVariable(), MI.getDebugExpression(),
751 MI.getDebugLoc()->getInlinedAt());
752 DebugVariableID VarID = DVMap.getDVID(Var);
753 // Any use-before-defs no longer apply.
754 UseBeforeDefVariables.erase(V: VarID);
755
756 // Erase any previous location.
757 auto It = ActiveVLocs.find(Val: VarID);
758 if (It != ActiveVLocs.end()) {
759 for (LocIdx Loc : It->second.loc_indices())
760 ActiveMLocs[Loc].erase(V: VarID);
761 }
762
763 // If there _is_ no new location, all we had to do was erase.
764 if (NewLocs.empty()) {
765 if (It != ActiveVLocs.end())
766 ActiveVLocs.erase(I: It);
767 return;
768 }
769
770 SmallVector<std::pair<LocIdx, DebugVariableID>> LostMLocs;
771 for (ResolvedDbgOp &Op : NewLocs) {
772 if (Op.IsConst)
773 continue;
774
775 LocIdx NewLoc = Op.Loc;
776
777 // Check whether our local copy of values-by-location in #VarLocs is out
778 // of date. Wipe old tracking data for the location if it's been clobbered
779 // in the meantime.
780 if (MTracker->readMLoc(L: NewLoc) != VarLocs[NewLoc.asU64()]) {
781 for (const auto &P : ActiveMLocs[NewLoc]) {
782 auto LostVLocIt = ActiveVLocs.find(Val: P);
783 if (LostVLocIt != ActiveVLocs.end()) {
784 for (LocIdx Loc : LostVLocIt->second.loc_indices()) {
785 // Every active variable mapping for NewLoc will be cleared, no
786 // need to track individual variables.
787 if (Loc == NewLoc)
788 continue;
789 LostMLocs.emplace_back(Args&: Loc, Args: P);
790 }
791 }
792 ActiveVLocs.erase(Val: P);
793 }
794 for (const auto &LostMLoc : LostMLocs)
795 ActiveMLocs[LostMLoc.first].erase(V: LostMLoc.second);
796 LostMLocs.clear();
797 It = ActiveVLocs.find(Val: VarID);
798 ActiveMLocs[NewLoc.asU64()].clear();
799 VarLocs[NewLoc.asU64()] = MTracker->readMLoc(L: NewLoc);
800 }
801
802 ActiveMLocs[NewLoc].insert(V: VarID);
803 }
804
805 if (It == ActiveVLocs.end()) {
806 ActiveVLocs.insert(
807 KV: std::make_pair(x&: VarID, y: ResolvedDbgValue(NewLocs, Properties)));
808 } else {
809 It->second.Ops.assign(RHS: NewLocs);
810 It->second.Properties = Properties;
811 }
812 }
813
814 /// Account for a location \p mloc being clobbered. Examine the variable
815 /// locations that will be terminated: and try to recover them by using
816 /// another location. Optionally, given \p MakeUndef, emit a DBG_VALUE to
817 /// explicitly terminate a location if it can't be recovered.
818 void clobberMloc(LocIdx MLoc, MachineBasicBlock::iterator Pos,
819 bool MakeUndef = true) {
820 auto ActiveMLocIt = ActiveMLocs.find(Val: MLoc);
821 if (ActiveMLocIt == ActiveMLocs.end())
822 return;
823
824 // What was the old variable value?
825 ValueIDNum OldValue = VarLocs[MLoc.asU64()];
826 clobberMloc(MLoc, OldValue, Pos, MakeUndef);
827 }
828 /// Overload that takes an explicit value \p OldValue for when the value in
829 /// \p MLoc has changed and the TransferTracker's locations have not been
830 /// updated yet.
831 void clobberMloc(LocIdx MLoc, ValueIDNum OldValue,
832 MachineBasicBlock::iterator Pos, bool MakeUndef = true) {
833 auto ActiveMLocIt = ActiveMLocs.find(Val: MLoc);
834 if (ActiveMLocIt == ActiveMLocs.end())
835 return;
836
837 VarLocs[MLoc.asU64()] = ValueIDNum::EmptyValue;
838
839 // Examine the remaining variable locations: if we can find the same value
840 // again, we can recover the location.
841 std::optional<LocIdx> NewLoc;
842 for (auto Loc : MTracker->locations())
843 if (Loc.Value == OldValue)
844 NewLoc = Loc.Idx;
845
846 // If there is no location, and we weren't asked to make the variable
847 // explicitly undef, then stop here.
848 if (!NewLoc && !MakeUndef) {
849 // Try and recover a few more locations with entry values.
850 for (DebugVariableID VarID : ActiveMLocIt->second) {
851 auto &Prop = ActiveVLocs.find(Val: VarID)->second.Properties;
852 recoverAsEntryValue(VarID, Prop, Num: OldValue);
853 }
854 flushDbgValues(Pos, MBB: nullptr);
855 return;
856 }
857
858 // Examine all the variables based on this location.
859 DenseSet<DebugVariableID> NewMLocs;
860 // If no new location has been found, every variable that depends on this
861 // MLoc is dead, so end their existing MLoc->Var mappings as well.
862 SmallVector<std::pair<LocIdx, DebugVariableID>> LostMLocs;
863 for (DebugVariableID VarID : ActiveMLocIt->second) {
864 auto ActiveVLocIt = ActiveVLocs.find(Val: VarID);
865 // Re-state the variable location: if there's no replacement then NewLoc
866 // is std::nullopt and a $noreg DBG_VALUE will be created. Otherwise, a
867 // DBG_VALUE identifying the alternative location will be emitted.
868 const DbgValueProperties &Properties = ActiveVLocIt->second.Properties;
869
870 // Produce the new list of debug ops - an empty list if no new location
871 // was found, or the existing list with the substitution MLoc -> NewLoc
872 // otherwise.
873 SmallVector<ResolvedDbgOp> DbgOps;
874 if (NewLoc) {
875 ResolvedDbgOp OldOp(MLoc);
876 ResolvedDbgOp NewOp(*NewLoc);
877 // Insert illegal ops to overwrite afterwards.
878 DbgOps.insert(I: DbgOps.begin(), NumToInsert: ActiveVLocIt->second.Ops.size(),
879 Elt: ResolvedDbgOp(LocIdx::MakeIllegalLoc()));
880 replace_copy(Range&: ActiveVLocIt->second.Ops, Out: DbgOps.begin(), OldValue: OldOp, NewValue: NewOp);
881 }
882
883 auto &[Var, DILoc] = DVMap.lookupDVID(ID: VarID);
884 PendingDbgValues.push_back(Elt: std::make_pair(
885 x&: VarID, y: &*MTracker->emitLoc(DbgOps, Var, DILoc, Properties)));
886
887 // Update machine locations <=> variable locations maps. Defer updating
888 // ActiveMLocs to avoid invalidating the ActiveMLocIt iterator.
889 if (!NewLoc) {
890 for (LocIdx Loc : ActiveVLocIt->second.loc_indices()) {
891 if (Loc != MLoc)
892 LostMLocs.emplace_back(Args&: Loc, Args&: VarID);
893 }
894 ActiveVLocs.erase(I: ActiveVLocIt);
895 } else {
896 ActiveVLocIt->second.Ops = DbgOps;
897 NewMLocs.insert(V: VarID);
898 }
899 }
900
901 // Remove variables from ActiveMLocs if they no longer use any other MLocs
902 // due to being killed by this clobber.
903 for (auto &LocVarIt : LostMLocs) {
904 auto LostMLocIt = ActiveMLocs.find(Val: LocVarIt.first);
905 assert(LostMLocIt != ActiveMLocs.end() &&
906 "Variable was using this MLoc, but ActiveMLocs[MLoc] has no "
907 "entries?");
908 LostMLocIt->second.erase(V: LocVarIt.second);
909 }
910
911 // We lazily track what locations have which values; if we've found a new
912 // location for the clobbered value, remember it.
913 if (NewLoc)
914 VarLocs[NewLoc->asU64()] = OldValue;
915
916 flushDbgValues(Pos, MBB: nullptr);
917
918 // Commit ActiveMLoc changes.
919 ActiveMLocIt->second.clear();
920 if (!NewMLocs.empty())
921 ActiveMLocs[*NewLoc].insert_range(R&: NewMLocs);
922 }
923
924 /// Transfer variables based on \p Src to be based on \p Dst. This handles
925 /// both register copies as well as spills and restores. Creates DBG_VALUEs
926 /// describing the movement.
927 void transferMlocs(LocIdx Src, LocIdx Dst, MachineBasicBlock::iterator Pos) {
928 // Does Src still contain the value num we expect? If not, it's been
929 // clobbered in the meantime, and our variable locations are stale.
930 if (VarLocs[Src.asU64()] != MTracker->readMLoc(L: Src))
931 return;
932
933 // assert(ActiveMLocs[Dst].size() == 0);
934 //^^^ Legitimate scenario on account of un-clobbered slot being assigned to?
935
936 // Move set of active variables from one location to another.
937 auto MovingVars = ActiveMLocs[Src];
938 ActiveMLocs[Dst].insert_range(R&: MovingVars);
939 VarLocs[Dst.asU64()] = VarLocs[Src.asU64()];
940
941 // For each variable based on Src; create a location at Dst.
942 ResolvedDbgOp SrcOp(Src);
943 ResolvedDbgOp DstOp(Dst);
944 for (DebugVariableID VarID : MovingVars) {
945 auto ActiveVLocIt = ActiveVLocs.find(Val: VarID);
946 assert(ActiveVLocIt != ActiveVLocs.end());
947
948 // Update all instances of Src in the variable's tracked values to Dst.
949 llvm::replace(Range&: ActiveVLocIt->second.Ops, OldValue: SrcOp, NewValue: DstOp);
950
951 auto &[Var, DILoc] = DVMap.lookupDVID(ID: VarID);
952 MachineInstr *MI = MTracker->emitLoc(DbgOps: ActiveVLocIt->second.Ops, Var, DILoc,
953 Properties: ActiveVLocIt->second.Properties);
954 PendingDbgValues.push_back(Elt: std::make_pair(x&: VarID, y&: MI));
955 }
956 ActiveMLocs[Src].clear();
957 flushDbgValues(Pos, MBB: nullptr);
958
959 // XXX XXX XXX "pretend to be old LDV" means dropping all tracking data
960 // about the old location.
961 if (EmulateOldLDV)
962 VarLocs[Src.asU64()] = ValueIDNum::EmptyValue;
963 }
964
965 MachineInstrBuilder emitMOLoc(const MachineOperand &MO,
966 const DebugVariable &Var,
967 const DbgValueProperties &Properties) {
968 DebugLoc DL = DILocation::get(Context&: Var.getVariable()->getContext(), Line: 0, Column: 0,
969 Scope: Var.getVariable()->getScope(),
970 InlinedAt: const_cast<DILocation *>(Var.getInlinedAt()));
971 auto MIB = BuildMI(MF, MIMD: DL, MCID: TII->get(Opcode: TargetOpcode::DBG_VALUE));
972 MIB.add(MO);
973 if (Properties.Indirect)
974 MIB.addImm(Val: 0);
975 else
976 MIB.addReg(RegNo: 0);
977 MIB.addMetadata(MD: Var.getVariable());
978 MIB.addMetadata(MD: Properties.DIExpr);
979 return MIB;
980 }
981};
982
983//===----------------------------------------------------------------------===//
984// Implementation
985//===----------------------------------------------------------------------===//
986
987ValueIDNum ValueIDNum::EmptyValue = {UINT_MAX, UINT_MAX, UINT_MAX};
988ValueIDNum ValueIDNum::TombstoneValue = {UINT_MAX, UINT_MAX, UINT_MAX - 1};
989
990#ifndef NDEBUG
991void ResolvedDbgOp::dump(const MLocTracker *MTrack) const {
992 if (IsConst) {
993 dbgs() << MO;
994 } else {
995 dbgs() << MTrack->LocIdxToName(Loc);
996 }
997}
998void DbgOp::dump(const MLocTracker *MTrack) const {
999 if (IsConst) {
1000 dbgs() << MO;
1001 } else if (!isUndef()) {
1002 dbgs() << MTrack->IDAsString(ID);
1003 }
1004}
1005void DbgOpID::dump(const MLocTracker *MTrack, const DbgOpIDMap *OpStore) const {
1006 if (!OpStore) {
1007 dbgs() << "ID(" << asU32() << ")";
1008 } else {
1009 OpStore->find(*this).dump(MTrack);
1010 }
1011}
1012void DbgValue::dump(const MLocTracker *MTrack,
1013 const DbgOpIDMap *OpStore) const {
1014 if (Kind == NoVal) {
1015 dbgs() << "NoVal(" << BlockNo << ")";
1016 } else if (Kind == VPHI || Kind == Def) {
1017 if (Kind == VPHI)
1018 dbgs() << "VPHI(" << BlockNo << ",";
1019 else
1020 dbgs() << "Def(";
1021 for (unsigned Idx = 0; Idx < getDbgOpIDs().size(); ++Idx) {
1022 getDbgOpID(Idx).dump(MTrack, OpStore);
1023 if (Idx != 0)
1024 dbgs() << ",";
1025 }
1026 dbgs() << ")";
1027 }
1028 if (Properties.Indirect)
1029 dbgs() << " indir";
1030 if (Properties.DIExpr)
1031 dbgs() << " " << *Properties.DIExpr;
1032}
1033#endif
1034
1035MLocTracker::MLocTracker(MachineFunction &MF, const TargetInstrInfo &TII,
1036 const TargetRegisterInfo &TRI,
1037 const TargetLowering &TLI)
1038 : MF(MF), TII(TII), TRI(TRI), TLI(TLI),
1039 LocIdxToIDNum(ValueIDNum::EmptyValue), LocIdxToLocID(0) {
1040 NumRegs = TRI.getNumRegs();
1041 reset();
1042 LocIDToLocIdx.resize(new_size: NumRegs, x: LocIdx::MakeIllegalLoc());
1043 assert(NumRegs < (1u << NUM_LOC_BITS)); // Detect bit packing failure
1044
1045 // Always track SP. This avoids the implicit clobbering caused by regmasks
1046 // from affectings its values. (LiveDebugValues disbelieves calls and
1047 // regmasks that claim to clobber SP).
1048 Register SP = TLI.getStackPointerRegisterToSaveRestore();
1049 if (SP) {
1050 unsigned ID = getLocID(Reg: SP);
1051 (void)lookupOrTrackRegister(ID);
1052
1053 for (MCRegAliasIterator RAI(SP, &TRI, true); RAI.isValid(); ++RAI)
1054 SPAliases.insert(V: *RAI);
1055 }
1056
1057 // Build some common stack positions -- full registers being spilt to the
1058 // stack.
1059 StackSlotIdxes.insert(KV: {{8, 0}, 0});
1060 StackSlotIdxes.insert(KV: {{16, 0}, 1});
1061 StackSlotIdxes.insert(KV: {{32, 0}, 2});
1062 StackSlotIdxes.insert(KV: {{64, 0}, 3});
1063 StackSlotIdxes.insert(KV: {{128, 0}, 4});
1064 StackSlotIdxes.insert(KV: {{256, 0}, 5});
1065 StackSlotIdxes.insert(KV: {{512, 0}, 6});
1066
1067 // Traverse all the subregister idxes, and ensure there's an index for them.
1068 // Duplicates are no problem: we're interested in their position in the
1069 // stack slot, we don't want to type the slot.
1070 for (unsigned int I = 1; I < TRI.getNumSubRegIndices(); ++I) {
1071 unsigned Size = TRI.getSubRegIdxSize(Idx: I);
1072 unsigned Offs = TRI.getSubRegIdxOffset(Idx: I);
1073 unsigned Idx = StackSlotIdxes.size();
1074
1075 // Some subregs have -1, -2 and so forth fed into their fields, to mean
1076 // special backend things. Ignore those.
1077 if (Size > 60000 || Offs > 60000)
1078 continue;
1079
1080 StackSlotIdxes.insert(KV: {{Size, Offs}, Idx});
1081 }
1082
1083 // There may also be strange register class sizes (think x86 fp80s).
1084 for (const TargetRegisterClass *RC : TRI.regclasses()) {
1085 unsigned Size = TRI.getRegSizeInBits(RC: *RC);
1086
1087 // We might see special reserved values as sizes, and classes for other
1088 // stuff the machine tries to model. If it's more than 512 bits, then it
1089 // is very unlikely to be a register than can be spilt.
1090 if (Size > 512)
1091 continue;
1092
1093 unsigned Idx = StackSlotIdxes.size();
1094 StackSlotIdxes.insert(KV: {{Size, 0}, Idx});
1095 }
1096
1097 for (auto &Idx : StackSlotIdxes)
1098 StackIdxesToPos[Idx.second] = Idx.first;
1099
1100 NumSlotIdxes = StackSlotIdxes.size();
1101}
1102
1103LocIdx MLocTracker::trackRegister(unsigned ID) {
1104 assert(ID != 0);
1105 LocIdx NewIdx = LocIdx(LocIdxToIDNum.size());
1106 LocIdxToIDNum.grow(n: NewIdx);
1107 LocIdxToLocID.grow(n: NewIdx);
1108
1109 // Default: it's an mphi.
1110 ValueIDNum ValNum = {CurBB, 0, NewIdx};
1111 // Was this reg ever touched by a regmask?
1112 for (const auto &MaskPair : reverse(C&: Masks)) {
1113 if (MaskPair.first->clobbersPhysReg(PhysReg: ID)) {
1114 // There was an earlier def we skipped.
1115 ValNum = {CurBB, MaskPair.second, NewIdx};
1116 break;
1117 }
1118 }
1119
1120 LocIdxToIDNum[NewIdx] = ValNum;
1121 LocIdxToLocID[NewIdx] = ID;
1122 return NewIdx;
1123}
1124
1125void MLocTracker::writeRegMask(const MachineOperand *MO, unsigned CurBB,
1126 unsigned InstID) {
1127 // Def any register we track have that isn't preserved. The regmask
1128 // terminates the liveness of a register, meaning its value can't be
1129 // relied upon -- we represent this by giving it a new value.
1130 for (auto Location : locations()) {
1131 unsigned ID = LocIdxToLocID[Location.Idx];
1132 // Don't clobber SP, even if the mask says it's clobbered.
1133 if (ID < NumRegs && !SPAliases.count(V: ID) && MO->clobbersPhysReg(PhysReg: ID))
1134 defReg(R: ID, BB: CurBB, Inst: InstID);
1135 }
1136 Masks.push_back(Elt: std::make_pair(x&: MO, y&: InstID));
1137}
1138
1139std::optional<SpillLocationNo> MLocTracker::getOrTrackSpillLoc(SpillLoc L) {
1140 SpillLocationNo SpillID(SpillLocs.idFor(Entry: L));
1141
1142 if (SpillID.id() == 0) {
1143 // If there is no location, and we have reached the limit of how many stack
1144 // slots to track, then don't track this one.
1145 if (SpillLocs.size() >= StackWorkingSetLimit)
1146 return std::nullopt;
1147
1148 // Spill location is untracked: create record for this one, and all
1149 // subregister slots too.
1150 SpillID = SpillLocationNo(SpillLocs.insert(Entry: L));
1151 for (unsigned StackIdx = 0; StackIdx < NumSlotIdxes; ++StackIdx) {
1152 unsigned L = getSpillIDWithIdx(Spill: SpillID, Idx: StackIdx);
1153 LocIdx Idx = LocIdx(LocIdxToIDNum.size()); // New idx
1154 LocIdxToIDNum.grow(n: Idx);
1155 LocIdxToLocID.grow(n: Idx);
1156 LocIDToLocIdx.push_back(x: Idx);
1157 LocIdxToLocID[Idx] = L;
1158 // Initialize to PHI value; corresponds to the location's live-in value
1159 // during transfer function construction.
