1 //===- LoopIdiomRecognize.cpp - Loop idiom recognition --------------------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This pass implements an idiom recognizer that transforms simple loops into a
11 // non-loop form. In cases that this kicks in, it can be a significant
14 // If compiling for code size we avoid idiom recognition if the resulting
15 // code could be larger than the code for the original loop. One way this could
16 // happen is if the loop is not removable after idiom recognition due to the
17 // presence of non-idiom instructions. The initial implementation of the
18 // heuristics applies to idioms in multi-block loops.
20 //===----------------------------------------------------------------------===//
24 // Future loop memory idioms to recognize:
25 // memcmp, memmove, strlen, etc.
26 // Future floating point idioms to recognize in -ffast-math mode:
28 // Future integer operation idioms to recognize:
31 // Beware that isel's default lowering for ctpop is highly inefficient for
32 // i64 and larger types when i64 is legal and the value has few bits set. It
33 // would be good to enhance isel to emit a loop for ctpop in this case.
35 // This could recognize common matrix multiplies and dot product idioms and
36 // replace them with calls to BLAS (if linked in??).
38 //===----------------------------------------------------------------------===//
40 #include "llvm/ADT/APInt.h"
41 #include "llvm/ADT/ArrayRef.h"
42 #include "llvm/ADT/DenseMap.h"
43 #include "llvm/ADT/MapVector.h"
44 #include "llvm/ADT/SetVector.h"
45 #include "llvm/ADT/SmallPtrSet.h"
46 #include "llvm/ADT/SmallVector.h"
47 #include "llvm/ADT/Statistic.h"
48 #include "llvm/ADT/StringRef.h"
49 #include "llvm/Analysis/AliasAnalysis.h"
50 #include "llvm/Analysis/LoopAccessAnalysis.h"
51 #include "llvm/Analysis/LoopInfo.h"
52 #include "llvm/Analysis/LoopPass.h"
53 #include "llvm/Analysis/MemoryLocation.h"
54 #include "llvm/Analysis/ScalarEvolution.h"
55 #include "llvm/Analysis/ScalarEvolutionExpander.h"
56 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
57 #include "llvm/Analysis/TargetLibraryInfo.h"
58 #include "llvm/Analysis/TargetTransformInfo.h"
59 #include "llvm/Transforms/Utils/Local.h"
60 #include "llvm/Analysis/ValueTracking.h"
61 #include "llvm/IR/Attributes.h"
62 #include "llvm/IR/BasicBlock.h"
63 #include "llvm/IR/Constant.h"
64 #include "llvm/IR/Constants.h"
65 #include "llvm/IR/DataLayout.h"
66 #include "llvm/IR/DebugLoc.h"
67 #include "llvm/IR/DerivedTypes.h"
68 #include "llvm/IR/Dominators.h"
69 #include "llvm/IR/GlobalValue.h"
70 #include "llvm/IR/GlobalVariable.h"
71 #include "llvm/IR/IRBuilder.h"
72 #include "llvm/IR/InstrTypes.h"
73 #include "llvm/IR/Instruction.h"
74 #include "llvm/IR/Instructions.h"
75 #include "llvm/IR/IntrinsicInst.h"
76 #include "llvm/IR/Intrinsics.h"
77 #include "llvm/IR/LLVMContext.h"
78 #include "llvm/IR/Module.h"
79 #include "llvm/IR/PassManager.h"
80 #include "llvm/IR/Type.h"
81 #include "llvm/IR/User.h"
82 #include "llvm/IR/Value.h"
83 #include "llvm/IR/ValueHandle.h"
84 #include "llvm/Pass.h"
85 #include "llvm/Support/Casting.h"
86 #include "llvm/Support/CommandLine.h"
87 #include "llvm/Support/Debug.h"
88 #include "llvm/Support/raw_ostream.h"
89 #include "llvm/Transforms/Scalar.h"
90 #include "llvm/Transforms/Scalar/LoopIdiomRecognize.h"
91 #include "llvm/Transforms/Utils/BuildLibCalls.h"
92 #include "llvm/Transforms/Utils/LoopUtils.h"
101 #define DEBUG_TYPE "loop-idiom"
103 STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
104 STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
106 static cl::opt<bool> UseLIRCodeSizeHeurs(
107 "use-lir-code-size-heurs",
108 cl::desc("Use loop idiom recognition code size heuristics when compiling"
110 cl::init(true), cl::Hidden);
114 class LoopIdiomRecognize {
115 Loop *CurLoop = nullptr;
120 TargetLibraryInfo *TLI;
121 const TargetTransformInfo *TTI;
122 const DataLayout *DL;
123 bool ApplyCodeSizeHeuristics;
126 explicit LoopIdiomRecognize(AliasAnalysis *AA, DominatorTree *DT,
127 LoopInfo *LI, ScalarEvolution *SE,
128 TargetLibraryInfo *TLI,
129 const TargetTransformInfo *TTI,
130 const DataLayout *DL)
131 : AA(AA), DT(DT), LI(LI), SE(SE), TLI(TLI), TTI(TTI), DL(DL) {}
133 bool runOnLoop(Loop *L);
136 using StoreList = SmallVector<StoreInst *, 8>;
137 using StoreListMap = MapVector<Value *, StoreList>;
139 StoreListMap StoreRefsForMemset;
140 StoreListMap StoreRefsForMemsetPattern;
141 StoreList StoreRefsForMemcpy;
143 bool HasMemsetPattern;
146 /// Return code for isLegalStore()
147 enum LegalStoreKind {
152 UnorderedAtomicMemcpy,
153 DontUse // Dummy retval never to be used. Allows catching errors in retval
157 /// \name Countable Loop Idiom Handling
160 bool runOnCountableLoop();
161 bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
162 SmallVectorImpl<BasicBlock *> &ExitBlocks);
164 void collectStores(BasicBlock *BB);
165 LegalStoreKind isLegalStore(StoreInst *SI);
166 enum class ForMemset { No, Yes };
167 bool processLoopStores(SmallVectorImpl<StoreInst *> &SL, const SCEV *BECount,
169 bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
171 bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
172 unsigned StoreAlignment, Value *StoredVal,
173 Instruction *TheStore,
174 SmallPtrSetImpl<Instruction *> &Stores,
175 const SCEVAddRecExpr *Ev, const SCEV *BECount,
176 bool NegStride, bool IsLoopMemset = false);
177 bool processLoopStoreOfLoopLoad(StoreInst *SI, const SCEV *BECount);
178 bool avoidLIRForMultiBlockLoop(bool IsMemset = false,
179 bool IsLoopMemset = false);
182 /// \name Noncountable Loop Idiom Handling
185 bool runOnNoncountableLoop();
187 bool recognizePopcount();
188 void transformLoopToPopcount(BasicBlock *PreCondBB, Instruction *CntInst,
189 PHINode *CntPhi, Value *Var);
190 bool recognizeAndInsertFFS(); /// Find First Set: ctlz or cttz
191 void transformLoopToCountable(Intrinsic::ID IntrinID, BasicBlock *PreCondBB,
192 Instruction *CntInst, PHINode *CntPhi,
193 Value *Var, Instruction *DefX,
194 const DebugLoc &DL, bool ZeroCheck,
195 bool IsCntPhiUsedOutsideLoop);
200 class LoopIdiomRecognizeLegacyPass : public LoopPass {
204 explicit LoopIdiomRecognizeLegacyPass() : LoopPass(ID) {
205 initializeLoopIdiomRecognizeLegacyPassPass(
206 *PassRegistry::getPassRegistry());
209 bool runOnLoop(Loop *L, LPPassManager &LPM) override {
213 AliasAnalysis *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
214 DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
215 LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
216 ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
217 TargetLibraryInfo *TLI =
218 &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
219 const TargetTransformInfo *TTI =
220 &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
221 *L->getHeader()->getParent());
222 const DataLayout *DL = &L->getHeader()->getModule()->getDataLayout();
224 LoopIdiomRecognize LIR(AA, DT, LI, SE, TLI, TTI, DL);
225 return LIR.runOnLoop(L);
228 /// This transformation requires natural loop information & requires that
229 /// loop preheaders be inserted into the CFG.
