1//===- StackColoring.cpp --------------------------------------------------===//
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//
9// This pass implements the stack-coloring optimization that looks for
10// lifetime markers machine instructions (LIFETIME_START and LIFETIME_END),
11// which represent the possible lifetime of stack slots. It attempts to
12// merge disjoint stack slots and reduce the used stack space.
13// NOTE: This pass is not StackSlotColoring, which optimizes spill slots.
14//
15// TODO: In the future we plan to improve stack coloring in the following ways:
16// 1. Allow merging multiple small slots into a single larger slot at different
17// offsets.
18// 2. Merge this pass with StackSlotColoring and allow merging of allocas with
19// spill slots.
20//
21//===----------------------------------------------------------------------===//
22
23#include "llvm/CodeGen/StackColoring.h"
24#include "llvm/ADT/BitVector.h"
25#include "llvm/ADT/DenseMap.h"
26#include "llvm/ADT/DepthFirstIterator.h"
27#include "llvm/ADT/SmallPtrSet.h"
28#include "llvm/ADT/SmallVector.h"
29#include "llvm/ADT/Statistic.h"
30#include "llvm/Analysis/ValueTracking.h"
31#include "llvm/CodeGen/LiveInterval.h"
32#include "llvm/CodeGen/MachineBasicBlock.h"
33#include "llvm/CodeGen/MachineFrameInfo.h"
34#include "llvm/CodeGen/MachineFunction.h"
35#include "llvm/CodeGen/MachineFunctionPass.h"
36#include "llvm/CodeGen/MachineInstr.h"
37#include "llvm/CodeGen/MachineMemOperand.h"
38#include "llvm/CodeGen/MachineOperand.h"
39#include "llvm/CodeGen/Passes.h"
40#include "llvm/CodeGen/PseudoSourceValueManager.h"
41#include "llvm/CodeGen/SlotIndexes.h"
42#include "llvm/CodeGen/TargetOpcodes.h"
43#include "llvm/CodeGen/WinEHFuncInfo.h"
44#include "llvm/Config/llvm-config.h"
45#include "llvm/IR/Constants.h"
46#include "llvm/IR/DebugInfoMetadata.h"
47#include "llvm/IR/Instructions.h"
48#include "llvm/IR/Metadata.h"
49#include "llvm/IR/Use.h"
50#include "llvm/IR/Value.h"
51#include "llvm/InitializePasses.h"
52#include "llvm/Pass.h"
53#include "llvm/Support/Casting.h"
54#include "llvm/Support/CommandLine.h"
55#include "llvm/Support/Compiler.h"
56#include "llvm/Support/Debug.h"
57#include "llvm/Support/raw_ostream.h"
58#include <algorithm>
59#include <cassert>
60#include <limits>
61#include <memory>
62#include <utility>
63
64using namespace llvm;
65
66#define DEBUG_TYPE "stack-coloring"
67
68static cl::opt<bool>
69DisableColoring("no-stack-coloring",
70 cl::init(Val: false), cl::Hidden,
71 cl::desc("Disable stack coloring"));
72
73/// The user may write code that uses allocas outside of the declared lifetime
74/// zone. This can happen when the user returns a reference to a local
75/// data-structure. We can detect these cases and decide not to optimize the
76/// code. If this flag is enabled, we try to save the user. This option
77/// is treated as overriding LifetimeStartOnFirstUse below.
78static cl::opt<bool>
79ProtectFromEscapedAllocas("protect-from-escaped-allocas",
80 cl::init(Val: false), cl::Hidden,
81 cl::desc("Do not optimize lifetime zones that "
82 "are broken"));
83
84/// Enable enhanced dataflow scheme for lifetime analysis (treat first
85/// use of stack slot as start of slot lifetime, as opposed to looking
86/// for LIFETIME_START marker). See "Implementation notes" below for
87/// more info.
88static cl::opt<bool>
89LifetimeStartOnFirstUse("stackcoloring-lifetime-start-on-first-use",
90 cl::init(Val: true), cl::Hidden,
91 cl::desc("Treat stack lifetimes as starting on first use, not on START marker."));
92
93
94STATISTIC(NumMarkerSeen, "Number of lifetime markers found.");
95STATISTIC(StackSpaceSaved, "Number of bytes saved due to merging slots.");
96STATISTIC(StackSlotMerged, "Number of stack slot merged.");
97STATISTIC(EscapedAllocas, "Number of allocas that escaped the lifetime region");
98
99//===----------------------------------------------------------------------===//
100// StackColoring Pass
101//===----------------------------------------------------------------------===//
102//
103// Stack Coloring reduces stack usage by merging stack slots when they
104// can't be used together. For example, consider the following C program:
105//
106// void bar(char *, int);
107// void foo(bool var) {
108// A: {
109// char z[4096];
110// bar(z, 0);
111// }
112//
113// char *p;
114// char x[4096];
115// char y[4096];
116// if (var) {
117// p = x;
118// } else {
119// bar(y, 1);
120// p = y + 1024;
121// }
122// B:
123// bar(p, 2);
124// }
125//
126// Naively-compiled, this program would use 12k of stack space. However, the
127// stack slot corresponding to `z` is always destroyed before either of the
128// stack slots for `x` or `y` are used, and then `x` is only used if `var`
129// is true, while `y` is only used if `var` is false. So in no time are 2
130// of the stack slots used together, and therefore we can merge them,
131// compiling the function using only a single 4k alloca:
132//
133// void foo(bool var) { // equivalent
134// char x[4096];
135// char *p;
136// bar(x, 0);
137// if (var) {
138// p = x;
139// } else {
140// bar(x, 1);
141// p = x + 1024;
142// }
143// bar(p, 2);
144// }
145//
146// This is an important optimization if we want stack space to be under
147// control in large functions, both open-coded ones and ones created by
148// inlining.
149//
150// Implementation Notes:
151// ---------------------
152//
153// An important part of the above reasoning is that `z` can't be accessed
154// while the latter 2 calls to `bar` are running. This is justified because
155// `z`'s lifetime is over after we exit from block `A:`, so any further
156// accesses to it would be UB. The way we represent this information
157// in LLVM is by having frontends delimit blocks with `lifetime.start`
158// and `lifetime.end` intrinsics.
159//
160// The effect of these intrinsics seems to be as follows (maybe I should
161// specify this in the reference?):
162//
163// L1) at start, each stack-slot is marked as *out-of-scope*, unless no
164// lifetime intrinsic refers to that stack slot, in which case
165// it is marked as *in-scope*.
166// L2) on a `lifetime.start`, a stack slot is marked as *in-scope* and
167// the stack slot is overwritten with `undef`.
168// L3) on a `lifetime.end`, a stack slot is marked as *out-of-scope*.
169// L4) on function exit, all stack slots are marked as *out-of-scope*.
170// L5) `lifetime.end` is a no-op when called on a slot that is already
171// *out-of-scope*.
172// L6) memory accesses to *out-of-scope* stack slots are UB.
173// L7) when a stack-slot is marked as *out-of-scope*, all pointers to it
174// are invalidated, unless the slot is "degenerate". This is used to
175// justify not marking slots as in-use until the pointer to them is
176// used, but feels a bit hacky in the presence of things like LICM. See
177// the "Degenerate Slots" section for more details.
178//
179// Now, let's ground stack coloring on these rules. We'll define a slot
180// as *in-use* at a (dynamic) point in execution if it either can be
181// written to at that point, or if it has a live and non-undef content
182// at that point.