1160 LocIdxToIDNum[Idx] = ValueIDNum(CurBB, 0, Idx);
1161 }
1162 }
1163 return SpillID;
1164}
1165
1166std::string MLocTracker::LocIdxToName(LocIdx Idx) const {
1167 unsigned ID = LocIdxToLocID[Idx];
1168 if (ID >= NumRegs) {
1169 StackSlotPos Pos = locIDToSpillIdx(ID);
1170 ID -= NumRegs;
1171 unsigned Slot = ID / NumSlotIdxes;
1172 return Twine("slot ")
1173 .concat(Suffix: Twine(Slot).concat(Suffix: Twine(" sz ").concat(Suffix: Twine(Pos.first)
1174 .concat(Suffix: Twine(" offs ").concat(Suffix: Twine(Pos.second))))))
1175 .str();
1176 } else {
1177 return TRI.getRegAsmName(Reg: ID).str();
1178 }
1179}
1180
1181std::string MLocTracker::IDAsString(const ValueIDNum &Num) const {
1182 std::string DefName = LocIdxToName(Idx: Num.getLoc());
1183 return Num.asString(mlocname: DefName);
1184}
1185
1186#ifndef NDEBUG
1187LLVM_DUMP_METHOD void MLocTracker::dump() {
1188 for (auto Location : locations()) {
1189 std::string MLocName = LocIdxToName(Location.Value.getLoc());
1190 std::string DefName = Location.Value.asString(MLocName);
1191 dbgs() << LocIdxToName(Location.Idx) << " --> " << DefName << "\n";
1192 }
1193}
1194
1195LLVM_DUMP_METHOD void MLocTracker::dump_mloc_map() {
1196 for (auto Location : locations()) {
1197 std::string foo = LocIdxToName(Location.Idx);
1198 dbgs() << "Idx " << Location.Idx.asU64() << " " << foo << "\n";
1199 }
1200}
1201#endif
1202
1203MachineInstrBuilder
1204MLocTracker::emitLoc(const SmallVectorImpl<ResolvedDbgOp> &DbgOps,
1205 const DebugVariable &Var, const DILocation *DILoc,
1206 const DbgValueProperties &Properties) {
1207 DebugLoc DL = DebugLoc(DILoc);
1208
1209 const MCInstrDesc &Desc = Properties.IsVariadic
1210 ? TII.get(Opcode: TargetOpcode::DBG_VALUE_LIST)
1211 : TII.get(Opcode: TargetOpcode::DBG_VALUE);
1212
1213#ifdef EXPENSIVE_CHECKS
1214 assert(all_of(DbgOps,
1215 [](const ResolvedDbgOp &Op) {
1216 return Op.IsConst || !Op.Loc.isIllegal();
1217 }) &&
1218 "Did not expect illegal ops in DbgOps.");
1219 assert((DbgOps.size() == 0 ||
1220 DbgOps.size() == Properties.getLocationOpCount()) &&
1221 "Expected to have either one DbgOp per MI LocationOp, or none.");
1222#endif
1223
1224 auto GetRegOp = [](unsigned Reg) -> MachineOperand {
1225 return MachineOperand::CreateReg(
1226 /* Reg */ Reg, /* isDef */ false, /* isImp */ false,
1227 /* isKill */ false, /* isDead */ false,
1228 /* isUndef */ false, /* isEarlyClobber */ false,
1229 /* SubReg */ 0, /* isDebug */ true);
1230 };
1231
1232 SmallVector<MachineOperand> MOs;
1233
1234 auto EmitUndef = [&]() {
1235 MOs.clear();
1236 MOs.assign(NumElts: Properties.getLocationOpCount(), Elt: GetRegOp(0));
1237 return BuildMI(MF, DL, MCID: Desc, IsIndirect: false, MOs, Variable: Var.getVariable(),
1238 Expr: Properties.DIExpr);
1239 };
1240
1241 // Don't bother passing any real operands to BuildMI if any of them would be
1242 // $noreg.
1243 if (DbgOps.empty())
1244 return EmitUndef();
1245
1246 bool Indirect = Properties.Indirect;
1247
1248 const DIExpression *Expr = Properties.DIExpr;
1249
1250 assert(DbgOps.size() == Properties.getLocationOpCount());
1251
1252 // If all locations are valid, accumulate them into our list of
1253 // MachineOperands. For any spilled locations, either update the indirectness
1254 // register or apply the appropriate transformations in the DIExpression.
1255 for (size_t Idx = 0; Idx < Properties.getLocationOpCount(); ++Idx) {
1256 const ResolvedDbgOp &Op = DbgOps[Idx];
1257
1258 if (Op.IsConst) {
1259 MOs.push_back(Elt: Op.MO);
1260 continue;
1261 }
1262
1263 LocIdx MLoc = Op.Loc;
1264 unsigned LocID = LocIdxToLocID[MLoc];
1265 if (LocID >= NumRegs) {
1266 SpillLocationNo SpillID = locIDToSpill(ID: LocID);
1267 StackSlotPos StackIdx = locIDToSpillIdx(ID: LocID);
1268 unsigned short Offset = StackIdx.second;
1269
1270 // TODO: support variables that are located in spill slots, with non-zero
1271 // offsets from the start of the spill slot. It would require some more
1272 // complex DIExpression calculations. This doesn't seem to be produced by
1273 // LLVM right now, so don't try and support it.
1274 // Accept no-subregister slots and subregisters where the offset is zero.
1275 // The consumer should already have type information to work out how large
1276 // the variable is.
1277 if (Offset == 0) {
1278 const SpillLoc &Spill = SpillLocs[SpillID.id()];
1279 unsigned Base = Spill.SpillBase;
1280
1281 // There are several ways we can dereference things, and several inputs
1282 // to consider:
1283 // * NRVO variables will appear with IsIndirect set, but should have
1284 // nothing else in their DIExpressions,
1285 // * Variables with DW_OP_stack_value in their expr already need an
1286 // explicit dereference of the stack location,
1287 // * Values that don't match the variable size need DW_OP_deref_size,
1288 // * Everything else can just become a simple location expression.
1289
1290 // We need to use deref_size whenever there's a mismatch between the
1291 // size of value and the size of variable portion being read.
1292 // Additionally, we should use it whenever dealing with stack_value
1293 // fragments, to avoid the consumer having to determine the deref size
1294 // from DW_OP_piece.
1295 bool UseDerefSize = false;
1296 unsigned ValueSizeInBits = getLocSizeInBits(L: MLoc);
1297 unsigned DerefSizeInBytes = ValueSizeInBits / 8;
1298 if (auto Fragment = Var.getFragment()) {
1299 unsigned VariableSizeInBits = Fragment->SizeInBits;
1300 if (VariableSizeInBits != ValueSizeInBits || Expr->isComplex())
1301 UseDerefSize = true;
1302 } else if (auto Size = Var.getVariable()->getSizeInBits()) {
1303 if (*Size != ValueSizeInBits) {
1304 UseDerefSize = true;
1305 }
1306 }
1307
1308 // https://github.com/llvm/llvm-project/issues/64093
1309 // in particular #issuecomment-2531264124. We use variable locations
1310 // such as DBG_VALUE $xmm0 as shorthand to refer to "the low lane of
1311 // $xmm0", and this is reflected in how DWARF is interpreted too.
1312 // However InstrRefBasedLDV tries to be smart and interprets such a
1313 // DBG_VALUE as a 128-bit reference. We then issue a DW_OP_deref_size
1314 // of 128 bits to the stack, which isn't permitted by DWARF (it's
1315 // larger than a pointer).
1316 //
1317 // Solve this for now by not using DW_OP_deref_size if it would be
1318 // illegal. Instead we'll use DW_OP_deref, and the consumer will load
1319 // the variable type from the stack, which should be correct.
1320 //
1321 // There's still a risk of imprecision when LLVM decides to use
1322 // smaller or larger value types than the source-variable type, which
1323 // manifests as too-little or too-much memory being read from the stack.
1324 // However we can't solve that without putting more type information in
1325 // debug-info.
1326 if (ValueSizeInBits > MF.getTarget().getPointerSizeInBits(AS: 0))
1327 UseDerefSize = false;
1328
1329 SmallVector<uint64_t, 5> OffsetOps;
1330 TRI.getOffsetOpcodes(Offset: Spill.SpillOffset, Ops&: OffsetOps);
1331 bool StackValue = false;
1332
1333 if (Properties.Indirect) {
1334 // This is something like an NRVO variable, where the pointer has been
1335 // spilt to the stack. It should end up being a memory location, with
1336 // the pointer to the variable loaded off the stack with a deref:
1337 assert(!Expr->isImplicit());
1338 OffsetOps.push_back(Elt: dwarf::DW_OP_deref);
1339 } else if (UseDerefSize && Expr->isSingleLocationExpression()) {
1340 // TODO: Figure out how to handle deref size issues for variadic
1341 // values.
1342 // We're loading a value off the stack that's not the same size as the
1343 // variable. Add / subtract stack offset, explicitly deref with a
1344 // size, and add DW_OP_stack_value if not already present.
1345 OffsetOps.push_back(Elt: dwarf::DW_OP_deref_size);
1346 OffsetOps.push_back(Elt: DerefSizeInBytes);
1347 StackValue = true;
1348 } else if (Expr->isComplex() || Properties.IsVariadic) {
1349 // A variable with no size ambiguity, but with extra elements in it's
1350 // expression. Manually dereference the stack location.
1351 OffsetOps.push_back(Elt: dwarf::DW_OP_deref);
1352 } else {
1353 // A plain value that has been spilt to the stack, with no further
1354 // context. Request a location expression, marking the DBG_VALUE as
1355 // IsIndirect.
1356 Indirect = true;
1357 }
1358
1359 Expr = DIExpression::appendOpsToArg(Expr, Ops: OffsetOps, ArgNo: Idx, StackValue);
1360 MOs.push_back(Elt: GetRegOp(Base));
1361 } else {
1362 // This is a stack location with a weird subregister offset: emit an
1363 // undef DBG_VALUE instead.
1364 return EmitUndef();
1365 }
1366 } else {
1367 // Non-empty, non-stack slot, must be a plain register.
1368 MOs.push_back(Elt: GetRegOp(LocID));
1369 }
1370 }
1371
1372 return BuildMI(MF, DL, MCID: Desc, IsIndirect: Indirect, MOs, Variable: Var.getVariable(), Expr);
1373}
1374
1375/// Default construct and initialize the pass.
1376InstrRefBasedLDV::InstrRefBasedLDV() = default;
1377
1378bool InstrRefBasedLDV::isCalleeSaved(LocIdx L) const {
1379 unsigned Reg = MTracker->LocIdxToLocID[L];
1380 return isCalleeSavedReg(R: Reg);
1381}
1382bool InstrRefBasedLDV::isCalleeSavedReg(Register R) const {
1383 for (MCRegAliasIterator RAI(R, TRI, true); RAI.isValid(); ++RAI)
1384 if (CalleeSavedRegs.test(Idx: (*RAI).id()))
1385 return true;
1386 return false;
1387}
1388
1389//===----------------------------------------------------------------------===//
1390// Debug Range Extension Implementation
1391//===----------------------------------------------------------------------===//
1392
1393#ifndef NDEBUG
1394// Something to restore in the future.
1395// void InstrRefBasedLDV::printVarLocInMBB(..)
1396#endif
1397
1398std::optional<SpillLocationNo>
1399InstrRefBasedLDV::extractSpillBaseRegAndOffset(const MachineInstr &MI) {
1400 assert(MI.hasOneMemOperand() &&
1401 "Spill instruction does not have exactly one memory operand?");
1402 auto MMOI = MI.memoperands_begin();
1403 const PseudoSourceValue *PVal = (*MMOI)->getPseudoValue();
1404 assert(PVal->kind() == PseudoSourceValue::FixedStack &&
1405 "Inconsistent memory operand in spill instruction");
1406 int FI = cast<FixedStackPseudoSourceValue>(Val: PVal)->getFrameIndex();
1407 const MachineBasicBlock *MBB = MI.getParent();
1408 Register Reg;
1409 StackOffset Offset = TFI->getFrameIndexReference(MF: *MBB->getParent(), FI, FrameReg&: Reg);
1410 return MTracker->getOrTrackSpillLoc(L: {.SpillBase: Reg, .SpillOffset: Offset});
1411}
1412
1413std::optional<LocIdx>
1414InstrRefBasedLDV::findLocationForMemOperand(const MachineInstr &MI) {
1415 std::optional<SpillLocationNo> SpillLoc = extractSpillBaseRegAndOffset(MI);
1416 if (!SpillLoc)
1417 return std::nullopt;
1418
1419 // Where in the stack slot is this value defined -- i.e., what size of value
1420 // is this? An important question, because it could be loaded into a register
1421 // from the stack at some point. Happily the memory operand will tell us
1422 // the size written to the stack.
1423 auto *MemOperand = *MI.memoperands_begin();
1424 LocationSize SizeInBits = MemOperand->getSizeInBits();
1425 assert(SizeInBits.hasValue() && "Expected to find a valid size!");
1426
1427 // Find that position in the stack indexes we're tracking.
1428 auto IdxIt = MTracker->StackSlotIdxes.find(Val: {SizeInBits.getValue(), 0});
1429 if (IdxIt == MTracker->StackSlotIdxes.end())
1430 // That index is not tracked. This is suprising, and unlikely to ever
1431 // occur, but the safe action is to indicate the variable is optimised out.
1432 return std::nullopt;
1433
1434 unsigned SpillID = MTracker->getSpillIDWithIdx(Spill: *SpillLoc, Idx: IdxIt->second);
1435 return MTracker->getSpillMLoc(SpillID);
1436}
1437
1438/// End all previous ranges related to @MI and start a new range from @MI
1439/// if it is a DBG_VALUE instr.
1440bool InstrRefBasedLDV::transferDebugValue(const MachineInstr &MI) {
1441 if (!MI.isDebugValue())
1442 return false;
1443
1444 assert(MI.getDebugVariable()->isValidLocationForIntrinsic(MI.getDebugLoc()) &&
1445 "Expected inlined-at fields to agree");
1446
1447 // If there are no instructions in this lexical scope, do no location tracking
1448 // at all, this variable shouldn't get a legitimate location range.
1449 auto *Scope = LS.findLexicalScope(DL: MI.getDebugLoc().get());
1450 if (Scope == nullptr)
1451 return true; // handled it; by doing nothing
1452
1453 // MLocTracker needs to know that this register is read, even if it's only
1454 // read by a debug inst.
1455 for (const MachineOperand &MO : MI.debug_operands())
1456 if (MO.isReg() && MO.getReg() != 0)
1457 (void)MTracker->readReg(R: MO.getReg());
1458
1459 // If we're preparing for the second analysis (variables), the machine value
1460 // locations are already solved, and we report this DBG_VALUE and the value
1461 // it refers to to VLocTracker.
1462 if (VTracker) {
1463 SmallVector<DbgOpID> DebugOps;
1464 // Feed defVar the new variable location, or if this is a DBG_VALUE $noreg,
1465 // feed defVar None.
1466 if (!MI.isUndefDebugValue()) {
1467 for (const MachineOperand &MO : MI.debug_operands()) {
1468 // There should be no undef registers here, as we've screened for undef
1469 // debug values.
1470 if (MO.isReg()) {
1471 DebugOps.push_back(Elt: DbgOpStore.insert(Op: MTracker->readReg(R: MO.getReg())));
1472 } else if (MO.isImm() || MO.isFPImm() || MO.isCImm()) {
1473 DebugOps.push_back(Elt: DbgOpStore.insert(Op: MO));
1474 } else {
1475 llvm_unreachable("Unexpected debug operand type.");
1476 }
1477 }
1478 }
1479 VTracker->defVar(MI, Properties: DbgValueProperties(MI), DebugOps);
1480 }
1481
1482 // If performing final tracking of transfers, report this variable definition
1483 // to the TransferTracker too.
1484 if (TTracker)
1485 TTracker->redefVar(MI);
1486 return true;
1487}
1488
1489std::optional<ValueIDNum> InstrRefBasedLDV::getValueForInstrRef(
1490 unsigned InstNo, unsigned OpNo, MachineInstr &MI,
1491 const FuncValueTable *MLiveOuts, const FuncValueTable *MLiveIns) {
1492 // Various optimizations may have happened to the value during codegen,
1493 // recorded in the value substitution table. Apply any substitutions to
1494 // the instruction / operand number in this DBG_INSTR_REF, and collect
1495 // any subregister extractions performed during optimization.
1496 const MachineFunction &MF = *MI.getParent()->getParent();
1497
1498 // Create dummy substitution with Src set, for lookup.
1499 auto SoughtSub =
1500 MachineFunction::DebugSubstitution({InstNo, OpNo}, {0, 0}, 0);
1501
1502 SmallVector<unsigned, 4> SeenSubregs;
1503 auto LowerBoundIt = llvm::lower_bound(Range: MF.DebugValueSubstitutions, Value&: SoughtSub);
1504 while (LowerBoundIt != MF.DebugValueSubstitutions.end() &&
1505 LowerBoundIt->Src == SoughtSub.Src) {
1506 std::tie(args&: InstNo, args&: OpNo) = LowerBoundIt->Dest;
1507 SoughtSub.Src = LowerBoundIt->Dest;
1508 if (unsigned Subreg = LowerBoundIt->Subreg)
1509 SeenSubregs.push_back(Elt: Subreg);
1510 LowerBoundIt = llvm::lower_bound(Range: MF.DebugValueSubstitutions, Value&: SoughtSub);
1511 }
1512
1513 // Default machine value number is <None> -- if no instruction defines
1514 // the corresponding value, it must have been optimized out.
1515 std::optional<ValueIDNum> NewID;
1516
1517 // Try to lookup the instruction number, and find the machine value number
1518 // that it defines. It could be an instruction, or a PHI.
1519 auto InstrIt = DebugInstrNumToInstr.find(x: InstNo);
1520 auto PHIIt = llvm::lower_bound(Range&: DebugPHINumToValue, Value&: InstNo);
1521 if (InstrIt != DebugInstrNumToInstr.end()) {
1522 const MachineInstr &TargetInstr = *InstrIt->second.first;
1523 uint64_t BlockNo = TargetInstr.getParent()->getNumber();
1524
1525 // Pick out the designated operand. It might be a memory reference, if
1526 // a register def was folded into a stack store.
1527 if (OpNo == MachineFunction::DebugOperandMemNumber &&
1528 TargetInstr.hasOneMemOperand()) {
1529 std::optional<LocIdx> L = findLocationForMemOperand(MI: TargetInstr);
1530 if (L)
1531 NewID = ValueIDNum(BlockNo, InstrIt->second.second, *L);
1532 } else if (OpNo != MachineFunction::DebugOperandMemNumber) {
1533 // Permit the debug-info to be completely wrong: identifying a nonexistant
1534 // operand, or one that is not a register definition, means something
1535 // unexpected happened during optimisation. Broken debug-info, however,
1536 // shouldn't crash the compiler -- instead leave the variable value as
1537 // None, which will make it appear "optimised out".
1538 if (OpNo < TargetInstr.getNumOperands()) {
1539 const MachineOperand &MO = TargetInstr.getOperand(i: OpNo);
1540
1541 if (MO.isReg() && MO.isDef() && MO.getReg()) {
1542 unsigned LocID = MTracker->getLocID(Reg: MO.getReg());
1543 LocIdx L = MTracker->LocIDToLocIdx[LocID];
1544 NewID = ValueIDNum(BlockNo, InstrIt->second.second, L);
1545 }
1546 }
1547
1548 if (!NewID) {
1549 LLVM_DEBUG(
1550 { dbgs() << "Seen instruction reference to illegal operand\n"; });
1551 }
1552 }
1553 // else: NewID is left as None.
1554 } else if (PHIIt != DebugPHINumToValue.end() && PHIIt->InstrNum == InstNo) {
1555 // It's actually a PHI value. Which value it is might not be obvious, use
1556 // the resolver helper to find out.
1557 assert(MLiveOuts && MLiveIns);
1558 NewID = resolveDbgPHIs(MF&: *MI.getParent()->getParent(), MLiveOuts: *MLiveOuts, MLiveIns: *MLiveIns,
1559 Here&: MI, InstrNum: InstNo);
1560 }
1561
1562 // Apply any subregister extractions, in reverse. We might have seen code
1563 // like this:
1564 // CALL64 @foo, implicit-def $rax
1565 // %0:gr64 = COPY $rax
1566 // %1:gr32 = COPY %0.sub_32bit
1567 // %2:gr16 = COPY %1.sub_16bit
1568 // %3:gr8 = COPY %2.sub_8bit
1569 // In which case each copy would have been recorded as a substitution with
1570 // a subregister qualifier. Apply those qualifiers now.
1571 if (NewID && !SeenSubregs.empty()) {
1572 unsigned Offset = 0;
1573 unsigned Size = 0;
1574
1575 // Look at each subregister that we passed through, and progressively
1576 // narrow in, accumulating any offsets that occur. Substitutions should
1577 // only ever be the same or narrower width than what they read from;
1578 // iterate in reverse order so that we go from wide to small.
1579 for (unsigned Subreg : reverse(C&: SeenSubregs)) {
1580 unsigned ThisSize = TRI->getSubRegIdxSize(Idx: Subreg);
1581 unsigned ThisOffset = TRI->getSubRegIdxOffset(Idx: Subreg);
1582 Offset += ThisOffset;
1583 Size = (Size == 0) ? ThisSize : std::min(a: Size, b: ThisSize);
1584 }
1585
1586 // If that worked, look for an appropriate subregister with the register
1587 // where the define happens. Don't look at values that were defined during
1588 // a stack write: we can't currently express register locations within
1589 // spills.
1590 LocIdx L = NewID->getLoc();
1591 if (NewID && !MTracker->isSpill(Idx: L)) {
1592 // Find the register class for the register where this def happened.
1593 // FIXME: no index for this?
1594 Register Reg = MTracker->LocIdxToLocID[L];
1595 const TargetRegisterClass *TRC = nullptr;
1596 for (const auto *TRCI : TRI->regclasses())
1597 if (TRCI->contains(Reg))
1598 TRC = TRCI;
1599 assert(TRC && "Couldn't find target register class?");
1600
1601 // If the register we have isn't the right size or in the right place,
1602 // Try to find a subregister inside it.
1603 unsigned MainRegSize = TRI->getRegSizeInBits(RC: *TRC);
1604 if (Size != MainRegSize || Offset) {
1605 // Enumerate all subregisters, searching.
1606 Register NewReg = 0;
1607 for (MCPhysReg SR : TRI->subregs(Reg)) {
1608 unsigned Subreg = TRI->getSubRegIndex(RegNo: Reg, SubRegNo: SR);
1609 unsigned SubregSize = TRI->getSubRegIdxSize(Idx: Subreg);
1610 unsigned SubregOffset = TRI->getSubRegIdxOffset(Idx: Subreg);
1611 if (SubregSize == Size && SubregOffset == Offset) {
1612 NewReg = SR;
1613 break;
1614 }
1615 }
1616
1617 // If we didn't find anything: there's no way to express our value.