230 void getAnalysisUsage(AnalysisUsage &AU) const override {
231 AU.addRequired<TargetLibraryInfoWrapperPass>();
232 AU.addRequired<TargetTransformInfoWrapperPass>();
233 getLoopAnalysisUsage(AU);
237 } // end anonymous namespace
239 char LoopIdiomRecognizeLegacyPass::ID = 0;
241 PreservedAnalyses LoopIdiomRecognizePass::run(Loop &L, LoopAnalysisManager &AM,
242 LoopStandardAnalysisResults &AR,
244 const auto *DL = &L.getHeader()->getModule()->getDataLayout();
246 LoopIdiomRecognize LIR(&AR.AA, &AR.DT, &AR.LI, &AR.SE, &AR.TLI, &AR.TTI, DL);
247 if (!LIR.runOnLoop(&L))
248 return PreservedAnalyses::all();
250 return getLoopPassPreservedAnalyses();
253 INITIALIZE_PASS_BEGIN(LoopIdiomRecognizeLegacyPass, "loop-idiom",
254 "Recognize loop idioms", false, false)
255 INITIALIZE_PASS_DEPENDENCY(LoopPass)
256 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
257 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
258 INITIALIZE_PASS_END(LoopIdiomRecognizeLegacyPass, "loop-idiom",
259 "Recognize loop idioms", false, false)
261 Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognizeLegacyPass(); }
263 static void deleteDeadInstruction(Instruction *I) {
264 I->replaceAllUsesWith(UndefValue::get(I->getType()));
265 I->eraseFromParent();
268 //===----------------------------------------------------------------------===//
270 // Implementation of LoopIdiomRecognize
272 //===----------------------------------------------------------------------===//
274 bool LoopIdiomRecognize::runOnLoop(Loop *L) {
276 // If the loop could not be converted to canonical form, it must have an
277 // indirectbr in it, just give up.
278 if (!L->getLoopPreheader())
281 // Disable loop idiom recognition if the function's name is a common idiom.
282 StringRef Name = L->getHeader()->getParent()->getName();
283 if (Name == "memset" || Name == "memcpy")
286 // Determine if code size heuristics need to be applied.
287 ApplyCodeSizeHeuristics =
288 L->getHeader()->getParent()->optForSize() && UseLIRCodeSizeHeurs;
290 HasMemset = TLI->has(LibFunc_memset);
291 HasMemsetPattern = TLI->has(LibFunc_memset_pattern16);
292 HasMemcpy = TLI->has(LibFunc_memcpy);
294 if (HasMemset || HasMemsetPattern || HasMemcpy)
295 if (SE->hasLoopInvariantBackedgeTakenCount(L))
296 return runOnCountableLoop();
298 return runOnNoncountableLoop();
301 bool LoopIdiomRecognize::runOnCountableLoop() {
302 const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
303 assert(!isa<SCEVCouldNotCompute>(BECount) &&
304 "runOnCountableLoop() called on a loop without a predictable"
305 "backedge-taken count");
307 // If this loop executes exactly one time, then it should be peeled, not
308 // optimized by this pass.
309 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
310 if (BECst->getAPInt() == 0)
313 SmallVector<BasicBlock *, 8> ExitBlocks;
314 CurLoop->getUniqueExitBlocks(ExitBlocks);
316 LLVM_DEBUG(dbgs() << "loop-idiom Scanning: F["
317 << CurLoop->getHeader()->getParent()->getName()
318 << "] Loop %" << CurLoop->getHeader()->getName() << "\n");
320 bool MadeChange = false;
322 // The following transforms hoist stores/memsets into the loop pre-header.
323 // Give up if the loop has instructions may throw.
324 SimpleLoopSafetyInfo SafetyInfo;
325 SafetyInfo.computeLoopSafetyInfo(CurLoop);
326 if (SafetyInfo.anyBlockMayThrow())
329 // Scan all the blocks in the loop that are not in subloops.
330 for (auto *BB : CurLoop->getBlocks()) {
331 // Ignore blocks in subloops.
332 if (LI->getLoopFor(BB) != CurLoop)
335 MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
340 static APInt getStoreStride(const SCEVAddRecExpr *StoreEv) {
341 const SCEVConstant *ConstStride = cast<SCEVConstant>(StoreEv->getOperand(1));
342 return ConstStride->getAPInt();
345 /// getMemSetPatternValue - If a strided store of the specified value is safe to
346 /// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
347 /// be passed in. Otherwise, return null.
349 /// Note that we don't ever attempt to use memset_pattern8 or 4, because these
350 /// just replicate their input array and then pass on to memset_pattern16.
351 static Constant *getMemSetPatternValue(Value *V, const DataLayout *DL) {
352 // FIXME: This could check for UndefValue because it can be merged into any
353 // other valid pattern.
355 // If the value isn't a constant, we can't promote it to being in a constant
356 // array. We could theoretically do a store to an alloca or something, but
357 // that doesn't seem worthwhile.
358 Constant *C = dyn_cast<Constant>(V);
362 // Only handle simple values that are a power of two bytes in size.
363 uint64_t Size = DL->getTypeSizeInBits(V->getType());
364 if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
367 // Don't care enough about darwin/ppc to implement this.
368 if (DL->isBigEndian())
371 // Convert to size in bytes.
374 // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
375 // if the top and bottom are the same (e.g. for vectors and large integers).
379 // If the constant is exactly 16 bytes, just use it.
383 // Otherwise, we'll use an array of the constants.
384 unsigned ArraySize = 16 / Size;
385 ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
386 return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
389 LoopIdiomRecognize::LegalStoreKind
390 LoopIdiomRecognize::isLegalStore(StoreInst *SI) {
391 // Don't touch volatile stores.
392 if (SI->isVolatile())
393 return LegalStoreKind::None;
394 // We only want simple or unordered-atomic stores.
395 if (!SI->isUnordered())
396 return LegalStoreKind::None;
398 // Don't convert stores of non-integral pointer types to memsets (which stores
400 if (DL->isNonIntegralPointerType(SI->getValueOperand()->getType()))
401 return LegalStoreKind::None;
403 // Avoid merging nontemporal stores.
404 if (SI->getMetadata(LLVMContext::MD_nontemporal))
405 return LegalStoreKind::None;
407 Value *StoredVal = SI->getValueOperand();
408 Value *StorePtr = SI->getPointerOperand();
410 // Reject stores that are so large that they overflow an unsigned.
411 uint64_t SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
412 if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
413 return LegalStoreKind::None;
415 // See if the pointer expression is an AddRec like {base,+,1} on the current
416 // loop, which indicates a strided store. If we have something else, it's a
417 // random store we can't handle.
