1//===-- ControlHeightReduction.cpp - Control Height Reduction -------------===//
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 merges conditional blocks of code and reduces the number of
10// conditional branches in the hot paths based on profiles.
11//
12//===----------------------------------------------------------------------===//
13
14#include "llvm/Transforms/Instrumentation/ControlHeightReduction.h"
15#include "llvm/ADT/DenseMap.h"
16#include "llvm/ADT/DenseSet.h"
17#include "llvm/ADT/SmallVector.h"
18#include "llvm/ADT/StringSet.h"
19#include "llvm/Analysis/BlockFrequencyInfo.h"
20#include "llvm/Analysis/GlobalsModRef.h"
21#include "llvm/Analysis/OptimizationRemarkEmitter.h"
22#include "llvm/Analysis/ProfileSummaryInfo.h"
23#include "llvm/Analysis/RegionInfo.h"
24#include "llvm/Analysis/RegionIterator.h"
25#include "llvm/Analysis/ValueTracking.h"
26#include "llvm/IR/CFG.h"
27#include "llvm/IR/Dominators.h"
28#include "llvm/IR/IRBuilder.h"
29#include "llvm/IR/IntrinsicInst.h"
30#include "llvm/IR/MDBuilder.h"
31#include "llvm/IR/Module.h"
32#include "llvm/IR/PassManager.h"
33#include "llvm/IR/ProfDataUtils.h"
34#include "llvm/Support/BranchProbability.h"
35#include "llvm/Support/CommandLine.h"
36#include "llvm/Support/MemoryBuffer.h"
37#include "llvm/Transforms/Utils/BasicBlockUtils.h"
38#include "llvm/Transforms/Utils/Cloning.h"
39#include "llvm/Transforms/Utils/ValueMapper.h"
40
41#include <optional>
42#include <set>
43#include <sstream>
44
45using namespace llvm;
46
47#define DEBUG_TYPE "chr"
48
49#define CHR_DEBUG(X) LLVM_DEBUG(X)
50
51static cl::opt<bool> DisableCHR("disable-chr", cl::init(Val: false), cl::Hidden,
52 cl::desc("Disable CHR for all functions"));
53
54static cl::opt<bool> ForceCHR("force-chr", cl::init(Val: false), cl::Hidden,
55 cl::desc("Apply CHR for all functions"));
56
57static cl::opt<double> CHRBiasThreshold(
58 "chr-bias-threshold", cl::init(Val: 0.99), cl::Hidden,
59 cl::desc("CHR considers a branch bias greater than this ratio as biased"));
60
61static cl::opt<unsigned> CHRMergeThreshold(
62 "chr-merge-threshold", cl::init(Val: 2), cl::Hidden,
63 cl::desc("CHR merges a group of N branches/selects where N >= this value"));
64
65static cl::opt<std::string> CHRModuleList(
66 "chr-module-list", cl::init(Val: ""), cl::Hidden,
67 cl::desc("Specify file to retrieve the list of modules to apply CHR to"));
68
69static cl::opt<std::string> CHRFunctionList(
70 "chr-function-list", cl::init(Val: ""), cl::Hidden,
71 cl::desc("Specify file to retrieve the list of functions to apply CHR to"));
72
73static cl::opt<unsigned> CHRDupThreshsold(
74 "chr-dup-threshold", cl::init(Val: 3), cl::Hidden,
75 cl::desc("Max number of duplications by CHR for a region"));
76
77static StringSet<> CHRModules;
78static StringSet<> CHRFunctions;
79
80static void parseCHRFilterFiles() {
81 if (!CHRModuleList.empty()) {
82 auto FileOrErr = MemoryBuffer::getFile(Filename: CHRModuleList);
83 if (!FileOrErr) {
84 errs() << "Error: Couldn't read the chr-module-list file " << CHRModuleList << "\n";
85 std::exit(status: 1);
86 }
87 StringRef Buf = FileOrErr->get()->getBuffer();
88 SmallVector<StringRef, 0> Lines;
89 Buf.split(A&: Lines, Separator: '\n');
90 for (StringRef Line : Lines) {
91 Line = Line.trim();
92 if (!Line.empty())
93 CHRModules.insert(key: Line);
94 }
95 }
96 if (!CHRFunctionList.empty()) {
97 auto FileOrErr = MemoryBuffer::getFile(Filename: CHRFunctionList);
98 if (!FileOrErr) {
99 errs() << "Error: Couldn't read the chr-function-list file " << CHRFunctionList << "\n";
100 std::exit(status: 1);
101 }
102 StringRef Buf = FileOrErr->get()->getBuffer();
103 SmallVector<StringRef, 0> Lines;
104 Buf.split(A&: Lines, Separator: '\n');
105 for (StringRef Line : Lines) {
106 Line = Line.trim();
107 if (!Line.empty())
108 CHRFunctions.insert(key: Line);
109 }
110 }
111}
112
113namespace {
114
115struct CHRStats {
116 CHRStats() = default;
117 void print(raw_ostream &OS) const {
118 OS << "CHRStats: NumBranches " << NumBranches
119 << " NumBranchesDelta " << NumBranchesDelta
120 << " WeightedNumBranchesDelta " << WeightedNumBranchesDelta;
121 }
122 // The original number of conditional branches / selects
123 uint64_t NumBranches = 0;
124 // The decrease of the number of conditional branches / selects in the hot
125 // paths due to CHR.
126 uint64_t NumBranchesDelta = 0;
127 // NumBranchesDelta weighted by the profile count at the scope entry.
128 uint64_t WeightedNumBranchesDelta = 0;
129};
130
131// RegInfo - some properties of a Region.
132struct RegInfo {
133 RegInfo() = default;
134 RegInfo(Region *RegionIn) : R(RegionIn) {}
135 Region *R = nullptr;
136 bool HasBranch = false;
137 SmallVector<SelectInst *, 8> Selects;
138};
139
140typedef DenseMap<Region *, DenseSet<Instruction *>> HoistStopMapTy;
141
142// CHRScope - a sequence of regions to CHR together. It corresponds to a
143// sequence of conditional blocks. It can have subscopes which correspond to
144// nested conditional blocks. Nested CHRScopes form a tree.
145class CHRScope {
146 public:
147 CHRScope(RegInfo RI) : BranchInsertPoint(nullptr) {
148 assert(RI.R && "Null RegionIn");
149 RegInfos.push_back(Elt: RI);
150 }
151
152 Region *getParentRegion() {
153 assert(RegInfos.size() > 0 && "Empty CHRScope");
154 Region *Parent = RegInfos[0].R->getParent();
155 assert(Parent && "Unexpected to call this on the top-level region");
156 return Parent;
157 }
158
159 BasicBlock *getEntryBlock() {
160 assert(RegInfos.size() > 0 && "Empty CHRScope");
161 return RegInfos.front().R->getEntry();
162 }
163
164 BasicBlock *getExitBlock() {
165 assert(RegInfos.size() > 0 && "Empty CHRScope");
166 return RegInfos.back().R->getExit();
167 }
168
169 bool appendable(CHRScope *Next) {
170 // The next scope is appendable only if this scope is directly connected to
171 // it (which implies it post-dominates this scope) and this scope dominates
172 // it (no edge to the next scope outside this scope).
173 BasicBlock *NextEntry = Next->getEntryBlock();
174 if (getExitBlock() != NextEntry)
175 // Not directly connected.
176 return false;
177 Region *LastRegion = RegInfos.back().R;
178 for (BasicBlock *Pred : predecessors(BB: NextEntry))
179 if (!LastRegion->contains(BB: Pred))
180 // There's an edge going into the entry of the next scope from outside
181 // of this scope.
182 return false;
183 return true;
184 }
185
186 void append(CHRScope *Next) {
187 assert(RegInfos.size() > 0 && "Empty CHRScope");
188 assert(Next->RegInfos.size() > 0 && "Empty CHRScope");
189 assert(getParentRegion() == Next->getParentRegion() &&
190 "Must be siblings");
191 assert(getExitBlock() == Next->getEntryBlock() &&
192 "Must be adjacent");
193 RegInfos.append(in_start: Next->RegInfos.begin(), in_end: Next->RegInfos.end());
194 Subs.append(in_start: Next->Subs.begin(), in_end: Next->Subs.end());
195 }
196
197 void addSub(CHRScope *SubIn) {
198#ifndef NDEBUG
199 bool IsChild = false;
200 for (RegInfo &RI : RegInfos)
201 if (RI.R == SubIn->getParentRegion()) {
202 IsChild = true;
203 break;
204 }
205 assert(IsChild && "Must be a child");
206#endif
207 Subs.push_back(Elt: SubIn);
208 }
209
210 // Split this scope at the boundary region into two, which will belong to the
211 // tail and returns the tail.
212 CHRScope *split(Region *Boundary) {
213 assert(Boundary && "Boundary null");
214 assert(RegInfos.begin()->R != Boundary &&
215 "Can't be split at beginning");
216 auto BoundaryIt = llvm::find_if(
217 Range&: RegInfos, P: [&Boundary](const RegInfo &RI) { return Boundary == RI.R; });
218 if (BoundaryIt == RegInfos.end())
219 return nullptr;
220 ArrayRef<RegInfo> TailRegInfos(BoundaryIt, RegInfos.end());
221 DenseSet<Region *> TailRegionSet;
222 for (const RegInfo &RI : TailRegInfos)
223 TailRegionSet.insert(V: RI.R);
224
225 auto TailIt =
226 std::stable_partition(first: Subs.begin(), last: Subs.end(), pred: [&](CHRScope *Sub) {
227 assert(Sub && "null Sub");
228 Region *Parent = Sub->getParentRegion();
229 if (TailRegionSet.count(V: Parent))
230 return false;
231
232 assert(llvm::any_of(
233 RegInfos,
234 [&Parent](const RegInfo &RI) { return Parent == RI.R; }) &&
235 "Must be in head");
236 return true;
237 });
238 ArrayRef<CHRScope *> TailSubs(TailIt, Subs.end());
239
240 assert(HoistStopMap.empty() && "MapHoistStops must be empty");
241 auto *Scope = new CHRScope(TailRegInfos, TailSubs);
242 RegInfos.erase(CS: BoundaryIt, CE: RegInfos.end());
243 Subs.erase(CS: TailIt, CE: Subs.end());
244 return Scope;
245 }
246
247 bool contains(Instruction *I) const {
248 BasicBlock *Parent = I->getParent();
249 for (const RegInfo &RI : RegInfos)
250 if (RI.R->contains(BB: Parent))
251 return true;
252 return false;
253 }
254
255 void print(raw_ostream &OS) const;
256
257 SmallVector<RegInfo, 8> RegInfos; // Regions that belong to this scope
258 SmallVector<CHRScope *, 8> Subs; // Subscopes.
259
260 // The instruction at which to insert the CHR conditional branch (and hoist
261 // the dependent condition values).
262 Instruction *BranchInsertPoint;
263
264 // True-biased and false-biased regions (conditional blocks),
265 // respectively. Used only for the outermost scope and includes regions in
266 // subscopes. The rest are unbiased.
267 DenseSet<Region *> TrueBiasedRegions;
268 DenseSet<Region *> FalseBiasedRegions;
269 // Among the biased regions, the regions that get CHRed.
270 SmallVector<RegInfo, 8> CHRRegions;
271
272 // True-biased and false-biased selects, respectively. Used only for the
273 // outermost scope and includes ones in subscopes.
274 DenseSet<SelectInst *> TrueBiasedSelects;
275 DenseSet<SelectInst *> FalseBiasedSelects;
276
277 // Map from one of the above regions to the instructions to stop
278 // hoisting instructions at through use-def chains.
279 HoistStopMapTy HoistStopMap;
280
281 private:
282 CHRScope(ArrayRef<RegInfo> RegInfosIn, ArrayRef<CHRScope *> SubsIn)
283 : RegInfos(RegInfosIn), Subs(SubsIn), BranchInsertPoint(nullptr) {}
284};
285
286class CHR {
287 public:
288 CHR(Function &Fin, BlockFrequencyInfo &BFIin, DominatorTree &DTin,
289 ProfileSummaryInfo &PSIin, RegionInfo &RIin,
290 OptimizationRemarkEmitter &OREin)
291 : F(Fin), BFI(BFIin), DT(DTin), PSI(PSIin), RI(RIin), ORE(OREin) {}
292
293 ~CHR() {
294 for (CHRScope *Scope : Scopes) {
295 delete Scope;
296 }
297 }
298
299 bool run();
300
301 private:
302 // See the comments in CHR::run() for the high level flow of the algorithm and
303 // what the following functions do.