183//
184// Obviously, slots that are never *in-use* together can be merged, and
185// in our example `foo`, the slots for `x`, `y` and `z` are never
186// in-use together (of course, sometimes slots that *are* in-use together
187// might still be mergable, but we don't care about that here).
188//
189// In this implementation, we successively merge pairs of slots that are
190// not *in-use* together. We could be smarter - for example, we could merge
191// a single large slot with 2 small slots, or we could construct the
192// interference graph and run a "smart" graph coloring algorithm, but with
193// that aside, how do we find out whether a pair of slots might be *in-use*
194// together?
195//
196// From our rules, we see that *out-of-scope* slots are never *in-use*,
197// and from (L7) we see that "non-degenerate" slots remain non-*in-use*
198// until their address is taken. Therefore, we can approximate slot activity
199// using dataflow.
200//
201// A subtle point: naively, we might try to figure out which pairs of
202// stack-slots interfere by propagating `S in-use` through the CFG for every
203// stack-slot `S`, and having `S` and `T` interfere if there is a CFG point in
204// which they are both *in-use*.
205//
206// That is sound, but overly conservative in some cases: in our (artificial)
207// example `foo`, either `x` or `y` might be in use at the label `B:`, but
208// as `x` is only in use if we came in from the `var` edge and `y` only
209// if we came from the `!var` edge, they still can't be in use together.
210// See PR32488 for an important real-life case.
211//
212// If we wanted to find all points of interference precisely, we could
213// propagate `S in-use` and `S&T in-use` predicates through the CFG. That
214// would be precise, but requires propagating `O(n^2)` dataflow facts.
215//
216// However, we aren't interested in the *set* of points of interference
217// between 2 stack slots, only *whether* there *is* such a point. So we
218// can rely on a little trick: for `S` and `T` to be in-use together,
219// one of them needs to become in-use while the other is in-use (or
220// they might both become in use simultaneously). We can check this
221// by also keeping track of the points at which a stack slot might *start*
222// being in-use.
223//
224// Exact first use:
225// ----------------
226//
227// Consider the following motivating example:
228//
229// int foo() {
230// char b1[1024], b2[1024];
231// if (...) {
232// char b3[1024];
233// <uses of b1, b3>;
234// return x;
235// } else {
236// char b4[1024], b5[1024];
237// <uses of b2, b4, b5>;
238// return y;
239// }
240// }
241//
242// In the code above, "b3" and "b4" are declared in distinct lexical
243// scopes, meaning that it is easy to prove that they can share the
244// same stack slot. Variables "b1" and "b2" are declared in the same
245// scope, meaning that from a lexical point of view, their lifetimes
246// overlap. From a control flow pointer of view, however, the two
247// variables are accessed in disjoint regions of the CFG, thus it
248// should be possible for them to share the same stack slot. An ideal
249// stack allocation for the function above would look like:
250//
251// slot 0: b1, b2
252// slot 1: b3, b4
253// slot 2: b5
254//
255// Achieving this allocation is tricky, however, due to the way
256// lifetime markers are inserted. Here is a simplified view of the
257// control flow graph for the code above:
258//
259// +------ block 0 -------+
260// 0| LIFETIME_START b1, b2 |
261// 1| <test 'if' condition> |
262// +-----------------------+
263// ./ \.
264// +------ block 1 -------+ +------ block 2 -------+
265// 2| LIFETIME_START b3 | 5| LIFETIME_START b4, b5 |
266// 3| <uses of b1, b3> | 6| <uses of b2, b4, b5> |
267// 4| LIFETIME_END b3 | 7| LIFETIME_END b4, b5 |
268// +-----------------------+ +-----------------------+
269// \. /.
270// +------ block 3 -------+
271// 8| <cleanupcode> |
272// 9| LIFETIME_END b1, b2 |
273// 10| return |
274// +-----------------------+
275//
276// If we create live intervals for the variables above strictly based
277// on the lifetime markers, we'll get the set of intervals on the
278// left. If we ignore the lifetime start markers and instead treat a
279// variable's lifetime as beginning with the first reference to the
280// var, then we get the intervals on the right.
281//
282// LIFETIME_START First Use
283// b1: [0,9] [3,4] [8,9]
284// b2: [0,9] [6,9]
285// b3: [2,4] [3,4]
286// b4: [5,7] [6,7]
287// b5: [5,7] [6,7]
288//
289// For the intervals on the left, the best we can do is overlap two
290// variables (b3 and b4, for example); this gives us a stack size of
291// 4*1024 bytes, not ideal. When treating first-use as the start of a
292// lifetime, we can additionally overlap b1 and b5, giving us a 3*1024
293// byte stack (better).
294//
295// Degenerate Slots:
296// -----------------
297//
298// Relying entirely on first-use of stack slots is problematic,
299// however, due to the fact that optimizations can sometimes migrate
300// uses of a variable outside of its lifetime start/end region. Here
301// is an example:
302//
303// int bar() {
304// char b1[1024], b2[1024];
305// if (...) {
306// <uses of b2>
307// return y;
308// } else {
309// <uses of b1>
310// while (...) {
311// char b3[1024];
312// <uses of b3>
313// }
314// }
315// }
316//
317// Before optimization, the control flow graph for the code above
318// might look like the following:
319//
320// +------ block 0 -------+
321// 0| LIFETIME_START b1, b2 |
322// 1| <test 'if' condition> |
323// +-----------------------+
324// ./ \.
325// +------ block 1 -------+ +------- block 2 -------+
326// 2| <uses of b2> | 3| <uses of b1> |
327// +-----------------------+ +-----------------------+
328// | |
329// | +------- block 3 -------+ <-\.
330// | 4| <while condition> | |
331// | +-----------------------+ |
332// | / | |
333// | / +------- block 4 -------+
334// \ / 5| LIFETIME_START b3 | |
335// \ / 6| <uses of b3> | |
336// \ / 7| LIFETIME_END b3 | |
337// \ | +------------------------+ |
338// \ | \ /
339// +------ block 5 -----+ \---------------
340// 8| <cleanupcode> |
341// 9| LIFETIME_END b1, b2 |
342// 10| return |
343// +---------------------+
344//
345// During optimization, however, it can happen that an instruction
346// computing an address in "b3" (for example, a loop-invariant GEP) is
347// hoisted up out of the loop from block 4 to block 2. [Note that
348// this is not an actual load from the stack, only an instruction that
349// computes the address to be loaded]. If this happens, there is now a
350// path leading from the first use of b3 to the return instruction
351// that does not encounter the b3 LIFETIME_END, hence b3's lifetime is
352// now larger than if we were computing live intervals strictly based
353// on lifetime markers. In the example above, this lengthened lifetime
354// would mean that it would appear illegal to overlap b3 with b2.
355//
356// To deal with this such cases, the code in ::collectMarkers() below
357// tries to identify "degenerate" slots -- those slots where on a single
358// forward pass through the CFG we encounter a first reference to slot
359// K before we hit the slot K lifetime start marker. For such slots,
360// we fall back on using the lifetime start marker as the beginning of
361// the variable's lifetime. NB: with this implementation, slots can
362// appear degenerate in cases where there is unstructured control flow:
363//
364// if (q) goto mid;
365// if (x > 9) {
366// int b[100];
367// memcpy(&b[0], ...);
368// mid: b[k] = ...;
369// abc(&b);
370// }
371//
372// If in RPO ordering chosen to walk the CFG we happen to visit the b[k]
373// before visiting the memcpy block (which will contain the lifetime start
374// for "b" then it will appear that 'b' has a degenerate lifetime.