1618 if (!NewReg) {
1619 NewID = std::nullopt;
1620 } else {
1621 // Re-state the value as being defined within the subregister
1622 // that we found.
1623 LocIdx NewLoc = MTracker->lookupOrTrackRegister(ID: NewReg);
1624 NewID = ValueIDNum(NewID->getBlock(), NewID->getInst(), NewLoc);
1625 }
1626 }
1627 } else {
1628 // If we can't handle subregisters, unset the new value.
1629 NewID = std::nullopt;
1630 }
1631 }
1632
1633 return NewID;
1634}
1635
1636bool InstrRefBasedLDV::transferDebugInstrRef(MachineInstr &MI,
1637 const FuncValueTable *MLiveOuts,
1638 const FuncValueTable *MLiveIns) {
1639 if (!MI.isDebugRef())
1640 return false;
1641
1642 // Only handle this instruction when we are building the variable value
1643 // transfer function.
1644 if (!VTracker && !TTracker)
1645 return false;
1646
1647 const DILocalVariable *Var = MI.getDebugVariable();
1648 const DIExpression *Expr = MI.getDebugExpression();
1649 const DILocation *DebugLoc = MI.getDebugLoc();
1650 const DILocation *InlinedAt = DebugLoc->getInlinedAt();
1651 assert(Var->isValidLocationForIntrinsic(DebugLoc) &&
1652 "Expected inlined-at fields to agree");
1653
1654 DebugVariable V(Var, Expr, InlinedAt);
1655
1656 auto *Scope = LS.findLexicalScope(DL: MI.getDebugLoc().get());
1657 if (Scope == nullptr)
1658 return true; // Handled by doing nothing. This variable is never in scope.
1659
1660 SmallVector<DbgOpID> DbgOpIDs;
1661 for (const MachineOperand &MO : MI.debug_operands()) {
1662 if (!MO.isDbgInstrRef()) {
1663 assert(!MO.isReg() && "DBG_INSTR_REF should not contain registers");
1664 DbgOpID ConstOpID = DbgOpStore.insert(Op: DbgOp(MO));
1665 DbgOpIDs.push_back(Elt: ConstOpID);
1666 continue;
1667 }
1668
1669 unsigned InstNo = MO.getInstrRefInstrIndex();
1670 unsigned OpNo = MO.getInstrRefOpIndex();
1671
1672 // Default machine value number is <None> -- if no instruction defines
1673 // the corresponding value, it must have been optimized out.
1674 std::optional<ValueIDNum> NewID =
1675 getValueForInstrRef(InstNo, OpNo, MI, MLiveOuts, MLiveIns);
1676 // We have a value number or std::nullopt. If the latter, then kill the
1677 // entire debug value.
1678 if (NewID) {
1679 DbgOpIDs.push_back(Elt: DbgOpStore.insert(Op: *NewID));
1680 } else {
1681 DbgOpIDs.clear();
1682 break;
1683 }
1684 }
1685
1686 // We have a DbgOpID for every value or for none. Tell the variable value
1687 // tracker about it. The rest of this LiveDebugValues implementation acts
1688 // exactly the same for DBG_INSTR_REFs as DBG_VALUEs (just, the former can
1689 // refer to values that aren't immediately available).
1690 DbgValueProperties Properties(Expr, false, true);
1691 if (VTracker)
1692 VTracker->defVar(MI, Properties, DebugOps: DbgOpIDs);
1693
1694 // If we're on the final pass through the function, decompose this INSTR_REF
1695 // into a plain DBG_VALUE.
1696 if (!TTracker)
1697 return true;
1698
1699 // Fetch the concrete DbgOps now, as we will need them later.
1700 SmallVector<DbgOp> DbgOps;
1701 for (DbgOpID OpID : DbgOpIDs) {
1702 DbgOps.push_back(Elt: DbgOpStore.find(ID: OpID));
1703 }
1704
1705 // Pick a location for the machine value number, if such a location exists.
1706 // (This information could be stored in TransferTracker to make it faster).
1707 SmallDenseMap<ValueIDNum, TransferTracker::LocationAndQuality> FoundLocs;
1708 SmallVector<ValueIDNum> ValuesToFind;
1709 // Initialized the preferred-location map with illegal locations, to be
1710 // filled in later.
1711 for (const DbgOp &Op : DbgOps) {
1712 if (!Op.IsConst)
1713 if (FoundLocs.try_emplace(Key: Op.ID).second)
1714 ValuesToFind.push_back(Elt: Op.ID);
1715 }
1716
1717 for (auto Location : MTracker->locations()) {
1718 LocIdx CurL = Location.Idx;
1719 ValueIDNum ID = MTracker->readMLoc(L: CurL);
1720 auto ValueToFindIt = find(Range&: ValuesToFind, Val: ID);
1721 if (ValueToFindIt == ValuesToFind.end())
1722 continue;
1723 auto &Previous = FoundLocs.find(Val: ID)->second;
1724 // If this is the first location with that value, pick it. Otherwise,
1725 // consider whether it's a "longer term" location.
1726 std::optional<TransferTracker::LocationQuality> ReplacementQuality =
1727 TTracker->getLocQualityIfBetter(L: CurL, Min: Previous.getQuality());
1728 if (ReplacementQuality) {
1729 Previous = TransferTracker::LocationAndQuality(CurL, *ReplacementQuality);
1730 if (Previous.isBest()) {
1731 ValuesToFind.erase(CI: ValueToFindIt);
1732 if (ValuesToFind.empty())
1733 break;
1734 }
1735 }
1736 }
1737
1738 SmallVector<ResolvedDbgOp> NewLocs;
1739 for (const DbgOp &DbgOp : DbgOps) {
1740 if (DbgOp.IsConst) {
1741 NewLocs.push_back(Elt: DbgOp.MO);
1742 continue;
1743 }
1744 LocIdx FoundLoc = FoundLocs.find(Val: DbgOp.ID)->second.getLoc();
1745 if (FoundLoc.isIllegal()) {
1746 NewLocs.clear();
1747 break;
1748 }
1749 NewLocs.push_back(Elt: FoundLoc);
1750 }
1751 // Tell transfer tracker that the variable value has changed.
1752 TTracker->redefVar(MI, Properties, NewLocs);
1753
1754 // If there were values with no location, but all such values are defined in
1755 // later instructions in this block, this is a block-local use-before-def.
1756 if (!DbgOps.empty() && NewLocs.empty()) {
1757 bool IsValidUseBeforeDef = true;
1758 uint64_t LastUseBeforeDef = 0;
1759 for (auto ValueLoc : FoundLocs) {
1760 ValueIDNum NewID = ValueLoc.first;
1761 LocIdx FoundLoc = ValueLoc.second.getLoc();
1762 if (!FoundLoc.isIllegal())
1763 continue;
1764 // If we have an value with no location that is not defined in this block,
1765 // then it has no location in this block, leaving this value undefined.
1766 if (NewID.getBlock() != CurBB || NewID.getInst() <= CurInst) {
1767 IsValidUseBeforeDef = false;
1768 break;
1769 }
1770 LastUseBeforeDef = std::max(a: LastUseBeforeDef, b: NewID.getInst());
1771 }
1772 if (IsValidUseBeforeDef) {
1773 DebugVariableID VID = DVMap.insertDVID(Var&: V, Loc: MI.getDebugLoc().get());
1774 TTracker->addUseBeforeDef(VarID: VID, Properties: {MI.getDebugExpression(), false, true},
1775 DbgOps, Inst: LastUseBeforeDef);
1776 }
1777 }
1778
1779 // Produce a DBG_VALUE representing what this DBG_INSTR_REF meant.
1780 // This DBG_VALUE is potentially a $noreg / undefined location, if
1781 // FoundLoc is illegal.
1782 // (XXX -- could morph the DBG_INSTR_REF in the future).
1783 MachineInstr *DbgMI =
1784 MTracker->emitLoc(DbgOps: NewLocs, Var: V, DILoc: MI.getDebugLoc().get(), Properties);
1785 DebugVariableID ID = DVMap.getDVID(Var: V);
1786
1787 TTracker->PendingDbgValues.push_back(Elt: std::make_pair(x&: ID, y&: DbgMI));
1788 TTracker->flushDbgValues(Pos: MI.getIterator(), MBB: nullptr);
1789 return true;
1790}
1791
1792bool InstrRefBasedLDV::transferDebugPHI(MachineInstr &MI) {
1793 if (!MI.isDebugPHI())
1794 return false;
1795
1796 // Analyse these only when solving the machine value location problem.
1797 if (VTracker || TTracker)
1798 return true;
1799
1800 // First operand is the value location, either a stack slot or register.
1801 // Second is the debug instruction number of the original PHI.
1802 const MachineOperand &MO = MI.getOperand(i: 0);
1803 unsigned InstrNum = MI.getOperand(i: 1).getImm();
1804
1805 auto EmitBadPHI = [this, &MI, InstrNum]() -> bool {
1806 // Helper lambda to do any accounting when we fail to find a location for
1807 // a DBG_PHI. This can happen if DBG_PHIs are malformed, or refer to a
1808 // dead stack slot, for example.
1809 // Record a DebugPHIRecord with an empty value + location.
1810 DebugPHINumToValue.push_back(
1811 Elt: {.InstrNum: InstrNum, .MBB: MI.getParent(), .ValueRead: std::nullopt, .ReadLoc: std::nullopt});
1812 return true;
1813 };
1814
1815 if (MO.isReg() && MO.getReg()) {
1816 // The value is whatever's currently in the register. Read and record it,
1817 // to be analysed later.
1818 Register Reg = MO.getReg();
1819 ValueIDNum Num = MTracker->readReg(R: Reg);
1820 auto PHIRec = DebugPHIRecord(
1821 {.InstrNum: InstrNum, .MBB: MI.getParent(), .ValueRead: Num, .ReadLoc: MTracker->lookupOrTrackRegister(ID: Reg)});
1822 DebugPHINumToValue.push_back(Elt: PHIRec);
1823
1824 // Ensure this register is tracked.
1825 for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
1826 MTracker->lookupOrTrackRegister(ID: *RAI);
1827 } else if (MO.isFI()) {
1828 // The value is whatever's in this stack slot.
1829 unsigned FI = MO.getIndex();
1830
1831 // If the stack slot is dead, then this was optimized away.
1832 // FIXME: stack slot colouring should account for slots that get merged.
1833 if (MFI->isDeadObjectIndex(ObjectIdx: FI))
1834 return EmitBadPHI();
1835
1836 // Identify this spill slot, ensure it's tracked.
1837 Register Base;
1838 StackOffset Offs = TFI->getFrameIndexReference(MF: *MI.getMF(), FI, FrameReg&: Base);
1839 SpillLoc SL = {.SpillBase: Base, .SpillOffset: Offs};
1840 std::optional<SpillLocationNo> SpillNo = MTracker->getOrTrackSpillLoc(L: SL);
1841
1842 // We might be able to find a value, but have chosen not to, to avoid
1843 // tracking too much stack information.
1844 if (!SpillNo)
1845 return EmitBadPHI();
1846
1847 // Any stack location DBG_PHI should have an associate bit-size.
1848 assert(MI.getNumOperands() == 3 && "Stack DBG_PHI with no size?");
1849 unsigned slotBitSize = MI.getOperand(i: 2).getImm();
1850
1851 unsigned SpillID = MTracker->getLocID(Spill: *SpillNo, Idx: {slotBitSize, 0});
1852 LocIdx SpillLoc = MTracker->getSpillMLoc(SpillID);
1853 ValueIDNum Result = MTracker->readMLoc(L: SpillLoc);
1854
1855 // Record this DBG_PHI for later analysis.
1856 auto DbgPHI = DebugPHIRecord({.InstrNum: InstrNum, .MBB: MI.getParent(), .ValueRead: Result, .ReadLoc: SpillLoc});
1857 DebugPHINumToValue.push_back(Elt: DbgPHI);
1858 } else {
1859 // Else: if the operand is neither a legal register or a stack slot, then
1860 // we're being fed illegal debug-info. Record an empty PHI, so that any
1861 // debug users trying to read this number will be put off trying to
1862 // interpret the value.
1863 LLVM_DEBUG(
1864 { dbgs() << "Seen DBG_PHI with unrecognised operand format\n"; });
1865 return EmitBadPHI();
1866 }
1867
1868 return true;
1869}
1870
1871void InstrRefBasedLDV::transferRegisterDef(MachineInstr &MI) {
1872 // Meta Instructions do not affect the debug liveness of any register they
1873 // define.
1874 if (MI.isImplicitDef()) {
1875 // Except when there's an implicit def, and the location it's defining has
1876 // no value number. The whole point of an implicit def is to announce that
1877 // the register is live, without be specific about it's value. So define
1878 // a value if there isn't one already.
1879 ValueIDNum Num = MTracker->readReg(R: MI.getOperand(i: 0).getReg());
1880 // Has a legitimate value -> ignore the implicit def.
1881 if (Num.getLoc() != 0)
1882 return;
1883 // Otherwise, def it here.
1884 } else if (MI.isMetaInstruction())
1885 return;
1886
1887 // We always ignore SP defines on call instructions, they don't actually
1888 // change the value of the stack pointer... except for win32's _chkstk. This
1889 // is rare: filter quickly for the common case (no stack adjustments, not a
1890 // call, etc). If it is a call that modifies SP, recognise the SP register
1891 // defs.
1892 bool CallChangesSP = false;
1893 if (AdjustsStackInCalls && MI.isCall() && MI.getOperand(i: 0).isSymbol() &&
1894 !strcmp(s1: MI.getOperand(i: 0).getSymbolName(), s2: StackProbeSymbolName.data()))
1895 CallChangesSP = true;
1896
1897 // Test whether we should ignore a def of this register due to it being part
1898 // of the stack pointer.
1899 auto IgnoreSPAlias = [this, &MI, CallChangesSP](Register R) -> bool {
1900 if (CallChangesSP)
1901 return false;
1902 return MI.isCall() && MTracker->SPAliases.count(V: R);
1903 };
1904
1905 // Find the regs killed by MI, and find regmasks of preserved regs.
1906 // Max out the number of statically allocated elements in `DeadRegs`, as this
1907 // prevents fallback to std::set::count() operations.
1908 SmallSet<uint32_t, 32> DeadRegs;
1909 SmallVector<const uint32_t *, 4> RegMasks;
1910 SmallVector<const MachineOperand *, 4> RegMaskPtrs;
1911 for (const MachineOperand &MO : MI.operands()) {
1912 // Determine whether the operand is a register def.
1913 if (MO.isReg() && MO.isDef() && MO.getReg() && MO.getReg().isPhysical() &&
1914 !IgnoreSPAlias(MO.getReg())) {
1915 // Remove ranges of all aliased registers.
1916 for (MCRegAliasIterator RAI(MO.getReg(), TRI, true); RAI.isValid(); ++RAI)
1917 // FIXME: Can we break out of this loop early if no insertion occurs?
1918 DeadRegs.insert(V: (*RAI).id());
1919 } else if (MO.isRegMask()) {
1920 RegMasks.push_back(Elt: MO.getRegMask());
1921 RegMaskPtrs.push_back(Elt: &MO);
1922 }
1923 }
1924
1925 // Tell MLocTracker about all definitions, of regmasks and otherwise.
1926 for (uint32_t DeadReg : DeadRegs)
1927 MTracker->defReg(R: DeadReg, BB: CurBB, Inst: CurInst);
1928
1929 for (const auto *MO : RegMaskPtrs)
1930 MTracker->writeRegMask(MO, CurBB, InstID: CurInst);
1931
1932 // If this instruction writes to a spill slot, def that slot.
1933 if (hasFoldedStackStore(MI)) {
1934 if (std::optional<SpillLocationNo> SpillNo =
1935 extractSpillBaseRegAndOffset(MI)) {
1936 for (unsigned int I = 0; I < MTracker->NumSlotIdxes; ++I) {
1937 unsigned SpillID = MTracker->getSpillIDWithIdx(Spill: *SpillNo, Idx: I);
1938 LocIdx L = MTracker->getSpillMLoc(SpillID);
1939 MTracker->setMLoc(L, Num: ValueIDNum(CurBB, CurInst, L));
1940 }
1941 }
1942 }
1943
1944 if (!TTracker)
1945 return;
1946
1947 // When committing variable values to locations: tell transfer tracker that
1948 // we've clobbered things. It may be able to recover the variable from a
1949 // different location.
1950
1951 // Inform TTracker about any direct clobbers.
1952 for (uint32_t DeadReg : DeadRegs) {
1953 LocIdx Loc = MTracker->lookupOrTrackRegister(ID: DeadReg);
1954 TTracker->clobberMloc(MLoc: Loc, Pos: MI.getIterator(), MakeUndef: false);
1955 }
1956
1957 // Look for any clobbers performed by a register mask. Only test locations
1958 // that are actually being tracked.
1959 if (!RegMaskPtrs.empty()) {
1960 for (auto L : MTracker->locations()) {
1961 // Stack locations can't be clobbered by regmasks.
1962 if (MTracker->isSpill(Idx: L.Idx))
1963 continue;
1964
1965 Register Reg = MTracker->LocIdxToLocID[L.Idx];
1966 if (IgnoreSPAlias(Reg))
1967 continue;
1968
1969 for (const auto *MO : RegMaskPtrs)
1970 if (MO->clobbersPhysReg(PhysReg: Reg))
1971 TTracker->clobberMloc(MLoc: L.Idx, Pos: MI.getIterator(), MakeUndef: false);
1972 }
1973 }
1974
1975 // Tell TTracker about any folded stack store.
1976 if (hasFoldedStackStore(MI)) {
1977 if (std::optional<SpillLocationNo> SpillNo =
1978 extractSpillBaseRegAndOffset(MI)) {
1979 for (unsigned int I = 0; I < MTracker->NumSlotIdxes; ++I) {
1980 unsigned SpillID = MTracker->getSpillIDWithIdx(Spill: *SpillNo, Idx: I);
1981 LocIdx L = MTracker->getSpillMLoc(SpillID);
1982 TTracker->clobberMloc(MLoc: L, Pos: MI.getIterator(), MakeUndef: true);
1983 }
1984 }
1985 }
1986}
1987
1988void InstrRefBasedLDV::performCopy(Register SrcRegNum, Register DstRegNum) {
1989 // In all circumstances, re-def all aliases. It's definitely a new value now.
1990 for (MCRegAliasIterator RAI(DstRegNum, TRI, true); RAI.isValid(); ++RAI)
1991 MTracker->defReg(R: *RAI, BB: CurBB, Inst: CurInst);
1992
1993 ValueIDNum SrcValue = MTracker->readReg(R: SrcRegNum);
1994 MTracker->setReg(R: DstRegNum, ValueID: SrcValue);
1995
1996 // Copy subregisters from one location to another.
1997 for (MCSubRegIndexIterator SRI(SrcRegNum, TRI); SRI.isValid(); ++SRI) {
1998 unsigned SrcSubReg = SRI.getSubReg();
1999 unsigned SubRegIdx = SRI.getSubRegIndex();
2000 unsigned DstSubReg = TRI->getSubReg(Reg: DstRegNum, Idx: SubRegIdx);
2001 if (!DstSubReg)
2002 continue;
2003
2004 // Do copy. There are two matching subregisters, the source value should
2005 // have been def'd when the super-reg was, the latter might not be tracked
2006 // yet.
2007 // This will force SrcSubReg to be tracked, if it isn't yet. Will read
2008 // mphi values if it wasn't tracked.
2009 LocIdx SrcL = MTracker->lookupOrTrackRegister(ID: SrcSubReg);
2010 LocIdx DstL = MTracker->lookupOrTrackRegister(ID: DstSubReg);
2011 (void)SrcL;
2012 (void)DstL;
2013 ValueIDNum CpyValue = MTracker->readReg(R: SrcSubReg);
2014
2015 MTracker->setReg(R: DstSubReg, ValueID: CpyValue);
2016 }
2017}
2018
2019std::optional<SpillLocationNo>
2020InstrRefBasedLDV::isSpillInstruction(const MachineInstr &MI,
2021 MachineFunction *MF) {
2022 // TODO: Handle multiple stores folded into one.
2023 if (!MI.hasOneMemOperand())
2024 return std::nullopt;
2025
2026 // Reject any memory operand that's aliased -- we can't guarantee its value.
2027 auto MMOI = MI.memoperands_begin();
2028 const PseudoSourceValue *PVal = (*MMOI)->getPseudoValue();
2029 if (PVal->isAliased(MFI))
2030 return std::nullopt;
2031
2032 if (!MI.getSpillSize(TII) && !MI.getFoldedSpillSize(TII))
2033 return std::nullopt; // This is not a spill instruction, since no valid size
2034 // was returned from either function.
2035
2036 return extractSpillBaseRegAndOffset(MI);
2037}
2038
2039bool InstrRefBasedLDV::isLocationSpill(const MachineInstr &MI,
2040 MachineFunction *MF, unsigned &Reg) {
2041 if (!isSpillInstruction(MI, MF))
2042 return false;
2043
2044 int FI;
2045 Reg = TII->isStoreToStackSlotPostFE(MI, FrameIndex&: FI);
2046 return Reg != 0;
2047}
2048
2049std::optional<SpillLocationNo>
2050InstrRefBasedLDV::isRestoreInstruction(const MachineInstr &MI,
2051 MachineFunction *MF, unsigned &Reg) {
2052 if (!MI.hasOneMemOperand())
2053 return std::nullopt;
2054
2055 // FIXME: Handle folded restore instructions with more than one memory
2056 // operand.