304
305 void findScopes(SmallVectorImpl<CHRScope *> &Output) {
306 Region *R = RI.getTopLevelRegion();
307 if (CHRScope *Scope = findScopes(R, NextRegion: nullptr, ParentRegion: nullptr, Scopes&: Output)) {
308 Output.push_back(Elt: Scope);
309 }
310 }
311 CHRScope *findScopes(Region *R, Region *NextRegion, Region *ParentRegion,
312 SmallVectorImpl<CHRScope *> &Scopes);
313 CHRScope *findScope(Region *R);
314 void checkScopeHoistable(CHRScope *Scope);
315
316 void splitScopes(SmallVectorImpl<CHRScope *> &Input,
317 SmallVectorImpl<CHRScope *> &Output);
318 SmallVector<CHRScope *, 8> splitScope(CHRScope *Scope,
319 CHRScope *Outer,
320 DenseSet<Value *> *OuterConditionValues,
321 Instruction *OuterInsertPoint,
322 SmallVectorImpl<CHRScope *> &Output,
323 DenseSet<Instruction *> &Unhoistables);
324
325 void classifyBiasedScopes(SmallVectorImpl<CHRScope *> &Scopes);
326 void classifyBiasedScopes(CHRScope *Scope, CHRScope *OutermostScope);
327
328 void filterScopes(SmallVectorImpl<CHRScope *> &Input,
329 SmallVectorImpl<CHRScope *> &Output);
330
331 void setCHRRegions(SmallVectorImpl<CHRScope *> &Input,
332 SmallVectorImpl<CHRScope *> &Output);
333 void setCHRRegions(CHRScope *Scope, CHRScope *OutermostScope);
334
335 void sortScopes(SmallVectorImpl<CHRScope *> &Input,
336 SmallVectorImpl<CHRScope *> &Output);
337
338 void transformScopes(SmallVectorImpl<CHRScope *> &CHRScopes);
339 void transformScopes(CHRScope *Scope, DenseSet<PHINode *> &TrivialPHIs);
340 void cloneScopeBlocks(CHRScope *Scope,
341 BasicBlock *PreEntryBlock,
342 BasicBlock *ExitBlock,
343 Region *LastRegion,
344 ValueToValueMapTy &VMap);
345 BranchInst *createMergedBranch(BasicBlock *PreEntryBlock,
346 BasicBlock *EntryBlock,
347 BasicBlock *NewEntryBlock,
348 ValueToValueMapTy &VMap);
349 void fixupBranchesAndSelects(CHRScope *Scope, BasicBlock *PreEntryBlock,
350 BranchInst *MergedBR, uint64_t ProfileCount);
351 void fixupBranch(Region *R, CHRScope *Scope, IRBuilder<> &IRB,
352 Value *&MergedCondition, BranchProbability &CHRBranchBias);
353 void fixupSelect(SelectInst *SI, CHRScope *Scope, IRBuilder<> &IRB,
354 Value *&MergedCondition, BranchProbability &CHRBranchBias);
355 void addToMergedCondition(bool IsTrueBiased, Value *Cond,
356 Instruction *BranchOrSelect, CHRScope *Scope,
357 IRBuilder<> &IRB, Value *&MergedCondition);
358 unsigned getRegionDuplicationCount(const Region *R) {
359 unsigned Count = 0;
360 // Find out how many times region R is cloned. Note that if the parent
361 // of R is cloned, R is also cloned, but R's clone count is not updated
362 // from the clone of the parent. We need to accumlate all the counts
363 // from the ancestors to get the clone count.
364 while (R) {
365 Count += DuplicationCount[R];
366 R = R->getParent();
367 }
368 return Count;
369 }
370
371 Function &F;
372 BlockFrequencyInfo &BFI;
373 DominatorTree &DT;
374 ProfileSummaryInfo &PSI;
375 RegionInfo &RI;
376 OptimizationRemarkEmitter &ORE;
377 CHRStats Stats;
378
379 // All the true-biased regions in the function
380 DenseSet<Region *> TrueBiasedRegionsGlobal;
381 // All the false-biased regions in the function
382 DenseSet<Region *> FalseBiasedRegionsGlobal;
383 // All the true-biased selects in the function
384 DenseSet<SelectInst *> TrueBiasedSelectsGlobal;
385 // All the false-biased selects in the function
386 DenseSet<SelectInst *> FalseBiasedSelectsGlobal;
387 // A map from biased regions to their branch bias
388 DenseMap<Region *, BranchProbability> BranchBiasMap;
389 // A map from biased selects to their branch bias
390 DenseMap<SelectInst *, BranchProbability> SelectBiasMap;
391 // All the scopes.
392 DenseSet<CHRScope *> Scopes;
393 // This maps records how many times this region is cloned.
394 DenseMap<const Region *, unsigned> DuplicationCount;
395};
396
397} // end anonymous namespace
398
399static inline
400raw_ostream LLVM_ATTRIBUTE_UNUSED &operator<<(raw_ostream &OS,
401 const CHRStats &Stats) {
402 Stats.print(OS);
403 return OS;
404}
405
406static inline
407raw_ostream &operator<<(raw_ostream &OS, const CHRScope &Scope) {
408 Scope.print(OS);
409 return OS;
410}
411
412static bool shouldApply(Function &F, ProfileSummaryInfo &PSI) {
413 if (DisableCHR)
414 return false;
415
416 if (ForceCHR)
417 return true;
418
419 if (!CHRModuleList.empty() || !CHRFunctionList.empty()) {
420 if (CHRModules.count(Key: F.getParent()->getName()))
421 return true;
422 return CHRFunctions.count(Key: F.getName());
423 }
424
425 return PSI.isFunctionEntryHot(F: &F);
426}
427
428static void LLVM_ATTRIBUTE_UNUSED dumpIR(Function &F, const char *Label,
429 CHRStats *Stats) {
430 StringRef FuncName = F.getName();
431 StringRef ModuleName = F.getParent()->getName();
432 (void)(FuncName); // Unused in release build.
433 (void)(ModuleName); // Unused in release build.
434 CHR_DEBUG(dbgs() << "CHR IR dump " << Label << " " << ModuleName << " "
435 << FuncName);
436 if (Stats)
437 CHR_DEBUG(dbgs() << " " << *Stats);
438 CHR_DEBUG(dbgs() << "\n");
439 CHR_DEBUG(F.dump());
440}
441
442void CHRScope::print(raw_ostream &OS) const {
443 assert(RegInfos.size() > 0 && "Empty CHRScope");
444 OS << "CHRScope[";
445 OS << RegInfos.size() << ", Regions[";
446 for (const RegInfo &RI : RegInfos) {
447 OS << RI.R->getNameStr();
448 if (RI.HasBranch)
449 OS << " B";
450 if (RI.Selects.size() > 0)
451 OS << " S" << RI.Selects.size();
452 OS << ", ";
453 }
454 if (RegInfos[0].R->getParent()) {
455 OS << "], Parent " << RegInfos[0].R->getParent()->getNameStr();
456 } else {
457 // top level region
458 OS << "]";
459 }
460 OS << ", Subs[";
461 for (CHRScope *Sub : Subs) {
462 OS << *Sub << ", ";
463 }
464 OS << "]]";
465}
466
467// Return true if the given instruction type can be hoisted by CHR.
468static bool isHoistableInstructionType(Instruction *I) {
469 return isa<BinaryOperator>(Val: I) || isa<CastInst>(Val: I) || isa<SelectInst>(Val: I) ||
470 isa<GetElementPtrInst>(Val: I) || isa<CmpInst>(Val: I) ||
471 isa<InsertElementInst>(Val: I) || isa<ExtractElementInst>(Val: I) ||
472 isa<ShuffleVectorInst>(Val: I) || isa<ExtractValueInst>(Val: I) ||
473 isa<InsertValueInst>(Val: I);
474}
475
476// Return true if the given instruction can be hoisted by CHR.
477static bool isHoistable(Instruction *I, DominatorTree &DT) {
478 if (!isHoistableInstructionType(I))
479 return false;
480 return isSafeToSpeculativelyExecute(I, CtxI: nullptr, AC: nullptr, DT: &DT);
481}
482
483// Recursively traverse the use-def chains of the given value and return a set
484// of the unhoistable base values defined within the scope (excluding the
485// first-region entry block) or the (hoistable or unhoistable) base values that
486// are defined outside (including the first-region entry block) of the
487// scope. The returned set doesn't include constants.
488static const std::set<Value *> &
489getBaseValues(Value *V, DominatorTree &DT,
490 DenseMap<Value *, std::set<Value *>> &Visited) {
491 auto It = Visited.find(Val: V);
492 if (It != Visited.end()) {
493 return It->second;
494 }
495 std::set<Value *> Result;
496 if (auto *I = dyn_cast<Instruction>(Val: V)) {
497 // We don't stop at a block that's not in the Scope because we would miss
498 // some instructions that are based on the same base values if we stop
499 // there.
500 if (!isHoistable(I, DT)) {
501 Result.insert(x: I);
502 return Visited.insert(KV: std::make_pair(x&: V, y: std::move(Result))).first->second;
503 }
504 // I is hoistable above the Scope.
505 for (Value *Op : I->operands()) {
506 const std::set<Value *> &OpResult = getBaseValues(V: Op, DT, Visited);
507 Result.insert(first: OpResult.begin(), last: OpResult.end());
508 }
509 return Visited.insert(KV: std::make_pair(x&: V, y: std::move(Result))).first->second;
510 }
511 if (isa<Argument>(Val: V)) {
512 Result.insert(x: V);
513 }
514 // We don't include others like constants because those won't lead to any
515 // chance of folding of conditions (eg two bit checks merged into one check)
516 // after CHR.
517 return Visited.insert(KV: std::make_pair(x&: V, y: std::move(Result))).first->second;
518}
519
520// Return true if V is already hoisted or can be hoisted (along with its
521// operands) above the insert point. When it returns true and HoistStops is
522// non-null, the instructions to stop hoisting at through the use-def chains are
523// inserted into HoistStops.
524static bool
525checkHoistValue(Value *V, Instruction *InsertPoint, DominatorTree &DT,
526 DenseSet<Instruction *> &Unhoistables,
527 DenseSet<Instruction *> *HoistStops,
528 DenseMap<Instruction *, bool> &Visited) {
529 assert(InsertPoint && "Null InsertPoint");
530 if (auto *I = dyn_cast<Instruction>(Val: V)) {
531 auto It = Visited.find(Val: I);
532 if (It != Visited.end()) {
533 return It->second;
534 }
535 assert(DT.getNode(I->getParent()) && "DT must contain I's parent block");
536 assert(DT.getNode(InsertPoint->getParent()) && "DT must contain Destination");
537 if (Unhoistables.count(V: I)) {
538 // Don't hoist if they are not to be hoisted.
539 Visited[I] = false;
540 return false;
541 }
542 if (DT.dominates(Def: I, User: InsertPoint)) {
543 // We are already above the insert point. Stop here.
544 if (HoistStops)
545 HoistStops->insert(V: I);
546 Visited[I] = true;
547 return true;
548 }
549 // We aren't not above the insert point, check if we can hoist it above the
550 // insert point.
551 if (isHoistable(I, DT)) {
552 // Check operands first.
553 DenseSet<Instruction *> OpsHoistStops;
554 bool AllOpsHoisted = true;
555 for (Value *Op : I->operands()) {
556 if (!checkHoistValue(V: Op, InsertPoint, DT, Unhoistables, HoistStops: &OpsHoistStops,
557 Visited)) {
558 AllOpsHoisted = false;
559 break;
560 }
561 }
562 if (AllOpsHoisted) {
563 CHR_DEBUG(dbgs() << "checkHoistValue " << *I << "\n");
564 if (HoistStops)
565 HoistStops->insert_range(R&: OpsHoistStops);
566 Visited[I] = true;
567 return true;
568 }
569 }
570 Visited[I] = false;
571 return false;
572 }
573 // Non-instructions are considered hoistable.
574 return true;
575}
576
577// Constructs the true and false branch probabilities if the the instruction has
578// valid branch weights. Returns true when this was successful, false otherwise.
579static bool extractBranchProbabilities(Instruction *I,
580 BranchProbability &TrueProb,
581 BranchProbability &FalseProb) {
582 uint64_t TrueWeight;
583 uint64_t FalseWeight;
584 if (!extractBranchWeights(I: *I, TrueVal&: TrueWeight, FalseVal&: FalseWeight))
585 return false;
586 uint64_t SumWeight = TrueWeight + FalseWeight;
587
588 assert(SumWeight >= TrueWeight && SumWeight >= FalseWeight &&
589 "Overflow calculating branch probabilities.");
590
591 // Guard against 0-to-0 branch weights to avoid a division-by-zero crash.