375
376namespace {
377
378/// StackColoring - A machine pass for merging disjoint stack allocations,
379/// marked by the LIFETIME_START and LIFETIME_END pseudo instructions.
380class StackColoring {
381 MachineFrameInfo *MFI = nullptr;
382 MachineFunction *MF = nullptr;
383
384 /// A class representing liveness information for a single basic block.
385 /// Each bit in the BitVector represents the liveness property
386 /// for a different stack slot.
387 struct BlockLifetimeInfo {
388 /// Which slots BEGINs in each basic block.
389 BitVector Begin;
390
391 /// Which slots ENDs in each basic block.
392 BitVector End;
393
394 /// Which slots are marked as LIVE_IN, coming into each basic block.
395 BitVector LiveIn;
396
397 /// Which slots are marked as LIVE_OUT, coming out of each basic block.
398 BitVector LiveOut;
399 };
400
401 /// Maps active slots (per bit) for each basic block.
402 using LivenessMap = DenseMap<const MachineBasicBlock *, BlockLifetimeInfo>;
403 LivenessMap BlockLiveness;
404
405 /// Maps serial numbers to basic blocks.
406 DenseMap<const MachineBasicBlock *, int> BasicBlocks;
407
408 /// Maps basic blocks to a serial number.
409 SmallVector<const MachineBasicBlock *, 8> BasicBlockNumbering;
410
411 /// Maps slots to their use interval. Outside of this interval, slots
412 /// values are either dead or `undef` and they will not be written to.
413 SmallVector<std::unique_ptr<LiveInterval>, 16> Intervals;
414
415 /// Maps slots to the points where they can become in-use.
416 SmallVector<SmallVector<SlotIndex, 4>, 16> LiveStarts;
417
418 /// VNInfo is used for the construction of LiveIntervals.
419 VNInfo::Allocator VNInfoAllocator;
420
421 /// SlotIndex analysis object.
422 SlotIndexes *Indexes = nullptr;
423
424 /// The list of lifetime markers found. These markers are to be removed
425 /// once the coloring is done.
426 SmallVector<MachineInstr*, 8> Markers;
427
428 /// Record the FI slots for which we have seen some sort of
429 /// lifetime marker (either start or end).
430 BitVector InterestingSlots;
431
432 /// FI slots that need to be handled conservatively (for these
433 /// slots lifetime-start-on-first-use is disabled).
434 BitVector ConservativeSlots;
435
436 /// Number of iterations taken during data flow analysis.
437 unsigned NumIterations;
438
439public:
440 StackColoring(SlotIndexes *Indexes) : Indexes(Indexes) {}
441 bool run(MachineFunction &Func);
442
443private:
444 /// Used in collectMarkers
445 using BlockBitVecMap = DenseMap<const MachineBasicBlock *, BitVector>;
446
447 /// Debug.
448 void dump() const;
449 void dumpIntervals() const;
450 void dumpBB(MachineBasicBlock *MBB) const;
451 void dumpBV(const char *tag, const BitVector &BV) const;
452
453 /// Removes all of the lifetime marker instructions from the function.
454 /// \returns true if any markers were removed.
455 bool removeAllMarkers();
456
457 /// Scan the machine function and find all of the lifetime markers.
458 /// Record the findings in the BEGIN and END vectors.
459 /// \returns the number of markers found.
460 unsigned collectMarkers(unsigned NumSlot);
461
462 /// Perform the dataflow calculation and calculate the lifetime for each of
463 /// the slots, based on the BEGIN/END vectors. Set the LifetimeLIVE_IN and
464 /// LifetimeLIVE_OUT maps that represent which stack slots are live coming
465 /// in and out blocks.
466 void calculateLocalLiveness();
467
468 /// Returns TRUE if we're using the first-use-begins-lifetime method for
469 /// this slot (if FALSE, then the start marker is treated as start of lifetime).
470 bool applyFirstUse(int Slot) {
471 if (!LifetimeStartOnFirstUse || ProtectFromEscapedAllocas)
472 return false;
473 if (ConservativeSlots.test(Idx: Slot))
474 return false;
475 return true;
476 }
477
478 /// Examines the specified instruction and returns TRUE if the instruction
479 /// represents the start or end of an interesting lifetime. The slot or slots
480 /// starting or ending are added to the vector "slots" and "isStart" is set
481 /// accordingly.
482 /// \returns True if inst contains a lifetime start or end
483 bool isLifetimeStartOrEnd(const MachineInstr &MI,
484 SmallVector<int, 4> &slots,
485 bool &isStart);
486
487 /// Construct the LiveIntervals for the slots.
488 void calculateLiveIntervals(unsigned NumSlots);
489
490 /// Go over the machine function and change instructions which use stack
491 /// slots to use the joint slots.
492 void remapInstructions(DenseMap<int, int> &SlotRemap);
493
494 /// The input program may contain instructions which are not inside lifetime
495 /// markers. This can happen due to a bug in the compiler or due to a bug in
496 /// user code (for example, returning a reference to a local variable).
497 /// This procedure checks all of the instructions in the function and
498 /// invalidates lifetime ranges which do not contain all of the instructions
499 /// which access that frame slot.
500 void removeInvalidSlotRanges();
501
502 /// Map entries which point to other entries to their destination.
503 /// A->B->C becomes A->C.
504 void expungeSlotMap(DenseMap<int, int> &SlotRemap, unsigned NumSlots);
505};
506
507class StackColoringLegacy : public MachineFunctionPass {
508public:
509 static char ID;
510
511 StackColoringLegacy() : MachineFunctionPass(ID) {}
512
513 void getAnalysisUsage(AnalysisUsage &AU) const override;
514 bool runOnMachineFunction(MachineFunction &Func) override;
515};
516
517} // end anonymous namespace
518
519char StackColoringLegacy::ID = 0;
520
521char &llvm::StackColoringLegacyID = StackColoringLegacy::ID;
522
523INITIALIZE_PASS_BEGIN(StackColoringLegacy, DEBUG_TYPE,
524 "Merge disjoint stack slots", false, false)
525INITIALIZE_PASS_DEPENDENCY(SlotIndexesWrapperPass)
526INITIALIZE_PASS_END(StackColoringLegacy, DEBUG_TYPE,
527 "Merge disjoint stack slots", false, false)
528
529void StackColoringLegacy::getAnalysisUsage(AnalysisUsage &AU) const {
530 AU.addRequired<SlotIndexesWrapperPass>();
531 MachineFunctionPass::getAnalysisUsage(AU);
532}
533
534#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
535LLVM_DUMP_METHOD void StackColoring::dumpBV(const char *tag,
536 const BitVector &BV) const {
537 dbgs() << tag << " : { ";
538 for (unsigned I = 0, E = BV.size(); I != E; ++I)
539 dbgs() << BV.test(I) << " ";
540 dbgs() << "}\n";
541}
542
543LLVM_DUMP_METHOD void StackColoring::dumpBB(MachineBasicBlock *MBB) const {
544 LivenessMap::const_iterator BI = BlockLiveness.find(MBB);
545 assert(BI != BlockLiveness.end() && "Block not found");
546 const BlockLifetimeInfo &BlockInfo = BI->second;
547
548 dumpBV("BEGIN", BlockInfo.Begin);
549 dumpBV("END", BlockInfo.End);
550 dumpBV("LIVE_IN", BlockInfo.LiveIn);
551 dumpBV("LIVE_OUT", BlockInfo.LiveOut);
552}
553
554LLVM_DUMP_METHOD void StackColoring::dump() const {
555 for (MachineBasicBlock *MBB : depth_first(MF)) {
556 dbgs() << "Inspecting block #" << MBB->getNumber() << " ["
557 << MBB->getName() << "]\n";
558 dumpBB(MBB);
559 }
560}
561
562LLVM_DUMP_METHOD void StackColoring::dumpIntervals() const {
563 for (unsigned I = 0, E = Intervals.size(); I != E; ++I) {
564 dbgs() << "Interval[" << I << "]:\n";
565 Intervals[I]->dump();
566 }
567}
568#endif
569
570static inline int getStartOrEndSlot(const MachineInstr &MI)
571{
572 assert((MI.getOpcode() == TargetOpcode::LIFETIME_START ||
573 MI.getOpcode() == TargetOpcode::LIFETIME_END) &&
574 "Expected LIFETIME_START or LIFETIME_END op");
575 const MachineOperand &MO = MI.getOperand(i: 0);
576 int Slot = MO.getIndex();
577 if (Slot >= 0)
578 return Slot;
579 return -1;
580}
581
582// At the moment the only way to end a variable lifetime is with
583// a VARIABLE_LIFETIME op (which can't contain a start). If things
584// change and the IR allows for a single inst that both begins
585// and ends lifetime(s), this interface will need to be reworked.