2057 if (MI.getRestoreSize(TII)) {
2058 Reg = MI.getOperand(i: 0).getReg();
2059 return extractSpillBaseRegAndOffset(MI);
2060 }
2061 return std::nullopt;
2062}
2063
2064bool InstrRefBasedLDV::transferSpillOrRestoreInst(MachineInstr &MI) {
2065 // XXX -- it's too difficult to implement VarLocBasedImpl's stack location
2066 // limitations under the new model. Therefore, when comparing them, compare
2067 // versions that don't attempt spills or restores at all.
2068 if (EmulateOldLDV)
2069 return false;
2070
2071 // Strictly limit ourselves to plain loads and stores, not all instructions
2072 // that can access the stack.
2073 int DummyFI = -1;
2074 if (!TII->isStoreToStackSlotPostFE(MI, FrameIndex&: DummyFI) &&
2075 !TII->isLoadFromStackSlotPostFE(MI, FrameIndex&: DummyFI))
2076 return false;
2077
2078 MachineFunction *MF = MI.getMF();
2079 unsigned Reg;
2080
2081 LLVM_DEBUG(dbgs() << "Examining instruction: "; MI.dump(););
2082
2083 // Strictly limit ourselves to plain loads and stores, not all instructions
2084 // that can access the stack.
2085 int FIDummy;
2086 if (!TII->isStoreToStackSlotPostFE(MI, FrameIndex&: FIDummy) &&
2087 !TII->isLoadFromStackSlotPostFE(MI, FrameIndex&: FIDummy))
2088 return false;
2089
2090 // First, if there are any DBG_VALUEs pointing at a spill slot that is
2091 // written to, terminate that variable location. The value in memory
2092 // will have changed. DbgEntityHistoryCalculator doesn't try to detect this.
2093 if (std::optional<SpillLocationNo> Loc = isSpillInstruction(MI, MF)) {
2094 // Un-set this location and clobber, so that earlier locations don't
2095 // continue past this store.
2096 for (unsigned SlotIdx = 0; SlotIdx < MTracker->NumSlotIdxes; ++SlotIdx) {
2097 unsigned SpillID = MTracker->getSpillIDWithIdx(Spill: *Loc, Idx: SlotIdx);
2098 std::optional<LocIdx> MLoc = MTracker->getSpillMLoc(SpillID);
2099 if (!MLoc)
2100 continue;
2101
2102 // We need to over-write the stack slot with something (here, a def at
2103 // this instruction) to ensure no values are preserved in this stack slot
2104 // after the spill. It also prevents TTracker from trying to recover the
2105 // location and re-installing it in the same place.
2106 ValueIDNum Def(CurBB, CurInst, *MLoc);
2107 MTracker->setMLoc(L: *MLoc, Num: Def);
2108 if (TTracker)
2109 TTracker->clobberMloc(MLoc: *MLoc, Pos: MI.getIterator());
2110 }
2111 }
2112
2113 // Try to recognise spill and restore instructions that may transfer a value.
2114 if (isLocationSpill(MI, MF, Reg)) {
2115 // isLocationSpill returning true should guarantee we can extract a
2116 // location.
2117 SpillLocationNo Loc = *extractSpillBaseRegAndOffset(MI);
2118
2119 auto DoTransfer = [&](Register SrcReg, unsigned SpillID) {
2120 auto ReadValue = MTracker->readReg(R: SrcReg);
2121 LocIdx DstLoc = MTracker->getSpillMLoc(SpillID);
2122 MTracker->setMLoc(L: DstLoc, Num: ReadValue);
2123
2124 if (TTracker) {
2125 LocIdx SrcLoc = MTracker->getRegMLoc(R: SrcReg);
2126 TTracker->transferMlocs(Src: SrcLoc, Dst: DstLoc, Pos: MI.getIterator());
2127 }
2128 };
2129
2130 // Then, transfer subreg bits.
2131 for (MCPhysReg SR : TRI->subregs(Reg)) {
2132 // Ensure this reg is tracked,
2133 (void)MTracker->lookupOrTrackRegister(ID: SR);
2134 unsigned SubregIdx = TRI->getSubRegIndex(RegNo: Reg, SubRegNo: SR);
2135 unsigned SpillID = MTracker->getLocID(Spill: Loc, SpillSubReg: SubregIdx);
2136 DoTransfer(SR, SpillID);
2137 }
2138
2139 // Directly lookup size of main source reg, and transfer.
2140 unsigned Size = TRI->getRegSizeInBits(Reg, MRI: *MRI);
2141 unsigned SpillID = MTracker->getLocID(Spill: Loc, Idx: {Size, 0});
2142 DoTransfer(Reg, SpillID);
2143 } else {
2144 std::optional<SpillLocationNo> Loc = isRestoreInstruction(MI, MF, Reg);
2145 if (!Loc)
2146 return false;
2147
2148 // Assumption: we're reading from the base of the stack slot, not some
2149 // offset into it. It seems very unlikely LLVM would ever generate
2150 // restores where this wasn't true. This then becomes a question of what
2151 // subregisters in the destination register line up with positions in the
2152 // stack slot.
2153
2154 // Def all registers that alias the destination.
2155 for (MCRegAliasIterator RAI(Reg, TRI, true); RAI.isValid(); ++RAI)
2156 MTracker->defReg(R: *RAI, BB: CurBB, Inst: CurInst);
2157
2158 // Now find subregisters within the destination register, and load values
2159 // from stack slot positions.
2160 auto DoTransfer = [&](Register DestReg, unsigned SpillID) {
2161 LocIdx SrcIdx = MTracker->getSpillMLoc(SpillID);
2162 auto ReadValue = MTracker->readMLoc(L: SrcIdx);
2163 MTracker->setReg(R: DestReg, ValueID: ReadValue);
2164 };
2165
2166 for (MCPhysReg SR : TRI->subregs(Reg)) {
2167 unsigned Subreg = TRI->getSubRegIndex(RegNo: Reg, SubRegNo: SR);
2168 unsigned SpillID = MTracker->getLocID(Spill: *Loc, SpillSubReg: Subreg);
2169 DoTransfer(SR, SpillID);
2170 }
2171
2172 // Directly look up this registers slot idx by size, and transfer.
2173 unsigned Size = TRI->getRegSizeInBits(Reg, MRI: *MRI);
2174 unsigned SpillID = MTracker->getLocID(Spill: *Loc, Idx: {Size, 0});
2175 DoTransfer(Reg, SpillID);
2176 }
2177 return true;
2178}
2179
2180bool InstrRefBasedLDV::transferRegisterCopy(MachineInstr &MI) {
2181 auto DestSrc = TII->isCopyLikeInstr(MI);
2182 if (!DestSrc)
2183 return false;
2184
2185 const MachineOperand *DestRegOp = DestSrc->Destination;
2186 const MachineOperand *SrcRegOp = DestSrc->Source;
2187
2188 Register SrcReg = SrcRegOp->getReg();
2189 Register DestReg = DestRegOp->getReg();
2190
2191 // Ignore identity copies. Yep, these make it as far as LiveDebugValues.
2192 if (SrcReg == DestReg)
2193 return true;
2194
2195 // For emulating VarLocBasedImpl:
2196 // We want to recognize instructions where destination register is callee
2197 // saved register. If register that could be clobbered by the call is
2198 // included, there would be a great chance that it is going to be clobbered
2199 // soon. It is more likely that previous register, which is callee saved, is
2200 // going to stay unclobbered longer, even if it is killed.
2201 //
2202 // For InstrRefBasedImpl, we can track multiple locations per value, so
2203 // ignore this condition.
2204 if (EmulateOldLDV && !isCalleeSavedReg(R: DestReg))
2205 return false;
2206
2207 // InstrRefBasedImpl only followed killing copies.
2208 if (EmulateOldLDV && !SrcRegOp->isKill())
2209 return false;
2210
2211 // Before we update MTracker, remember which values were present in each of
2212 // the locations about to be overwritten, so that we can recover any
2213 // potentially clobbered variables.
2214 DenseMap<LocIdx, ValueIDNum> ClobberedLocs;
2215 if (TTracker) {
2216 for (MCRegAliasIterator RAI(DestReg, TRI, true); RAI.isValid(); ++RAI) {
2217 LocIdx ClobberedLoc = MTracker->getRegMLoc(R: *RAI);
2218 auto MLocIt = TTracker->ActiveMLocs.find(Val: ClobberedLoc);
2219 // If ActiveMLocs isn't tracking this location or there are no variables
2220 // using it, don't bother remembering.
2221 if (MLocIt == TTracker->ActiveMLocs.end() || MLocIt->second.empty())
2222 continue;
2223 ValueIDNum Value = MTracker->readReg(R: *RAI);
2224 ClobberedLocs[ClobberedLoc] = Value;
2225 }
2226 }
2227
2228 // Copy MTracker info, including subregs if available.
2229 InstrRefBasedLDV::performCopy(SrcRegNum: SrcReg, DstRegNum: DestReg);
2230
2231 // The copy might have clobbered variables based on the destination register.
2232 // Tell TTracker about it, passing the old ValueIDNum to search for
2233 // alternative locations (or else terminating those variables).
2234 if (TTracker) {
2235 for (auto LocVal : ClobberedLocs) {
2236 TTracker->clobberMloc(MLoc: LocVal.first, OldValue: LocVal.second, Pos: MI.getIterator(), MakeUndef: false);
2237 }
2238 }
2239
2240 // Only produce a transfer of DBG_VALUE within a block where old LDV
2241 // would have. We might make use of the additional value tracking in some
2242 // other way, later.
2243 if (TTracker && isCalleeSavedReg(R: DestReg) && SrcRegOp->isKill())
2244 TTracker->transferMlocs(Src: MTracker->getRegMLoc(R: SrcReg),
2245 Dst: MTracker->getRegMLoc(R: DestReg), Pos: MI.getIterator());
2246
2247 // VarLocBasedImpl would quit tracking the old location after copying.
2248 if (EmulateOldLDV && SrcReg != DestReg)
2249 MTracker->defReg(R: SrcReg, BB: CurBB, Inst: CurInst);
2250
2251 return true;
2252}
2253
2254/// Accumulate a mapping between each DILocalVariable fragment and other
2255/// fragments of that DILocalVariable which overlap. This reduces work during
2256/// the data-flow stage from "Find any overlapping fragments" to "Check if the
2257/// known-to-overlap fragments are present".
2258/// \param MI A previously unprocessed debug instruction to analyze for
2259/// fragment usage.
2260void InstrRefBasedLDV::accumulateFragmentMap(MachineInstr &MI) {
2261 assert(MI.isDebugValueLike());
2262 DebugVariable MIVar(MI.getDebugVariable(), MI.getDebugExpression(),
2263 MI.getDebugLoc()->getInlinedAt());
2264 FragmentInfo ThisFragment = MIVar.getFragmentOrDefault();
2265
2266 // If this is the first sighting of this variable, then we are guaranteed
2267 // there are currently no overlapping fragments either. Initialize the set
2268 // of seen fragments, record no overlaps for the current one, and return.
2269 auto [SeenIt, Inserted] = SeenFragments.try_emplace(Key: MIVar.getVariable());
2270 if (Inserted) {
2271 SeenIt->second.insert(V: ThisFragment);
2272
2273 OverlapFragments.insert(KV: {{MIVar.getVariable(), ThisFragment}, {}});
2274 return;
2275 }
2276
2277 // If this particular Variable/Fragment pair already exists in the overlap
2278 // map, it has already been accounted for.
2279 auto IsInOLapMap =
2280 OverlapFragments.insert(KV: {{MIVar.getVariable(), ThisFragment}, {}});
2281 if (!IsInOLapMap.second)
2282 return;
2283
2284 auto &ThisFragmentsOverlaps = IsInOLapMap.first->second;
2285 auto &AllSeenFragments = SeenIt->second;
2286
2287 // Otherwise, examine all other seen fragments for this variable, with "this"
2288 // fragment being a previously unseen fragment. Record any pair of
2289 // overlapping fragments.
2290 for (const auto &ASeenFragment : AllSeenFragments) {
2291 // Does this previously seen fragment overlap?
2292 if (DIExpression::fragmentsOverlap(A: ThisFragment, B: ASeenFragment)) {
2293 // Yes: Mark the current fragment as being overlapped.
2294 ThisFragmentsOverlaps.push_back(Elt: ASeenFragment);
2295 // Mark the previously seen fragment as being overlapped by the current
2296 // one.
2297 auto ASeenFragmentsOverlaps =
2298 OverlapFragments.find(Val: {MIVar.getVariable(), ASeenFragment});
2299 assert(ASeenFragmentsOverlaps != OverlapFragments.end() &&
2300 "Previously seen var fragment has no vector of overlaps");
2301 ASeenFragmentsOverlaps->second.push_back(Elt: ThisFragment);
2302 }
2303 }
2304
2305 AllSeenFragments.insert(V: ThisFragment);
2306}
2307
2308void InstrRefBasedLDV::process(MachineInstr &MI,
2309 const FuncValueTable *MLiveOuts,
2310 const FuncValueTable *MLiveIns) {
2311 // Try to interpret an MI as a debug or transfer instruction. Only if it's
2312 // none of these should we interpret it's register defs as new value
2313 // definitions.
2314 if (transferDebugValue(MI))
2315 return;
2316 if (transferDebugInstrRef(MI, MLiveOuts, MLiveIns))
2317 return;
2318 if (transferDebugPHI(MI))
2319 return;
2320 if (transferRegisterCopy(MI))
2321 return;
2322 if (transferSpillOrRestoreInst(MI))
2323 return;
2324 transferRegisterDef(MI);
2325}
2326
2327void InstrRefBasedLDV::produceMLocTransferFunction(
2328 MachineFunction &MF, SmallVectorImpl<MLocTransferMap> &MLocTransfer,
2329 unsigned MaxNumBlocks) {
2330 // Because we try to optimize around register mask operands by ignoring regs
2331 // that aren't currently tracked, we set up something ugly for later: RegMask
2332 // operands that are seen earlier than the first use of a register, still need
2333 // to clobber that register in the transfer function. But this information
2334 // isn't actively recorded. Instead, we track each RegMask used in each block,
2335 // and accumulated the clobbered but untracked registers in each block into
2336 // the following bitvector. Later, if new values are tracked, we can add
2337 // appropriate clobbers.
2338 SmallVector<BitVector, 32> BlockMasks;
2339 BlockMasks.resize(N: MaxNumBlocks);
2340
2341 // Reserve one bit per register for the masks described above.
2342 unsigned BVWords = MachineOperand::getRegMaskSize(NumRegs: TRI->getNumRegs());
2343 for (auto &BV : BlockMasks)
2344 BV.resize(N: TRI->getNumRegs(), t: true);
2345
2346 // Step through all instructions and inhale the transfer function.
2347 for (auto &MBB : MF) {
2348 // Object fields that are read by trackers to know where we are in the
2349 // function.
2350 CurBB = MBB.getNumber();
2351 CurInst = 1;
2352
2353 // Set all machine locations to a PHI value. For transfer function
2354 // production only, this signifies the live-in value to the block.
2355 MTracker->reset();
2356 MTracker->setMPhis(CurBB);
2357
2358 // Step through each instruction in this block.
2359 for (auto &MI : MBB) {
2360 // Pass in an empty unique_ptr for the value tables when accumulating the
2361 // machine transfer function.
2362 process(MI, MLiveOuts: nullptr, MLiveIns: nullptr);
2363
2364 // Also accumulate fragment map.
2365 if (MI.isDebugValueLike())
2366 accumulateFragmentMap(MI);
2367
2368 // Create a map from the instruction number (if present) to the
2369 // MachineInstr and its position.
2370 if (uint64_t InstrNo = MI.peekDebugInstrNum()) {
2371 auto InstrAndPos = std::make_pair(x: &MI, y&: CurInst);
2372 auto InsertResult =
2373 DebugInstrNumToInstr.insert(x: std::make_pair(x&: InstrNo, y&: InstrAndPos));
2374
2375 // There should never be duplicate instruction numbers.
2376 assert(InsertResult.second);
2377 (void)InsertResult;
2378 }
2379
2380 ++CurInst;
2381 }
2382
2383 // Produce the transfer function, a map of machine location to new value. If
2384 // any machine location has the live-in phi value from the start of the
2385 // block, it's live-through and doesn't need recording in the transfer
2386 // function.
2387 for (auto Location : MTracker->locations()) {
2388 LocIdx Idx = Location.Idx;
2389 ValueIDNum &P = Location.Value;
2390 if (P.isPHI() && P.getLoc() == Idx.asU64())
2391 continue;
2392
2393 // Insert-or-update.
2394 auto &TransferMap = MLocTransfer[CurBB];
2395 auto Result = TransferMap.insert(KV: std::make_pair(x: Idx.asU64(), y&: P));
2396 if (!Result.second)
2397 Result.first->second = P;
2398 }
2399
2400 // Accumulate any bitmask operands into the clobbered reg mask for this
2401 // block.
2402 for (auto &P : MTracker->Masks) {
2403 BlockMasks[CurBB].clearBitsNotInMask(Mask: P.first->getRegMask(), MaskWords: BVWords);
2404 }
2405 }
2406
2407 // Compute a bitvector of all the registers that are tracked in this block.
2408 BitVector UsedRegs(TRI->getNumRegs());
2409 for (auto Location : MTracker->locations()) {
2410 unsigned ID = MTracker->LocIdxToLocID[Location.Idx];
2411 // Ignore stack slots, and aliases of the stack pointer.
2412 if (ID >= TRI->getNumRegs() || MTracker->SPAliases.count(V: ID))
2413 continue;
2414 UsedRegs.set(ID);
2415 }
2416
2417 // Check that any regmask-clobber of a register that gets tracked, is not
2418 // live-through in the transfer function. It needs to be clobbered at the
2419 // very least.
2420 for (unsigned int I = 0; I < MaxNumBlocks; ++I) {
2421 BitVector &BV = BlockMasks[I];
2422 BV.flip();
2423 BV &= UsedRegs;
2424 // This produces all the bits that we clobber, but also use. Check that
2425 // they're all clobbered or at least set in the designated transfer
2426 // elem.
2427 for (unsigned Bit : BV.set_bits()) {
2428 unsigned ID = MTracker->getLocID(Reg: Bit);
2429 LocIdx Idx = MTracker->LocIDToLocIdx[ID];
2430 auto &TransferMap = MLocTransfer[I];
2431
2432 // Install a value representing the fact that this location is effectively
2433 // written to in this block. As there's no reserved value, instead use
2434 // a value number that is never generated. Pick the value number for the
2435 // first instruction in the block, def'ing this location, which we know
2436 // this block never used anyway.
2437 ValueIDNum NotGeneratedNum = ValueIDNum(I, 1, Idx);
2438 auto Result =
2439 TransferMap.insert(KV: std::make_pair(x: Idx.asU64(), y&: NotGeneratedNum));
2440 if (!Result.second) {
2441 ValueIDNum &ValueID = Result.first->second;
2442 if (ValueID.getBlock() == I && ValueID.isPHI())
2443 // It was left as live-through. Set it to clobbered.
2444 ValueID = NotGeneratedNum;
2445 }
2446 }
2447 }
2448}
2449
2450bool InstrRefBasedLDV::mlocJoin(
2451 MachineBasicBlock &MBB, SmallPtrSet<const MachineBasicBlock *, 16> &Visited,
2452 FuncValueTable &OutLocs, ValueTable &InLocs) {
2453 LLVM_DEBUG(dbgs() << "join MBB: " << MBB.getNumber() << "\n");
2454 bool Changed = false;
2455
2456 // Handle value-propagation when control flow merges on entry to a block. For
2457 // any location without a PHI already placed, the location has the same value
2458 // as its predecessors. If a PHI is placed, test to see whether it's now a
2459 // redundant PHI that we can eliminate.
2460
2461 SmallVector<const MachineBasicBlock *, 8> BlockOrders(MBB.predecessors());
2462
2463 // Visit predecessors in RPOT order.
2464 auto Cmp = [&](const MachineBasicBlock *A, const MachineBasicBlock *B) {
2465 return BBToOrder.find(Val: A)->second < BBToOrder.find(Val: B)->second;
2466 };
2467 llvm::sort(C&: BlockOrders, Comp: Cmp);
2468
2469 // Skip entry block.
2470 if (BlockOrders.size() == 0) {
2471 // FIXME: We don't use assert here to prevent instr-ref-unreachable.mir
2472 // failing.
2473 LLVM_DEBUG(if (!MBB.isEntryBlock()) dbgs()
2474 << "Found not reachable block " << MBB.getFullName()
2475 << " from entry which may lead out of "
2476 "bound access to VarLocs\n");
2477 return false;
2478 }
2479
2480 // Step through all machine locations, look at each predecessor and test
2481 // whether we can eliminate redundant PHIs.
2482 for (auto Location : MTracker->locations()) {
2483 LocIdx Idx = Location.Idx;
2484
2485 // Pick out the first predecessors live-out value for this location. It's
2486 // guaranteed to not be a backedge, as we order by RPO.
2487 ValueIDNum FirstVal = OutLocs[*BlockOrders[0]][Idx.asU64()];
2488
2489 // If we've already eliminated a PHI here, do no further checking, just
2490 // propagate the first live-in value into this block.