592 if (SumWeight == 0)
593 return false;
594
595 TrueProb = BranchProbability::getBranchProbability(Numerator: TrueWeight, Denominator: SumWeight);
596 FalseProb = BranchProbability::getBranchProbability(Numerator: FalseWeight, Denominator: SumWeight);
597 return true;
598}
599
600static BranchProbability getCHRBiasThreshold() {
601 return BranchProbability::getBranchProbability(
602 Numerator: static_cast<uint64_t>(CHRBiasThreshold * 1000000), Denominator: 1000000);
603}
604
605// A helper for CheckBiasedBranch and CheckBiasedSelect. If TrueProb >=
606// CHRBiasThreshold, put Key into TrueSet and return true. If FalseProb >=
607// CHRBiasThreshold, put Key into FalseSet and return true. Otherwise, return
608// false.
609template <typename K, typename S, typename M>
610static bool checkBias(K *Key, BranchProbability TrueProb,
611 BranchProbability FalseProb, S &TrueSet, S &FalseSet,
612 M &BiasMap) {
613 BranchProbability Threshold = getCHRBiasThreshold();
614 if (TrueProb >= Threshold) {
615 TrueSet.insert(Key);
616 BiasMap[Key] = TrueProb;
617 return true;
618 } else if (FalseProb >= Threshold) {
619 FalseSet.insert(Key);
620 BiasMap[Key] = FalseProb;
621 return true;
622 }
623 return false;
624}
625
626// Returns true and insert a region into the right biased set and the map if the
627// branch of the region is biased.
628static bool checkBiasedBranch(BranchInst *BI, Region *R,
629 DenseSet<Region *> &TrueBiasedRegionsGlobal,
630 DenseSet<Region *> &FalseBiasedRegionsGlobal,
631 DenseMap<Region *, BranchProbability> &BranchBiasMap) {
632 if (!BI->isConditional())
633 return false;
634 BranchProbability ThenProb, ElseProb;
635 if (!extractBranchProbabilities(I: BI, TrueProb&: ThenProb, FalseProb&: ElseProb))
636 return false;
637 BasicBlock *IfThen = BI->getSuccessor(i: 0);
638 BasicBlock *IfElse = BI->getSuccessor(i: 1);
639 assert((IfThen == R->getExit() || IfElse == R->getExit()) &&
640 IfThen != IfElse &&
641 "Invariant from findScopes");
642 if (IfThen == R->getExit()) {
643 // Swap them so that IfThen/ThenProb means going into the conditional code
644 // and IfElse/ElseProb means skipping it.
645 std::swap(a&: IfThen, b&: IfElse);
646 std::swap(a&: ThenProb, b&: ElseProb);
647 }
648 CHR_DEBUG(dbgs() << "BI " << *BI << " ");
649 CHR_DEBUG(dbgs() << "ThenProb " << ThenProb << " ");
650 CHR_DEBUG(dbgs() << "ElseProb " << ElseProb << "\n");
651 return checkBias(Key: R, TrueProb: ThenProb, FalseProb: ElseProb,
652 TrueSet&: TrueBiasedRegionsGlobal, FalseSet&: FalseBiasedRegionsGlobal,
653 BiasMap&: BranchBiasMap);
654}
655
656// Returns true and insert a select into the right biased set and the map if the
657// select is biased.
658static bool checkBiasedSelect(
659 SelectInst *SI, Region *R,
660 DenseSet<SelectInst *> &TrueBiasedSelectsGlobal,
661 DenseSet<SelectInst *> &FalseBiasedSelectsGlobal,
662 DenseMap<SelectInst *, BranchProbability> &SelectBiasMap) {
663 BranchProbability TrueProb, FalseProb;
664 if (!extractBranchProbabilities(I: SI, TrueProb, FalseProb))
665 return false;
666 CHR_DEBUG(dbgs() << "SI " << *SI << " ");
667 CHR_DEBUG(dbgs() << "TrueProb " << TrueProb << " ");
668 CHR_DEBUG(dbgs() << "FalseProb " << FalseProb << "\n");
669 return checkBias(Key: SI, TrueProb, FalseProb,
670 TrueSet&: TrueBiasedSelectsGlobal, FalseSet&: FalseBiasedSelectsGlobal,
671 BiasMap&: SelectBiasMap);
672}
673
674// Returns the instruction at which to hoist the dependent condition values and
675// insert the CHR branch for a region. This is the terminator branch in the
676// entry block or the first select in the entry block, if any.
677static Instruction* getBranchInsertPoint(RegInfo &RI) {
678 Region *R = RI.R;
679 BasicBlock *EntryBB = R->getEntry();
680 // The hoist point is by default the terminator of the entry block, which is
681 // the same as the branch instruction if RI.HasBranch is true.
682 Instruction *HoistPoint = EntryBB->getTerminator();
683 for (SelectInst *SI : RI.Selects) {
684 if (SI->getParent() == EntryBB) {
685 // Pick the first select in Selects in the entry block. Note Selects is
686 // sorted in the instruction order within a block (asserted below).
687 HoistPoint = SI;
688 break;
689 }
690 }
691 assert(HoistPoint && "Null HoistPoint");
692#ifndef NDEBUG
693 // Check that HoistPoint is the first one in Selects in the entry block,
694 // if any.
695 DenseSet<Instruction *> EntryBlockSelectSet;
696 for (SelectInst *SI : RI.Selects) {
697 if (SI->getParent() == EntryBB) {
698 EntryBlockSelectSet.insert(SI);
699 }
700 }
701 for (Instruction &I : *EntryBB) {
702 if (EntryBlockSelectSet.contains(&I)) {
703 assert(&I == HoistPoint &&
704 "HoistPoint must be the first one in Selects");
705 break;
706 }
707 }
708#endif
709 return HoistPoint;
710}
711
712// Find a CHR scope in the given region.
713CHRScope * CHR::findScope(Region *R) {
714 CHRScope *Result = nullptr;
715 BasicBlock *Entry = R->getEntry();
716 BasicBlock *Exit = R->getExit(); // null if top level.
717 assert(Entry && "Entry must not be null");
718 assert((Exit == nullptr) == (R->isTopLevelRegion()) &&
719 "Only top level region has a null exit");
720 if (Entry)
721 CHR_DEBUG(dbgs() << "Entry " << Entry->getName() << "\n");
722 else
723 CHR_DEBUG(dbgs() << "Entry null\n");
724 if (Exit)
725 CHR_DEBUG(dbgs() << "Exit " << Exit->getName() << "\n");
726 else
727 CHR_DEBUG(dbgs() << "Exit null\n");
728 // Exclude cases where Entry is part of a subregion (hence it doesn't belong
729 // to this region).
730 bool EntryInSubregion = RI.getRegionFor(BB: Entry) != R;
731 if (EntryInSubregion)
732 return nullptr;
733 // Exclude loops
734 for (BasicBlock *Pred : predecessors(BB: Entry))
735 if (R->contains(BB: Pred))
736 return nullptr;
737 // If any of the basic blocks have address taken, we must skip this region
738 // because we cannot clone basic blocks that have address taken.
739 for (BasicBlock *BB : R->blocks()) {
740 if (BB->hasAddressTaken())
741 return nullptr;
742 // If we encounter llvm.coro.id, skip this region because if the basic block
743 // is cloned, we end up inserting a token type PHI node to the block with
744 // llvm.coro.begin.
745 // FIXME: This could lead to less optimal codegen, because the region is
746 // excluded, it can prevent CHR from merging adjacent regions into bigger
747 // scope and hoisting more branches.
748 for (Instruction &I : *BB)
749 if (auto *II = dyn_cast<IntrinsicInst>(Val: &I))
750 if (II->getIntrinsicID() == Intrinsic::coro_id)
751 return nullptr;
752 }
753
754 if (Exit) {
755 // Try to find an if-then block (check if R is an if-then).
756 // if (cond) {
757 // ...
758 // }
759 auto *BI = dyn_cast<BranchInst>(Val: Entry->getTerminator());
760 if (BI)
761 CHR_DEBUG(dbgs() << "BI.isConditional " << BI->isConditional() << "\n");
762 else
763 CHR_DEBUG(dbgs() << "BI null\n");
764 if (BI && BI->isConditional()) {
765 BasicBlock *S0 = BI->getSuccessor(i: 0);
766 BasicBlock *S1 = BI->getSuccessor(i: 1);
767 CHR_DEBUG(dbgs() << "S0 " << S0->getName() << "\n");
768 CHR_DEBUG(dbgs() << "S1 " << S1->getName() << "\n");
769 if (S0 != S1 && (S0 == Exit || S1 == Exit)) {
770 RegInfo RI(R);
771 RI.HasBranch = checkBiasedBranch(
772 BI, R, TrueBiasedRegionsGlobal, FalseBiasedRegionsGlobal,
773 BranchBiasMap);
774 Result = new CHRScope(RI);
775 Scopes.insert(V: Result);
776 CHR_DEBUG(dbgs() << "Found a region with a branch\n");
777 ++Stats.NumBranches;
778 if (!RI.HasBranch) {
779 ORE.emit(RemarkBuilder: [&]() {
780 return OptimizationRemarkMissed(DEBUG_TYPE, "BranchNotBiased", BI)
781 << "Branch not biased";
782 });
783 }
784 }
785 }
786 }
787 {
788 // Try to look for selects in the direct child blocks (as opposed to in
789 // subregions) of R.
790 // ...
791 // if (..) { // Some subregion
792 // ...
793 // }
794 // if (..) { // Some subregion
795 // ...
796 // }
797 // ...
798 // a = cond ? b : c;
799 // ...
800 SmallVector<SelectInst *, 8> Selects;
801 for (RegionNode *E : R->elements()) {
802 if (E->isSubRegion())
803 continue;
804 // This returns the basic block of E if E is a direct child of R (not a
805 // subregion.)
806 BasicBlock *BB = E->getEntry();
807 // Need to push in the order to make it easier to find the first Select
808 // later.
809 for (Instruction &I : *BB) {
810 if (auto *SI = dyn_cast<SelectInst>(Val: &I)) {
811 Selects.push_back(Elt: SI);
812 ++Stats.NumBranches;
813 }
814 }
815 }
816 if (Selects.size() > 0) {
817 auto AddSelects = [&](RegInfo &RI) {
818 for (auto *SI : Selects)
819 if (checkBiasedSelect(SI, R: RI.R,
820 TrueBiasedSelectsGlobal,
821 FalseBiasedSelectsGlobal,
822 SelectBiasMap))
823 RI.Selects.push_back(Elt: SI);
824 else
825 ORE.emit(RemarkBuilder: [&]() {
826 return OptimizationRemarkMissed(DEBUG_TYPE, "SelectNotBiased", SI)
827 << "Select not biased";
828 });
829 };
830 if (!Result) {
831 CHR_DEBUG(dbgs() << "Found a select-only region\n");
832 RegInfo RI(R);
833 AddSelects(RI);
834 Result = new CHRScope(RI);
835 Scopes.insert(V: Result);
836 } else {
837 CHR_DEBUG(dbgs() << "Found select(s) in a region with a branch\n");
838 AddSelects(Result->RegInfos[0]);
839 }
840 }
841 }
842
843 if (Result) {
844 checkScopeHoistable(Scope: Result);
845 }
846 return Result;
847}
848
849// Check that any of the branch and the selects in the region could be
850// hoisted above the the CHR branch insert point (the most dominating of
851// them, either the branch (at the end of the first block) or the first
852// select in the first block). If the branch can't be hoisted, drop the
853// selects in the first blocks.
854//
855// For example, for the following scope/region with selects, we want to insert
856// the merged branch right before the first select in the first/entry block by
857// hoisting c1, c2, c3, and c4.
858//
859// // Branch insert point here.
860// a = c1 ? b : c; // Select 1
861// d = c2 ? e : f; // Select 2
862// if (c3) { // Branch
863// ...
864// c4 = foo() // A call.
865// g = c4 ? h : i; // Select 3
866// }
867//
868// But suppose we can't hoist c4 because it's dependent on the preceding
869// call. Then, we drop Select 3. Furthermore, if we can't hoist c2, we also drop
870// Select 2. If we can't hoist c3, we drop Selects 1 & 2.
871void CHR::checkScopeHoistable(CHRScope *Scope) {
872 RegInfo &RI = Scope->RegInfos[0];
873 Region *R = RI.R;
874 BasicBlock *EntryBB = R->getEntry();
875 auto *Branch = RI.HasBranch ?