586bool StackColoring::isLifetimeStartOrEnd(const MachineInstr &MI,
587 SmallVector<int, 4> &slots,
588 bool &isStart) {
589 if (MI.getOpcode() == TargetOpcode::LIFETIME_START ||
590 MI.getOpcode() == TargetOpcode::LIFETIME_END) {
591 int Slot = getStartOrEndSlot(MI);
592 if (Slot < 0)
593 return false;
594 if (!InterestingSlots.test(Idx: Slot))
595 return false;
596 slots.push_back(Elt: Slot);
597 if (MI.getOpcode() == TargetOpcode::LIFETIME_END) {
598 isStart = false;
599 return true;
600 }
601 if (!applyFirstUse(Slot)) {
602 isStart = true;
603 return true;
604 }
605 } else if (LifetimeStartOnFirstUse && !ProtectFromEscapedAllocas) {
606 if (!MI.isDebugInstr()) {
607 bool found = false;
608 for (const MachineOperand &MO : MI.operands()) {
609 if (!MO.isFI())
610 continue;
611 int Slot = MO.getIndex();
612 if (Slot<0)
613 continue;
614 if (InterestingSlots.test(Idx: Slot) && applyFirstUse(Slot)) {
615 slots.push_back(Elt: Slot);
616 found = true;
617 }
618 }
619 if (found) {
620 isStart = true;
621 return true;
622 }
623 }
624 }
625 return false;
626}
627
628unsigned StackColoring::collectMarkers(unsigned NumSlot) {
629 unsigned MarkersFound = 0;
630 BlockBitVecMap SeenStartMap;
631 InterestingSlots.clear();
632 InterestingSlots.resize(N: NumSlot);
633 ConservativeSlots.clear();
634 ConservativeSlots.resize(N: NumSlot);
635
636 // number of start and end lifetime ops for each slot
637 SmallVector<int, 8> NumStartLifetimes(NumSlot, 0);
638 SmallVector<int, 8> NumEndLifetimes(NumSlot, 0);
639
640 // Step 1: collect markers and populate the "InterestingSlots"
641 // and "ConservativeSlots" sets.
642 for (MachineBasicBlock *MBB : depth_first(G: MF)) {
643 // Compute the set of slots for which we've seen a START marker but have
644 // not yet seen an END marker at this point in the walk (e.g. on entry
645 // to this bb).
646 BitVector BetweenStartEnd;
647 BetweenStartEnd.resize(N: NumSlot);
648 for (const MachineBasicBlock *Pred : MBB->predecessors()) {
649 BlockBitVecMap::const_iterator I = SeenStartMap.find(Val: Pred);
650 if (I != SeenStartMap.end()) {
651 BetweenStartEnd |= I->second;
652 }
653 }
654
655 // Walk the instructions in the block to look for start/end ops.
656 for (MachineInstr &MI : *MBB) {
657 if (MI.isDebugInstr())
658 continue;
659 if (MI.getOpcode() == TargetOpcode::LIFETIME_START ||
660 MI.getOpcode() == TargetOpcode::LIFETIME_END) {
661 int Slot = getStartOrEndSlot(MI);
662 if (Slot < 0)
663 continue;
664 InterestingSlots.set(Slot);
665 if (MI.getOpcode() == TargetOpcode::LIFETIME_START) {
666 BetweenStartEnd.set(Slot);
667 NumStartLifetimes[Slot] += 1;
668 } else {
669 BetweenStartEnd.reset(Idx: Slot);
670 NumEndLifetimes[Slot] += 1;
671 }
672 const AllocaInst *Allocation = MFI->getObjectAllocation(ObjectIdx: Slot);
673 if (Allocation) {
674 LLVM_DEBUG(dbgs() << "Found a lifetime ");
675 LLVM_DEBUG(dbgs() << (MI.getOpcode() == TargetOpcode::LIFETIME_START
676 ? "start"
677 : "end"));
678 LLVM_DEBUG(dbgs() << " marker for slot #" << Slot);
679 LLVM_DEBUG(dbgs()
680 << " with allocation: " << Allocation->getName() << "\n");
681 }
682 Markers.push_back(Elt: &MI);
683 MarkersFound += 1;
684 } else {
685 for (const MachineOperand &MO : MI.operands()) {
686 if (!MO.isFI())
687 continue;
688 int Slot = MO.getIndex();
689 if (Slot < 0)
690 continue;
691 if (! BetweenStartEnd.test(Idx: Slot)) {
692 ConservativeSlots.set(Slot);
693 }
694 }
695 }
696 }
697 BitVector &SeenStart = SeenStartMap[MBB];
698 SeenStart |= BetweenStartEnd;
699 }
700 if (!MarkersFound) {
701 return 0;
702 }
703
704 // PR27903: slots with multiple start or end lifetime ops are not
705 // safe to enable for "lifetime-start-on-first-use".
706 for (unsigned slot = 0; slot < NumSlot; ++slot) {
707 if (NumStartLifetimes[slot] > 1 || NumEndLifetimes[slot] > 1)
708 ConservativeSlots.set(slot);
709 }
710
711 // The write to the catch object by the personality function is not propely
712 // modeled in IR: It happens before any cleanuppads are executed, even if the
713 // first mention of the catch object is in a catchpad. As such, mark catch
714 // object slots as conservative, so they are excluded from first-use analysis.
715 if (WinEHFuncInfo *EHInfo = MF->getWinEHFuncInfo())
716 for (WinEHTryBlockMapEntry &TBME : EHInfo->TryBlockMap)
717 for (WinEHHandlerType &H : TBME.HandlerArray)
718 if (H.CatchObj.FrameIndex != std::numeric_limits<int>::max() &&
719 H.CatchObj.FrameIndex >= 0)
720 ConservativeSlots.set(H.CatchObj.FrameIndex);
721
722 LLVM_DEBUG(dumpBV("Conservative slots", ConservativeSlots));
723
724 // Step 2: compute begin/end sets for each block
725
726 // NOTE: We use a depth-first iteration to ensure that we obtain a
727 // deterministic numbering.