2491 if (InLocs[Idx.asU64()] != ValueIDNum(MBB.getNumber(), 0, Idx)) {
2492 if (InLocs[Idx.asU64()] != FirstVal) {
2493 InLocs[Idx.asU64()] = FirstVal;
2494 Changed |= true;
2495 }
2496 continue;
2497 }
2498
2499 // We're now examining a PHI to see whether it's un-necessary. Loop around
2500 // the other live-in values and test whether they're all the same.
2501 bool Disagree = false;
2502 for (unsigned int I = 1; I < BlockOrders.size(); ++I) {
2503 const MachineBasicBlock *PredMBB = BlockOrders[I];
2504 const ValueIDNum &PredLiveOut = OutLocs[*PredMBB][Idx.asU64()];
2505
2506 // Incoming values agree, continue trying to eliminate this PHI.
2507 if (FirstVal == PredLiveOut)
2508 continue;
2509
2510 // We can also accept a PHI value that feeds back into itself.
2511 if (PredLiveOut == ValueIDNum(MBB.getNumber(), 0, Idx))
2512 continue;
2513
2514 // Live-out of a predecessor disagrees with the first predecessor.
2515 Disagree = true;
2516 }
2517
2518 // No disagreement? No PHI. Otherwise, leave the PHI in live-ins.
2519 if (!Disagree) {
2520 InLocs[Idx.asU64()] = FirstVal;
2521 Changed |= true;
2522 }
2523 }
2524
2525 // TODO: Reimplement NumInserted and NumRemoved.
2526 return Changed;
2527}
2528
2529void InstrRefBasedLDV::findStackIndexInterference(
2530 SmallVectorImpl<unsigned> &Slots) {
2531 // We could spend a bit of time finding the exact, minimal, set of stack
2532 // indexes that interfere with each other, much like reg units. Or, we can
2533 // rely on the fact that:
2534 // * The smallest / lowest index will interfere with everything at zero
2535 // offset, which will be the largest set of registers,
2536 // * Most indexes with non-zero offset will end up being interference units
2537 // anyway.
2538 // So just pick those out and return them.
2539
2540 // We can rely on a single-byte stack index existing already, because we
2541 // initialize them in MLocTracker.
2542 auto It = MTracker->StackSlotIdxes.find(Val: {8, 0});
2543 assert(It != MTracker->StackSlotIdxes.end());
2544 Slots.push_back(Elt: It->second);
2545
2546 // Find anything that has a non-zero offset and add that too.
2547 for (auto &Pair : MTracker->StackSlotIdxes) {
2548 // Is offset zero? If so, ignore.
2549 if (!Pair.first.second)
2550 continue;
2551 Slots.push_back(Elt: Pair.second);
2552 }
2553}
2554
2555void InstrRefBasedLDV::placeMLocPHIs(
2556 MachineFunction &MF, SmallPtrSetImpl<MachineBasicBlock *> &AllBlocks,
2557 FuncValueTable &MInLocs, SmallVectorImpl<MLocTransferMap> &MLocTransfer) {
2558 SmallVector<unsigned, 4> StackUnits;
2559 findStackIndexInterference(Slots&: StackUnits);
2560
2561 // To avoid repeatedly running the PHI placement algorithm, leverage the
2562 // fact that a def of register MUST also def its register units. Find the
2563 // units for registers, place PHIs for them, and then replicate them for
2564 // aliasing registers. Some inputs that are never def'd (DBG_PHIs of
2565 // arguments) don't lead to register units being tracked, just place PHIs for
2566 // those registers directly. Stack slots have their own form of "unit",
2567 // store them to one side.
2568 SmallSet<Register, 32> RegUnitsToPHIUp;
2569 SmallSet<LocIdx, 32> NormalLocsToPHI;
2570 SmallSet<SpillLocationNo, 32> StackSlots;
2571 for (auto Location : MTracker->locations()) {
2572 LocIdx L = Location.Idx;
2573 if (MTracker->isSpill(Idx: L)) {
2574 StackSlots.insert(V: MTracker->locIDToSpill(ID: MTracker->LocIdxToLocID[L]));
2575 continue;
2576 }
2577
2578 Register R = MTracker->LocIdxToLocID[L];
2579 SmallSet<Register, 8> FoundRegUnits;
2580 bool AnyIllegal = false;
2581 for (MCRegUnit Unit : TRI->regunits(Reg: R.asMCReg())) {
2582 for (MCRegUnitRootIterator URoot(Unit, TRI); URoot.isValid(); ++URoot) {
2583 if (!MTracker->isRegisterTracked(R: *URoot)) {
2584 // Not all roots were loaded into the tracking map: this register
2585 // isn't actually def'd anywhere, we only read from it. Generate PHIs
2586 // for this reg, but don't iterate units.
2587 AnyIllegal = true;
2588 } else {
2589 FoundRegUnits.insert(V: *URoot);
2590 }
2591 }
2592 }
2593
2594 if (AnyIllegal) {
2595 NormalLocsToPHI.insert(V: L);
2596 continue;
2597 }
2598
2599 RegUnitsToPHIUp.insert_range(R&: FoundRegUnits);
2600 }
2601
2602 // Lambda to fetch PHIs for a given location, and write into the PHIBlocks
2603 // collection.
2604 SmallVector<MachineBasicBlock *, 32> PHIBlocks;
2605 auto CollectPHIsForLoc = [&](LocIdx L) {
2606 // Collect the set of defs.
2607 SmallPtrSet<MachineBasicBlock *, 32> DefBlocks;
2608 for (MachineBasicBlock *MBB : OrderToBB) {
2609 const auto &TransferFunc = MLocTransfer[MBB->getNumber()];
2610 if (TransferFunc.contains(Val: L))
2611 DefBlocks.insert(Ptr: MBB);
2612 }
2613
2614 // The entry block defs the location too: it's the live-in / argument value.
2615 // Only insert if there are other defs though; everything is trivially live
2616 // through otherwise.
2617 if (!DefBlocks.empty())
2618 DefBlocks.insert(Ptr: &*MF.begin());
2619
2620 // Ask the SSA construction algorithm where we should put PHIs. Clear
2621 // anything that might have been hanging around from earlier.
2622 PHIBlocks.clear();
2623 BlockPHIPlacement(AllBlocks, DefBlocks, PHIBlocks);
2624 };
2625
2626 auto InstallPHIsAtLoc = [&PHIBlocks, &MInLocs](LocIdx L) {
2627 for (const MachineBasicBlock *MBB : PHIBlocks)
2628 MInLocs[*MBB][L.asU64()] = ValueIDNum(MBB->getNumber(), 0, L);
2629 };
2630
2631 // For locations with no reg units, just place PHIs.
2632 for (LocIdx L : NormalLocsToPHI) {
2633 CollectPHIsForLoc(L);
2634 // Install those PHI values into the live-in value array.
2635 InstallPHIsAtLoc(L);
2636 }
2637
2638 // For stack slots, calculate PHIs for the equivalent of the units, then
2639 // install for each index.
2640 for (SpillLocationNo Slot : StackSlots) {
2641 for (unsigned Idx : StackUnits) {
2642 unsigned SpillID = MTracker->getSpillIDWithIdx(Spill: Slot, Idx);
2643 LocIdx L = MTracker->getSpillMLoc(SpillID);
2644 CollectPHIsForLoc(L);
2645 InstallPHIsAtLoc(L);
2646
2647 // Find anything that aliases this stack index, install PHIs for it too.
2648 unsigned Size, Offset;
2649 std::tie(args&: Size, args&: Offset) = MTracker->StackIdxesToPos[Idx];
2650 for (auto &Pair : MTracker->StackSlotIdxes) {
2651 unsigned ThisSize, ThisOffset;
2652 std::tie(args&: ThisSize, args&: ThisOffset) = Pair.first;
2653 if (ThisSize + ThisOffset <= Offset || Size + Offset <= ThisOffset)
2654 continue;
2655
2656 unsigned ThisID = MTracker->getSpillIDWithIdx(Spill: Slot, Idx: Pair.second);
2657 LocIdx ThisL = MTracker->getSpillMLoc(SpillID: ThisID);
2658 InstallPHIsAtLoc(ThisL);
2659 }
2660 }
2661 }
2662
2663 // For reg units, place PHIs, and then place them for any aliasing registers.
2664 for (Register R : RegUnitsToPHIUp) {
2665 LocIdx L = MTracker->lookupOrTrackRegister(ID: R);
2666 CollectPHIsForLoc(L);
2667
2668 // Install those PHI values into the live-in value array.
2669 InstallPHIsAtLoc(L);
2670
2671 // Now find aliases and install PHIs for those.
2672 for (MCRegAliasIterator RAI(R, TRI, true); RAI.isValid(); ++RAI) {
2673 // Super-registers that are "above" the largest register read/written by
2674 // the function will alias, but will not be tracked.
2675 if (!MTracker->isRegisterTracked(R: *RAI))
2676 continue;
2677
2678 LocIdx AliasLoc = MTracker->lookupOrTrackRegister(ID: *RAI);
2679 InstallPHIsAtLoc(AliasLoc);
2680 }
2681 }
2682}
2683
2684void InstrRefBasedLDV::buildMLocValueMap(
2685 MachineFunction &MF, FuncValueTable &MInLocs, FuncValueTable &MOutLocs,
2686 SmallVectorImpl<MLocTransferMap> &MLocTransfer) {
2687 std::priority_queue<unsigned int, std::vector<unsigned int>,
2688 std::greater<unsigned int>>
2689 Worklist, Pending;
2690
2691 // We track what is on the current and pending worklist to avoid inserting
2692 // the same thing twice. We could avoid this with a custom priority queue,
2693 // but this is probably not worth it.
2694 SmallPtrSet<MachineBasicBlock *, 16> OnPending, OnWorklist;
2695
2696 // Initialize worklist with every block to be visited. Also produce list of
2697 // all blocks.
2698 SmallPtrSet<MachineBasicBlock *, 32> AllBlocks;
2699 for (unsigned int I = 0; I < BBToOrder.size(); ++I) {
2700 Worklist.push(x: I);
2701 OnWorklist.insert(Ptr: OrderToBB[I]);
2702 AllBlocks.insert(Ptr: OrderToBB[I]);
2703 }
2704
2705 // Initialize entry block to PHIs. These represent arguments.
2706 for (auto Location : MTracker->locations())
2707 MInLocs.tableForEntryMBB()[Location.Idx.asU64()] =
2708 ValueIDNum(0, 0, Location.Idx);
2709
2710 MTracker->reset();
2711
2712 // Start by placing PHIs, using the usual SSA constructor algorithm. Consider
2713 // any machine-location that isn't live-through a block to be def'd in that
2714 // block.
2715 placeMLocPHIs(MF, AllBlocks, MInLocs, MLocTransfer);
2716
2717 // Propagate values to eliminate redundant PHIs. At the same time, this
2718 // produces the table of Block x Location => Value for the entry to each
2719 // block.
2720 // The kind of PHIs we can eliminate are, for example, where one path in a
2721 // conditional spills and restores a register, and the register still has
2722 // the same value once control flow joins, unbeknowns to the PHI placement
2723 // code. Propagating values allows us to identify such un-necessary PHIs and
2724 // remove them.
2725 SmallPtrSet<const MachineBasicBlock *, 16> Visited;
2726 while (!Worklist.empty() || !Pending.empty()) {
2727 // Vector for storing the evaluated block transfer function.
2728 SmallVector<std::pair<LocIdx, ValueIDNum>, 32> ToRemap;
2729
2730 while (!Worklist.empty()) {
2731 MachineBasicBlock *MBB = OrderToBB[Worklist.top()];
2732 CurBB = MBB->getNumber();
2733 Worklist.pop();
2734
2735 // Join the values in all predecessor blocks.
2736 bool InLocsChanged;
2737 InLocsChanged = mlocJoin(MBB&: *MBB, Visited, OutLocs&: MOutLocs, InLocs&: MInLocs[*MBB]);
2738 InLocsChanged |= Visited.insert(Ptr: MBB).second;
2739
2740 // Don't examine transfer function if we've visited this loc at least
2741 // once, and inlocs haven't changed.
2742 if (!InLocsChanged)
2743 continue;
2744
2745 // Load the current set of live-ins into MLocTracker.
2746 MTracker->loadFromArray(Locs&: MInLocs[*MBB], NewCurBB: CurBB);
2747
2748 // Each element of the transfer function can be a new def, or a read of
2749 // a live-in value. Evaluate each element, and store to "ToRemap".
2750 ToRemap.clear();
2751 for (auto &P : MLocTransfer[CurBB]) {
2752 if (P.second.getBlock() == CurBB && P.second.isPHI()) {
2753 // This is a movement of whatever was live in. Read it.
2754 ValueIDNum NewID = MTracker->readMLoc(L: P.second.getLoc());
2755 ToRemap.push_back(Elt: std::make_pair(x&: P.first, y&: NewID));
2756 } else {
2757 // It's a def. Just set it.
2758 assert(P.second.getBlock() == CurBB);
2759 ToRemap.push_back(Elt: std::make_pair(x&: P.first, y&: P.second));
2760 }
2761 }
2762
2763 // Commit the transfer function changes into mloc tracker, which
2764 // transforms the contents of the MLocTracker into the live-outs.
2765 for (auto &P : ToRemap)
2766 MTracker->setMLoc(L: P.first, Num: P.second);
2767
2768 // Now copy out-locs from mloc tracker into out-loc vector, checking
2769 // whether changes have occurred. These changes can have come from both
2770 // the transfer function, and mlocJoin.
2771 bool OLChanged = false;
2772 for (auto Location : MTracker->locations()) {
2773 OLChanged |= MOutLocs[*MBB][Location.Idx.asU64()] != Location.Value;
2774 MOutLocs[*MBB][Location.Idx.asU64()] = Location.Value;
2775 }
2776
2777 MTracker->reset();
2778
2779 // No need to examine successors again if out-locs didn't change.
2780 if (!OLChanged)
2781 continue;
2782
2783 // All successors should be visited: put any back-edges on the pending
2784 // list for the next pass-through, and any other successors to be
2785 // visited this pass, if they're not going to be already.
2786 for (auto *s : MBB->successors()) {
2787 // Does branching to this successor represent a back-edge?
2788 unsigned Order = BBToOrder[s];
2789 if (Order > BBToOrder[MBB]) {
2790 // No: visit it during this dataflow iteration.
2791 if (OnWorklist.insert(Ptr: s).second)
2792 Worklist.push(x: Order);
2793 } else {
2794 // Yes: visit it on the next iteration.
2795 if (OnPending.insert(Ptr: s).second)
2796 Pending.push(x: Order);
2797 }
2798 }
2799 }
2800
2801 Worklist.swap(pq&: Pending);
2802 std::swap(LHS&: OnPending, RHS&: OnWorklist);
2803 OnPending.clear();
2804 // At this point, pending must be empty, since it was just the empty
2805 // worklist
2806 assert(Pending.empty() && "Pending should be empty");
2807 }
2808
2809 // Once all the live-ins don't change on mlocJoin(), we've eliminated all
2810 // redundant PHIs.
2811}
2812
2813void InstrRefBasedLDV::BlockPHIPlacement(
2814 const SmallPtrSetImpl<MachineBasicBlock *> &AllBlocks,
2815 const SmallPtrSetImpl<MachineBasicBlock *> &DefBlocks,
2816 SmallVectorImpl<MachineBasicBlock *> &PHIBlocks) {
2817 // Apply IDF calculator to the designated set of location defs, storing
2818 // required PHIs into PHIBlocks. Uses the dominator tree stored in the
2819 // InstrRefBasedLDV object.
2820 IDFCalculatorBase<MachineBasicBlock, false> IDF(*DomTree);
2821
2822 IDF.setLiveInBlocks(AllBlocks);
2823 IDF.setDefiningBlocks(DefBlocks);
2824 IDF.calculate(IDFBlocks&: PHIBlocks);
2825}
2826
2827bool InstrRefBasedLDV::pickVPHILoc(
2828 SmallVectorImpl<DbgOpID> &OutValues, const MachineBasicBlock &MBB,
2829 const LiveIdxT &LiveOuts, FuncValueTable &MOutLocs,
2830 const SmallVectorImpl<const MachineBasicBlock *> &BlockOrders) {
2831
2832 // No predecessors means no PHIs.
2833 if (BlockOrders.empty())
2834 return false;
2835
2836 // All the location operands that do not already agree need to be joined,
2837 // track the indices of each such location operand here.
2838 SmallDenseSet<unsigned> LocOpsToJoin;
2839
2840 auto FirstValueIt = LiveOuts.find(Val: BlockOrders[0]);
2841 if (FirstValueIt == LiveOuts.end())
2842 return false;
2843 const DbgValue &FirstValue = *FirstValueIt->second;
2844
2845 for (const auto p : BlockOrders) {
2846 auto OutValIt = LiveOuts.find(Val: p);
2847 if (OutValIt == LiveOuts.end())
2848 // If we have a predecessor not in scope, we'll never find a PHI position.
2849 return false;
2850 const DbgValue &OutVal = *OutValIt->second;
2851
2852 // No-values cannot have locations we can join on.
2853 if (OutVal.Kind == DbgValue::NoVal)
2854 return false;
2855
2856 // For unjoined VPHIs where we don't know the location, we definitely
2857 // can't find a join loc unless the VPHI is a backedge.
2858 if (OutVal.isUnjoinedPHI() && OutVal.BlockNo != MBB.getNumber())
2859 return false;
2860
2861 if (!FirstValue.Properties.isJoinable(Other: OutVal.Properties))
2862 return false;
2863
2864 for (unsigned Idx = 0; Idx < FirstValue.getLocationOpCount(); ++Idx) {
2865 // An unjoined PHI has no defined locations, and so a shared location must
2866 // be found for every operand.
2867 if (OutVal.isUnjoinedPHI()) {
2868 LocOpsToJoin.insert(V: Idx);
2869 continue;
2870 }
2871 DbgOpID FirstValOp = FirstValue.getDbgOpID(Index: Idx);
2872 DbgOpID OutValOp = OutVal.getDbgOpID(Index: Idx);
2873 if (FirstValOp != OutValOp) {
2874 // We can never join constant ops - the ops must either both be equal
2875 // constant ops or non-const ops.
2876 if (FirstValOp.isConst() || OutValOp.isConst())
2877 return false;
2878 else
2879 LocOpsToJoin.insert(V: Idx);
2880 }
2881 }
2882 }
2883
2884 SmallVector<DbgOpID> NewDbgOps;
2885
2886 for (unsigned Idx = 0; Idx < FirstValue.getLocationOpCount(); ++Idx) {
2887 // If this op doesn't need to be joined because the values agree, use that
2888 // already-agreed value.
2889 if (!LocOpsToJoin.contains(V: Idx)) {
2890 NewDbgOps.push_back(Elt: FirstValue.getDbgOpID(Index: Idx));
2891 continue;
2892 }
2893
2894 std::optional<ValueIDNum> JoinedOpLoc =
2895 pickOperandPHILoc(DbgOpIdx: Idx, MBB, LiveOuts, MOutLocs, BlockOrders);
2896
2897 if (!JoinedOpLoc)
2898 return false;
2899
2900 NewDbgOps.push_back(Elt: DbgOpStore.insert(Op: *JoinedOpLoc));
2901 }
2902
2903 OutValues.append(RHS: NewDbgOps);
2904 return true;
2905}
2906
2907std::optional<ValueIDNum> InstrRefBasedLDV::pickOperandPHILoc(
2908 unsigned DbgOpIdx, const MachineBasicBlock &MBB, const LiveIdxT &LiveOuts,
2909 FuncValueTable &MOutLocs,
2910 const SmallVectorImpl<const MachineBasicBlock *> &BlockOrders) {
2911
2912 // Collect a set of locations from predecessor where its live-out value can
2913 // be found.
2914 SmallVector<SmallVector<LocIdx, 4>, 8> Locs;
2915 unsigned NumLocs = MTracker->getNumLocs();
2916
2917 for (const auto p : BlockOrders) {
2918 auto OutValIt = LiveOuts.find(Val: p);
2919 assert(OutValIt != LiveOuts.end());
2920 const DbgValue &OutVal = *OutValIt->second;
2921 DbgOpID OutValOpID = OutVal.getDbgOpID(Index: DbgOpIdx);
2922 DbgOp OutValOp = DbgOpStore.find(ID: OutValOpID);
2923 assert(!OutValOp.IsConst);
2924
2925 // Create new empty vector of locations.
2926 Locs.resize(N: Locs.size() + 1);
2927
2928 // If the live-in value is a def, find the locations where that value is
2929 // present. Do the same for VPHIs where we know the VPHI value.
2930 if (OutVal.Kind == DbgValue::Def ||
2931 (OutVal.Kind == DbgValue::VPHI && OutVal.BlockNo != MBB.getNumber() &&
2932 !OutValOp.isUndef())) {
2933 ValueIDNum ValToLookFor = OutValOp.ID;
2934 // Search the live-outs of the predecessor for the specified value.
2935 for (unsigned int I = 0; I < NumLocs; ++I) {
2936 if (MOutLocs[*p][I] == ValToLookFor)
2937 Locs.back().push_back(Elt: LocIdx(I));
2938 }
2939 } else {
2940 assert(OutVal.Kind == DbgValue::VPHI);
2941 // Otherwise: this is a VPHI on a backedge feeding back into itself, i.e.