876 cast<BranchInst>(Val: EntryBB->getTerminator()) : nullptr;
877 SmallVector<SelectInst *, 8> &Selects = RI.Selects;
878 if (RI.HasBranch || !Selects.empty()) {
879 Instruction *InsertPoint = getBranchInsertPoint(RI);
880 CHR_DEBUG(dbgs() << "InsertPoint " << *InsertPoint << "\n");
881 // Avoid a data dependence from a select or a branch to a(nother)
882 // select. Note no instruction can't data-depend on a branch (a branch
883 // instruction doesn't produce a value).
884 // Initialize Unhoistables with the selects.
885 DenseSet<Instruction *> Unhoistables(llvm::from_range, Selects);
886 // Remove Selects that can't be hoisted.
887 for (auto it = Selects.begin(); it != Selects.end(); ) {
888 SelectInst *SI = *it;
889 if (SI == InsertPoint) {
890 ++it;
891 continue;
892 }
893 DenseMap<Instruction *, bool> Visited;
894 bool IsHoistable = checkHoistValue(V: SI->getCondition(), InsertPoint,
895 DT, Unhoistables, HoistStops: nullptr, Visited);
896 if (!IsHoistable) {
897 CHR_DEBUG(dbgs() << "Dropping select " << *SI << "\n");
898 ORE.emit(RemarkBuilder: [&]() {
899 return OptimizationRemarkMissed(DEBUG_TYPE,
900 "DropUnhoistableSelect", SI)
901 << "Dropped unhoistable select";
902 });
903 it = Selects.erase(CI: it);
904 // Since we are dropping the select here, we also drop it from
905 // Unhoistables.
906 Unhoistables.erase(V: SI);
907 } else
908 ++it;
909 }
910 // Update InsertPoint after potentially removing selects.
911 InsertPoint = getBranchInsertPoint(RI);
912 CHR_DEBUG(dbgs() << "InsertPoint " << *InsertPoint << "\n");
913 if (RI.HasBranch && InsertPoint != Branch) {
914 DenseMap<Instruction *, bool> Visited;
915 bool IsHoistable = checkHoistValue(V: Branch->getCondition(), InsertPoint,
916 DT, Unhoistables, HoistStops: nullptr, Visited);
917 if (!IsHoistable) {
918 // If the branch isn't hoistable, drop the selects in the entry
919 // block, preferring the branch, which makes the branch the hoist
920 // point.
921 assert(InsertPoint != Branch && "Branch must not be the hoist point");
922 CHR_DEBUG(dbgs() << "Dropping selects in entry block \n");
923 CHR_DEBUG(
924 for (SelectInst *SI : Selects) {
925 dbgs() << "SI " << *SI << "\n";
926 });
927 for (SelectInst *SI : Selects) {
928 ORE.emit(RemarkBuilder: [&]() {
929 return OptimizationRemarkMissed(DEBUG_TYPE,
930 "DropSelectUnhoistableBranch", SI)
931 << "Dropped select due to unhoistable branch";
932 });
933 }
934 llvm::erase_if(C&: Selects, P: [EntryBB](SelectInst *SI) {
935 return SI->getParent() == EntryBB;
936 });
937 Unhoistables.clear();
938 InsertPoint = Branch;
939 }
940 }
941 CHR_DEBUG(dbgs() << "InsertPoint " << *InsertPoint << "\n");
942#ifndef NDEBUG
943 if (RI.HasBranch) {
944 assert(!DT.dominates(Branch, InsertPoint) &&
945 "Branch can't be already above the hoist point");
946 DenseMap<Instruction *, bool> Visited;
947 assert(checkHoistValue(Branch->getCondition(), InsertPoint,
948 DT, Unhoistables, nullptr, Visited) &&
949 "checkHoistValue for branch");
950 }
951 for (auto *SI : Selects) {
952 assert(!DT.dominates(SI, InsertPoint) &&
953 "SI can't be already above the hoist point");
954 DenseMap<Instruction *, bool> Visited;
955 assert(checkHoistValue(SI->getCondition(), InsertPoint, DT,
956 Unhoistables, nullptr, Visited) &&
957 "checkHoistValue for selects");
958 }
959 CHR_DEBUG(dbgs() << "Result\n");
960 if (RI.HasBranch) {
961 CHR_DEBUG(dbgs() << "BI " << *Branch << "\n");
962 }
963 for (auto *SI : Selects) {
964 CHR_DEBUG(dbgs() << "SI " << *SI << "\n");
965 }
966#endif
967 }
968}
969
970// Traverse the region tree, find all nested scopes and merge them if possible.
971CHRScope * CHR::findScopes(Region *R, Region *NextRegion, Region *ParentRegion,
972 SmallVectorImpl<CHRScope *> &Scopes) {
973 CHR_DEBUG(dbgs() << "findScopes " << R->getNameStr() << "\n");
974 CHRScope *Result = findScope(R);
975 // Visit subscopes.
976 CHRScope *ConsecutiveSubscope = nullptr;
977 SmallVector<CHRScope *, 8> Subscopes;
978 for (auto It = R->begin(); It != R->end(); ++It) {
979 const std::unique_ptr<Region> &SubR = *It;
980 auto NextIt = std::next(x: It);
981 Region *NextSubR = NextIt != R->end() ? NextIt->get() : nullptr;
982 CHR_DEBUG(dbgs() << "Looking at subregion " << SubR.get()->getNameStr()
983 << "\n");
984 CHRScope *SubCHRScope = findScopes(R: SubR.get(), NextRegion: NextSubR, ParentRegion: R, Scopes);
985 if (SubCHRScope) {
986 CHR_DEBUG(dbgs() << "Subregion Scope " << *SubCHRScope << "\n");
987 } else {
988 CHR_DEBUG(dbgs() << "Subregion Scope null\n");
989 }
990 if (SubCHRScope) {
991 if (!ConsecutiveSubscope)
992 ConsecutiveSubscope = SubCHRScope;
993 else if (!ConsecutiveSubscope->appendable(Next: SubCHRScope)) {
994 Subscopes.push_back(Elt: ConsecutiveSubscope);
995 ConsecutiveSubscope = SubCHRScope;
996 } else
997 ConsecutiveSubscope->append(Next: SubCHRScope);
998 } else {
999 if (ConsecutiveSubscope) {
1000 Subscopes.push_back(Elt: ConsecutiveSubscope);
1001 }
1002 ConsecutiveSubscope = nullptr;
1003 }
1004 }
1005 if (ConsecutiveSubscope) {
1006 Subscopes.push_back(Elt: ConsecutiveSubscope);
1007 }
1008 for (CHRScope *Sub : Subscopes) {
1009 if (Result) {
1010 // Combine it with the parent.
1011 Result->addSub(SubIn: Sub);
1012 } else {
1013 // Push Subscopes as they won't be combined with the parent.
1014 Scopes.push_back(Elt: Sub);
1015 }
1016 }
1017 return Result;
1018}
1019
1020static DenseSet<Value *> getCHRConditionValuesForRegion(RegInfo &RI) {
1021 DenseSet<Value *> ConditionValues;
1022 if (RI.HasBranch) {
1023 auto *BI = cast<BranchInst>(Val: RI.R->getEntry()->getTerminator());
1024 ConditionValues.insert(V: BI->getCondition());
1025 }
1026 for (SelectInst *SI : RI.Selects) {
1027 ConditionValues.insert(V: SI->getCondition());
1028 }
1029 return ConditionValues;
1030}
1031
1032
1033// Determine whether to split a scope depending on the sets of the branch
1034// condition values of the previous region and the current region. We split
1035// (return true) it if 1) the condition values of the inner/lower scope can't be
1036// hoisted up to the outer/upper scope, or 2) the two sets of the condition
1037// values have an empty intersection (because the combined branch conditions
1038// won't probably lead to a simpler combined condition).
1039static bool shouldSplit(Instruction *InsertPoint,
1040 DenseSet<Value *> &PrevConditionValues,
1041 DenseSet<Value *> &ConditionValues,
1042 DominatorTree &DT,
1043 DenseSet<Instruction *> &Unhoistables) {
1044 assert(InsertPoint && "Null InsertPoint");
1045 CHR_DEBUG(
1046 dbgs() << "shouldSplit " << *InsertPoint << " PrevConditionValues ";
1047 for (Value *V : PrevConditionValues) {
1048 dbgs() << *V << ", ";
1049 }
1050 dbgs() << " ConditionValues ";
1051 for (Value *V : ConditionValues) {
1052 dbgs() << *V << ", ";
1053 }
1054 dbgs() << "\n");
1055 // If any of Bases isn't hoistable to the hoist point, split.
1056 for (Value *V : ConditionValues) {
1057 DenseMap<Instruction *, bool> Visited;
1058 if (!checkHoistValue(V, InsertPoint, DT, Unhoistables, HoistStops: nullptr, Visited)) {
1059 CHR_DEBUG(dbgs() << "Split. checkHoistValue false " << *V << "\n");
1060 return true; // Not hoistable, split.
1061 }
1062 }
1063 // If PrevConditionValues or ConditionValues is empty, don't split to avoid
1064 // unnecessary splits at scopes with no branch/selects. If
1065 // PrevConditionValues and ConditionValues don't intersect at all, split.
1066 if (!PrevConditionValues.empty() && !ConditionValues.empty()) {
1067 // Use std::set as DenseSet doesn't work with set_intersection.
1068 std::set<Value *> PrevBases, Bases;
1069 DenseMap<Value *, std::set<Value *>> Visited;
1070 for (Value *V : PrevConditionValues) {
1071 const std::set<Value *> &BaseValues = getBaseValues(V, DT, Visited);
1072 PrevBases.insert(first: BaseValues.begin(), last: BaseValues.end());
1073 }
1074 for (Value *V : ConditionValues) {
1075 const std::set<Value *> &BaseValues = getBaseValues(V, DT, Visited);
1076 Bases.insert(first: BaseValues.begin(), last: BaseValues.end());
1077 }
1078 CHR_DEBUG(
1079 dbgs() << "PrevBases ";
1080 for (Value *V : PrevBases) {
1081 dbgs() << *V << ", ";
1082 }
1083 dbgs() << " Bases ";
1084 for (Value *V : Bases) {
1085 dbgs() << *V << ", ";
1086 }
1087 dbgs() << "\n");
1088 std::vector<Value *> Intersection;
1089 std::set_intersection(first1: PrevBases.begin(), last1: PrevBases.end(), first2: Bases.begin(),
1090 last2: Bases.end(), result: std::back_inserter(x&: Intersection));
1091 if (Intersection.empty()) {
1092 // Empty intersection, split.
1093 CHR_DEBUG(dbgs() << "Split. Intersection empty\n");
1094 return true;
1095 }
1096 }
1097 CHR_DEBUG(dbgs() << "No split\n");
1098 return false; // Don't split.
1099}
1100
1101static void getSelectsInScope(CHRScope *Scope,
1102 DenseSet<Instruction *> &Output) {
1103 for (RegInfo &RI : Scope->RegInfos)
1104 Output.insert_range(R&: RI.Selects);
1105 for (CHRScope *Sub : Scope->Subs)
1106 getSelectsInScope(Scope: Sub, Output);
1107}
1108
1109void CHR::splitScopes(SmallVectorImpl<CHRScope *> &Input,
1110 SmallVectorImpl<CHRScope *> &Output) {
1111 for (CHRScope *Scope : Input) {
1112 assert(!Scope->BranchInsertPoint &&
1113 "BranchInsertPoint must not be set");
1114 DenseSet<Instruction *> Unhoistables;
1115 getSelectsInScope(Scope, Output&: Unhoistables);
1116 splitScope(Scope, Outer: nullptr, OuterConditionValues: nullptr, OuterInsertPoint: nullptr, Output, Unhoistables);
1117 }
1118#ifndef NDEBUG
1119 for (CHRScope *Scope : Output) {
1120 assert(Scope->BranchInsertPoint && "BranchInsertPoint must be set");
1121 }
1122#endif
1123}
1124
1125SmallVector<CHRScope *, 8> CHR::splitScope(
1126 CHRScope *Scope,
1127 CHRScope *Outer,
1128 DenseSet<Value *> *OuterConditionValues,
1129 Instruction *OuterInsertPoint,
1130 SmallVectorImpl<CHRScope *> &Output,
1131 DenseSet<Instruction *> &Unhoistables) {
1132 if (Outer) {
1133 assert(OuterConditionValues && "Null OuterConditionValues");
1134 assert(OuterInsertPoint && "Null OuterInsertPoint");
1135 }
1136 bool PrevSplitFromOuter = true;
1137 DenseSet<Value *> PrevConditionValues;
1138 Instruction *PrevInsertPoint = nullptr;
1139 SmallVector<CHRScope *, 8> Splits;
1140 SmallVector<bool, 8> SplitsSplitFromOuter;
1141 SmallVector<DenseSet<Value *>, 8> SplitsConditionValues;
1142 SmallVector<Instruction *, 8> SplitsInsertPoints;
1143 SmallVector<RegInfo, 8> RegInfos(Scope->RegInfos); // Copy
1144 for (RegInfo &RI : RegInfos) {
1145 Instruction *InsertPoint = getBranchInsertPoint(RI);
1146 DenseSet<Value *> ConditionValues = getCHRConditionValuesForRegion(RI);
1147 CHR_DEBUG(
1148 dbgs() << "ConditionValues ";
1149 for (Value *V : ConditionValues) {
1150 dbgs() << *V << ", ";
1151 }
1152 dbgs() << "\n");
1153 if (RI.R == RegInfos[0].R) {
1154 // First iteration. Check to see if we should split from the outer.