418 const SCEVAddRecExpr *StoreEv =
419 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
420 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
421 return LegalStoreKind::None;
423 // Check to see if we have a constant stride.
424 if (!isa<SCEVConstant>(StoreEv->getOperand(1)))
425 return LegalStoreKind::None;
427 // See if the store can be turned into a memset.
429 // If the stored value is a byte-wise value (like i32 -1), then it may be
430 // turned into a memset of i8 -1, assuming that all the consecutive bytes
431 // are stored. A store of i32 0x01020304 can never be turned into a memset,
432 // but it can be turned into memset_pattern if the target supports it.
433 Value *SplatValue = isBytewiseValue(StoredVal);
434 Constant *PatternValue = nullptr;
436 // Note: memset and memset_pattern on unordered-atomic is yet not supported
437 bool UnorderedAtomic = SI->isUnordered() && !SI->isSimple();
439 // If we're allowed to form a memset, and the stored value would be
440 // acceptable for memset, use it.
441 if (!UnorderedAtomic && HasMemset && SplatValue &&
442 // Verify that the stored value is loop invariant. If not, we can't
443 // promote the memset.
444 CurLoop->isLoopInvariant(SplatValue)) {
445 // It looks like we can use SplatValue.
446 return LegalStoreKind::Memset;
447 } else if (!UnorderedAtomic && HasMemsetPattern &&
448 // Don't create memset_pattern16s with address spaces.
449 StorePtr->getType()->getPointerAddressSpace() == 0 &&
450 (PatternValue = getMemSetPatternValue(StoredVal, DL))) {
451 // It looks like we can use PatternValue!
452 return LegalStoreKind::MemsetPattern;
455 // Otherwise, see if the store can be turned into a memcpy.
457 // Check to see if the stride matches the size of the store. If so, then we
458 // know that every byte is touched in the loop.
459 APInt Stride = getStoreStride(StoreEv);
460 unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
461 if (StoreSize != Stride && StoreSize != -Stride)
462 return LegalStoreKind::None;
464 // The store must be feeding a non-volatile load.
465 LoadInst *LI = dyn_cast<LoadInst>(SI->getValueOperand());
467 // Only allow non-volatile loads
468 if (!LI || LI->isVolatile())
469 return LegalStoreKind::None;
470 // Only allow simple or unordered-atomic loads
471 if (!LI->isUnordered())
472 return LegalStoreKind::None;
474 // See if the pointer expression is an AddRec like {base,+,1} on the current
475 // loop, which indicates a strided load. If we have something else, it's a
476 // random load we can't handle.
477 const SCEVAddRecExpr *LoadEv =
478 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getPointerOperand()));
479 if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
480 return LegalStoreKind::None;
482 // The store and load must share the same stride.
483 if (StoreEv->getOperand(1) != LoadEv->getOperand(1))
484 return LegalStoreKind::None;
486 // Success. This store can be converted into a memcpy.
487 UnorderedAtomic = UnorderedAtomic || LI->isAtomic();
488 return UnorderedAtomic ? LegalStoreKind::UnorderedAtomicMemcpy
489 : LegalStoreKind::Memcpy;
491 // This store can't be transformed into a memset/memcpy.
492 return LegalStoreKind::None;
495 void LoopIdiomRecognize::collectStores(BasicBlock *BB) {
496 StoreRefsForMemset.clear();
497 StoreRefsForMemsetPattern.clear();
498 StoreRefsForMemcpy.clear();
499 for (Instruction &I : *BB) {
500 StoreInst *SI = dyn_cast<StoreInst>(&I);
504 // Make sure this is a strided store with a constant stride.
505 switch (isLegalStore(SI)) {
506 case LegalStoreKind::None:
509 case LegalStoreKind::Memset: {
510 // Find the base pointer.
511 Value *Ptr = GetUnderlyingObject(SI->getPointerOperand(), *DL);
512 StoreRefsForMemset[Ptr].push_back(SI);
514 case LegalStoreKind::MemsetPattern: {
515 // Find the base pointer.
516 Value *Ptr = GetUnderlyingObject(SI->getPointerOperand(), *DL);
517 StoreRefsForMemsetPattern[Ptr].push_back(SI);
519 case LegalStoreKind::Memcpy:
520 case LegalStoreKind::UnorderedAtomicMemcpy:
521 StoreRefsForMemcpy.push_back(SI);
524 assert(false && "unhandled return value");
530 /// runOnLoopBlock - Process the specified block, which lives in a counted loop
531 /// with the specified backedge count. This block is known to be in the current
532 /// loop and not in any subloops.
533 bool LoopIdiomRecognize::runOnLoopBlock(
534 BasicBlock *BB, const SCEV *BECount,
535 SmallVectorImpl<BasicBlock *> &ExitBlocks) {
536 // We can only promote stores in this block if they are unconditionally
537 // executed in the loop. For a block to be unconditionally executed, it has
538 // to dominate all the exit blocks of the loop. Verify this now.
539 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
540 if (!DT->dominates(BB, ExitBlocks[i]))
543 bool MadeChange = false;
544 // Look for store instructions, which may be optimized to memset/memcpy.
547 // Look for a single store or sets of stores with a common base, which can be
548 // optimized into a memset (memset_pattern). The latter most commonly happens
549 // with structs and handunrolled loops.
550 for (auto &SL : StoreRefsForMemset)
551 MadeChange |= processLoopStores(SL.second, BECount, ForMemset::Yes);
553 for (auto &SL : StoreRefsForMemsetPattern)
554 MadeChange |= processLoopStores(SL.second, BECount, ForMemset::No);
556 // Optimize the store into a memcpy, if it feeds an similarly strided load.
557 for (auto &SI : StoreRefsForMemcpy)
558 MadeChange |= processLoopStoreOfLoopLoad(SI, BECount);
560 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
561 Instruction *Inst = &*I++;
562 // Look for memset instructions, which may be optimized to a larger memset.
563 if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst)) {
564 WeakTrackingVH InstPtr(&*I);
565 if (!processLoopMemSet(MSI, BECount))
569 // If processing the memset invalidated our iterator, start over from the
580 /// See if this store(s) can be promoted to a memset.
581 bool LoopIdiomRecognize::processLoopStores(SmallVectorImpl<StoreInst *> &SL,
582 const SCEV *BECount, ForMemset For) {
583 // Try to find consecutive stores that can be transformed into memsets.
584 SetVector<StoreInst *> Heads, Tails;
585 SmallDenseMap<StoreInst *, StoreInst *> ConsecutiveChain;
587 // Do a quadratic search on all of the given stores and find
588 // all of the pairs of stores that follow each other.
589 SmallVector<unsigned, 16> IndexQueue;
590 for (unsigned i = 0, e = SL.size(); i < e; ++i) {
591 assert(SL[i]->isSimple() && "Expected only non-volatile stores.");
593 Value *FirstStoredVal = SL[i]->getValueOperand();
594 Value *FirstStorePtr = SL[i]->getPointerOperand();
595 const SCEVAddRecExpr *FirstStoreEv =
596 cast<SCEVAddRecExpr>(SE->getSCEV(FirstStorePtr));
597 APInt FirstStride = getStoreStride(FirstStoreEv);
598 unsigned FirstStoreSize = DL->getTypeStoreSize(SL[i]->getValueOperand()->getType());
600 // See if we can optimize just this store in isolation.