2942 // a value that's live-through the whole loop. (It has to be a backedge,
2943 // because a block can't dominate itself). We can accept as a PHI location
2944 // any location where the other predecessors agree, _and_ the machine
2945 // locations feed back into themselves. Therefore, add all self-looping
2946 // machine-value PHI locations.
2947 for (unsigned int I = 0; I < NumLocs; ++I) {
2948 ValueIDNum MPHI(MBB.getNumber(), 0, LocIdx(I));
2949 if (MOutLocs[*p][I] == MPHI)
2950 Locs.back().push_back(Elt: LocIdx(I));
2951 }
2952 }
2953 }
2954 // We should have found locations for all predecessors, or returned.
2955 assert(Locs.size() == BlockOrders.size());
2956
2957 // Starting with the first set of locations, take the intersection with
2958 // subsequent sets.
2959 SmallVector<LocIdx, 4> CandidateLocs = Locs[0];
2960 for (unsigned int I = 1; I < Locs.size(); ++I) {
2961 auto &LocVec = Locs[I];
2962 SmallVector<LocIdx, 4> NewCandidates;
2963 std::set_intersection(first1: CandidateLocs.begin(), last1: CandidateLocs.end(),
2964 first2: LocVec.begin(), last2: LocVec.end(), result: std::inserter(x&: NewCandidates, i: NewCandidates.begin()));
2965 CandidateLocs = std::move(NewCandidates);
2966 }
2967 if (CandidateLocs.empty())
2968 return std::nullopt;
2969
2970 // We now have a set of LocIdxes that contain the right output value in
2971 // each of the predecessors. Pick the lowest; if there's a register loc,
2972 // that'll be it.
2973 LocIdx L = *CandidateLocs.begin();
2974
2975 // Return a PHI-value-number for the found location.
2976 ValueIDNum PHIVal = {(unsigned)MBB.getNumber(), 0, L};
2977 return PHIVal;
2978}
2979
2980bool InstrRefBasedLDV::vlocJoin(
2981 MachineBasicBlock &MBB, LiveIdxT &VLOCOutLocs,
2982 SmallPtrSet<const MachineBasicBlock *, 8> &BlocksToExplore,
2983 DbgValue &LiveIn) {
2984 LLVM_DEBUG(dbgs() << "join MBB: " << MBB.getNumber() << "\n");
2985 bool Changed = false;
2986
2987 // Order predecessors by RPOT order, for exploring them in that order.
2988 SmallVector<MachineBasicBlock *, 8> BlockOrders(MBB.predecessors());
2989
2990 auto Cmp = [&](MachineBasicBlock *A, MachineBasicBlock *B) {
2991 return BBToOrder[A] < BBToOrder[B];
2992 };
2993
2994 llvm::sort(C&: BlockOrders, Comp: Cmp);
2995
2996 unsigned CurBlockRPONum = BBToOrder[&MBB];
2997
2998 // Collect all the incoming DbgValues for this variable, from predecessor
2999 // live-out values.
3000 SmallVector<InValueT, 8> Values;
3001 bool Bail = false;
3002 int BackEdgesStart = 0;
3003 for (auto *p : BlockOrders) {
3004 // If the predecessor isn't in scope / to be explored, we'll never be
3005 // able to join any locations.
3006 if (!BlocksToExplore.contains(Ptr: p)) {
3007 Bail = true;
3008 break;
3009 }
3010
3011 // All Live-outs will have been initialized.
3012 DbgValue &OutLoc = *VLOCOutLocs.find(Val: p)->second;
3013
3014 // Keep track of where back-edges begin in the Values vector. Relies on
3015 // BlockOrders being sorted by RPO.
3016 unsigned ThisBBRPONum = BBToOrder[p];
3017 if (ThisBBRPONum < CurBlockRPONum)
3018 ++BackEdgesStart;
3019
3020 Values.push_back(Elt: std::make_pair(x&: p, y: &OutLoc));
3021 }
3022
3023 // If there were no values, or one of the predecessors couldn't have a
3024 // value, then give up immediately. It's not safe to produce a live-in
3025 // value. Leave as whatever it was before.
3026 if (Bail || Values.size() == 0)
3027 return false;
3028
3029 // All (non-entry) blocks have at least one non-backedge predecessor.
3030 // Pick the variable value from the first of these, to compare against
3031 // all others.
3032 const DbgValue &FirstVal = *Values[0].second;
3033
3034 // If the old live-in value is not a PHI then either a) no PHI is needed
3035 // here, or b) we eliminated the PHI that was here. If so, we can just
3036 // propagate in the first parent's incoming value.
3037 if (LiveIn.Kind != DbgValue::VPHI || LiveIn.BlockNo != MBB.getNumber()) {
3038 Changed = LiveIn != FirstVal;
3039 if (Changed)
3040 LiveIn = FirstVal;
3041 return Changed;
3042 }
3043
3044 // Scan for variable values that can never be resolved: if they have
3045 // different DIExpressions, different indirectness, or are mixed constants /
3046 // non-constants.
3047 for (const auto &V : Values) {
3048 if (!V.second->Properties.isJoinable(Other: FirstVal.Properties))
3049 return false;
3050 if (V.second->Kind == DbgValue::NoVal)
3051 return false;
3052 if (!V.second->hasJoinableLocOps(Other: FirstVal))
3053 return false;
3054 }
3055
3056 // Try to eliminate this PHI. Do the incoming values all agree?
3057 bool Disagree = false;
3058 for (auto &V : Values) {
3059 if (*V.second == FirstVal)
3060 continue; // No disagreement.
3061
3062 // If both values are not equal but have equal non-empty IDs then they refer
3063 // to the same value from different sources (e.g. one is VPHI and the other
3064 // is Def), which does not cause disagreement.
3065 if (V.second->hasIdenticalValidLocOps(Other: FirstVal))
3066 continue;
3067
3068 // Eliminate if a backedge feeds a VPHI back into itself.
3069 if (V.second->Kind == DbgValue::VPHI &&
3070 V.second->BlockNo == MBB.getNumber() &&
3071 // Is this a backedge?
3072 std::distance(first: Values.begin(), last: &V) >= BackEdgesStart)
3073 continue;
3074
3075 Disagree = true;
3076 }
3077
3078 // No disagreement -> live-through value.
3079 if (!Disagree) {
3080 Changed = LiveIn != FirstVal;
3081 if (Changed)
3082 LiveIn = FirstVal;
3083 return Changed;
3084 } else {
3085 // Otherwise use a VPHI.
3086 DbgValue VPHI(MBB.getNumber(), FirstVal.Properties, DbgValue::VPHI);
3087 Changed = LiveIn != VPHI;
3088 if (Changed)
3089 LiveIn = VPHI;
3090 return Changed;
3091 }
3092}
3093
3094void InstrRefBasedLDV::getBlocksForScope(
3095 const DILocation *DILoc,
3096 SmallPtrSetImpl<const MachineBasicBlock *> &BlocksToExplore,
3097 const SmallPtrSetImpl<MachineBasicBlock *> &AssignBlocks) {
3098 // Get the set of "normal" in-lexical-scope blocks.
3099 LS.getMachineBasicBlocks(DL: DILoc, MBBs&: BlocksToExplore);
3100
3101 // VarLoc LiveDebugValues tracks variable locations that are defined in
3102 // blocks not in scope. This is something we could legitimately ignore, but
3103 // lets allow it for now for the sake of coverage.
3104 BlocksToExplore.insert_range(R: AssignBlocks);
3105
3106 // Storage for artificial blocks we intend to add to BlocksToExplore.
3107 DenseSet<const MachineBasicBlock *> ToAdd;
3108
3109 // To avoid needlessly dropping large volumes of variable locations, propagate
3110 // variables through aritifical blocks, i.e. those that don't have any
3111 // instructions in scope at all. To accurately replicate VarLoc
3112 // LiveDebugValues, this means exploring all artificial successors too.
3113 // Perform a depth-first-search to enumerate those blocks.
3114 for (const auto *MBB : BlocksToExplore) {
3115 // Depth-first-search state: each node is a block and which successor
3116 // we're currently exploring.
3117 SmallVector<std::pair<const MachineBasicBlock *,
3118 MachineBasicBlock::const_succ_iterator>,
3119 8>
3120 DFS;
3121
3122 // Find any artificial successors not already tracked.
3123 for (auto *succ : MBB->successors()) {
3124 if (BlocksToExplore.count(Ptr: succ))
3125 continue;
3126 if (!ArtificialBlocks.count(Ptr: succ))
3127 continue;
3128 ToAdd.insert(V: succ);
3129 DFS.push_back(Elt: {succ, succ->succ_begin()});
3130 }
3131
3132 // Search all those blocks, depth first.
3133 while (!DFS.empty()) {
3134 const MachineBasicBlock *CurBB = DFS.back().first;
3135 MachineBasicBlock::const_succ_iterator &CurSucc = DFS.back().second;
3136 // Walk back if we've explored this blocks successors to the end.
3137 if (CurSucc == CurBB->succ_end()) {
3138 DFS.pop_back();
3139 continue;
3140 }
3141
3142 // If the current successor is artificial and unexplored, descend into
3143 // it.
3144 if (!ToAdd.count(V: *CurSucc) && ArtificialBlocks.count(Ptr: *CurSucc)) {
3145 ToAdd.insert(V: *CurSucc);
3146 DFS.push_back(Elt: {*CurSucc, (*CurSucc)->succ_begin()});
3147 continue;
3148 }
3149
3150 ++CurSucc;
3151 }
3152 };
3153
3154 BlocksToExplore.insert_range(R&: ToAdd);
3155}
3156
3157void InstrRefBasedLDV::buildVLocValueMap(
3158 const DILocation *DILoc,
3159 const SmallSet<DebugVariableID, 4> &VarsWeCareAbout,
3160 SmallPtrSetImpl<MachineBasicBlock *> &AssignBlocks, LiveInsT &Output,
3161 FuncValueTable &MOutLocs, FuncValueTable &MInLocs,
3162 SmallVectorImpl<VLocTracker> &AllTheVLocs) {
3163 // This method is much like buildMLocValueMap: but focuses on a single
3164 // LexicalScope at a time. Pick out a set of blocks and variables that are
3165 // to have their value assignments solved, then run our dataflow algorithm
3166 // until a fixedpoint is reached.
3167 std::priority_queue<unsigned int, std::vector<unsigned int>,
3168 std::greater<unsigned int>>
3169 Worklist, Pending;
3170 SmallPtrSet<MachineBasicBlock *, 16> OnWorklist, OnPending;
3171
3172 // The set of blocks we'll be examining.
3173 SmallPtrSet<const MachineBasicBlock *, 8> BlocksToExplore;
3174
3175 // The order in which to examine them (RPO).
3176 SmallVector<MachineBasicBlock *, 16> BlockOrders;
3177 SmallVector<unsigned, 32> BlockOrderNums;
3178
3179 getBlocksForScope(DILoc, BlocksToExplore, AssignBlocks);
3180
3181 // Single block scope: not interesting! No propagation at all. Note that
3182 // this could probably go above ArtificialBlocks without damage, but
3183 // that then produces output differences from original-live-debug-values,
3184 // which propagates from a single block into many artificial ones.
3185 if (BlocksToExplore.size() == 1)
3186 return;
3187
3188 // Convert a const set to a non-const set. LexicalScopes
3189 // getMachineBasicBlocks returns const MBB pointers, IDF wants mutable ones.
3190 // (Neither of them mutate anything).
3191 SmallPtrSet<MachineBasicBlock *, 8> MutBlocksToExplore;
3192 for (const auto *MBB : BlocksToExplore)
3193 MutBlocksToExplore.insert(Ptr: const_cast<MachineBasicBlock *>(MBB));
3194
3195 // Picks out relevants blocks RPO order and sort them. Sort their
3196 // order-numbers and map back to MBB pointers later, to avoid repeated
3197 // DenseMap queries during comparisons.
3198 for (const auto *MBB : BlocksToExplore)
3199 BlockOrderNums.push_back(Elt: BBToOrder[MBB]);
3200
3201 llvm::sort(C&: BlockOrderNums);
3202 for (unsigned int I : BlockOrderNums)
3203 BlockOrders.push_back(Elt: OrderToBB[I]);
3204 BlockOrderNums.clear();
3205 unsigned NumBlocks = BlockOrders.size();
3206
3207 // Allocate some vectors for storing the live ins and live outs. Large.
3208 SmallVector<DbgValue, 32> LiveIns, LiveOuts;
3209 LiveIns.reserve(N: NumBlocks);
3210 LiveOuts.reserve(N: NumBlocks);
3211
3212 // Initialize all values to start as NoVals. This signifies "it's live
3213 // through, but we don't know what it is".
3214 DbgValueProperties EmptyProperties(EmptyExpr, false, false);
3215 for (unsigned int I = 0; I < NumBlocks; ++I) {
3216 DbgValue EmptyDbgValue(I, EmptyProperties, DbgValue::NoVal);
3217 LiveIns.push_back(Elt: EmptyDbgValue);
3218 LiveOuts.push_back(Elt: EmptyDbgValue);
3219 }
3220
3221 // Produce by-MBB indexes of live-in/live-outs, to ease lookup within
3222 // vlocJoin.
3223 LiveIdxT LiveOutIdx, LiveInIdx;
3224 LiveOutIdx.reserve(NumEntries: NumBlocks);
3225 LiveInIdx.reserve(NumEntries: NumBlocks);
3226 for (unsigned I = 0; I < NumBlocks; ++I) {
3227 LiveOutIdx[BlockOrders[I]] = &LiveOuts[I];
3228 LiveInIdx[BlockOrders[I]] = &LiveIns[I];
3229 }
3230
3231 // Loop over each variable and place PHIs for it, then propagate values
3232 // between blocks. This keeps the locality of working on one lexical scope at
3233 // at time, but avoids re-processing variable values because some other
3234 // variable has been assigned.
3235 for (DebugVariableID VarID : VarsWeCareAbout) {
3236 // Re-initialize live-ins and live-outs, to clear the remains of previous
3237 // variables live-ins / live-outs.
3238 for (unsigned int I = 0; I < NumBlocks; ++I) {
3239 DbgValue EmptyDbgValue(I, EmptyProperties, DbgValue::NoVal);
3240 LiveIns[I] = EmptyDbgValue;
3241 LiveOuts[I] = EmptyDbgValue;
3242 }
3243
3244 // Place PHIs for variable values, using the LLVM IDF calculator.
3245 // Collect the set of blocks where variables are def'd.
3246 SmallPtrSet<MachineBasicBlock *, 32> DefBlocks;
3247 for (const MachineBasicBlock *ExpMBB : BlocksToExplore) {
3248 auto &TransferFunc = AllTheVLocs[ExpMBB->getNumber()].Vars;
3249 if (TransferFunc.contains(Key: VarID))
3250 DefBlocks.insert(Ptr: const_cast<MachineBasicBlock *>(ExpMBB));
3251 }
3252
3253 SmallVector<MachineBasicBlock *, 32> PHIBlocks;
3254
3255 // Request the set of PHIs we should insert for this variable. If there's
3256 // only one value definition, things are very simple.
3257 if (DefBlocks.size() == 1) {
3258 placePHIsForSingleVarDefinition(InScopeBlocks: MutBlocksToExplore, MBB: *DefBlocks.begin(),
3259 AllTheVLocs, Var: VarID, Output);
3260 continue;
3261 }
3262
3263 // Otherwise: we need to place PHIs through SSA and propagate values.
3264 BlockPHIPlacement(AllBlocks: MutBlocksToExplore, DefBlocks, PHIBlocks);
3265
3266 // Insert PHIs into the per-block live-in tables for this variable.
3267 for (MachineBasicBlock *PHIMBB : PHIBlocks) {
3268 unsigned BlockNo = PHIMBB->getNumber();
3269 DbgValue *LiveIn = LiveInIdx[PHIMBB];
3270 *LiveIn = DbgValue(BlockNo, EmptyProperties, DbgValue::VPHI);
3271 }
3272
3273 for (auto *MBB : BlockOrders) {
3274 Worklist.push(x: BBToOrder[MBB]);
3275 OnWorklist.insert(Ptr: MBB);
3276 }
3277
3278 // Iterate over all the blocks we selected, propagating the variables value.
3279 // This loop does two things:
3280 // * Eliminates un-necessary VPHIs in vlocJoin,
3281 // * Evaluates the blocks transfer function (i.e. variable assignments) and
3282 // stores the result to the blocks live-outs.
3283 // Always evaluate the transfer function on the first iteration, and when
3284 // the live-ins change thereafter.
3285 bool FirstTrip = true;
3286 while (!Worklist.empty() || !Pending.empty()) {
3287 while (!Worklist.empty()) {
3288 auto *MBB = OrderToBB[Worklist.top()];
3289 CurBB = MBB->getNumber();
3290 Worklist.pop();
3291
3292 auto LiveInsIt = LiveInIdx.find(Val: MBB);
3293 assert(LiveInsIt != LiveInIdx.end());
3294 DbgValue *LiveIn = LiveInsIt->second;
3295
3296 // Join values from predecessors. Updates LiveInIdx, and writes output
3297 // into JoinedInLocs.
3298 bool InLocsChanged =
3299 vlocJoin(MBB&: *MBB, VLOCOutLocs&: LiveOutIdx, BlocksToExplore, LiveIn&: *LiveIn);
3300
3301 SmallVector<const MachineBasicBlock *, 8> Preds(MBB->predecessors());
3302
3303 // If this block's live-in value is a VPHI, try to pick a machine-value
3304 // for it. This makes the machine-value available and propagated
3305 // through all blocks by the time value propagation finishes. We can't
3306 // do this any earlier as it needs to read the block live-outs.
3307 if (LiveIn->Kind == DbgValue::VPHI && LiveIn->BlockNo == (int)CurBB) {
3308 // There's a small possibility that on a preceeding path, a VPHI is
3309 // eliminated and transitions from VPHI-with-location to
3310 // live-through-value. As a result, the selected location of any VPHI
3311 // might change, so we need to re-compute it on each iteration.
3312 SmallVector<DbgOpID> JoinedOps;
3313
3314 if (pickVPHILoc(OutValues&: JoinedOps, MBB: *MBB, LiveOuts: LiveOutIdx, MOutLocs, BlockOrders: Preds)) {
3315 bool NewLocPicked = !equal(LRange: LiveIn->getDbgOpIDs(), RRange&: JoinedOps);
3316 InLocsChanged |= NewLocPicked;
3317 if (NewLocPicked)
3318 LiveIn->setDbgOpIDs(JoinedOps);
3319 }
3320 }
3321
3322 if (!InLocsChanged && !FirstTrip)
3323 continue;
3324
3325 DbgValue *LiveOut = LiveOutIdx[MBB];
3326 bool OLChanged = false;
3327
3328 // Do transfer function.
3329 auto &VTracker = AllTheVLocs[MBB->getNumber()];
3330 auto TransferIt = VTracker.Vars.find(Key: VarID);
3331 if (TransferIt != VTracker.Vars.end()) {
3332 // Erase on empty transfer (DBG_VALUE $noreg).
3333 if (TransferIt->second.Kind == DbgValue::Undef) {
3334 DbgValue NewVal(MBB->getNumber(), EmptyProperties, DbgValue::NoVal);
3335 if (*LiveOut != NewVal) {
3336 *LiveOut = NewVal;
3337 OLChanged = true;
3338 }
3339 } else {
3340 // Insert new variable value; or overwrite.
3341 if (*LiveOut != TransferIt->second) {
3342 *LiveOut = TransferIt->second;
3343 OLChanged = true;
3344 }
3345 }
3346 } else {
3347 // Just copy live-ins to live-outs, for anything not transferred.
3348 if (*LiveOut != *LiveIn) {
3349 *LiveOut = *LiveIn;
3350 OLChanged = true;
3351 }
3352 }
3353
3354 // If no live-out value changed, there's no need to explore further.
3355 if (!OLChanged)
3356 continue;
3357
3358 // We should visit all successors. Ensure we'll visit any non-backedge
3359 // successors during this dataflow iteration; book backedge successors
3360 // to be visited next time around.
3361 for (auto *s : MBB->successors()) {
3362 // Ignore out of scope / not-to-be-explored successors.
3363 if (!LiveInIdx.contains(Val: s))
3364 continue;
3365
3366 unsigned Order = BBToOrder[s];
3367 if (Order > BBToOrder[MBB]) {
3368 if (OnWorklist.insert(Ptr: s).second)
3369 Worklist.push(x: Order);
3370 } else if (OnPending.insert(Ptr: s).second && (FirstTrip || OLChanged)) {
3371 Pending.push(x: Order);
3372 }
3373 }
3374 }
3375 Worklist.swap(pq&: Pending);
3376 std::swap(LHS&: OnWorklist, RHS&: OnPending);
3377 OnPending.clear();
3378 assert(Pending.empty());
3379 FirstTrip = false;
3380 }
3381
3382 // Save live-ins to output vector. Ignore any that are still marked as being
3383 // VPHIs with no location -- those are variables that we know the value of,
3384 // but are not actually available in the register file.