1155 if (Outer) {
1156 CHR_DEBUG(dbgs() << "Outer " << *Outer << "\n");
1157 CHR_DEBUG(dbgs() << "Should split from outer at "
1158 << RI.R->getNameStr() << "\n");
1159 if (shouldSplit(InsertPoint: OuterInsertPoint, PrevConditionValues&: *OuterConditionValues,
1160 ConditionValues, DT, Unhoistables)) {
1161 PrevConditionValues = ConditionValues;
1162 PrevInsertPoint = InsertPoint;
1163 ORE.emit(RemarkBuilder: [&]() {
1164 return OptimizationRemarkMissed(DEBUG_TYPE,
1165 "SplitScopeFromOuter",
1166 RI.R->getEntry()->getTerminator())
1167 << "Split scope from outer due to unhoistable branch/select "
1168 << "and/or lack of common condition values";
1169 });
1170 } else {
1171 // Not splitting from the outer. Use the outer bases and insert
1172 // point. Union the bases.
1173 PrevSplitFromOuter = false;
1174 PrevConditionValues = *OuterConditionValues;
1175 PrevConditionValues.insert_range(R&: ConditionValues);
1176 PrevInsertPoint = OuterInsertPoint;
1177 }
1178 } else {
1179 CHR_DEBUG(dbgs() << "Outer null\n");
1180 PrevConditionValues = ConditionValues;
1181 PrevInsertPoint = InsertPoint;
1182 }
1183 } else {
1184 CHR_DEBUG(dbgs() << "Should split from prev at "
1185 << RI.R->getNameStr() << "\n");
1186 if (shouldSplit(InsertPoint: PrevInsertPoint, PrevConditionValues, ConditionValues,
1187 DT, Unhoistables)) {
1188 CHRScope *Tail = Scope->split(Boundary: RI.R);
1189 Scopes.insert(V: Tail);
1190 Splits.push_back(Elt: Scope);
1191 SplitsSplitFromOuter.push_back(Elt: PrevSplitFromOuter);
1192 SplitsConditionValues.push_back(Elt: PrevConditionValues);
1193 SplitsInsertPoints.push_back(Elt: PrevInsertPoint);
1194 Scope = Tail;
1195 PrevConditionValues = ConditionValues;
1196 PrevInsertPoint = InsertPoint;
1197 PrevSplitFromOuter = true;
1198 ORE.emit(RemarkBuilder: [&]() {
1199 return OptimizationRemarkMissed(DEBUG_TYPE,
1200 "SplitScopeFromPrev",
1201 RI.R->getEntry()->getTerminator())
1202 << "Split scope from previous due to unhoistable branch/select "
1203 << "and/or lack of common condition values";
1204 });
1205 } else {
1206 // Not splitting. Union the bases. Keep the hoist point.
1207 PrevConditionValues.insert_range(R&: ConditionValues);
1208 }
1209 }
1210 }
1211 Splits.push_back(Elt: Scope);
1212 SplitsSplitFromOuter.push_back(Elt: PrevSplitFromOuter);
1213 SplitsConditionValues.push_back(Elt: PrevConditionValues);
1214 assert(PrevInsertPoint && "Null PrevInsertPoint");
1215 SplitsInsertPoints.push_back(Elt: PrevInsertPoint);
1216 assert(Splits.size() == SplitsConditionValues.size() &&
1217 Splits.size() == SplitsSplitFromOuter.size() &&
1218 Splits.size() == SplitsInsertPoints.size() && "Mismatching sizes");
1219 for (size_t I = 0; I < Splits.size(); ++I) {
1220 CHRScope *Split = Splits[I];
1221 DenseSet<Value *> &SplitConditionValues = SplitsConditionValues[I];
1222 Instruction *SplitInsertPoint = SplitsInsertPoints[I];
1223 SmallVector<CHRScope *, 8> NewSubs;
1224 DenseSet<Instruction *> SplitUnhoistables;
1225 getSelectsInScope(Scope: Split, Output&: SplitUnhoistables);
1226 for (CHRScope *Sub : Split->Subs) {
1227 SmallVector<CHRScope *, 8> SubSplits = splitScope(
1228 Scope: Sub, Outer: Split, OuterConditionValues: &SplitConditionValues, OuterInsertPoint: SplitInsertPoint, Output,
1229 Unhoistables&: SplitUnhoistables);
1230 llvm::append_range(C&: NewSubs, R&: SubSplits);
1231 }
1232 Split->Subs = NewSubs;
1233 }
1234 SmallVector<CHRScope *, 8> Result;
1235 for (size_t I = 0; I < Splits.size(); ++I) {
1236 CHRScope *Split = Splits[I];
1237 if (SplitsSplitFromOuter[I]) {
1238 // Split from the outer.
1239 Output.push_back(Elt: Split);
1240 Split->BranchInsertPoint = SplitsInsertPoints[I];
1241 CHR_DEBUG(dbgs() << "BranchInsertPoint " << *SplitsInsertPoints[I]
1242 << "\n");
1243 } else {
1244 // Connected to the outer.
1245 Result.push_back(Elt: Split);
1246 }
1247 }
1248 if (!Outer)
1249 assert(Result.empty() &&
1250 "If no outer (top-level), must return no nested ones");
1251 return Result;
1252}
1253
1254void CHR::classifyBiasedScopes(SmallVectorImpl<CHRScope *> &Scopes) {
1255 for (CHRScope *Scope : Scopes) {
1256 assert(Scope->TrueBiasedRegions.empty() && Scope->FalseBiasedRegions.empty() && "Empty");
1257 classifyBiasedScopes(Scope, OutermostScope: Scope);
1258 CHR_DEBUG(
1259 dbgs() << "classifyBiasedScopes " << *Scope << "\n";
1260 dbgs() << "TrueBiasedRegions ";
1261 for (Region *R : Scope->TrueBiasedRegions) {
1262 dbgs() << R->getNameStr() << ", ";
1263 }
1264 dbgs() << "\n";
1265 dbgs() << "FalseBiasedRegions ";
1266 for (Region *R : Scope->FalseBiasedRegions) {
1267 dbgs() << R->getNameStr() << ", ";
1268 }
1269 dbgs() << "\n";
1270 dbgs() << "TrueBiasedSelects ";
1271 for (SelectInst *SI : Scope->TrueBiasedSelects) {
1272 dbgs() << *SI << ", ";
1273 }
1274 dbgs() << "\n";
1275 dbgs() << "FalseBiasedSelects ";
1276 for (SelectInst *SI : Scope->FalseBiasedSelects) {
1277 dbgs() << *SI << ", ";
1278 }
1279 dbgs() << "\n";);
1280 }
1281}
1282
1283void CHR::classifyBiasedScopes(CHRScope *Scope, CHRScope *OutermostScope) {
1284 for (RegInfo &RI : Scope->RegInfos) {
1285 if (RI.HasBranch) {
1286 Region *R = RI.R;
1287 if (TrueBiasedRegionsGlobal.contains(V: R))
1288 OutermostScope->TrueBiasedRegions.insert(V: R);
1289 else if (FalseBiasedRegionsGlobal.contains(V: R))
1290 OutermostScope->FalseBiasedRegions.insert(V: R);
1291 else
1292 llvm_unreachable("Must be biased");
1293 }
1294 for (SelectInst *SI : RI.Selects) {
1295 if (TrueBiasedSelectsGlobal.contains(V: SI))
1296 OutermostScope->TrueBiasedSelects.insert(V: SI);
1297 else if (FalseBiasedSelectsGlobal.contains(V: SI))
1298 OutermostScope->FalseBiasedSelects.insert(V: SI);
1299 else
1300 llvm_unreachable("Must be biased");
1301 }
1302 }
1303 for (CHRScope *Sub : Scope->Subs) {
1304 classifyBiasedScopes(Scope: Sub, OutermostScope);
1305 }
1306}
1307
1308static bool hasAtLeastTwoBiasedBranches(CHRScope *Scope) {
1309 unsigned NumBiased = Scope->TrueBiasedRegions.size() +
1310 Scope->FalseBiasedRegions.size() +
1311 Scope->TrueBiasedSelects.size() +
1312 Scope->FalseBiasedSelects.size();
1313 return NumBiased >= CHRMergeThreshold;
1314}
1315
1316void CHR::filterScopes(SmallVectorImpl<CHRScope *> &Input,
1317 SmallVectorImpl<CHRScope *> &Output) {
1318 for (CHRScope *Scope : Input) {
1319 // Filter out the ones with only one region and no subs.
1320 if (!hasAtLeastTwoBiasedBranches(Scope)) {
1321 CHR_DEBUG(dbgs() << "Filtered out by biased branches truthy-regions "
1322 << Scope->TrueBiasedRegions.size()
1323 << " falsy-regions " << Scope->FalseBiasedRegions.size()
1324 << " true-selects " << Scope->TrueBiasedSelects.size()
1325 << " false-selects " << Scope->FalseBiasedSelects.size() << "\n");
1326 ORE.emit(RemarkBuilder: [&]() {
1327 return OptimizationRemarkMissed(
1328 DEBUG_TYPE,
1329 "DropScopeWithOneBranchOrSelect",
1330 Scope->RegInfos[0].R->getEntry()->getTerminator())
1331 << "Drop scope with < "
1332 << ore::NV("CHRMergeThreshold", CHRMergeThreshold)
1333 << " biased branch(es) or select(s)";
1334 });
1335 continue;
1336 }
1337 Output.push_back(Elt: Scope);
1338 }
1339}
1340
1341void CHR::setCHRRegions(SmallVectorImpl<CHRScope *> &Input,
1342 SmallVectorImpl<CHRScope *> &Output) {
1343 for (CHRScope *Scope : Input) {
1344 assert(Scope->HoistStopMap.empty() && Scope->CHRRegions.empty() &&
1345 "Empty");
1346 setCHRRegions(Scope, OutermostScope: Scope);
1347 Output.push_back(Elt: Scope);
1348 CHR_DEBUG(
1349 dbgs() << "setCHRRegions HoistStopMap " << *Scope << "\n";
1350 for (auto pair : Scope->HoistStopMap) {
1351 Region *R = pair.first;
1352 dbgs() << "Region " << R->getNameStr() << "\n";
1353 for (Instruction *I : pair.second) {
1354 dbgs() << "HoistStop " << *I << "\n";
1355 }
1356 }
1357 dbgs() << "CHRRegions" << "\n";
1358 for (RegInfo &RI : Scope->CHRRegions) {
1359 dbgs() << RI.R->getNameStr() << "\n";
1360 });
1361 }
1362}
1363
1364void CHR::setCHRRegions(CHRScope *Scope, CHRScope *OutermostScope) {
1365 DenseSet<Instruction *> Unhoistables;
1366 // Put the biased selects in Unhoistables because they should stay where they
1367 // are and constant-folded after CHR (in case one biased select or a branch
1368 // can depend on another biased select.)
1369 for (RegInfo &RI : Scope->RegInfos)
1370 Unhoistables.insert_range(R&: RI.Selects);
1371 Instruction *InsertPoint = OutermostScope->BranchInsertPoint;
1372 for (RegInfo &RI : Scope->RegInfos) {
1373 Region *R = RI.R;
1374 DenseSet<Instruction *> HoistStops;
1375 bool IsHoisted = false;
1376 if (RI.HasBranch) {
1377 assert((OutermostScope->TrueBiasedRegions.contains(R) ||
1378 OutermostScope->FalseBiasedRegions.contains(R)) &&
1379 "Must be truthy or falsy");
1380 auto *BI = cast<BranchInst>(Val: R->getEntry()->getTerminator());
1381 // Note checkHoistValue fills in HoistStops.