601 if (FirstStride == FirstStoreSize || -FirstStride == FirstStoreSize) {
606 Value *FirstSplatValue = nullptr;
607 Constant *FirstPatternValue = nullptr;
609 if (For == ForMemset::Yes)
610 FirstSplatValue = isBytewiseValue(FirstStoredVal);
612 FirstPatternValue = getMemSetPatternValue(FirstStoredVal, DL);
614 assert((FirstSplatValue || FirstPatternValue) &&
615 "Expected either splat value or pattern value.");
618 // If a store has multiple consecutive store candidates, search Stores
619 // array according to the sequence: from i+1 to e, then from i-1 to 0.
620 // This is because usually pairing with immediate succeeding or preceding
621 // candidate create the best chance to find memset opportunity.
623 for (j = i + 1; j < e; ++j)
624 IndexQueue.push_back(j);
625 for (j = i; j > 0; --j)
626 IndexQueue.push_back(j - 1);
628 for (auto &k : IndexQueue) {
629 assert(SL[k]->isSimple() && "Expected only non-volatile stores.");
630 Value *SecondStorePtr = SL[k]->getPointerOperand();
631 const SCEVAddRecExpr *SecondStoreEv =
632 cast<SCEVAddRecExpr>(SE->getSCEV(SecondStorePtr));
633 APInt SecondStride = getStoreStride(SecondStoreEv);
635 if (FirstStride != SecondStride)
638 Value *SecondStoredVal = SL[k]->getValueOperand();
639 Value *SecondSplatValue = nullptr;
640 Constant *SecondPatternValue = nullptr;
642 if (For == ForMemset::Yes)
643 SecondSplatValue = isBytewiseValue(SecondStoredVal);
645 SecondPatternValue = getMemSetPatternValue(SecondStoredVal, DL);
647 assert((SecondSplatValue || SecondPatternValue) &&
648 "Expected either splat value or pattern value.");
650 if (isConsecutiveAccess(SL[i], SL[k], *DL, *SE, false)) {
651 if (For == ForMemset::Yes) {
652 if (isa<UndefValue>(FirstSplatValue))
653 FirstSplatValue = SecondSplatValue;
654 if (FirstSplatValue != SecondSplatValue)
657 if (isa<UndefValue>(FirstPatternValue))
658 FirstPatternValue = SecondPatternValue;
659 if (FirstPatternValue != SecondPatternValue)
664 ConsecutiveChain[SL[i]] = SL[k];
670 // We may run into multiple chains that merge into a single chain. We mark the
671 // stores that we transformed so that we don't visit the same store twice.
672 SmallPtrSet<Value *, 16> TransformedStores;
673 bool Changed = false;
675 // For stores that start but don't end a link in the chain:
676 for (SetVector<StoreInst *>::iterator it = Heads.begin(), e = Heads.end();
678 if (Tails.count(*it))
681 // We found a store instr that starts a chain. Now follow the chain and try
683 SmallPtrSet<Instruction *, 8> AdjacentStores;
686 StoreInst *HeadStore = I;
687 unsigned StoreSize = 0;
689 // Collect the chain into a list.
690 while (Tails.count(I) || Heads.count(I)) {
691 if (TransformedStores.count(I))
693 AdjacentStores.insert(I);
695 StoreSize += DL->getTypeStoreSize(I->getValueOperand()->getType());
696 // Move to the next value in the chain.
697 I = ConsecutiveChain[I];
700 Value *StoredVal = HeadStore->getValueOperand();
701 Value *StorePtr = HeadStore->getPointerOperand();
702 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
703 APInt Stride = getStoreStride(StoreEv);
705 // Check to see if the stride matches the size of the stores. If so, then
706 // we know that every byte is touched in the loop.
707 if (StoreSize != Stride && StoreSize != -Stride)
710 bool NegStride = StoreSize == -Stride;
712 if (processLoopStridedStore(StorePtr, StoreSize, HeadStore->getAlignment(),
713 StoredVal, HeadStore, AdjacentStores, StoreEv,
714 BECount, NegStride)) {
715 TransformedStores.insert(AdjacentStores.begin(), AdjacentStores.end());
723 /// processLoopMemSet - See if this memset can be promoted to a large memset.
724 bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
725 const SCEV *BECount) {
726 // We can only handle non-volatile memsets with a constant size.
727 if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength()))
730 // If we're not allowed to hack on memset, we fail.
734 Value *Pointer = MSI->getDest();
736 // See if the pointer expression is an AddRec like {base,+,1} on the current
737 // loop, which indicates a strided store. If we have something else, it's a
738 // random store we can't handle.
739 const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
740 if (!Ev || Ev->getLoop() != CurLoop || !Ev->isAffine())
743 // Reject memsets that are so large that they overflow an unsigned.
744 uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
745 if ((SizeInBytes >> 32) != 0)
748 // Check to see if the stride matches the size of the memset. If so, then we
749 // know that every byte is touched in the loop.
750 const SCEVConstant *ConstStride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
754 APInt Stride = ConstStride->getAPInt();
755 if (SizeInBytes != Stride && SizeInBytes != -Stride)
758 // Verify that the memset value is loop invariant. If not, we can't promote
760 Value *SplatValue = MSI->getValue();
761 if (!SplatValue || !CurLoop->isLoopInvariant(SplatValue))
764 SmallPtrSet<Instruction *, 1> MSIs;
766 bool NegStride = SizeInBytes == -Stride;
767 return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
768 MSI->getDestAlignment(), SplatValue, MSI, MSIs,
769 Ev, BECount, NegStride, /*IsLoopMemset=*/true);
772 /// mayLoopAccessLocation - Return true if the specified loop might access the
773 /// specified pointer location, which is a loop-strided access. The 'Access'
774 /// argument specifies what the verboten forms of access are (read or write).
776 mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
777 const SCEV *BECount, unsigned StoreSize,
779 SmallPtrSetImpl<Instruction *> &IgnoredStores) {
780 // Get the location that may be stored across the loop. Since the access is
781 // strided positively through memory, we say that the modified location starts
782 // at the pointer and has infinite size.
783 LocationSize AccessSize = LocationSize::unknown();
785 // If the loop iterates a fixed number of times, we can refine the access size
786 // to be exactly the size of the memset, which is (BECount+1)*StoreSize
787 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
788 AccessSize = LocationSize::precise((BECst->getValue()->getZExtValue() + 1) *
791 // TODO: For this to be really effective, we have to dive into the pointer
792 // operand in the store. Store to &A[i] of 100 will always return may alias
793 // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
794 // which will then no-alias a store to &A[100].
795 MemoryLocation StoreLoc(Ptr, AccessSize);
797 for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
799 for (Instruction &I : **BI)
800 if (IgnoredStores.count(&I) == 0 &&
802 intersectModRef(AA.getModRefInfo(&I, StoreLoc), Access)))
808 // If we have a negative stride, Start refers to the end of the memory location
809 // we're trying to memset. Therefore, we need to recompute the base pointer,
810 // which is just Start - BECount*Size.
811 static const SCEV *getStartForNegStride(const SCEV *Start, const SCEV *BECount,
812 Type *IntPtr, unsigned StoreSize,
813 ScalarEvolution *SE) {
814 const SCEV *Index = SE->getTruncateOrZeroExtend(BECount, IntPtr);
816 Index = SE->getMulExpr(Index, SE->getConstant(IntPtr, StoreSize),
818 return SE->getMinusSCEV(Start, Index);
821 /// Compute the number of bytes as a SCEV from the backedge taken count.