3385 for (auto *MBB : BlockOrders) {
3386 DbgValue *BlockLiveIn = LiveInIdx[MBB];
3387 if (BlockLiveIn->Kind == DbgValue::NoVal)
3388 continue;
3389 if (BlockLiveIn->isUnjoinedPHI())
3390 continue;
3391 if (BlockLiveIn->Kind == DbgValue::VPHI)
3392 BlockLiveIn->Kind = DbgValue::Def;
3393 [[maybe_unused]] auto &[Var, DILoc] = DVMap.lookupDVID(ID: VarID);
3394 assert(BlockLiveIn->Properties.DIExpr->getFragmentInfo() ==
3395 Var.getFragment() &&
3396 "Fragment info missing during value prop");
3397 Output[MBB->getNumber()].push_back(Elt: std::make_pair(x&: VarID, y&: *BlockLiveIn));
3398 }
3399 } // Per-variable loop.
3400
3401 BlockOrders.clear();
3402 BlocksToExplore.clear();
3403}
3404
3405void InstrRefBasedLDV::placePHIsForSingleVarDefinition(
3406 const SmallPtrSetImpl<MachineBasicBlock *> &InScopeBlocks,
3407 MachineBasicBlock *AssignMBB, SmallVectorImpl<VLocTracker> &AllTheVLocs,
3408 DebugVariableID VarID, LiveInsT &Output) {
3409 // If there is a single definition of the variable, then working out it's
3410 // value everywhere is very simple: it's every block dominated by the
3411 // definition. At the dominance frontier, the usual algorithm would:
3412 // * Place PHIs,
3413 // * Propagate values into them,
3414 // * Find there's no incoming variable value from the other incoming branches
3415 // of the dominance frontier,
3416 // * Specify there's no variable value in blocks past the frontier.
3417 // This is a common case, hence it's worth special-casing it.
3418
3419 // Pick out the variables value from the block transfer function.
3420 VLocTracker &VLocs = AllTheVLocs[AssignMBB->getNumber()];
3421 auto ValueIt = VLocs.Vars.find(Key: VarID);
3422 const DbgValue &Value = ValueIt->second;
3423
3424 // If it's an explicit assignment of "undef", that means there is no location
3425 // anyway, anywhere.
3426 if (Value.Kind == DbgValue::Undef)
3427 return;
3428
3429 // Assign the variable value to entry to each dominated block that's in scope.
3430 // Skip the definition block -- it's assigned the variable value in the middle
3431 // of the block somewhere.
3432 for (auto *ScopeBlock : InScopeBlocks) {
3433 if (!DomTree->properlyDominates(A: AssignMBB, B: ScopeBlock))
3434 continue;
3435
3436 Output[ScopeBlock->getNumber()].push_back(Elt: {VarID, Value});
3437 }
3438
3439 // All blocks that aren't dominated have no live-in value, thus no variable
3440 // value will be given to them.
3441}
3442
3443#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
3444void InstrRefBasedLDV::dump_mloc_transfer(
3445 const MLocTransferMap &mloc_transfer) const {
3446 for (const auto &P : mloc_transfer) {
3447 std::string foo = MTracker->LocIdxToName(P.first);
3448 std::string bar = MTracker->IDAsString(P.second);
3449 dbgs() << "Loc " << foo << " --> " << bar << "\n";
3450 }
3451}
3452#endif
3453
3454void InstrRefBasedLDV::initialSetup(MachineFunction &MF) {
3455 // Build some useful data structures.
3456
3457 LLVMContext &Context = MF.getFunction().getContext();
3458 EmptyExpr = DIExpression::get(Context, Elements: {});
3459
3460 auto hasNonArtificialLocation = [](const MachineInstr &MI) -> bool {
3461 if (const DebugLoc &DL = MI.getDebugLoc())
3462 return DL.getLine() != 0;
3463 return false;
3464 };
3465
3466 // Collect a set of all the artificial blocks. Collect the size too, ilist
3467 // size calls are O(n).
3468 unsigned int Size = 0;
3469 for (auto &MBB : MF) {
3470 ++Size;
3471 if (none_of(Range: MBB.instrs(), P: hasNonArtificialLocation))
3472 ArtificialBlocks.insert(Ptr: &MBB);
3473 }
3474
3475 // Compute mappings of block <=> RPO order.
3476 ReversePostOrderTraversal<MachineFunction *> RPOT(&MF);
3477 unsigned int RPONumber = 0;
3478 OrderToBB.reserve(N: Size);
3479 BBToOrder.reserve(NumEntries: Size);
3480 BBNumToRPO.reserve(NumEntries: Size);
3481 auto processMBB = [&](MachineBasicBlock *MBB) {
3482 OrderToBB.push_back(Elt: MBB);
3483 BBToOrder[MBB] = RPONumber;
3484 BBNumToRPO[MBB->getNumber()] = RPONumber;
3485 ++RPONumber;
3486 };
3487 for (MachineBasicBlock *MBB : RPOT)
3488 processMBB(MBB);
3489 for (MachineBasicBlock &MBB : MF)
3490 if (!BBToOrder.contains(Val: &MBB))
3491 processMBB(&MBB);
3492
3493 // Order value substitutions by their "source" operand pair, for quick lookup.
3494 llvm::sort(C&: MF.DebugValueSubstitutions);
3495
3496#ifdef EXPENSIVE_CHECKS
3497 // As an expensive check, test whether there are any duplicate substitution
3498 // sources in the collection.
3499 if (MF.DebugValueSubstitutions.size() > 2) {
3500 for (auto It = MF.DebugValueSubstitutions.begin();
3501 It != std::prev(MF.DebugValueSubstitutions.end()); ++It) {
3502 assert(It->Src != std::next(It)->Src && "Duplicate variable location "
3503 "substitution seen");
3504 }
3505 }
3506#endif
3507}
3508
3509// Produce an "ejection map" for blocks, i.e., what's the highest-numbered
3510// lexical scope it's used in. When exploring in DFS order and we pass that
3511// scope, the block can be processed and any tracking information freed.
3512void InstrRefBasedLDV::makeDepthFirstEjectionMap(
3513 SmallVectorImpl<unsigned> &EjectionMap,
3514 const ScopeToDILocT &ScopeToDILocation,
3515 ScopeToAssignBlocksT &ScopeToAssignBlocks) {
3516 SmallPtrSet<const MachineBasicBlock *, 8> BlocksToExplore;
3517 SmallVector<std::pair<LexicalScope *, ssize_t>, 4> WorkStack;
3518 auto *TopScope = LS.getCurrentFunctionScope();
3519
3520 // Unlike lexical scope explorers, we explore in reverse order, to find the
3521 // "last" lexical scope used for each block early.
3522 WorkStack.push_back(Elt: {TopScope, TopScope->getChildren().size() - 1});
3523
3524 while (!WorkStack.empty()) {
3525 auto &ScopePosition = WorkStack.back();
3526 LexicalScope *WS = ScopePosition.first;
3527 ssize_t ChildNum = ScopePosition.second--;
3528
3529 const SmallVectorImpl<LexicalScope *> &Children = WS->getChildren();
3530 if (ChildNum >= 0) {
3531 // If ChildNum is positive, there are remaining children to explore.
3532 // Push the child and its children-count onto the stack.
3533 auto &ChildScope = Children[ChildNum];
3534 WorkStack.push_back(
3535 Elt: std::make_pair(x: ChildScope, y: ChildScope->getChildren().size() - 1));
3536 } else {
3537 WorkStack.pop_back();
3538
3539 // We've explored all children and any later blocks: examine all blocks
3540 // in our scope. If they haven't yet had an ejection number set, then
3541 // this scope will be the last to use that block.
3542 auto DILocationIt = ScopeToDILocation.find(Val: WS);
3543 if (DILocationIt != ScopeToDILocation.end()) {
3544 getBlocksForScope(DILoc: DILocationIt->second, BlocksToExplore,
3545 AssignBlocks: ScopeToAssignBlocks.find(Val: WS)->second);
3546 for (const auto *MBB : BlocksToExplore) {
3547 unsigned BBNum = MBB->getNumber();
3548 if (EjectionMap[BBNum] == 0)
3549 EjectionMap[BBNum] = WS->getDFSOut();
3550 }
3551
3552 BlocksToExplore.clear();
3553 }
3554 }
3555 }
3556}
3557
3558bool InstrRefBasedLDV::depthFirstVLocAndEmit(
3559 unsigned MaxNumBlocks, const ScopeToDILocT &ScopeToDILocation,
3560 const ScopeToVarsT &ScopeToVars, ScopeToAssignBlocksT &ScopeToAssignBlocks,
3561 LiveInsT &Output, FuncValueTable &MOutLocs, FuncValueTable &MInLocs,
3562 SmallVectorImpl<VLocTracker> &AllTheVLocs, MachineFunction &MF,
3563 bool ShouldEmitDebugEntryValues) {
3564 TTracker = new TransferTracker(TII, MTracker, MF, DVMap, *TRI,
3565 CalleeSavedRegs, ShouldEmitDebugEntryValues);
3566 unsigned NumLocs = MTracker->getNumLocs();
3567 VTracker = nullptr;
3568
3569 // No scopes? No variable locations.
3570 if (!LS.getCurrentFunctionScope())
3571 return false;
3572
3573 // Build map from block number to the last scope that uses the block.
3574 SmallVector<unsigned, 16> EjectionMap;
3575 EjectionMap.resize(N: MaxNumBlocks, NV: 0);
3576 makeDepthFirstEjectionMap(EjectionMap, ScopeToDILocation,
3577 ScopeToAssignBlocks);
3578
3579 // Helper lambda for ejecting a block -- if nothing is going to use the block,
3580 // we can translate the variable location information into DBG_VALUEs and then
3581 // free all of InstrRefBasedLDV's data structures.
3582 auto EjectBlock = [&](MachineBasicBlock &MBB) -> void {
3583 unsigned BBNum = MBB.getNumber();
3584 AllTheVLocs[BBNum].clear();
3585
3586 // Prime the transfer-tracker, and then step through all the block
3587 // instructions, installing transfers.
3588 MTracker->reset();
3589 MTracker->loadFromArray(Locs&: MInLocs[MBB], NewCurBB: BBNum);
3590 TTracker->loadInlocs(MBB, MLocs&: MInLocs[MBB], DbgOpStore, VLocs: Output[BBNum], NumLocs);
3591
3592 CurBB = BBNum;
3593 CurInst = 1;
3594 for (auto &MI : MBB) {
3595 process(MI, MLiveOuts: &MOutLocs, MLiveIns: &MInLocs);
3596 TTracker->checkInstForNewValues(Inst: CurInst, pos: MI.getIterator());
3597 ++CurInst;
3598 }
3599
3600 // Free machine-location tables for this block.
3601 MInLocs.ejectTableForBlock(MBB);
3602 MOutLocs.ejectTableForBlock(MBB);
3603 // We don't need live-in variable values for this block either.
3604 Output[BBNum].clear();
3605 AllTheVLocs[BBNum].clear();
3606 };
3607
3608 SmallPtrSet<const MachineBasicBlock *, 8> BlocksToExplore;
3609 SmallVector<std::pair<LexicalScope *, ssize_t>, 4> WorkStack;
3610 WorkStack.push_back(Elt: {LS.getCurrentFunctionScope(), 0});
3611 unsigned HighestDFSIn = 0;
3612
3613 // Proceed to explore in depth first order.
3614 while (!WorkStack.empty()) {
3615 auto &ScopePosition = WorkStack.back();
3616 LexicalScope *WS = ScopePosition.first;
3617 ssize_t ChildNum = ScopePosition.second++;
3618
3619 // We obesrve scopes with children twice here, once descending in, once
3620 // ascending out of the scope nest. Use HighestDFSIn as a ratchet to ensure
3621 // we don't process a scope twice. Additionally, ignore scopes that don't
3622 // have a DILocation -- by proxy, this means we never tracked any variable
3623 // assignments in that scope.
3624 auto DILocIt = ScopeToDILocation.find(Val: WS);
3625 if (HighestDFSIn <= WS->getDFSIn() && DILocIt != ScopeToDILocation.end()) {
3626 const DILocation *DILoc = DILocIt->second;
3627 auto &VarsWeCareAbout = ScopeToVars.find(Val: WS)->second;
3628 auto &BlocksInScope = ScopeToAssignBlocks.find(Val: WS)->second;
3629
3630 buildVLocValueMap(DILoc, VarsWeCareAbout, AssignBlocks&: BlocksInScope, Output, MOutLocs,
3631 MInLocs, AllTheVLocs);
3632 }
3633
3634 HighestDFSIn = std::max(a: HighestDFSIn, b: WS->getDFSIn());
3635
3636 // Descend into any scope nests.
3637 const SmallVectorImpl<LexicalScope *> &Children = WS->getChildren();
3638 if (ChildNum < (ssize_t)Children.size()) {
3639 // There are children to explore -- push onto stack and continue.
3640 auto &ChildScope = Children[ChildNum];
3641 WorkStack.push_back(Elt: std::make_pair(x: ChildScope, y: 0));
3642 } else {
3643 WorkStack.pop_back();
3644
3645 // We've explored a leaf, or have explored all the children of a scope.
3646 // Try to eject any blocks where this is the last scope it's relevant to.
3647 auto DILocationIt = ScopeToDILocation.find(Val: WS);
3648 if (DILocationIt == ScopeToDILocation.end())
3649 continue;
3650
3651 getBlocksForScope(DILoc: DILocationIt->second, BlocksToExplore,
3652 AssignBlocks: ScopeToAssignBlocks.find(Val: WS)->second);
3653 for (const auto *MBB : BlocksToExplore)
3654 if (WS->getDFSOut() == EjectionMap[MBB->getNumber()])
3655 EjectBlock(const_cast<MachineBasicBlock &>(*MBB));
3656
3657 BlocksToExplore.clear();
3658 }
3659 }
3660
3661 // Some artificial blocks may not have been ejected, meaning they're not
3662 // connected to an actual legitimate scope. This can technically happen
3663 // with things like the entry block. In theory, we shouldn't need to do
3664 // anything for such out-of-scope blocks, but for the sake of being similar
3665 // to VarLocBasedLDV, eject these too.
3666 for (auto *MBB : ArtificialBlocks)
3667 if (MInLocs.hasTableFor(MBB&: *MBB))
3668 EjectBlock(*MBB);
3669
3670 return emitTransfers();
3671}
3672
3673bool InstrRefBasedLDV::emitTransfers() {
3674 // Go through all the transfers recorded in the TransferTracker -- this is
3675 // both the live-ins to a block, and any movements of values that happen
3676 // in the middle.
3677 for (auto &P : TTracker->Transfers) {
3678 // We have to insert DBG_VALUEs in a consistent order, otherwise they
3679 // appear in DWARF in different orders. Use the order that they appear
3680 // when walking through each block / each instruction, stored in
3681 // DVMap.
3682 llvm::sort(C&: P.Insts, Comp: llvm::less_first());
3683
3684 // Insert either before or after the designated point...
3685 if (P.MBB) {
3686 MachineBasicBlock &MBB = *P.MBB;
3687 for (const auto &Pair : P.Insts)
3688 MBB.insert(I: P.Pos, M: Pair.second);
3689 } else {
3690 // Terminators, like tail calls, can clobber things. Don't try and place
3691 // transfers after them.
3692 if (P.Pos->isTerminator())
3693 continue;
3694
3695 MachineBasicBlock &MBB = *P.Pos->getParent();
3696 for (const auto &Pair : P.Insts)
3697 MBB.insertAfterBundle(I: P.Pos, MI: Pair.second);
3698 }
3699 }
3700
3701 return TTracker->Transfers.size() != 0;
3702}
3703
3704/// Calculate the liveness information for the given machine function and
3705/// extend ranges across basic blocks.
3706bool InstrRefBasedLDV::ExtendRanges(MachineFunction &MF,
3707 MachineDominatorTree *DomTree,
3708 bool ShouldEmitDebugEntryValues,
3709 unsigned InputBBLimit,
3710 unsigned InputDbgValLimit) {
3711 // No subprogram means this function contains no debuginfo.
3712 if (!MF.getFunction().getSubprogram())
3713 return false;
3714
3715 LLVM_DEBUG(dbgs() << "\nDebug Range Extension\n");
3716
3717 this->DomTree = DomTree;
3718 TRI = MF.getSubtarget().getRegisterInfo();
3719 MRI = &MF.getRegInfo();
3720 TII = MF.getSubtarget().getInstrInfo();
3721 TFI = MF.getSubtarget().getFrameLowering();
3722 TFI->getCalleeSaves(MF, SavedRegs&: CalleeSavedRegs);
3723 MFI = &MF.getFrameInfo();
3724 LS.initialize(MF);
3725
3726 const auto &STI = MF.getSubtarget();
3727 AdjustsStackInCalls = MFI->adjustsStack() &&
3728 STI.getFrameLowering()->stackProbeFunctionModifiesSP();
3729 if (AdjustsStackInCalls)
3730 StackProbeSymbolName = STI.getTargetLowering()->getStackProbeSymbolName(MF);
3731
3732 MTracker =
3733 new MLocTracker(MF, *TII, *TRI, *MF.getSubtarget().getTargetLowering());
3734 VTracker = nullptr;
3735 TTracker = nullptr;
3736
3737 SmallVector<MLocTransferMap, 32> MLocTransfer;
3738 SmallVector<VLocTracker, 8> vlocs;
3739 LiveInsT SavedLiveIns;
3740
3741 int MaxNumBlocks = -1;
3742 for (auto &MBB : MF)
3743 MaxNumBlocks = std::max(a: MBB.getNumber(), b: MaxNumBlocks);
3744 assert(MaxNumBlocks >= 0);
3745 ++MaxNumBlocks;
3746
3747 initialSetup(MF);
3748
3749 MLocTransfer.resize(N: MaxNumBlocks);
3750 vlocs.resize(N: MaxNumBlocks, NV: VLocTracker(DVMap, OverlapFragments, EmptyExpr));
3751 SavedLiveIns.resize(N: MaxNumBlocks);
3752
3753 produceMLocTransferFunction(MF, MLocTransfer, MaxNumBlocks);
3754
3755 // Allocate and initialize two array-of-arrays for the live-in and live-out
3756 // machine values. The outer dimension is the block number; while the inner
3757 // dimension is a LocIdx from MLocTracker.
3758 unsigned NumLocs = MTracker->getNumLocs();
3759 FuncValueTable MOutLocs(MaxNumBlocks, NumLocs);
3760 FuncValueTable MInLocs(MaxNumBlocks, NumLocs);
3761
3762 // Solve the machine value dataflow problem using the MLocTransfer function,
3763 // storing the computed live-ins / live-outs into the array-of-arrays. We use
3764 // both live-ins and live-outs for decision making in the variable value
3765 // dataflow problem.
3766 buildMLocValueMap(MF, MInLocs, MOutLocs, MLocTransfer);
3767
3768 // Patch up debug phi numbers, turning unknown block-live-in values into
3769 // either live-through machine values, or PHIs.
3770 for (auto &DBG_PHI : DebugPHINumToValue) {
3771 // Identify unresolved block-live-ins.
3772 if (!DBG_PHI.ValueRead)
3773 continue;
3774
3775 ValueIDNum &Num = *DBG_PHI.ValueRead;
3776 if (!Num.isPHI())
3777 continue;
3778
3779 unsigned BlockNo = Num.getBlock();
3780 LocIdx LocNo = Num.getLoc();
3781 ValueIDNum ResolvedValue = MInLocs[BlockNo][LocNo.asU64()];
3782 // If there is no resolved value for this live-in then it is not directly
3783 // reachable from the entry block -- model it as a PHI on entry to this
3784 // block, which means we leave the ValueIDNum unchanged.
3785 if (ResolvedValue != ValueIDNum::EmptyValue)
3786 Num = ResolvedValue;
3787 }
3788 // Later, we'll be looking up ranges of instruction numbers.
3789 llvm::sort(C&: DebugPHINumToValue);
3790
3791 // Walk back through each block / instruction, collecting DBG_VALUE
3792 // instructions and recording what machine value their operands refer to.
3793 for (MachineBasicBlock *MBB : OrderToBB) {
3794 CurBB = MBB->getNumber();
3795 VTracker = &vlocs[CurBB];
3796 VTracker->MBB = MBB;
3797 MTracker->loadFromArray(Locs&: MInLocs[*MBB], NewCurBB: CurBB);
3798 CurInst = 1;
3799 for (auto &MI : *MBB) {
3800 process(MI, MLiveOuts: &MOutLocs, MLiveIns: &MInLocs);
3801 ++CurInst;
3802 }
3803 MTracker->reset();
3804 }
3805
3806 // Map from one LexicalScope to all the variables in that scope.
3807 ScopeToVarsT ScopeToVars;
3808
3809 // Map from One lexical scope to all blocks where assignments happen for
3810 // that scope.
3811 ScopeToAssignBlocksT ScopeToAssignBlocks;
3812
3813 // Store map of DILocations that describes scopes.
3814 ScopeToDILocT ScopeToDILocation;
3815
3816 // To mirror old LiveDebugValues, enumerate variables in RPOT order. Otherwise
3817 // the order is unimportant, it just has to be stable.
3818 unsigned VarAssignCount = 0;
3819 for (MachineBasicBlock *MBB : OrderToBB) {
3820 auto *VTracker = &vlocs[MBB->getNumber()];
3821 // Collect each variable with a DBG_VALUE in this block.
3822 for (auto &idx : VTracker->Vars) {
3823 DebugVariableID VarID = idx.first;
3824 const DILocation *ScopeLoc = VTracker->Scopes[VarID];
3825 assert(ScopeLoc != nullptr);
3826 auto *Scope = LS.findLexicalScope(DL: ScopeLoc);
3827
3828 // No insts in scope -> shouldn't have been recorded.