1382 DenseMap<Instruction *, bool> Visited;
1383 bool IsHoistable = checkHoistValue(V: BI->getCondition(), InsertPoint, DT,
1384 Unhoistables, HoistStops: &HoistStops, Visited);
1385 assert(IsHoistable && "Must be hoistable");
1386 (void)(IsHoistable); // Unused in release build
1387 IsHoisted = true;
1388 }
1389 for (SelectInst *SI : RI.Selects) {
1390 assert((OutermostScope->TrueBiasedSelects.contains(SI) ||
1391 OutermostScope->FalseBiasedSelects.contains(SI)) &&
1392 "Must be true or false biased");
1393 // Note checkHoistValue fills in HoistStops.
1394 DenseMap<Instruction *, bool> Visited;
1395 bool IsHoistable = checkHoistValue(V: SI->getCondition(), InsertPoint, DT,
1396 Unhoistables, HoistStops: &HoistStops, Visited);
1397 assert(IsHoistable && "Must be hoistable");
1398 (void)(IsHoistable); // Unused in release build
1399 IsHoisted = true;
1400 }
1401 if (IsHoisted) {
1402 OutermostScope->CHRRegions.push_back(Elt: RI);
1403 OutermostScope->HoistStopMap[R] = HoistStops;
1404 }
1405 }
1406 for (CHRScope *Sub : Scope->Subs)
1407 setCHRRegions(Scope: Sub, OutermostScope);
1408}
1409
1410static bool CHRScopeSorter(CHRScope *Scope1, CHRScope *Scope2) {
1411 return Scope1->RegInfos[0].R->getDepth() < Scope2->RegInfos[0].R->getDepth();
1412}
1413
1414void CHR::sortScopes(SmallVectorImpl<CHRScope *> &Input,
1415 SmallVectorImpl<CHRScope *> &Output) {
1416 Output.resize(N: Input.size());
1417 llvm::copy(Range&: Input, Out: Output.begin());
1418 llvm::stable_sort(Range&: Output, C: CHRScopeSorter);
1419}
1420
1421// Return true if V is already hoisted or was hoisted (along with its operands)
1422// to the insert point.
1423static void hoistValue(Value *V, Instruction *HoistPoint, Region *R,
1424 HoistStopMapTy &HoistStopMap,
1425 DenseSet<Instruction *> &HoistedSet,
1426 DenseSet<PHINode *> &TrivialPHIs,
1427 DominatorTree &DT) {
1428 auto IT = HoistStopMap.find(Val: R);
1429 assert(IT != HoistStopMap.end() && "Region must be in hoist stop map");
1430 DenseSet<Instruction *> &HoistStops = IT->second;
1431 if (auto *I = dyn_cast<Instruction>(Val: V)) {
1432 if (I == HoistPoint)
1433 return;
1434 if (HoistStops.count(V: I))
1435 return;
1436 if (auto *PN = dyn_cast<PHINode>(Val: I))
1437 if (TrivialPHIs.count(V: PN))
1438 // The trivial phi inserted by the previous CHR scope could replace a
1439 // non-phi in HoistStops. Note that since this phi is at the exit of a
1440 // previous CHR scope, which dominates this scope, it's safe to stop
1441 // hoisting there.
1442 return;
1443 if (HoistedSet.count(V: I))
1444 // Already hoisted, return.
1445 return;
1446 assert(isHoistableInstructionType(I) && "Unhoistable instruction type");
1447 assert(DT.getNode(I->getParent()) && "DT must contain I's block");
1448 assert(DT.getNode(HoistPoint->getParent()) &&
1449 "DT must contain HoistPoint block");
1450 if (DT.dominates(Def: I, User: HoistPoint))
1451 // We are already above the hoist point. Stop here. This may be necessary
1452 // when multiple scopes would independently hoist the same
1453 // instruction. Since an outer (dominating) scope would hoist it to its
1454 // entry before an inner (dominated) scope would to its entry, the inner
1455 // scope may see the instruction already hoisted, in which case it
1456 // potentially wrong for the inner scope to hoist it and could cause bad
1457 // IR (non-dominating def), but safe to skip hoisting it instead because
1458 // it's already in a block that dominates the inner scope.
1459 return;
1460 for (Value *Op : I->operands()) {
1461 hoistValue(V: Op, HoistPoint, R, HoistStopMap, HoistedSet, TrivialPHIs, DT);
1462 }
1463 I->moveBefore(InsertPos: HoistPoint->getIterator());
1464 HoistedSet.insert(V: I);
1465 CHR_DEBUG(dbgs() << "hoistValue " << *I << "\n");
1466 }
1467}
1468
1469// Hoist the dependent condition values of the branches and the selects in the
1470// scope to the insert point.
1471static void hoistScopeConditions(CHRScope *Scope, Instruction *HoistPoint,
1472 DenseSet<PHINode *> &TrivialPHIs,
1473 DominatorTree &DT) {
1474 DenseSet<Instruction *> HoistedSet;
1475 for (const RegInfo &RI : Scope->CHRRegions) {
1476 Region *R = RI.R;
1477 bool IsTrueBiased = Scope->TrueBiasedRegions.count(V: R);
1478 bool IsFalseBiased = Scope->FalseBiasedRegions.count(V: R);
1479 if (RI.HasBranch && (IsTrueBiased || IsFalseBiased)) {
1480 auto *BI = cast<BranchInst>(Val: R->getEntry()->getTerminator());
1481 hoistValue(V: BI->getCondition(), HoistPoint, R, HoistStopMap&: Scope->HoistStopMap,
1482 HoistedSet, TrivialPHIs, DT);
1483 }
1484 for (SelectInst *SI : RI.Selects) {
1485 bool IsTrueBiased = Scope->TrueBiasedSelects.count(V: SI);
1486 bool IsFalseBiased = Scope->FalseBiasedSelects.count(V: SI);
1487 if (!(IsTrueBiased || IsFalseBiased))
1488 continue;
1489 hoistValue(V: SI->getCondition(), HoistPoint, R, HoistStopMap&: Scope->HoistStopMap,
1490 HoistedSet, TrivialPHIs, DT);
1491 }
1492 }
1493}
1494
1495// Negate the predicate if an ICmp if it's used only by branches or selects by
1496// swapping the operands of the branches or the selects. Returns true if success.
1497static bool negateICmpIfUsedByBranchOrSelectOnly(ICmpInst *ICmp,
1498 Instruction *ExcludedUser,
1499 CHRScope *Scope) {
1500 for (User *U : ICmp->users()) {
1501 if (U == ExcludedUser)
1502 continue;
1503 if (isa<BranchInst>(Val: U) && cast<BranchInst>(Val: U)->isConditional())
1504 continue;
1505 if (isa<SelectInst>(Val: U) && cast<SelectInst>(Val: U)->getCondition() == ICmp)
1506 continue;
1507 return false;
1508 }
1509 for (User *U : ICmp->users()) {
1510 if (U == ExcludedUser)
1511 continue;
1512 if (auto *BI = dyn_cast<BranchInst>(Val: U)) {
1513 assert(BI->isConditional() && "Must be conditional");
1514 BI->swapSuccessors();
1515 // Don't need to swap this in terms of
1516 // TrueBiasedRegions/FalseBiasedRegions because true-based/false-based
1517 // mean whehter the branch is likely go into the if-then rather than
1518 // successor0/successor1 and because we can tell which edge is the then or
1519 // the else one by comparing the destination to the region exit block.
1520 continue;
1521 }
1522 if (auto *SI = dyn_cast<SelectInst>(Val: U)) {
1523 // Swap operands
1524 SI->swapValues();
1525 SI->swapProfMetadata();
1526 if (Scope->TrueBiasedSelects.count(V: SI)) {
1527 assert(!Scope->FalseBiasedSelects.contains(SI) &&
1528 "Must not be already in");
1529 Scope->FalseBiasedSelects.insert(V: SI);
1530 } else if (Scope->FalseBiasedSelects.count(V: SI)) {
1531 assert(!Scope->TrueBiasedSelects.contains(SI) &&
1532 "Must not be already in");
1533 Scope->TrueBiasedSelects.insert(V: SI);
1534 }
1535 continue;
1536 }
1537 llvm_unreachable("Must be a branch or a select");
1538 }
1539 ICmp->setPredicate(CmpInst::getInversePredicate(pred: ICmp->getPredicate()));
1540 return true;
1541}
1542
1543// A helper for transformScopes. Insert a trivial phi at the scope exit block
1544// for a value that's defined in the scope but used outside it (meaning it's
1545// alive at the exit block).
1546static void insertTrivialPHIs(CHRScope *Scope,
1547 BasicBlock *EntryBlock, BasicBlock *ExitBlock,
1548 DenseSet<PHINode *> &TrivialPHIs) {
1549 SmallSetVector<BasicBlock *, 8> BlocksInScope;
1550 for (RegInfo &RI : Scope->RegInfos) {
1551 for (BasicBlock *BB : RI.R->blocks()) { // This includes the blocks in the
1552 // sub-Scopes.
1553 BlocksInScope.insert(X: BB);
1554 }
1555 }
1556 CHR_DEBUG({
1557 dbgs() << "Inserting redundant phis\n";
1558 for (BasicBlock *BB : BlocksInScope)
1559 dbgs() << "BlockInScope " << BB->getName() << "\n";
1560 });
1561 for (BasicBlock *BB : BlocksInScope) {
1562 for (Instruction &I : *BB) {
1563 SmallVector<Instruction *, 8> Users;
1564 for (User *U : I.users()) {
1565 if (auto *UI = dyn_cast<Instruction>(Val: U)) {
1566 if (!BlocksInScope.contains(key: UI->getParent()) &&
1567 // Unless there's already a phi for I at the exit block.
1568 !(isa<PHINode>(Val: UI) && UI->getParent() == ExitBlock)) {
1569 CHR_DEBUG(dbgs() << "V " << I << "\n");
1570 CHR_DEBUG(dbgs() << "Used outside scope by user " << *UI << "\n");
1571 Users.push_back(Elt: UI);
1572 } else if (UI->getParent() == EntryBlock && isa<PHINode>(Val: UI)) {
1573 // There's a loop backedge from a block that's dominated by this
1574 // scope to the entry block.
1575 CHR_DEBUG(dbgs() << "V " << I << "\n");
1576 CHR_DEBUG(dbgs()
1577 << "Used at entry block (for a back edge) by a phi user "
1578 << *UI << "\n");
1579 Users.push_back(Elt: UI);
1580 }
1581 }
1582 }
1583 if (Users.size() > 0) {
1584 // Insert a trivial phi for I (phi [&I, P0], [&I, P1], ...) at
1585 // ExitBlock. Replace I with the new phi in UI unless UI is another
1586 // phi at ExitBlock.
1587 PHINode *PN = PHINode::Create(Ty: I.getType(), NumReservedValues: pred_size(BB: ExitBlock), NameStr: "");
1588 PN->insertBefore(InsertPos: ExitBlock->begin());
1589 for (BasicBlock *Pred : predecessors(BB: ExitBlock)) {
1590 PN->addIncoming(V: &I, BB: Pred);
1591 }
1592 TrivialPHIs.insert(V: PN);
1593 CHR_DEBUG(dbgs() << "Insert phi " << *PN << "\n");
1594 for (Instruction *UI : Users) {
1595 for (unsigned J = 0, NumOps = UI->getNumOperands(); J < NumOps; ++J) {
1596 if (UI->getOperand(i: J) == &I) {
1597 UI->setOperand(i: J, Val: PN);
1598 }
1599 }
1600 CHR_DEBUG(dbgs() << "Updated user " << *UI << "\n");
1601 }
1602 }
1603 }
1604 }
1605}
1606
1607// Assert that all the CHR regions of the scope have a biased branch or select.
1608static void LLVM_ATTRIBUTE_UNUSED
1609assertCHRRegionsHaveBiasedBranchOrSelect(CHRScope *Scope) {
1610#ifndef NDEBUG
1611 auto HasBiasedBranchOrSelect = [](RegInfo &RI, CHRScope *Scope) {
1612 if (Scope->TrueBiasedRegions.count(RI.R) ||
1613 Scope->FalseBiasedRegions.count(RI.R))
1614 return true;
1615 for (SelectInst *SI : RI.Selects)
1616 if (Scope->TrueBiasedSelects.count(SI) ||
1617 Scope->FalseBiasedSelects.count(SI))
1618 return true;
1619 return false;
1620 };
1621 for (RegInfo &RI : Scope->CHRRegions) {
1622 assert(HasBiasedBranchOrSelect(RI, Scope) &&
1623 "Must have biased branch or select");
1624 }
1625#endif
1626}
1627
1628// Assert that all the condition values of the biased branches and selects have
1629// been hoisted to the pre-entry block or outside of the scope.