823 /// This also maps the SCEV into the provided type and tries to handle the
824 /// computation in a way that will fold cleanly.
825 static const SCEV *getNumBytes(const SCEV *BECount, Type *IntPtr,
826 unsigned StoreSize, Loop *CurLoop,
827 const DataLayout *DL, ScalarEvolution *SE) {
828 const SCEV *NumBytesS;
829 // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
830 // pointer size if it isn't already.
832 // If we're going to need to zero extend the BE count, check if we can add
833 // one to it prior to zero extending without overflow. Provided this is safe,
834 // it allows better simplification of the +1.
835 if (DL->getTypeSizeInBits(BECount->getType()) <
836 DL->getTypeSizeInBits(IntPtr) &&
837 SE->isLoopEntryGuardedByCond(
838 CurLoop, ICmpInst::ICMP_NE, BECount,
839 SE->getNegativeSCEV(SE->getOne(BECount->getType())))) {
840 NumBytesS = SE->getZeroExtendExpr(
841 SE->getAddExpr(BECount, SE->getOne(BECount->getType()), SCEV::FlagNUW),
844 NumBytesS = SE->getAddExpr(SE->getTruncateOrZeroExtend(BECount, IntPtr),
845 SE->getOne(IntPtr), SCEV::FlagNUW);
848 // And scale it based on the store size.
849 if (StoreSize != 1) {
850 NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
856 /// processLoopStridedStore - We see a strided store of some value. If we can
857 /// transform this into a memset or memset_pattern in the loop preheader, do so.
858 bool LoopIdiomRecognize::processLoopStridedStore(
859 Value *DestPtr, unsigned StoreSize, unsigned StoreAlignment,
860 Value *StoredVal, Instruction *TheStore,
861 SmallPtrSetImpl<Instruction *> &Stores, const SCEVAddRecExpr *Ev,
862 const SCEV *BECount, bool NegStride, bool IsLoopMemset) {
863 Value *SplatValue = isBytewiseValue(StoredVal);
864 Constant *PatternValue = nullptr;
867 PatternValue = getMemSetPatternValue(StoredVal, DL);
869 assert((SplatValue || PatternValue) &&
870 "Expected either splat value or pattern value.");
872 // The trip count of the loop and the base pointer of the addrec SCEV is
873 // guaranteed to be loop invariant, which means that it should dominate the
874 // header. This allows us to insert code for it in the preheader.
875 unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
876 BasicBlock *Preheader = CurLoop->getLoopPreheader();
877 IRBuilder<> Builder(Preheader->getTerminator());
878 SCEVExpander Expander(*SE, *DL, "loop-idiom");
880 Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
881 Type *IntPtr = Builder.getIntPtrTy(*DL, DestAS);
883 const SCEV *Start = Ev->getStart();
884 // Handle negative strided loops.
886 Start = getStartForNegStride(Start, BECount, IntPtr, StoreSize, SE);
888 // TODO: ideally we should still be able to generate memset if SCEV expander
889 // is taught to generate the dependencies at the latest point.
890 if (!isSafeToExpand(Start, *SE))
893 // Okay, we have a strided store "p[i]" of a splattable value. We can turn
894 // this into a memset in the loop preheader now if we want. However, this
895 // would be unsafe to do if there is anything else in the loop that may read
896 // or write to the aliased location. Check for any overlap by generating the
897 // base pointer and checking the region.
899 Expander.expandCodeFor(Start, DestInt8PtrTy, Preheader->getTerminator());
900 if (mayLoopAccessLocation(BasePtr, ModRefInfo::ModRef, CurLoop, BECount,
901 StoreSize, *AA, Stores)) {
903 // If we generated new code for the base pointer, clean up.
904 RecursivelyDeleteTriviallyDeadInstructions(BasePtr, TLI);
908 if (avoidLIRForMultiBlockLoop(/*IsMemset=*/true, IsLoopMemset))
911 // Okay, everything looks good, insert the memset.
913 const SCEV *NumBytesS =
914 getNumBytes(BECount, IntPtr, StoreSize, CurLoop, DL, SE);
916 // TODO: ideally we should still be able to generate memset if SCEV expander
917 // is taught to generate the dependencies at the latest point.
918 if (!isSafeToExpand(NumBytesS, *SE))
922 Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
927 Builder.CreateMemSet(BasePtr, SplatValue, NumBytes, StoreAlignment);
929 // Everything is emitted in default address space
930 Type *Int8PtrTy = DestInt8PtrTy;
932 Module *M = TheStore->getModule();
933 StringRef FuncName = "memset_pattern16";
935 M->getOrInsertFunction(FuncName, Builder.getVoidTy(),
936 Int8PtrTy, Int8PtrTy, IntPtr);
937 inferLibFuncAttributes(M, FuncName, *TLI);
939 // Otherwise we should form a memset_pattern16. PatternValue is known to be
940 // an constant array of 16-bytes. Plop the value into a mergable global.
941 GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
942 GlobalValue::PrivateLinkage,
943 PatternValue, ".memset_pattern");
944 GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global); // Ok to merge these.
945 GV->setAlignment(16);
946 Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
947 NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
950 LLVM_DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"
951 << " from store to: " << *Ev << " at: " << *TheStore
953 NewCall->setDebugLoc(TheStore->getDebugLoc());
955 // Okay, the memset has been formed. Zap the original store and anything that
957 for (auto *I : Stores)
958 deleteDeadInstruction(I);
963 /// If the stored value is a strided load in the same loop with the same stride
964 /// this may be transformable into a memcpy. This kicks in for stuff like
965 /// for (i) A[i] = B[i];
966 bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
967 const SCEV *BECount) {
968 assert(SI->isUnordered() && "Expected only non-volatile non-ordered stores.");
970 Value *StorePtr = SI->getPointerOperand();
971 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
972 APInt Stride = getStoreStride(StoreEv);
973 unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
974 bool NegStride = StoreSize == -Stride;
976 // The store must be feeding a non-volatile load.
977 LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
978 assert(LI->isUnordered() && "Expected only non-volatile non-ordered loads.");
980 // See if the pointer expression is an AddRec like {base,+,1} on the current
981 // loop, which indicates a strided load. If we have something else, it's a
982 // random load we can't handle.
983 const SCEVAddRecExpr *LoadEv =
984 cast<SCEVAddRecExpr>(SE->getSCEV(LI->getPointerOperand()));
986 // The trip count of the loop and the base pointer of the addrec SCEV is
987 // guaranteed to be loop invariant, which means that it should dominate the
988 // header. This allows us to insert code for it in the preheader.
989 BasicBlock *Preheader = CurLoop->getLoopPreheader();
990 IRBuilder<> Builder(Preheader->getTerminator());
991 SCEVExpander Expander(*SE, *DL, "loop-idiom");
993 const SCEV *StrStart = StoreEv->getStart();
994 unsigned StrAS = SI->getPointerAddressSpace();
995 Type *IntPtrTy = Builder.getIntPtrTy(*DL, StrAS);
997 // Handle negative strided loops.
999 StrStart = getStartForNegStride(StrStart, BECount, IntPtrTy, StoreSize, SE);
1001 // Okay, we have a strided store "p[i]" of a loaded value. We can turn
1002 // this into a memcpy in the loop preheader now if we want. However, this
1003 // would be unsafe to do if there is anything else in the loop that may read
1004 // or write the memory region we're storing to. This includes the load that
1005 // feeds the stores. Check for an alias by generating the base address and
1006 // checking everything.