728 for (MachineBasicBlock *MBB : depth_first(G: MF)) {
729 // Assign a serial number to this basic block.
730 BasicBlocks[MBB] = BasicBlockNumbering.size();
731 BasicBlockNumbering.push_back(Elt: MBB);
732
733 // Keep a reference to avoid repeated lookups.
734 BlockLifetimeInfo &BlockInfo = BlockLiveness[MBB];
735
736 BlockInfo.Begin.resize(N: NumSlot);
737 BlockInfo.End.resize(N: NumSlot);
738
739 SmallVector<int, 4> slots;
740 for (MachineInstr &MI : *MBB) {
741 bool isStart = false;
742 slots.clear();
743 if (isLifetimeStartOrEnd(MI, slots, isStart)) {
744 if (!isStart) {
745 assert(slots.size() == 1 && "unexpected: MI ends multiple slots");
746 int Slot = slots[0];
747 if (BlockInfo.Begin.test(Idx: Slot)) {
748 BlockInfo.Begin.reset(Idx: Slot);
749 }
750 BlockInfo.End.set(Slot);
751 } else {
752 for (auto Slot : slots) {
753 LLVM_DEBUG(dbgs() << "Found a use of slot #" << Slot);
754 LLVM_DEBUG(dbgs()
755 << " at " << printMBBReference(*MBB) << " index ");
756 LLVM_DEBUG(Indexes->getInstructionIndex(MI).print(dbgs()));
757 const AllocaInst *Allocation = MFI->getObjectAllocation(ObjectIdx: Slot);
758 if (Allocation) {
759 LLVM_DEBUG(dbgs()
760 << " with allocation: " << Allocation->getName());
761 }
762 LLVM_DEBUG(dbgs() << "\n");
763 if (BlockInfo.End.test(Idx: Slot)) {
764 BlockInfo.End.reset(Idx: Slot);
765 }
766 BlockInfo.Begin.set(Slot);
767 }
768 }
769 }
770 }
771 }
772
773 // Update statistics.
774 NumMarkerSeen += MarkersFound;
775 return MarkersFound;
776}
777
778void StackColoring::calculateLocalLiveness() {
779 unsigned NumIters = 0;
780 bool changed = true;
781 // Create BitVector outside the loop and reuse them to avoid repeated heap
782 // allocations.
783 BitVector LocalLiveIn;
784 BitVector LocalLiveOut;
785 while (changed) {
786 changed = false;
787 ++NumIters;
788
789 for (const MachineBasicBlock *BB : BasicBlockNumbering) {
790 // Use an iterator to avoid repeated lookups.
791 LivenessMap::iterator BI = BlockLiveness.find(Val: BB);
792 assert(BI != BlockLiveness.end() && "Block not found");
793 BlockLifetimeInfo &BlockInfo = BI->second;
794
795 // Compute LiveIn by unioning together the LiveOut sets of all preds.
796 LocalLiveIn.clear();
797 for (MachineBasicBlock *Pred : BB->predecessors()) {
798 LivenessMap::const_iterator I = BlockLiveness.find(Val: Pred);
799 // PR37130: transformations prior to stack coloring can
800 // sometimes leave behind statically unreachable blocks; these
801 // can be safely skipped here.
802 if (I != BlockLiveness.end())
803 LocalLiveIn |= I->second.LiveOut;
804 }
805
806 // Compute LiveOut by subtracting out lifetimes that end in this
807 // block, then adding in lifetimes that begin in this block. If
808 // we have both BEGIN and END markers in the same basic block
809 // then we know that the BEGIN marker comes after the END,
810 // because we already handle the case where the BEGIN comes
811 // before the END when collecting the markers (and building the
812 // BEGIN/END vectors).
813 LocalLiveOut = LocalLiveIn;
814 LocalLiveOut.reset(RHS: BlockInfo.End);
815 LocalLiveOut |= BlockInfo.Begin;
816
817 // Update block LiveIn set, noting whether it has changed.
818 if (LocalLiveIn.test(RHS: BlockInfo.LiveIn)) {
819 changed = true;
820 BlockInfo.LiveIn |= LocalLiveIn;
821 }
822
823 // Update block LiveOut set, noting whether it has changed.
824 if (LocalLiveOut.test(RHS: BlockInfo.LiveOut)) {
825 changed = true;
826 BlockInfo.LiveOut |= LocalLiveOut;
827 }
828 }
829 } // while changed.
830
831 NumIterations = NumIters;
832}
833
834void StackColoring::calculateLiveIntervals(unsigned NumSlots) {
835 SmallVector<SlotIndex, 16> Starts;
836 SmallVector<bool, 16> DefinitelyInUse;
837
838 // For each block, find which slots are active within this block
839 // and update the live intervals.
840 for (const MachineBasicBlock &MBB : *MF) {
841 Starts.clear();
842 Starts.resize(N: NumSlots);
843 DefinitelyInUse.clear();
844 DefinitelyInUse.resize(N: NumSlots);
845
846 // Start the interval of the slots that we previously found to be 'in-use'.
847 BlockLifetimeInfo &MBBLiveness = BlockLiveness[&MBB];
848 for (int pos = MBBLiveness.LiveIn.find_first(); pos != -1;
849 pos = MBBLiveness.LiveIn.find_next(Prev: pos)) {
850 Starts[pos] = Indexes->getMBBStartIdx(mbb: &MBB);
851 }
852
853 // Create the interval for the basic blocks containing lifetime begin/end.
854 for (const MachineInstr &MI : MBB) {
855 SmallVector<int, 4> slots;
856 bool IsStart = false;
857 if (!isLifetimeStartOrEnd(MI, slots, isStart&: IsStart))
858 continue;
859 SlotIndex ThisIndex = Indexes->getInstructionIndex(MI);
860 for (auto Slot : slots) {
861 if (IsStart) {
862 // If a slot is already definitely in use, we don't have to emit
863 // a new start marker because there is already a pre-existing
864 // one.
865 if (!DefinitelyInUse[Slot]) {
866 LiveStarts[Slot].push_back(Elt: ThisIndex);
867 DefinitelyInUse[Slot] = true;
868 }
869 if (!Starts[Slot].isValid())
870 Starts[Slot] = ThisIndex;
871 } else {
872 if (Starts[Slot].isValid()) {
873 VNInfo *VNI = Intervals[Slot]->getValNumInfo(ValNo: 0);
874 Intervals[Slot]->addSegment(
875 S: LiveInterval::Segment(Starts[Slot], ThisIndex, VNI));
876 Starts[Slot] = SlotIndex(); // Invalidate the start index
877 DefinitelyInUse[Slot] = false;
878 }
879 }
880 }
881 }
882
883 // Finish up started segments
884 for (unsigned i = 0; i < NumSlots; ++i) {
885 if (!Starts[i].isValid())
886 continue;
887
888 SlotIndex EndIdx = Indexes->getMBBEndIdx(mbb: &MBB);
889 VNInfo *VNI = Intervals[i]->getValNumInfo(ValNo: 0);
890 Intervals[i]->addSegment(S: LiveInterval::Segment(Starts[i], EndIdx, VNI));
891 }
892 }
893}
894
895bool StackColoring::removeAllMarkers() {
896 unsigned Count = 0;
897 for (MachineInstr *MI : Markers) {
898 MI->eraseFromParent();
899 Count++;
900 }
901 Markers.clear();
902
903 LLVM_DEBUG(dbgs() << "Removed " << Count << " markers.\n");
904 return Count;
905}
906
907void StackColoring::remapInstructions(DenseMap<int, int> &SlotRemap) {
908 unsigned FixedInstr = 0;
909 unsigned FixedMemOp = 0;
910 unsigned FixedDbg = 0;
911
912 // Remap debug information that refers to stack slots.