1630static void LLVM_ATTRIBUTE_UNUSED assertBranchOrSelectConditionHoisted(
1631 CHRScope *Scope, BasicBlock *PreEntryBlock) {
1632 CHR_DEBUG(dbgs() << "Biased regions condition values \n");
1633 for (RegInfo &RI : Scope->CHRRegions) {
1634 Region *R = RI.R;
1635 bool IsTrueBiased = Scope->TrueBiasedRegions.count(V: R);
1636 bool IsFalseBiased = Scope->FalseBiasedRegions.count(V: R);
1637 if (RI.HasBranch && (IsTrueBiased || IsFalseBiased)) {
1638 auto *BI = cast<BranchInst>(Val: R->getEntry()->getTerminator());
1639 Value *V = BI->getCondition();
1640 CHR_DEBUG(dbgs() << *V << "\n");
1641 if (auto *I = dyn_cast<Instruction>(Val: V)) {
1642 (void)(I); // Unused in release build.
1643 assert((I->getParent() == PreEntryBlock ||
1644 !Scope->contains(I)) &&
1645 "Must have been hoisted to PreEntryBlock or outside the scope");
1646 }
1647 }
1648 for (SelectInst *SI : RI.Selects) {
1649 bool IsTrueBiased = Scope->TrueBiasedSelects.count(V: SI);
1650 bool IsFalseBiased = Scope->FalseBiasedSelects.count(V: SI);
1651 if (!(IsTrueBiased || IsFalseBiased))
1652 continue;
1653 Value *V = SI->getCondition();
1654 CHR_DEBUG(dbgs() << *V << "\n");
1655 if (auto *I = dyn_cast<Instruction>(Val: V)) {
1656 (void)(I); // Unused in release build.
1657 assert((I->getParent() == PreEntryBlock ||
1658 !Scope->contains(I)) &&
1659 "Must have been hoisted to PreEntryBlock or outside the scope");
1660 }
1661 }
1662 }
1663}
1664
1665void CHR::transformScopes(CHRScope *Scope, DenseSet<PHINode *> &TrivialPHIs) {
1666 CHR_DEBUG(dbgs() << "transformScopes " << *Scope << "\n");
1667
1668 assert(Scope->RegInfos.size() >= 1 && "Should have at least one Region");
1669
1670 for (RegInfo &RI : Scope->RegInfos) {
1671 const Region *R = RI.R;
1672 unsigned Duplication = getRegionDuplicationCount(R);
1673 CHR_DEBUG(dbgs() << "Dup count for R=" << R << " is " << Duplication
1674 << "\n");
1675 if (Duplication >= CHRDupThreshsold) {
1676 CHR_DEBUG(dbgs() << "Reached the dup threshold of " << Duplication
1677 << " for this region");
1678 ORE.emit(RemarkBuilder: [&]() {
1679 return OptimizationRemarkMissed(DEBUG_TYPE, "DupThresholdReached",
1680 R->getEntry()->getTerminator())
1681 << "Reached the duplication threshold for the region";
1682 });
1683 return;
1684 }
1685 }
1686 for (RegInfo &RI : Scope->RegInfos) {
1687 DuplicationCount[RI.R]++;
1688 }
1689
1690 Region *FirstRegion = Scope->RegInfos[0].R;
1691 BasicBlock *EntryBlock = FirstRegion->getEntry();
1692 Region *LastRegion = Scope->RegInfos[Scope->RegInfos.size() - 1].R;
1693 BasicBlock *ExitBlock = LastRegion->getExit();
1694 std::optional<uint64_t> ProfileCount = BFI.getBlockProfileCount(BB: EntryBlock);
1695
1696 if (ExitBlock) {
1697 // Insert a trivial phi at the exit block (where the CHR hot path and the
1698 // cold path merges) for a value that's defined in the scope but used
1699 // outside it (meaning it's alive at the exit block). We will add the
1700 // incoming values for the CHR cold paths to it below. Without this, we'd
1701 // miss updating phi's for such values unless there happens to already be a
1702 // phi for that value there.
1703 insertTrivialPHIs(Scope, EntryBlock, ExitBlock, TrivialPHIs);
1704 }
1705
1706 // Split the entry block of the first region. The new block becomes the new
1707 // entry block of the first region. The old entry block becomes the block to
1708 // insert the CHR branch into. Note DT gets updated. Since DT gets updated
1709 // through the split, we update the entry of the first region after the split,
1710 // and Region only points to the entry and the exit blocks, rather than
1711 // keeping everything in a list or set, the blocks membership and the
1712 // entry/exit blocks of the region are still valid after the split.
1713 CHR_DEBUG(dbgs() << "Splitting entry block " << EntryBlock->getName()
1714 << " at " << *Scope->BranchInsertPoint << "\n");
1715 BasicBlock *NewEntryBlock =
1716 SplitBlock(Old: EntryBlock, SplitPt: Scope->BranchInsertPoint, DT: &DT);
1717 assert(NewEntryBlock->getSinglePredecessor() == EntryBlock &&
1718 "NewEntryBlock's only pred must be EntryBlock");
1719 FirstRegion->replaceEntryRecursive(NewEntry: NewEntryBlock);
1720 BasicBlock *PreEntryBlock = EntryBlock;
1721
1722 ValueToValueMapTy VMap;
1723 // Clone the blocks in the scope (excluding the PreEntryBlock) to split into a
1724 // hot path (originals) and a cold path (clones) and update the PHIs at the
1725 // exit block.
1726 cloneScopeBlocks(Scope, PreEntryBlock, ExitBlock, LastRegion, VMap);
1727
1728 // Replace the old (placeholder) branch with the new (merged) conditional
1729 // branch.
1730 BranchInst *MergedBr = createMergedBranch(PreEntryBlock, EntryBlock,
1731 NewEntryBlock, VMap);
1732
1733#ifndef NDEBUG
1734 assertCHRRegionsHaveBiasedBranchOrSelect(Scope);
1735#endif
1736
1737 // Hoist the conditional values of the branches/selects.
1738 hoistScopeConditions(Scope, HoistPoint: PreEntryBlock->getTerminator(), TrivialPHIs, DT);
1739
1740#ifndef NDEBUG
1741 assertBranchOrSelectConditionHoisted(Scope, PreEntryBlock);
1742#endif
1743
1744 // Create the combined branch condition and constant-fold the branches/selects
1745 // in the hot path.
1746 fixupBranchesAndSelects(Scope, PreEntryBlock, MergedBR: MergedBr,
1747 ProfileCount: ProfileCount.value_or(u: 0));
1748}
1749
1750// A helper for transformScopes. Clone the blocks in the scope (excluding the
1751// PreEntryBlock) to split into a hot path and a cold path and update the PHIs
1752// at the exit block.
1753void CHR::cloneScopeBlocks(CHRScope *Scope,
1754 BasicBlock *PreEntryBlock,
1755 BasicBlock *ExitBlock,
1756 Region *LastRegion,
1757 ValueToValueMapTy &VMap) {
1758 // Clone all the blocks. The original blocks will be the hot-path
1759 // CHR-optimized code and the cloned blocks will be the original unoptimized
1760 // code. This is so that the block pointers from the
1761 // CHRScope/Region/RegionInfo can stay valid in pointing to the hot-path code
1762 // which CHR should apply to.
1763 SmallVector<BasicBlock*, 8> NewBlocks;
1764 for (RegInfo &RI : Scope->RegInfos)
1765 for (BasicBlock *BB : RI.R->blocks()) { // This includes the blocks in the
1766 // sub-Scopes.
1767 assert(BB != PreEntryBlock && "Don't copy the preetntry block");
1768 BasicBlock *NewBB = CloneBasicBlock(BB, VMap, NameSuffix: ".nonchr", F: &F);
1769 NewBlocks.push_back(Elt: NewBB);
1770 VMap[BB] = NewBB;
1771
1772 // Unreachable predecessors will not be cloned and will not have an edge
1773 // to the cloned block. As such, also remove them from any phi nodes.
1774 for (PHINode &PN : make_early_inc_range(Range: NewBB->phis()))
1775 PN.removeIncomingValueIf(Predicate: [&](unsigned Idx) {
1776 return !DT.isReachableFromEntry(A: PN.getIncomingBlock(i: Idx));
1777 });
1778 }
1779
1780 // Place the cloned blocks right after the original blocks (right before the
1781 // exit block of.)
1782 if (ExitBlock)
1783 F.splice(ToIt: ExitBlock->getIterator(), FromF: &F, FromBeginIt: NewBlocks[0]->getIterator(),
1784 FromEndIt: F.end());
1785
1786 // Update the cloned blocks/instructions to refer to themselves.
1787 for (BasicBlock *NewBB : NewBlocks)
1788 for (Instruction &I : *NewBB)
1789 RemapInstruction(I: &I, VM&: VMap,
1790 Flags: RF_NoModuleLevelChanges | RF_IgnoreMissingLocals);
1791
1792 // Add the cloned blocks to the PHIs of the exit blocks. ExitBlock is null for
1793 // the top-level region but we don't need to add PHIs. The trivial PHIs
1794 // inserted above will be updated here.
1795 if (ExitBlock)
1796 for (PHINode &PN : ExitBlock->phis())
1797 for (unsigned I = 0, NumOps = PN.getNumIncomingValues(); I < NumOps;
1798 ++I) {
1799 BasicBlock *Pred = PN.getIncomingBlock(i: I);
1800 if (LastRegion->contains(BB: Pred)) {
1801 Value *V = PN.getIncomingValue(i: I);
1802 auto It = VMap.find(Val: V);
1803 if (It != VMap.end()) V = It->second;
1804 assert(VMap.find(Pred) != VMap.end() && "Pred must have been cloned");
1805 PN.addIncoming(V, BB: cast<BasicBlock>(Val&: VMap[Pred]));
1806 }
1807 }
1808}
1809
1810// A helper for transformScope. Replace the old (placeholder) branch with the
1811// new (merged) conditional branch.
1812BranchInst *CHR::createMergedBranch(BasicBlock *PreEntryBlock,
1813 BasicBlock *EntryBlock,
1814 BasicBlock *NewEntryBlock,
1815 ValueToValueMapTy &VMap) {
1816 BranchInst *OldBR = cast<BranchInst>(Val: PreEntryBlock->getTerminator());
1817 assert(OldBR->isUnconditional() && OldBR->getSuccessor(0) == NewEntryBlock &&
1818 "SplitBlock did not work correctly!");
1819 assert(NewEntryBlock->getSinglePredecessor() == EntryBlock &&
1820 "NewEntryBlock's only pred must be EntryBlock");
1821 assert(VMap.find(NewEntryBlock) != VMap.end() &&
1822 "NewEntryBlock must have been copied");
1823 OldBR->dropAllReferences();
1824 OldBR->eraseFromParent();
1825 // The true predicate is a placeholder. It will be replaced later in
1826 // fixupBranchesAndSelects().
1827 BranchInst *NewBR = BranchInst::Create(IfTrue: NewEntryBlock,
1828 IfFalse: cast<BasicBlock>(Val&: VMap[NewEntryBlock]),
1829 Cond: ConstantInt::getTrue(Context&: F.getContext()));
1830 NewBR->insertInto(ParentBB: PreEntryBlock, It: PreEntryBlock->end());
1831 assert(NewEntryBlock->getSinglePredecessor() == EntryBlock &&
1832 "NewEntryBlock's only pred must be EntryBlock");
1833 return NewBR;
1834}
1835
1836// A helper for transformScopes. Create the combined branch condition and
1837// constant-fold the branches/selects in the hot path.