1007 Value *StoreBasePtr = Expander.expandCodeFor(
1008 StrStart, Builder.getInt8PtrTy(StrAS), Preheader->getTerminator());
1010 SmallPtrSet<Instruction *, 1> Stores;
1012 if (mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop, BECount,
1013 StoreSize, *AA, Stores)) {
1015 // If we generated new code for the base pointer, clean up.
1016 RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
1020 const SCEV *LdStart = LoadEv->getStart();
1021 unsigned LdAS = LI->getPointerAddressSpace();
1023 // Handle negative strided loops.
1025 LdStart = getStartForNegStride(LdStart, BECount, IntPtrTy, StoreSize, SE);
1027 // For a memcpy, we have to make sure that the input array is not being
1028 // mutated by the loop.
1029 Value *LoadBasePtr = Expander.expandCodeFor(
1030 LdStart, Builder.getInt8PtrTy(LdAS), Preheader->getTerminator());
1032 if (mayLoopAccessLocation(LoadBasePtr, ModRefInfo::Mod, CurLoop, BECount,
1033 StoreSize, *AA, Stores)) {
1035 // If we generated new code for the base pointer, clean up.
1036 RecursivelyDeleteTriviallyDeadInstructions(LoadBasePtr, TLI);
1037 RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
1041 if (avoidLIRForMultiBlockLoop())
1044 // Okay, everything is safe, we can transform this!
1046 const SCEV *NumBytesS =
1047 getNumBytes(BECount, IntPtrTy, StoreSize, CurLoop, DL, SE);
1050 Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
1052 CallInst *NewCall = nullptr;
1053 // Check whether to generate an unordered atomic memcpy:
1054 // If the load or store are atomic, then they must necessarily be unordered
1055 // by previous checks.
1056 if (!SI->isAtomic() && !LI->isAtomic())
1057 NewCall = Builder.CreateMemCpy(StoreBasePtr, SI->getAlignment(),
1058 LoadBasePtr, LI->getAlignment(), NumBytes);
1060 // We cannot allow unaligned ops for unordered load/store, so reject
1061 // anything where the alignment isn't at least the element size.
1062 unsigned Align = std::min(SI->getAlignment(), LI->getAlignment());
1063 if (Align < StoreSize)
1066 // If the element.atomic memcpy is not lowered into explicit
1067 // loads/stores later, then it will be lowered into an element-size
1068 // specific lib call. If the lib call doesn't exist for our store size, then
1069 // we shouldn't generate the memcpy.
1070 if (StoreSize > TTI->getAtomicMemIntrinsicMaxElementSize())
1074 // Note that unordered atomic loads/stores are *required* by the spec to
1075 // have an alignment but non-atomic loads/stores may not.
1076 NewCall = Builder.CreateElementUnorderedAtomicMemCpy(
1077 StoreBasePtr, SI->getAlignment(), LoadBasePtr, LI->getAlignment(),
1078 NumBytes, StoreSize);
1080 NewCall->setDebugLoc(SI->getDebugLoc());
1082 LLVM_DEBUG(dbgs() << " Formed memcpy: " << *NewCall << "\n"
1083 << " from load ptr=" << *LoadEv << " at: " << *LI << "\n"
1084 << " from store ptr=" << *StoreEv << " at: " << *SI
1087 // Okay, the memcpy has been formed. Zap the original store and anything that
1089 deleteDeadInstruction(SI);
1094 // When compiling for codesize we avoid idiom recognition for a multi-block loop
1095 // unless it is a loop_memset idiom or a memset/memcpy idiom in a nested loop.
1097 bool LoopIdiomRecognize::avoidLIRForMultiBlockLoop(bool IsMemset,
1098 bool IsLoopMemset) {
1099 if (ApplyCodeSizeHeuristics && CurLoop->getNumBlocks() > 1) {
1100 if (!CurLoop->getParentLoop() && (!IsMemset || !IsLoopMemset)) {
1101 LLVM_DEBUG(dbgs() << " " << CurLoop->getHeader()->getParent()->getName()
1102 << " : LIR " << (IsMemset ? "Memset" : "Memcpy")
1103 << " avoided: multi-block top-level loop\n");
1111 bool LoopIdiomRecognize::runOnNoncountableLoop() {
1112 return recognizePopcount() || recognizeAndInsertFFS();
1115 /// Check if the given conditional branch is based on the comparison between
1116 /// a variable and zero, and if the variable is non-zero or zero (JmpOnZero is
1117 /// true), the control yields to the loop entry. If the branch matches the
1118 /// behavior, the variable involved in the comparison is returned. This function
1119 /// will be called to see if the precondition and postcondition of the loop are
1120 /// in desirable form.
1121 static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
1122 bool JmpOnZero = false) {
1123 if (!BI || !BI->isConditional())
1126 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
1130 ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
1131 if (!CmpZero || !CmpZero->isZero())
1134 BasicBlock *TrueSucc = BI->getSuccessor(0);
1135 BasicBlock *FalseSucc = BI->getSuccessor(1);
1137 std::swap(TrueSucc, FalseSucc);
1139 ICmpInst::Predicate Pred = Cond->getPredicate();
1140 if ((Pred == ICmpInst::ICMP_NE && TrueSucc == LoopEntry) ||
1141 (Pred == ICmpInst::ICMP_EQ && FalseSucc == LoopEntry))
1142 return Cond->getOperand(0);
1147 // Check if the recurrence variable `VarX` is in the right form to create
1148 // the idiom. Returns the value coerced to a PHINode if so.
1149 static PHINode *getRecurrenceVar(Value *VarX, Instruction *DefX,
1150 BasicBlock *LoopEntry) {
1151 auto *PhiX = dyn_cast<PHINode>(VarX);
1152 if (PhiX && PhiX->getParent() == LoopEntry &&
1153 (PhiX->getOperand(0) == DefX || PhiX->getOperand(1) == DefX))
1158 /// Return true iff the idiom is detected in the loop.
1161 /// 1) \p CntInst is set to the instruction counting the population bit.
1162 /// 2) \p CntPhi is set to the corresponding phi node.
1163 /// 3) \p Var is set to the value whose population bits are being counted.
1165 /// The core idiom we are trying to detect is:
1168 /// goto loop-exit // the precondition of the loop
1169 /// cnt0 = init-val;
1171 /// x1 = phi (x0, x2);
1172 /// cnt1 = phi(cnt0, cnt2);
1174 /// cnt2 = cnt1 + 1;
1176 /// x2 = x1 & (x1 - 1);
1178 /// } while(x != 0);
1182 static bool detectPopcountIdiom(Loop *CurLoop, BasicBlock *PreCondBB,
1183 Instruction *&CntInst, PHINode *&CntPhi,
1185 // step 1: Check to see if the look-back branch match this pattern:
1186 // "if (a!=0) goto loop-entry".
1187 BasicBlock *LoopEntry;
1188 Instruction *DefX2, *CountInst;
1189 Value *VarX1, *VarX0;
1190 PHINode *PhiX, *CountPhi;
1192 DefX2 = CountInst = nullptr;
1193 VarX1 = VarX0 = nullptr;
1194 PhiX = CountPhi = nullptr;
1195 LoopEntry = *(CurLoop->block_begin());
1197 // step 1: Check if the loop-back branch is in desirable form.