913 for (auto &VI : MF->getVariableDbgInfo()) {
914 if (!VI.Var || !VI.inStackSlot())
915 continue;
916 int Slot = VI.getStackSlot();
917 if (auto It = SlotRemap.find(Val: Slot); It != SlotRemap.end()) {
918 LLVM_DEBUG(dbgs() << "Remapping debug info for ["
919 << cast<DILocalVariable>(VI.Var)->getName() << "].\n");
920 VI.updateStackSlot(NewSlot: It->second);
921 FixedDbg++;
922 }
923 }
924
925 // Keep a list of *allocas* which need to be remapped.
926 DenseMap<const AllocaInst*, const AllocaInst*> Allocas;
927
928 // Keep a list of allocas which has been affected by the remap.
929 SmallPtrSet<const AllocaInst*, 32> MergedAllocas;
930
931 for (const std::pair<int, int> &SI : SlotRemap) {
932 const AllocaInst *From = MFI->getObjectAllocation(ObjectIdx: SI.first);
933 const AllocaInst *To = MFI->getObjectAllocation(ObjectIdx: SI.second);
934 assert(To && From && "Invalid allocation object");
935 Allocas[From] = To;
936
937 // If From is before wo, its possible that there is a use of From between
938 // them.
939 if (From->comesBefore(Other: To))
940 const_cast<AllocaInst *>(To)->moveBefore(
941 InsertPos: const_cast<AllocaInst *>(From)->getIterator());
942
943 // AA might be used later for instruction scheduling, and we need it to be
944 // able to deduce the correct aliasing releationships between pointers
945 // derived from the alloca being remapped and the target of that remapping.
946 // The only safe way, without directly informing AA about the remapping
947 // somehow, is to directly update the IR to reflect the change being made
948 // here.
949 Instruction *Inst = const_cast<AllocaInst *>(To);
950 if (From->getType() != To->getType()) {
951 BitCastInst *Cast = new BitCastInst(Inst, From->getType());
952 Cast->insertAfter(InsertPos: Inst->getIterator());
953 Inst = Cast;
954 }
955
956 // We keep both slots to maintain AliasAnalysis metadata later.
957 MergedAllocas.insert(Ptr: From);
958 MergedAllocas.insert(Ptr: To);
959
960 // Transfer the stack protector layout tag, but make sure that SSPLK_AddrOf
961 // does not overwrite SSPLK_SmallArray or SSPLK_LargeArray, and make sure
962 // that SSPLK_SmallArray does not overwrite SSPLK_LargeArray.
963 MachineFrameInfo::SSPLayoutKind FromKind
964 = MFI->getObjectSSPLayout(ObjectIdx: SI.first);
965 MachineFrameInfo::SSPLayoutKind ToKind = MFI->getObjectSSPLayout(ObjectIdx: SI.second);
966 if (FromKind != MachineFrameInfo::SSPLK_None &&
967 (ToKind == MachineFrameInfo::SSPLK_None ||
968 (ToKind != MachineFrameInfo::SSPLK_LargeArray &&
969 FromKind != MachineFrameInfo::SSPLK_AddrOf)))
970 MFI->setObjectSSPLayout(ObjectIdx: SI.second, Kind: FromKind);
971
972 // The new alloca might not be valid in a llvm.dbg.declare for this
973 // variable, so poison out the use to make the verifier happy.
974 AllocaInst *FromAI = const_cast<AllocaInst *>(From);
975 if (FromAI->isUsedByMetadata())
976 ValueAsMetadata::handleRAUW(From: FromAI, To: PoisonValue::get(T: FromAI->getType()));
977 for (auto &Use : FromAI->uses()) {
978 if (BitCastInst *BCI = dyn_cast<BitCastInst>(Val: Use.get()))
979 if (BCI->isUsedByMetadata())
980 ValueAsMetadata::handleRAUW(From: BCI, To: PoisonValue::get(T: BCI->getType()));
981 }
982
983 // Note that this will not replace uses in MMOs (which we'll update below),
984 // or anywhere else (which is why we won't delete the original
985 // instruction).
986 FromAI->replaceAllUsesWith(V: Inst);
987 }
988
989 // Remap all instructions to the new stack slots.
990 std::vector<std::vector<MachineMemOperand *>> SSRefs(
991 MFI->getObjectIndexEnd());
992 for (MachineBasicBlock &BB : *MF)
993 for (MachineInstr &I : BB) {
994 // Skip lifetime markers. We'll remove them soon.
995 if (I.getOpcode() == TargetOpcode::LIFETIME_START ||
996 I.getOpcode() == TargetOpcode::LIFETIME_END)
997 continue;
998
999 // Update the MachineMemOperand to use the new alloca.
1000 for (MachineMemOperand *MMO : I.memoperands()) {
1001 // We've replaced IR-level uses of the remapped allocas, so we only
1002 // need to replace direct uses here.
1003 const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(Val: MMO->getValue());
1004 if (!AI)
1005 continue;
1006
1007 auto It = Allocas.find(Val: AI);
1008 if (It == Allocas.end())
1009 continue;
1010
1011 MMO->setValue(It->second);
1012 FixedMemOp++;
1013 }
1014
1015 // Update all of the machine instruction operands.
1016 for (MachineOperand &MO : I.operands()) {
1017 if (!MO.isFI())
1018 continue;
1019 int FromSlot = MO.getIndex();
1020
1021 // Don't touch arguments.
1022 if (FromSlot<0)
1023 continue;
1024
1025 // Only look at mapped slots.
1026 if (!SlotRemap.count(Val: FromSlot))
1027 continue;
1028
1029 // In a debug build, check that the instruction that we are modifying is
1030 // inside the expected live range. If the instruction is not inside
1031 // the calculated range then it means that the alloca usage moved
1032 // outside of the lifetime markers, or that the user has a bug.
1033 // NOTE: Alloca address calculations which happen outside the lifetime
1034 // zone are okay, despite the fact that we don't have a good way
1035 // for validating all of the usages of the calculation.
1036#ifndef NDEBUG
1037 bool TouchesMemory = I.mayLoadOrStore();
1038 // If we *don't* protect the user from escaped allocas, don't bother
1039 // validating the instructions.
1040 if (!I.isDebugInstr() && TouchesMemory && ProtectFromEscapedAllocas) {
1041 SlotIndex Index = Indexes->getInstructionIndex(I);
1042 const LiveInterval *Interval = &*Intervals[FromSlot];
1043 assert(Interval->find(Index) != Interval->end() &&
1044 "Found instruction usage outside of live range.");
1045 }
1046#endif
1047
1048 // Fix the machine instructions.
1049 int ToSlot = SlotRemap[FromSlot];
1050 MO.setIndex(ToSlot);
1051 FixedInstr++;
1052 }
1053
1054 // We adjust AliasAnalysis information for merged stack slots.