3829 assert(Scope != nullptr);
3830
3831 ScopeToVars[Scope].insert(V: VarID);
3832 ScopeToAssignBlocks[Scope].insert(Ptr: VTracker->MBB);
3833 ScopeToDILocation[Scope] = ScopeLoc;
3834 ++VarAssignCount;
3835 }
3836 }
3837
3838 bool Changed = false;
3839
3840 // If we have an extremely large number of variable assignments and blocks,
3841 // bail out at this point. We've burnt some time doing analysis already,
3842 // however we should cut our losses.
3843 if ((unsigned)MaxNumBlocks > InputBBLimit &&
3844 VarAssignCount > InputDbgValLimit) {
3845 LLVM_DEBUG(dbgs() << "Disabling InstrRefBasedLDV: " << MF.getName()
3846 << " has " << MaxNumBlocks << " basic blocks and "
3847 << VarAssignCount
3848 << " variable assignments, exceeding limits.\n");
3849 } else {
3850 // Optionally, solve the variable value problem and emit to blocks by using
3851 // a lexical-scope-depth search. It should be functionally identical to
3852 // the "else" block of this condition.
3853 Changed = depthFirstVLocAndEmit(
3854 MaxNumBlocks, ScopeToDILocation, ScopeToVars, ScopeToAssignBlocks,
3855 Output&: SavedLiveIns, MOutLocs, MInLocs, AllTheVLocs&: vlocs, MF, ShouldEmitDebugEntryValues);
3856 }
3857
3858 delete MTracker;
3859 delete TTracker;
3860 MTracker = nullptr;
3861 VTracker = nullptr;
3862 TTracker = nullptr;
3863
3864 ArtificialBlocks.clear();
3865 OrderToBB.clear();
3866 BBToOrder.clear();
3867 BBNumToRPO.clear();
3868 DebugInstrNumToInstr.clear();
3869 DebugPHINumToValue.clear();
3870 OverlapFragments.clear();
3871 SeenFragments.clear();
3872 SeenDbgPHIs.clear();
3873 DbgOpStore.clear();
3874 DVMap.clear();
3875
3876 return Changed;
3877}
3878
3879LDVImpl *llvm::makeInstrRefBasedLiveDebugValues() {
3880 return new InstrRefBasedLDV();
3881}
3882
3883namespace {
3884class LDVSSABlock;
3885class LDVSSAUpdater;
3886
3887// Pick a type to identify incoming block values as we construct SSA. We
3888// can't use anything more robust than an integer unfortunately, as SSAUpdater
3889// expects to zero-initialize the type.
3890typedef uint64_t BlockValueNum;
3891
3892/// Represents an SSA PHI node for the SSA updater class. Contains the block
3893/// this PHI is in, the value number it would have, and the expected incoming
3894/// values from parent blocks.
3895class LDVSSAPhi {
3896public:
3897 SmallVector<std::pair<LDVSSABlock *, BlockValueNum>, 4> IncomingValues;
3898 LDVSSABlock *ParentBlock;
3899 BlockValueNum PHIValNum;
3900 LDVSSAPhi(BlockValueNum PHIValNum, LDVSSABlock *ParentBlock)
3901 : ParentBlock(ParentBlock), PHIValNum(PHIValNum) {}
3902
3903 LDVSSABlock *getParent() { return ParentBlock; }
3904};
3905
3906/// Thin wrapper around a block predecessor iterator. Only difference from a
3907/// normal block iterator is that it dereferences to an LDVSSABlock.
3908class LDVSSABlockIterator {
3909public:
3910 MachineBasicBlock::pred_iterator PredIt;
3911 LDVSSAUpdater &Updater;
3912
3913 LDVSSABlockIterator(MachineBasicBlock::pred_iterator PredIt,
3914 LDVSSAUpdater &Updater)
3915 : PredIt(PredIt), Updater(Updater) {}
3916
3917 bool operator!=(const LDVSSABlockIterator &OtherIt) const {
3918 return OtherIt.PredIt != PredIt;
3919 }
3920
3921 LDVSSABlockIterator &operator++() {
3922 ++PredIt;
3923 return *this;
3924 }
3925
3926 LDVSSABlock *operator*();
3927};
3928
3929/// Thin wrapper around a block for SSA Updater interface. Necessary because
3930/// we need to track the PHI value(s) that we may have observed as necessary
3931/// in this block.
3932class LDVSSABlock {
3933public:
3934 MachineBasicBlock &BB;
3935 LDVSSAUpdater &Updater;
3936 using PHIListT = SmallVector<LDVSSAPhi, 1>;
3937 /// List of PHIs in this block. There should only ever be one.
3938 PHIListT PHIList;
3939
3940 LDVSSABlock(MachineBasicBlock &BB, LDVSSAUpdater &Updater)
3941 : BB(BB), Updater(Updater) {}
3942
3943 LDVSSABlockIterator succ_begin() {
3944 return LDVSSABlockIterator(BB.succ_begin(), Updater);
3945 }
3946
3947 LDVSSABlockIterator succ_end() {
3948 return LDVSSABlockIterator(BB.succ_end(), Updater);
3949 }
3950
3951 /// SSAUpdater has requested a PHI: create that within this block record.
3952 LDVSSAPhi *newPHI(BlockValueNum Value) {
3953 PHIList.emplace_back(Args&: Value, Args: this);
3954 return &PHIList.back();
3955 }
3956
3957 /// SSAUpdater wishes to know what PHIs already exist in this block.
3958 PHIListT &phis() { return PHIList; }
3959};
3960
3961/// Utility class for the SSAUpdater interface: tracks blocks, PHIs and values
3962/// while SSAUpdater is exploring the CFG. It's passed as a handle / baton to
3963// SSAUpdaterTraits<LDVSSAUpdater>.
3964class LDVSSAUpdater {
3965public:
3966 /// Map of value numbers to PHI records.
3967 DenseMap<BlockValueNum, LDVSSAPhi *> PHIs;
3968 /// Map of which blocks generate Undef values -- blocks that are not
3969 /// dominated by any Def.
3970 DenseMap<MachineBasicBlock *, BlockValueNum> PoisonMap;
3971 /// Map of machine blocks to our own records of them.
3972 DenseMap<MachineBasicBlock *, LDVSSABlock *> BlockMap;
3973 /// Machine location where any PHI must occur.
3974 LocIdx Loc;
3975 /// Table of live-in machine value numbers for blocks / locations.
3976 const FuncValueTable &MLiveIns;
3977
3978 LDVSSAUpdater(LocIdx L, const FuncValueTable &MLiveIns)
3979 : Loc(L), MLiveIns(MLiveIns) {}
3980
3981 void reset() {
3982 for (auto &Block : BlockMap)
3983 delete Block.second;
3984
3985 PHIs.clear();
3986 PoisonMap.clear();
3987 BlockMap.clear();
3988 }
3989
3990 ~LDVSSAUpdater() { reset(); }
3991
3992 /// For a given MBB, create a wrapper block for it. Stores it in the
3993 /// LDVSSAUpdater block map.
3994 LDVSSABlock *getSSALDVBlock(MachineBasicBlock *BB) {
3995 auto [It, Inserted] = BlockMap.try_emplace(Key: BB);
3996 if (Inserted)
3997 It->second = new LDVSSABlock(*BB, *this);
3998 return It->second;
3999 }
4000
4001 /// Find the live-in value number for the given block. Looks up the value at
4002 /// the PHI location on entry.
4003 BlockValueNum getValue(LDVSSABlock *LDVBB) {
4004 return MLiveIns[LDVBB->BB][Loc.asU64()].asU64();
4005 }
4006};
4007
4008LDVSSABlock *LDVSSABlockIterator::operator*() {
4009 return Updater.getSSALDVBlock(BB: *PredIt);
4010}
4011
4012#ifndef NDEBUG
4013
4014raw_ostream &operator<<(raw_ostream &out, const LDVSSAPhi &PHI) {
4015 out << "SSALDVPHI " << PHI.PHIValNum;
4016 return out;
4017}
4018
4019#endif
4020
4021} // namespace
4022
4023namespace llvm {
4024
4025/// Template specialization to give SSAUpdater access to CFG and value
4026/// information. SSAUpdater calls methods in these traits, passing in the
4027/// LDVSSAUpdater object, to learn about blocks and the values they define.
4028/// It also provides methods to create PHI nodes and track them.
4029template <> class SSAUpdaterTraits<LDVSSAUpdater> {
4030public:
4031 using BlkT = LDVSSABlock;
4032 using ValT = BlockValueNum;
4033 using PhiT = LDVSSAPhi;
4034 using BlkSucc_iterator = LDVSSABlockIterator;
4035
4036 // Methods to access block successors -- dereferencing to our wrapper class.
4037 static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
4038 static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
4039
4040 /// Iterator for PHI operands.
4041 class PHI_iterator {
4042 private:
4043 LDVSSAPhi *PHI;
4044 unsigned Idx;
4045
4046 public:
4047 explicit PHI_iterator(LDVSSAPhi *P) // begin iterator
4048 : PHI(P), Idx(0) {}
4049 PHI_iterator(LDVSSAPhi *P, bool) // end iterator
4050 : PHI(P), Idx(PHI->IncomingValues.size()) {}
4051
4052 PHI_iterator &operator++() {
4053 Idx++;
4054 return *this;
4055 }
4056 bool operator==(const PHI_iterator &X) const { return Idx == X.Idx; }
4057 bool operator!=(const PHI_iterator &X) const { return !operator==(X); }
4058
4059 BlockValueNum getIncomingValue() { return PHI->IncomingValues[Idx].second; }
4060
4061 LDVSSABlock *getIncomingBlock() { return PHI->IncomingValues[Idx].first; }
4062 };
4063
4064 static inline PHI_iterator PHI_begin(PhiT *PHI) { return PHI_iterator(PHI); }
4065
4066 static inline PHI_iterator PHI_end(PhiT *PHI) {
4067 return PHI_iterator(PHI, true);
4068 }
4069
4070 /// FindPredecessorBlocks - Put the predecessors of BB into the Preds
4071 /// vector.
4072 static void FindPredecessorBlocks(LDVSSABlock *BB,
4073 SmallVectorImpl<LDVSSABlock *> *Preds) {
4074 for (MachineBasicBlock *Pred : BB->BB.predecessors())
4075 Preds->push_back(Elt: BB->Updater.getSSALDVBlock(BB: Pred));
4076 }
4077
4078 /// GetPoisonVal - Normally creates an IMPLICIT_DEF instruction with a new
4079 /// register. For LiveDebugValues, represents a block identified as not having
4080 /// any DBG_PHI predecessors.
4081 static BlockValueNum GetPoisonVal(LDVSSABlock *BB, LDVSSAUpdater *Updater) {
4082 // Create a value number for this block -- it needs to be unique and in the
4083 // "poison" collection, so that we know it's not real. Use a number
4084 // representing a PHI into this block.
4085 BlockValueNum Num = ValueIDNum(BB->BB.getNumber(), 0, Updater->Loc).asU64();
4086 Updater->PoisonMap[&BB->BB] = Num;
4087 return Num;
4088 }
4089
4090 /// CreateEmptyPHI - Create a (representation of a) PHI in the given block.
4091 /// SSAUpdater will populate it with information about incoming values. The
4092 /// value number of this PHI is whatever the machine value number problem
4093 /// solution determined it to be. This includes non-phi values if SSAUpdater
4094 /// tries to create a PHI where the incoming values are identical.
4095 static BlockValueNum CreateEmptyPHI(LDVSSABlock *BB, unsigned NumPreds,
4096 LDVSSAUpdater *Updater) {
4097 BlockValueNum PHIValNum = Updater->getValue(LDVBB: BB);
4098 LDVSSAPhi *PHI = BB->newPHI(Value: PHIValNum);
4099 Updater->PHIs[PHIValNum] = PHI;
4100 return PHIValNum;
4101 }
4102
4103 /// AddPHIOperand - Add the specified value as an operand of the PHI for
4104 /// the specified predecessor block.
4105 static void AddPHIOperand(LDVSSAPhi *PHI, BlockValueNum Val, LDVSSABlock *Pred) {
4106 PHI->IncomingValues.push_back(Elt: std::make_pair(x&: Pred, y&: Val));
4107 }
4108
4109 /// ValueIsPHI - Check if the instruction that defines the specified value
4110 /// is a PHI instruction.
4111 static LDVSSAPhi *ValueIsPHI(BlockValueNum Val, LDVSSAUpdater *Updater) {
4112 return Updater->PHIs.lookup(Val);
4113 }
4114
4115 /// ValueIsNewPHI - Like ValueIsPHI but also check if the PHI has no source
4116 /// operands, i.e., it was just added.
4117 static LDVSSAPhi *ValueIsNewPHI(BlockValueNum Val, LDVSSAUpdater *Updater) {
4118 LDVSSAPhi *PHI = ValueIsPHI(Val, Updater);
4119 if (PHI && PHI->IncomingValues.size() == 0)
4120 return PHI;
4121 return nullptr;
4122 }
4123
4124 /// GetPHIValue - For the specified PHI instruction, return the value
4125 /// that it defines.
4126 static BlockValueNum GetPHIValue(LDVSSAPhi *PHI) { return PHI->PHIValNum; }
4127};
4128
4129} // end namespace llvm
4130
4131std::optional<ValueIDNum> InstrRefBasedLDV::resolveDbgPHIs(
4132 MachineFunction &MF, const FuncValueTable &MLiveOuts,
4133 const FuncValueTable &MLiveIns, MachineInstr &Here, uint64_t InstrNum) {
4134 // This function will be called twice per DBG_INSTR_REF, and might end up
4135 // computing lots of SSA information: memoize it.
4136 auto SeenDbgPHIIt = SeenDbgPHIs.find(Val: std::make_pair(x: &Here, y&: InstrNum));
4137 if (SeenDbgPHIIt != SeenDbgPHIs.end())
4138 return SeenDbgPHIIt->second;
4139
4140 std::optional<ValueIDNum> Result =
4141 resolveDbgPHIsImpl(MF, MLiveOuts, MLiveIns, Here, InstrNum);
4142 SeenDbgPHIs.insert(KV: {std::make_pair(x: &Here, y&: InstrNum), Result});
4143 return Result;
4144}
4145
4146std::optional<ValueIDNum> InstrRefBasedLDV::resolveDbgPHIsImpl(
4147 MachineFunction &MF, const FuncValueTable &MLiveOuts,
4148 const FuncValueTable &MLiveIns, MachineInstr &Here, uint64_t InstrNum) {
4149 // Pick out records of DBG_PHI instructions that have been observed. If there
4150 // are none, then we cannot compute a value number.
4151 auto RangePair = std::equal_range(first: DebugPHINumToValue.begin(),
4152 last: DebugPHINumToValue.end(), val: InstrNum);
4153 auto LowerIt = RangePair.first;
4154 auto UpperIt = RangePair.second;
4155
4156 // No DBG_PHI means there can be no location.
4157 if (LowerIt == UpperIt)
4158 return std::nullopt;
4159
4160 // If any DBG_PHIs referred to a location we didn't understand, don't try to
4161 // compute a value. There might be scenarios where we could recover a value
4162 // for some range of DBG_INSTR_REFs, but at this point we can have high
4163 // confidence that we've seen a bug.
4164 auto DBGPHIRange = make_range(x: LowerIt, y: UpperIt);
4165 for (const DebugPHIRecord &DBG_PHI : DBGPHIRange)
4166 if (!DBG_PHI.ValueRead)
4167 return std::nullopt;
4168
4169 // If there's only one DBG_PHI, then that is our value number.
4170 if (std::distance(first: LowerIt, last: UpperIt) == 1)
4171 return *LowerIt->ValueRead;
4172
4173 // Pick out the location (physreg, slot) where any PHIs must occur. It's
4174 // technically possible for us to merge values in different registers in each
4175 // block, but highly unlikely that LLVM will generate such code after register
4176 // allocation.
4177 LocIdx Loc = *LowerIt->ReadLoc;
4178
4179 // We have several DBG_PHIs, and a use position (the Here inst). All each
4180 // DBG_PHI does is identify a value at a program position. We can treat each
4181 // DBG_PHI like it's a Def of a value, and the use position is a Use of a
4182 // value, just like SSA. We use the bulk-standard LLVM SSA updater class to
4183 // determine which Def is used at the Use, and any PHIs that happen along
4184 // the way.
4185 // Adapted LLVM SSA Updater:
4186 LDVSSAUpdater Updater(Loc, MLiveIns);
4187 // Map of which Def or PHI is the current value in each block.
4188 DenseMap<LDVSSABlock *, BlockValueNum> AvailableValues;
4189 // Set of PHIs that we have created along the way.
4190 SmallVector<LDVSSAPhi *, 8> CreatedPHIs;
4191
4192 // Each existing DBG_PHI is a Def'd value under this model. Record these Defs
4193 // for the SSAUpdater.
4194 for (const auto &DBG_PHI : DBGPHIRange) {
4195 LDVSSABlock *Block = Updater.getSSALDVBlock(BB: DBG_PHI.MBB);
4196 const ValueIDNum &Num = *DBG_PHI.ValueRead;
4197 AvailableValues.insert(KV: std::make_pair(x&: Block, y: Num.asU64()));
4198 }
4199
4200 LDVSSABlock *HereBlock = Updater.getSSALDVBlock(BB: Here.getParent());
4201 const auto &AvailIt = AvailableValues.find(Val: HereBlock);
4202 if (AvailIt != AvailableValues.end()) {
4203 // Actually, we already know what the value is -- the Use is in the same
4204 // block as the Def.
4205 return ValueIDNum::fromU64(v: AvailIt->second);
4206 }
4207
4208 // Otherwise, we must use the SSA Updater. It will identify the value number
4209 // that we are to use, and the PHIs that must happen along the way.
4210 SSAUpdaterImpl<LDVSSAUpdater> Impl(&Updater, &AvailableValues, &CreatedPHIs);
4211 BlockValueNum ResultInt = Impl.GetValue(BB: Updater.getSSALDVBlock(BB: Here.getParent()));
4212 ValueIDNum Result = ValueIDNum::fromU64(v: ResultInt);
4213
4214 // We have the number for a PHI, or possibly live-through value, to be used
4215 // at this Use. There are a number of things we have to check about it though:
4216 // * Does any PHI use an 'Undef' (like an IMPLICIT_DEF) value? If so, this
4217 // Use was not completely dominated by DBG_PHIs and we should abort.
4218 // * Are the Defs or PHIs clobbered in a block? SSAUpdater isn't aware that
4219 // we've left SSA form. Validate that the inputs to each PHI are the
4220 // expected values.
4221 // * Is a PHI we've created actually a merging of values, or are all the
4222 // predecessor values the same, leading to a non-PHI machine value number?
4223 // (SSAUpdater doesn't know that either). Remap validated PHIs into the
4224 // the ValidatedValues collection below to sort this out.
4225 DenseMap<LDVSSABlock *, ValueIDNum> ValidatedValues;
4226
4227 // Define all the input DBG_PHI values in ValidatedValues.
4228 for (const auto &DBG_PHI : DBGPHIRange) {
4229 LDVSSABlock *Block = Updater.getSSALDVBlock(BB: DBG_PHI.MBB);
4230 const ValueIDNum &Num = *DBG_PHI.ValueRead;
4231 ValidatedValues.insert(KV: std::make_pair(x&: Block, y: Num));
4232 }
4233
4234 // Sort PHIs to validate into RPO-order.
4235 SmallVector<LDVSSAPhi *, 8> SortedPHIs(CreatedPHIs);
4236
4237 llvm::sort(C&: SortedPHIs, Comp: [&](LDVSSAPhi *A, LDVSSAPhi *B) {
4238 return BBToOrder[&A->getParent()->BB] < BBToOrder[&B->getParent()->BB];
4239 });
4240
4241 for (auto &PHI : SortedPHIs) {
4242 ValueIDNum ThisBlockValueNum = MLiveIns[PHI->ParentBlock->BB][Loc.asU64()];
4243
4244 // Are all these things actually defined?
4245 for (auto &PHIIt : PHI->IncomingValues) {
4246 // Any undef input means DBG_PHIs didn't dominate the use point.
4247 if (Updater.PoisonMap.contains(Val: &PHIIt.first->BB))
4248 return std::nullopt;
4249
4250 ValueIDNum ValueToCheck;
4251 const ValueTable &BlockLiveOuts = MLiveOuts[PHIIt.first->BB];
4252
4253 auto VVal = ValidatedValues.find(Val: PHIIt.first);
4254 if (VVal == ValidatedValues.end()) {
4255 // We cross a loop, and this is a backedge. LLVMs tail duplication
4256 // happens so late that DBG_PHI instructions should not be able to
4257 // migrate into loops -- meaning we can only be live-through this
4258 // loop.
4259 ValueToCheck = ThisBlockValueNum;
4260 } else {
4261 // Does the block have as a live-out, in the location we're examining,
4262 // the value that we expect? If not, it's been moved or clobbered.
4263 ValueToCheck = VVal->second;
4264 }
4265
4266 if (BlockLiveOuts[Loc.asU64()] != ValueToCheck)
4267 return std::nullopt;
4268 }
4269
4270 // Record this value as validated.
4271 ValidatedValues.insert(KV: {PHI->ParentBlock, ThisBlockValueNum});
4272 }
4273
4274 // All the PHIs are valid: we can return what the SSAUpdater said our value
4275 // number was.
4276 return Result;
4277}
4278