1199 if (Value *T = matchCondition(
1200 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
1201 DefX2 = dyn_cast<Instruction>(T);
1206 // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
1208 if (!DefX2 || DefX2->getOpcode() != Instruction::And)
1211 BinaryOperator *SubOneOp;
1213 if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
1214 VarX1 = DefX2->getOperand(1);
1216 VarX1 = DefX2->getOperand(0);
1217 SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
1219 if (!SubOneOp || SubOneOp->getOperand(0) != VarX1)
1222 ConstantInt *Dec = dyn_cast<ConstantInt>(SubOneOp->getOperand(1));
1224 !((SubOneOp->getOpcode() == Instruction::Sub && Dec->isOne()) ||
1225 (SubOneOp->getOpcode() == Instruction::Add &&
1226 Dec->isMinusOne()))) {
1231 // step 3: Check the recurrence of variable X
1232 PhiX = getRecurrenceVar(VarX1, DefX2, LoopEntry);
1236 // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
1238 CountInst = nullptr;
1239 for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI()->getIterator(),
1240 IterE = LoopEntry->end();
1241 Iter != IterE; Iter++) {
1242 Instruction *Inst = &*Iter;
1243 if (Inst->getOpcode() != Instruction::Add)
1246 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
1247 if (!Inc || !Inc->isOne())
1250 PHINode *Phi = getRecurrenceVar(Inst->getOperand(0), Inst, LoopEntry);
1254 // Check if the result of the instruction is live of the loop.
1255 bool LiveOutLoop = false;
1256 for (User *U : Inst->users()) {
1257 if ((cast<Instruction>(U))->getParent() != LoopEntry) {
1274 // step 5: check if the precondition is in this form:
1275 // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
1277 auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1278 Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
1279 if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
1282 CntInst = CountInst;
1290 /// Return true if the idiom is detected in the loop.
1293 /// 1) \p CntInst is set to the instruction Counting Leading Zeros (CTLZ)
1294 /// or nullptr if there is no such.
1295 /// 2) \p CntPhi is set to the corresponding phi node
1296 /// or nullptr if there is no such.
1297 /// 3) \p Var is set to the value whose CTLZ could be used.
1298 /// 4) \p DefX is set to the instruction calculating Loop exit condition.
1300 /// The core idiom we are trying to detect is:
1303 /// goto loop-exit // the precondition of the loop
1304 /// cnt0 = init-val;
1306 /// x = phi (x0, x.next); //PhiX
1307 /// cnt = phi(cnt0, cnt.next);
1309 /// cnt.next = cnt + 1;
1311 /// x.next = x >> 1; // DefX
1313 /// } while(x.next != 0);
1317 static bool detectShiftUntilZeroIdiom(Loop *CurLoop, const DataLayout &DL,
1318 Intrinsic::ID &IntrinID, Value *&InitX,
1319 Instruction *&CntInst, PHINode *&CntPhi,
1320 Instruction *&DefX) {
1321 BasicBlock *LoopEntry;
1322 Value *VarX = nullptr;
1327 LoopEntry = *(CurLoop->block_begin());
1329 // step 1: Check if the loop-back branch is in desirable form.
1330 if (Value *T = matchCondition(
1331 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
1332 DefX = dyn_cast<Instruction>(T);
1336 // step 2: detect instructions corresponding to "x.next = x >> 1 or x << 1"
1337 if (!DefX || !DefX->isShift())
1339 IntrinID = DefX->getOpcode() == Instruction::Shl ? Intrinsic::cttz :
1341 ConstantInt *Shft = dyn_cast<ConstantInt>(DefX->getOperand(1));
1342 if (!Shft || !Shft->isOne())
1344 VarX = DefX->getOperand(0);
1346 // step 3: Check the recurrence of variable X
1347 PHINode *PhiX = getRecurrenceVar(VarX, DefX, LoopEntry);
1351 InitX = PhiX->getIncomingValueForBlock(CurLoop->getLoopPreheader());
1353 // Make sure the initial value can't be negative otherwise the ashr in the
1354 // loop might never reach zero which would make the loop infinite.
1355 if (DefX->getOpcode() == Instruction::AShr && !isKnownNonNegative(InitX, DL))
1358 // step 4: Find the instruction which count the CTLZ: cnt.next = cnt + 1
1359 // TODO: We can skip the step. If loop trip count is known (CTLZ),
1360 // then all uses of "cnt.next" could be optimized to the trip count
1361 // plus "cnt0". Currently it is not optimized.
1362 // This step could be used to detect POPCNT instruction:
1363 // cnt.next = cnt + (x.next & 1)
1364 for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI()->getIterator(),
1365 IterE = LoopEntry->end();
1366 Iter != IterE; Iter++) {
1367 Instruction *Inst = &*Iter;
1368 if (Inst->getOpcode() != Instruction::Add)
1371 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
1372 if (!Inc || !Inc->isOne())
1375 PHINode *Phi = getRecurrenceVar(Inst->getOperand(0), Inst, LoopEntry);
1389 /// Recognize CTLZ or CTTZ idiom in a non-countable loop and convert the loop
1390 /// to countable (with CTLZ / CTTZ trip count). If CTLZ / CTTZ inserted as a new
1391 /// trip count returns true; otherwise, returns false.
1392 bool LoopIdiomRecognize::recognizeAndInsertFFS() {
1393 // Give up if the loop has multiple blocks or multiple backedges.
1394 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
1397 Intrinsic::ID IntrinID;
1399 Instruction *DefX = nullptr;
1400 PHINode *CntPhi = nullptr;
1401 Instruction *CntInst = nullptr;
1402 // Help decide if transformation is profitable. For ShiftUntilZero idiom,
1403 // this is always 6.
1404 size_t IdiomCanonicalSize = 6;
1406 if (!detectShiftUntilZeroIdiom(CurLoop, *DL, IntrinID, InitX,
1407 CntInst, CntPhi, DefX))
1410 bool IsCntPhiUsedOutsideLoop = false;
1411 for (User *U : CntPhi->users())
1412 if (!CurLoop->contains(cast<Instruction>(U))) {
1413 IsCntPhiUsedOutsideLoop = true;
1416 bool IsCntInstUsedOutsideLoop = false;
1417 for (User *U : CntInst->users())
1418 if (!CurLoop->contains(cast<Instruction>(U))) {
1419 IsCntInstUsedOutsideLoop = true;
1422 // If both CntInst and CntPhi are used outside the loop the profitability
1424 if (IsCntInstUsedOutsideLoop && IsCntPhiUsedOutsideLoop)
1427 // For some CPUs result of CTLZ(X) intrinsic is undefined
1428 // when X is 0. If we can not guarantee X != 0, we need to check this
1430 bool ZeroCheck = false;
1431 // It is safe to assume Preheader exist as it was checked in
1432 // parent function RunOnLoop.
1433 BasicBlock *PH = CurLoop->getLoopPreheader();
1435 // If we are using the count instruction outside the loop, make sure we
1436 // have a zero check as a precondition. Without the check the loop would run
1437 // one iteration for before any check of the input value. This means 0 and 1
1438 // would have identical behavior in the original loop and thus
1439 if (!IsCntPhiUsedOutsideLoop) {
1440 auto *PreCondBB = PH->getSinglePredecessor();
1443 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1446 if (matchCondition(PreCondBI, PH) != InitX)
1451 // Check if CTLZ / CTTZ intrinsic is profitable. Assume it is always
1452 // profitable if we delete the loop.