1055 SmallVector<MachineMemOperand *, 2> NewMMOs;
1056 bool ReplaceMemOps = false;
1057 for (MachineMemOperand *MMO : I.memoperands()) {
1058 // Collect MachineMemOperands which reference
1059 // FixedStackPseudoSourceValues with old frame indices.
1060 if (const auto *FSV = dyn_cast_or_null<FixedStackPseudoSourceValue>(
1061 Val: MMO->getPseudoValue())) {
1062 int FI = FSV->getFrameIndex();
1063 auto To = SlotRemap.find(Val: FI);
1064 if (To != SlotRemap.end())
1065 SSRefs[FI].push_back(x: MMO);
1066 }
1067
1068 // If this memory location can be a slot remapped here,
1069 // we remove AA information.
1070 bool MayHaveConflictingAAMD = false;
1071 if (MMO->getAAInfo()) {
1072 if (const Value *MMOV = MMO->getValue()) {
1073 SmallVector<Value *, 4> Objs;
1074 getUnderlyingObjectsForCodeGen(V: MMOV, Objects&: Objs);
1075
1076 if (Objs.empty())
1077 MayHaveConflictingAAMD = true;
1078 else
1079 for (Value *V : Objs) {
1080 // If this memory location comes from a known stack slot
1081 // that is not remapped, we continue checking.
1082 // Otherwise, we need to invalidate AA infomation.
1083 const AllocaInst *AI = dyn_cast_or_null<AllocaInst>(Val: V);
1084 if (AI && MergedAllocas.count(Ptr: AI)) {
1085 MayHaveConflictingAAMD = true;
1086 break;
1087 }
1088 }
1089 }
1090 }
1091 if (MayHaveConflictingAAMD) {
1092 NewMMOs.push_back(Elt: MF->getMachineMemOperand(MMO, AAInfo: AAMDNodes()));
1093 ReplaceMemOps = true;
1094 } else {
1095 NewMMOs.push_back(Elt: MMO);
1096 }
1097 }
1098
1099 // If any memory operand is updated, set memory references of
1100 // this instruction.
1101 if (ReplaceMemOps)
1102 I.setMemRefs(MF&: *MF, MemRefs: NewMMOs);
1103 }
1104
1105 // Rewrite MachineMemOperands that reference old frame indices.
1106 for (auto E : enumerate(First&: SSRefs))
1107 if (!E.value().empty()) {
1108 const PseudoSourceValue *NewSV =
1109 MF->getPSVManager().getFixedStack(FI: SlotRemap.find(Val: E.index())->second);
1110 for (MachineMemOperand *Ref : E.value())
1111 Ref->setValue(NewSV);
1112 }
1113
1114 // Update the location of C++ catch objects for the MSVC personality routine.
1115 if (WinEHFuncInfo *EHInfo = MF->getWinEHFuncInfo())
1116 for (WinEHTryBlockMapEntry &TBME : EHInfo->TryBlockMap)
1117 for (WinEHHandlerType &H : TBME.HandlerArray)
1118 if (H.CatchObj.FrameIndex != std::numeric_limits<int>::max())
1119 if (auto It = SlotRemap.find(Val: H.CatchObj.FrameIndex);
1120 It != SlotRemap.end())
1121 H.CatchObj.FrameIndex = It->second;
1122
1123 LLVM_DEBUG(dbgs() << "Fixed " << FixedMemOp << " machine memory operands.\n");
1124 LLVM_DEBUG(dbgs() << "Fixed " << FixedDbg << " debug locations.\n");
1125 LLVM_DEBUG(dbgs() << "Fixed " << FixedInstr << " machine instructions.\n");
1126 (void) FixedMemOp;
1127 (void) FixedDbg;
1128 (void) FixedInstr;
1129}
1130
1131void StackColoring::removeInvalidSlotRanges() {
1132 for (MachineBasicBlock &BB : *MF)
1133 for (MachineInstr &I : BB) {
1134 if (I.getOpcode() == TargetOpcode::LIFETIME_START ||
1135 I.getOpcode() == TargetOpcode::LIFETIME_END || I.isDebugInstr())
1136 continue;
1137
1138 // Some intervals are suspicious! In some cases we find address
1139 // calculations outside of the lifetime zone, but not actual memory
1140 // read or write. Memory accesses outside of the lifetime zone are a clear
1141 // violation, but address calculations are okay. This can happen when
1142 // GEPs are hoisted outside of the lifetime zone.
1143 // So, in here we only check instructions which can read or write memory.
1144 if (!I.mayLoad() && !I.mayStore())
1145 continue;
1146
1147 // Check all of the machine operands.
1148 for (const MachineOperand &MO : I.operands()) {
1149 if (!MO.isFI())
1150 continue;
1151
1152 int Slot = MO.getIndex();
1153
1154 if (Slot<0)
1155 continue;
1156
1157 if (Intervals[Slot]->empty())
1158 continue;
1159
1160 // Check that the used slot is inside the calculated lifetime range.
1161 // If it is not, warn about it and invalidate the range.
1162 LiveInterval *Interval = &*Intervals[Slot];
1163 SlotIndex Index = Indexes->getInstructionIndex(MI: I);
1164 if (Interval->find(Pos: Index) == Interval->end()) {
1165 Interval->clear();
1166 LLVM_DEBUG(dbgs() << "Invalidating range #" << Slot << "\n");
1167 EscapedAllocas++;
1168 }
1169 }
1170 }
1171}
1172
1173void StackColoring::expungeSlotMap(DenseMap<int, int> &SlotRemap,
1174 unsigned NumSlots) {
1175 // Expunge slot remap map.
1176 for (unsigned i=0; i < NumSlots; ++i) {
1177 // If we are remapping i
1178 if (auto It = SlotRemap.find(Val: i); It != SlotRemap.end()) {
1179 int Target = It->second;
1180 // As long as our target is mapped to something else, follow it.
1181 while (true) {
1182 auto It = SlotRemap.find(Val: Target);
1183 if (It == SlotRemap.end())
1184 break;
1185 Target = It->second;
1186 SlotRemap[i] = Target;
1187 }
1188 }
1189 }
1190}
1191
1192bool StackColoringLegacy::runOnMachineFunction(MachineFunction &MF) {
1193 if (skipFunction(F: MF.getFunction()))
1194 return false;
1195
1196 StackColoring SC(&getAnalysis<SlotIndexesWrapperPass>().getSI());
1197 return SC.run(Func&: MF);
1198}
1199
1200PreservedAnalyses StackColoringPass::run(MachineFunction &MF,
1201 MachineFunctionAnalysisManager &MFAM) {
1202 StackColoring SC(&MFAM.getResult<SlotIndexesAnalysis>(IR&: MF));
1203 if (SC.run(Func&: MF))
1204 return PreservedAnalyses::none();
1205 return PreservedAnalyses::all();
1206}
1207
1208bool StackColoring::run(MachineFunction &Func) {
1209 LLVM_DEBUG(dbgs() << "********** Stack Coloring **********\n"
1210 << "********** Function: " << Func.getName() << '\n');
1211 MF = &Func;
1212 MFI = &MF->getFrameInfo();
1213 BlockLiveness.clear();
1214 BasicBlocks.clear();
1215 BasicBlockNumbering.clear();
1216 Markers.clear();
1217 Intervals.clear();
1218 LiveStarts.clear();
1219 VNInfoAllocator.Reset();
1220
1221 unsigned NumSlots = MFI->getObjectIndexEnd();
1222
1223 // If there are no stack slots then there are no markers to remove.