1838void CHR::fixupBranchesAndSelects(CHRScope *Scope,
1839 BasicBlock *PreEntryBlock,
1840 BranchInst *MergedBR,
1841 uint64_t ProfileCount) {
1842 Value *MergedCondition = ConstantInt::getTrue(Context&: F.getContext());
1843 BranchProbability CHRBranchBias(1, 1);
1844 uint64_t NumCHRedBranches = 0;
1845 IRBuilder<> IRB(PreEntryBlock->getTerminator());
1846 for (RegInfo &RI : Scope->CHRRegions) {
1847 Region *R = RI.R;
1848 if (RI.HasBranch) {
1849 fixupBranch(R, Scope, IRB, MergedCondition, CHRBranchBias);
1850 ++NumCHRedBranches;
1851 }
1852 for (SelectInst *SI : RI.Selects) {
1853 fixupSelect(SI, Scope, IRB, MergedCondition, CHRBranchBias);
1854 ++NumCHRedBranches;
1855 }
1856 }
1857 assert(NumCHRedBranches > 0);
1858 Stats.NumBranchesDelta += NumCHRedBranches - 1;
1859 Stats.WeightedNumBranchesDelta += (NumCHRedBranches - 1) * ProfileCount;
1860 ORE.emit(RemarkBuilder: [&]() {
1861 return OptimizationRemark(DEBUG_TYPE,
1862 "CHR",
1863 // Refer to the hot (original) path
1864 MergedBR->getSuccessor(i: 0)->getTerminator())
1865 << "Merged " << ore::NV("NumCHRedBranches", NumCHRedBranches)
1866 << " branches or selects";
1867 });
1868 MergedBR->setCondition(MergedCondition);
1869 uint32_t Weights[] = {
1870 static_cast<uint32_t>(CHRBranchBias.scale(Num: 1000)),
1871 static_cast<uint32_t>(CHRBranchBias.getCompl().scale(Num: 1000)),
1872 };
1873 setBranchWeights(I&: *MergedBR, Weights, /*IsExpected=*/false);
1874 CHR_DEBUG(dbgs() << "CHR branch bias " << Weights[0] << ":" << Weights[1]
1875 << "\n");
1876}
1877
1878// A helper for fixupBranchesAndSelects. Add to the combined branch condition
1879// and constant-fold a branch in the hot path.
1880void CHR::fixupBranch(Region *R, CHRScope *Scope,
1881 IRBuilder<> &IRB,
1882 Value *&MergedCondition,
1883 BranchProbability &CHRBranchBias) {
1884 bool IsTrueBiased = Scope->TrueBiasedRegions.count(V: R);
1885 assert((IsTrueBiased || Scope->FalseBiasedRegions.count(R)) &&
1886 "Must be truthy or falsy");
1887 auto *BI = cast<BranchInst>(Val: R->getEntry()->getTerminator());
1888 assert(BranchBiasMap.contains(R) && "Must be in the bias map");
1889 BranchProbability Bias = BranchBiasMap[R];
1890 assert(Bias >= getCHRBiasThreshold() && "Must be highly biased");
1891 // Take the min.
1892 if (CHRBranchBias > Bias)
1893 CHRBranchBias = Bias;
1894 BasicBlock *IfThen = BI->getSuccessor(i: 1);
1895 BasicBlock *IfElse = BI->getSuccessor(i: 0);
1896 BasicBlock *RegionExitBlock = R->getExit();
1897 assert(RegionExitBlock && "Null ExitBlock");
1898 assert((IfThen == RegionExitBlock || IfElse == RegionExitBlock) &&
1899 IfThen != IfElse && "Invariant from findScopes");
1900 if (IfThen == RegionExitBlock) {
1901 // Swap them so that IfThen means going into it and IfElse means skipping
1902 // it.
1903 std::swap(a&: IfThen, b&: IfElse);
1904 }
1905 CHR_DEBUG(dbgs() << "IfThen " << IfThen->getName()
1906 << " IfElse " << IfElse->getName() << "\n");
1907 Value *Cond = BI->getCondition();
1908 BasicBlock *HotTarget = IsTrueBiased ? IfThen : IfElse;
1909 bool ConditionTrue = HotTarget == BI->getSuccessor(i: 0);
1910 addToMergedCondition(IsTrueBiased: ConditionTrue, Cond, BranchOrSelect: BI, Scope, IRB,
1911 MergedCondition);
1912 // Constant-fold the branch at ClonedEntryBlock.
1913 assert(ConditionTrue == (HotTarget == BI->getSuccessor(0)) &&
1914 "The successor shouldn't change");
1915 Value *NewCondition = ConditionTrue ?
1916 ConstantInt::getTrue(Context&: F.getContext()) :
1917 ConstantInt::getFalse(Context&: F.getContext());
1918 BI->setCondition(NewCondition);
1919}
1920
1921// A helper for fixupBranchesAndSelects. Add to the combined branch condition
1922// and constant-fold a select in the hot path.
1923void CHR::fixupSelect(SelectInst *SI, CHRScope *Scope,
1924 IRBuilder<> &IRB,
1925 Value *&MergedCondition,
1926 BranchProbability &CHRBranchBias) {
1927 bool IsTrueBiased = Scope->TrueBiasedSelects.count(V: SI);
1928 assert((IsTrueBiased ||
1929 Scope->FalseBiasedSelects.count(SI)) && "Must be biased");
1930 assert(SelectBiasMap.contains(SI) && "Must be in the bias map");
1931 BranchProbability Bias = SelectBiasMap[SI];
1932 assert(Bias >= getCHRBiasThreshold() && "Must be highly biased");
1933 // Take the min.
1934 if (CHRBranchBias > Bias)
1935 CHRBranchBias = Bias;
1936 Value *Cond = SI->getCondition();
1937 addToMergedCondition(IsTrueBiased, Cond, BranchOrSelect: SI, Scope, IRB,
1938 MergedCondition);
1939 Value *NewCondition = IsTrueBiased ?
1940 ConstantInt::getTrue(Context&: F.getContext()) :
1941 ConstantInt::getFalse(Context&: F.getContext());
1942 SI->setCondition(NewCondition);
1943}
1944
1945// A helper for fixupBranch/fixupSelect. Add a branch condition to the merged
1946// condition.
1947void CHR::addToMergedCondition(bool IsTrueBiased, Value *Cond,
1948 Instruction *BranchOrSelect, CHRScope *Scope,
1949 IRBuilder<> &IRB, Value *&MergedCondition) {
1950 if (!IsTrueBiased) {
1951 // If Cond is an icmp and all users of V except for BranchOrSelect is a
1952 // branch, negate the icmp predicate and swap the branch targets and avoid
1953 // inserting an Xor to negate Cond.
1954 auto *ICmp = dyn_cast<ICmpInst>(Val: Cond);
1955 if (!ICmp ||
1956 !negateICmpIfUsedByBranchOrSelectOnly(ICmp, ExcludedUser: BranchOrSelect, Scope))
1957 Cond = IRB.CreateXor(LHS: ConstantInt::getTrue(Context&: F.getContext()), RHS: Cond);
1958 }
1959
1960 // Freeze potentially poisonous conditions.
1961 if (!isGuaranteedNotToBeUndefOrPoison(V: Cond))
1962 Cond = IRB.CreateFreeze(V: Cond);
1963
1964 // Use logical and to avoid propagating poison from later conditions.
1965 MergedCondition = IRB.CreateLogicalAnd(Cond1: MergedCondition, Cond2: Cond);
1966}
1967
1968void CHR::transformScopes(SmallVectorImpl<CHRScope *> &CHRScopes) {
1969 unsigned I = 0;
1970 DenseSet<PHINode *> TrivialPHIs;
1971 for (CHRScope *Scope : CHRScopes) {
1972 transformScopes(Scope, TrivialPHIs);
1973 CHR_DEBUG(
1974 std::ostringstream oss;
1975 oss << " after transformScopes " << I++;
1976 dumpIR(F, oss.str().c_str(), nullptr));
1977 (void)I;
1978 }
1979}
1980
1981static void LLVM_ATTRIBUTE_UNUSED
1982dumpScopes(SmallVectorImpl<CHRScope *> &Scopes, const char *Label) {
1983 dbgs() << Label << " " << Scopes.size() << "\n";
1984 for (CHRScope *Scope : Scopes) {
1985 dbgs() << *Scope << "\n";
1986 }
1987}
1988
1989bool CHR::run() {
1990 if (!shouldApply(F, PSI))
1991 return false;
1992
1993 CHR_DEBUG(dumpIR(F, "before", nullptr));
1994
1995 bool Changed = false;
1996 {
1997 CHR_DEBUG(
1998 dbgs() << "RegionInfo:\n";
1999 RI.print(dbgs()));
2000
2001 // Recursively traverse the region tree and find regions that have biased
2002 // branches and/or selects and create scopes.
2003 SmallVector<CHRScope *, 8> AllScopes;
2004 findScopes(Output&: AllScopes);
2005 CHR_DEBUG(dumpScopes(AllScopes, "All scopes"));
2006
2007 // Split the scopes if 1) the conditional values of the biased
2008 // branches/selects of the inner/lower scope can't be hoisted up to the
2009 // outermost/uppermost scope entry, or 2) the condition values of the biased
2010 // branches/selects in a scope (including subscopes) don't share at least
2011 // one common value.
2012 SmallVector<CHRScope *, 8> SplitScopes;
2013 splitScopes(Input&: AllScopes, Output&: SplitScopes);
2014 CHR_DEBUG(dumpScopes(SplitScopes, "Split scopes"));
2015
2016 // After splitting, set the biased regions and selects of a scope (a tree
2017 // root) that include those of the subscopes.
2018 classifyBiasedScopes(Scopes&: SplitScopes);
2019 CHR_DEBUG(dbgs() << "Set per-scope bias " << SplitScopes.size() << "\n");
2020
2021 // Filter out the scopes that has only one biased region or select (CHR
2022 // isn't useful in such a case).
2023 SmallVector<CHRScope *, 8> FilteredScopes;
2024 filterScopes(Input&: SplitScopes, Output&: FilteredScopes);
2025 CHR_DEBUG(dumpScopes(FilteredScopes, "Filtered scopes"));
2026
2027 // Set the regions to be CHR'ed and their hoist stops for each scope.
2028 SmallVector<CHRScope *, 8> SetScopes;
2029 setCHRRegions(Input&: FilteredScopes, Output&: SetScopes);
2030 CHR_DEBUG(dumpScopes(SetScopes, "Set CHR regions"));
2031
2032 // Sort CHRScopes by the depth so that outer CHRScopes comes before inner
2033 // ones. We need to apply CHR from outer to inner so that we apply CHR only
2034 // to the hot path, rather than both hot and cold paths.
2035 SmallVector<CHRScope *, 8> SortedScopes;
2036 sortScopes(Input&: SetScopes, Output&: SortedScopes);
2037 CHR_DEBUG(dumpScopes(SortedScopes, "Sorted scopes"));
2038
2039 CHR_DEBUG(
2040 dbgs() << "RegionInfo:\n";
2041 RI.print(dbgs()));
2042
2043 // Apply the CHR transformation.
2044 if (!SortedScopes.empty()) {
2045 transformScopes(CHRScopes&: SortedScopes);
2046 Changed = true;
2047 }
2048 }
2049
2050 if (Changed) {
2051 CHR_DEBUG(dumpIR(F, "after", &Stats));
2052 ORE.emit(RemarkBuilder: [&]() {
2053 return OptimizationRemark(DEBUG_TYPE, "Stats", &F)
2054 << ore::NV("Function", &F) << " "
2055 << "Reduced the number of branches in hot paths by "
2056 << ore::NV("NumBranchesDelta", Stats.NumBranchesDelta)
2057 << " (static) and "
2058 << ore::NV("WeightedNumBranchesDelta", Stats.WeightedNumBranchesDelta)
2059 << " (weighted by PGO count)";
2060 });
2061 }
2062
2063 return Changed;
2064}
2065
2066namespace llvm {
2067
2068ControlHeightReductionPass::ControlHeightReductionPass() {
2069 parseCHRFilterFiles();
2070}
2071
2072PreservedAnalyses ControlHeightReductionPass::run(
2073 Function &F,
2074 FunctionAnalysisManager &FAM) {
2075 auto &MAMProxy = FAM.getResult<ModuleAnalysisManagerFunctionProxy>(IR&: F);
2076 auto PPSI = MAMProxy.getCachedResult<ProfileSummaryAnalysis>(IR&: *F.getParent());
2077 // If there is no profile summary, we should not do CHR.
2078 if (!PPSI || !PPSI->hasProfileSummary())
2079 return PreservedAnalyses::all();
2080 auto &PSI = *PPSI;
2081 auto &BFI = FAM.getResult<BlockFrequencyAnalysis>(IR&: F);
2082 auto &DT = FAM.getResult<DominatorTreeAnalysis>(IR&: F);
2083 auto &RI = FAM.getResult<RegionInfoAnalysis>(IR&: F);
2084 auto &ORE = FAM.getResult<OptimizationRemarkEmitterAnalysis>(IR&: F);
2085 bool Changed = CHR(F, BFI, DT, PSI, RI, ORE).run();
2086 if (!Changed)
2087 return PreservedAnalyses::all();
2088 return PreservedAnalyses::none();
2089}
2090
2091} // namespace llvm
2092