1224 if (!NumSlots)
1225 return false;
1226
1227 SmallVector<int, 8> SortedSlots;
1228 SortedSlots.reserve(N: NumSlots);
1229 Intervals.reserve(N: NumSlots);
1230 LiveStarts.resize(N: NumSlots);
1231
1232 unsigned NumMarkers = collectMarkers(NumSlot: NumSlots);
1233
1234 unsigned TotalSize = 0;
1235 LLVM_DEBUG(dbgs() << "Found " << NumMarkers << " markers and " << NumSlots
1236 << " slots\n");
1237 LLVM_DEBUG(dbgs() << "Slot structure:\n");
1238
1239 for (int i=0; i < MFI->getObjectIndexEnd(); ++i) {
1240 LLVM_DEBUG(dbgs() << "Slot #" << i << " - " << MFI->getObjectSize(i)
1241 << " bytes.\n");
1242 TotalSize += MFI->getObjectSize(ObjectIdx: i);
1243 }
1244
1245 LLVM_DEBUG(dbgs() << "Total Stack size: " << TotalSize << " bytes\n\n");
1246
1247 // Don't continue because there are not enough lifetime markers, or the
1248 // stack is too small, or we are told not to optimize the slots.
1249 if (NumMarkers < 2 || TotalSize < 16 || DisableColoring) {
1250 LLVM_DEBUG(dbgs() << "Will not try to merge slots.\n");
1251 return removeAllMarkers();
1252 }
1253
1254 for (unsigned i=0; i < NumSlots; ++i) {
1255 std::unique_ptr<LiveInterval> LI(new LiveInterval(i, 0));
1256 LI->getNextValue(Def: Indexes->getZeroIndex(), VNInfoAllocator);
1257 Intervals.push_back(Elt: std::move(LI));
1258 SortedSlots.push_back(Elt: i);
1259 }
1260
1261 // Calculate the liveness of each block.
1262 calculateLocalLiveness();
1263 LLVM_DEBUG(dbgs() << "Dataflow iterations: " << NumIterations << "\n");
1264 LLVM_DEBUG(dump());
1265
1266 // Propagate the liveness information.
1267 calculateLiveIntervals(NumSlots);
1268 LLVM_DEBUG(dumpIntervals());
1269
1270 // Search for allocas which are used outside of the declared lifetime
1271 // markers.
1272 if (ProtectFromEscapedAllocas)
1273 removeInvalidSlotRanges();
1274
1275 // Maps old slots to new slots.
1276 DenseMap<int, int> SlotRemap;
1277 unsigned RemovedSlots = 0;
1278 unsigned ReducedSize = 0;
1279
1280 // Do not bother looking at empty intervals.
1281 for (unsigned I = 0; I < NumSlots; ++I) {
1282 if (Intervals[SortedSlots[I]]->empty())
1283 SortedSlots[I] = -1;
1284 }
1285
1286 // This is a simple greedy algorithm for merging allocas. First, sort the
1287 // slots, placing the largest slots first. Next, perform an n^2 scan and look
1288 // for disjoint slots. When you find disjoint slots, merge the smaller one
1289 // into the bigger one and update the live interval. Remove the small alloca
1290 // and continue.
1291
1292 // Sort the slots according to their size. Place unused slots at the end.
1293 // Use stable sort to guarantee deterministic code generation.
1294 llvm::stable_sort(Range&: SortedSlots, C: [this](int LHS, int RHS) {
1295 // We use -1 to denote a uninteresting slot. Place these slots at the end.
1296 if (LHS == -1)
1297 return false;
1298 if (RHS == -1)
1299 return true;
1300 // Sort according to size.
1301 return MFI->getObjectSize(ObjectIdx: LHS) > MFI->getObjectSize(ObjectIdx: RHS);
1302 });
1303
1304 for (auto &s : LiveStarts)
1305 llvm::sort(C&: s);
1306
1307 bool Changed = true;
1308 while (Changed) {
1309 Changed = false;
1310 for (unsigned I = 0; I < NumSlots; ++I) {
1311 if (SortedSlots[I] == -1)
1312 continue;
1313
1314 for (unsigned J=I+1; J < NumSlots; ++J) {
1315 if (SortedSlots[J] == -1)
1316 continue;
1317
1318 int FirstSlot = SortedSlots[I];
1319 int SecondSlot = SortedSlots[J];
1320
1321 // Objects with different stack IDs cannot be merged.
1322 if (MFI->getStackID(ObjectIdx: FirstSlot) != MFI->getStackID(ObjectIdx: SecondSlot))
1323 continue;
1324
1325 LiveInterval *First = &*Intervals[FirstSlot];
1326 LiveInterval *Second = &*Intervals[SecondSlot];
1327 auto &FirstS = LiveStarts[FirstSlot];
1328 auto &SecondS = LiveStarts[SecondSlot];
1329 assert(!First->empty() && !Second->empty() && "Found an empty range");
1330
1331 // Merge disjoint slots. This is a little bit tricky - see the
1332 // Implementation Notes section for an explanation.
1333 if (!First->isLiveAtIndexes(Slots: SecondS) &&
1334 !Second->isLiveAtIndexes(Slots: FirstS)) {
1335 Changed = true;
1336 First->MergeSegmentsInAsValue(RHS: *Second, LHSValNo: First->getValNumInfo(ValNo: 0));
1337
1338 int OldSize = FirstS.size();
1339 FirstS.append(in_start: SecondS.begin(), in_end: SecondS.end());
1340 auto Mid = FirstS.begin() + OldSize;
1341 std::inplace_merge(first: FirstS.begin(), middle: Mid, last: FirstS.end());
1342
1343 SlotRemap[SecondSlot] = FirstSlot;
1344 SortedSlots[J] = -1;
1345 LLVM_DEBUG(dbgs() << "Merging #" << FirstSlot << " and slots #"
1346 << SecondSlot << " together.\n");
1347 Align MaxAlignment = std::max(a: MFI->getObjectAlign(ObjectIdx: FirstSlot),
1348 b: MFI->getObjectAlign(ObjectIdx: SecondSlot));
1349
1350 assert(MFI->getObjectSize(FirstSlot) >=
1351 MFI->getObjectSize(SecondSlot) &&
1352 "Merging a small object into a larger one");
1353
1354 RemovedSlots+=1;
1355 ReducedSize += MFI->getObjectSize(ObjectIdx: SecondSlot);
1356 MFI->setObjectAlignment(ObjectIdx: FirstSlot, Alignment: MaxAlignment);
1357 MFI->RemoveStackObject(ObjectIdx: SecondSlot);
1358 }
1359 }
1360 }
1361 }// While changed.
1362
1363 // Record statistics.
1364 StackSpaceSaved += ReducedSize;
1365 StackSlotMerged += RemovedSlots;
1366 LLVM_DEBUG(dbgs() << "Merge " << RemovedSlots << " slots. Saved "
1367 << ReducedSize << " bytes\n");
1368
1369 // Scan the entire function and update all machine operands that use frame
1370 // indices to use the remapped frame index.
1371 if (!SlotRemap.empty()) {
1372 expungeSlotMap(SlotRemap, NumSlots);
1373 remapInstructions(SlotRemap);
1374 }
1375
1376 return removeAllMarkers();
1377}
1378