1454 // the loop has only 6 instructions:
1455 // %n.addr.0 = phi [ %n, %entry ], [ %shr, %while.cond ]
1456 // %i.0 = phi [ %i0, %entry ], [ %inc, %while.cond ]
1457 // %shr = ashr %n.addr.0, 1
1458 // %tobool = icmp eq %shr, 0
1459 // %inc = add nsw %i.0, 1
1462 const Value *Args[] =
1463 {InitX, ZeroCheck ? ConstantInt::getTrue(InitX->getContext())
1464 : ConstantInt::getFalse(InitX->getContext())};
1465 if (CurLoop->getHeader()->size() != IdiomCanonicalSize &&
1466 TTI->getIntrinsicCost(IntrinID, InitX->getType(), Args) >
1467 TargetTransformInfo::TCC_Basic)
1470 transformLoopToCountable(IntrinID, PH, CntInst, CntPhi, InitX, DefX,
1471 DefX->getDebugLoc(), ZeroCheck,
1472 IsCntPhiUsedOutsideLoop);
1476 /// Recognizes a population count idiom in a non-countable loop.
1478 /// If detected, transforms the relevant code to issue the popcount intrinsic
1479 /// function call, and returns true; otherwise, returns false.
1480 bool LoopIdiomRecognize::recognizePopcount() {
1481 if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
1484 // Counting population are usually conducted by few arithmetic instructions.
1485 // Such instructions can be easily "absorbed" by vacant slots in a
1486 // non-compact loop. Therefore, recognizing popcount idiom only makes sense
1487 // in a compact loop.
1489 // Give up if the loop has multiple blocks or multiple backedges.
1490 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
1493 BasicBlock *LoopBody = *(CurLoop->block_begin());
1494 if (LoopBody->size() >= 20) {
1495 // The loop is too big, bail out.
1499 // It should have a preheader containing nothing but an unconditional branch.
1500 BasicBlock *PH = CurLoop->getLoopPreheader();
1501 if (!PH || &PH->front() != PH->getTerminator())
1503 auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
1504 if (!EntryBI || EntryBI->isConditional())
1507 // It should have a precondition block where the generated popcount intrinsic
1508 // function can be inserted.
1509 auto *PreCondBB = PH->getSinglePredecessor();
1512 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
1513 if (!PreCondBI || PreCondBI->isUnconditional())
1516 Instruction *CntInst;
1519 if (!detectPopcountIdiom(CurLoop, PreCondBB, CntInst, CntPhi, Val))
1522 transformLoopToPopcount(PreCondBB, CntInst, CntPhi, Val);
1526 static CallInst *createPopcntIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
1527 const DebugLoc &DL) {
1528 Value *Ops[] = {Val};
1529 Type *Tys[] = {Val->getType()};
1531 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
1532 Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
1533 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
1534 CI->setDebugLoc(DL);
1539 static CallInst *createFFSIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
1540 const DebugLoc &DL, bool ZeroCheck,
1541 Intrinsic::ID IID) {
1542 Value *Ops[] = {Val, ZeroCheck ? IRBuilder.getTrue() : IRBuilder.getFalse()};
1543 Type *Tys[] = {Val->getType()};
1545 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
1546 Value *Func = Intrinsic::getDeclaration(M, IID, Tys);
1547 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
1548 CI->setDebugLoc(DL);
1553 /// Transform the following loop (Using CTLZ, CTTZ is similar):
1555 /// CntPhi = PHI [Cnt0, CntInst]
1556 /// PhiX = PHI [InitX, DefX]
1557 /// CntInst = CntPhi + 1
1558 /// DefX = PhiX >> 1
1560 /// Br: loop if (DefX != 0)
1561 /// Use(CntPhi) or Use(CntInst)
1564 /// If CntPhi used outside the loop:
1565 /// CountPrev = BitWidth(InitX) - CTLZ(InitX >> 1)
1566 /// Count = CountPrev + 1
1568 /// Count = BitWidth(InitX) - CTLZ(InitX)
1570 /// CntPhi = PHI [Cnt0, CntInst]
1571 /// PhiX = PHI [InitX, DefX]
1572 /// PhiCount = PHI [Count, Dec]
1573 /// CntInst = CntPhi + 1
1574 /// DefX = PhiX >> 1
1575 /// Dec = PhiCount - 1
1577 /// Br: loop if (Dec != 0)
1578 /// Use(CountPrev + Cnt0) // Use(CntPhi)
1580 /// Use(Count + Cnt0) // Use(CntInst)
1582 /// If LOOP_BODY is empty the loop will be deleted.
1583 /// If CntInst and DefX are not used in LOOP_BODY they will be removed.
1584 void LoopIdiomRecognize::transformLoopToCountable(
1585 Intrinsic::ID IntrinID, BasicBlock *Preheader, Instruction *CntInst,
1586 PHINode *CntPhi, Value *InitX, Instruction *DefX, const DebugLoc &DL,
1587 bool ZeroCheck, bool IsCntPhiUsedOutsideLoop) {
1588 BranchInst *PreheaderBr = cast<BranchInst>(Preheader->getTerminator());
1590 // Step 1: Insert the CTLZ/CTTZ instruction at the end of the preheader block
1591 IRBuilder<> Builder(PreheaderBr);
1592 Builder.SetCurrentDebugLocation(DL);
1593 Value *FFS, *Count, *CountPrev, *NewCount, *InitXNext;
1595 // Count = BitWidth - CTLZ(InitX);
1596 // If there are uses of CntPhi create:
1597 // CountPrev = BitWidth - CTLZ(InitX >> 1);
1598 if (IsCntPhiUsedOutsideLoop) {
1599 if (DefX->getOpcode() == Instruction::AShr)
1601 Builder.CreateAShr(InitX, ConstantInt::get(InitX->getType(), 1));
1602 else if (DefX->getOpcode() == Instruction::LShr)
1604 Builder.CreateLShr(InitX, ConstantInt::get(InitX->getType(), 1));
1605 else if (DefX->getOpcode() == Instruction::Shl) // cttz
1607 Builder.CreateShl(InitX, ConstantInt::get(InitX->getType(), 1));
1609 llvm_unreachable("Unexpected opcode!");
1612 FFS = createFFSIntrinsic(Builder, InitXNext, DL, ZeroCheck, IntrinID);
1613 Count = Builder.CreateSub(
1614 ConstantInt::get(FFS->getType(),
1615 FFS->getType()->getIntegerBitWidth()),
1617 if (IsCntPhiUsedOutsideLoop) {
1619 Count = Builder.CreateAdd(
1621 ConstantInt::get(CountPrev->getType(), 1));
1624 NewCount = Builder.CreateZExtOrTrunc(
1625 IsCntPhiUsedOutsideLoop ? CountPrev : Count,
1626 cast<IntegerType>(CntInst->getType()));
1628 // If the counter's initial value is not zero, insert Add Inst.
1629 Value *CntInitVal = CntPhi->getIncomingValueForBlock(Preheader);
1630 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
1631 if (!InitConst || !InitConst->isZero())
1632 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
1634 // Step 2: Insert new IV and loop condition:
1637 // PhiCount = PHI [Count, Dec]
1639 // Dec = PhiCount - 1
1641 // Br: loop if (Dec != 0)
1642 BasicBlock *Body = *(CurLoop->block_begin());
1643 auto *LbBr = cast<BranchInst>(Body->getTerminator());
1644 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
1645 Type *Ty = Count->getType();
1647 PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
1649 Builder.SetInsertPoint(LbCond);
1650 Instruction *TcDec = cast<Instruction>(
1651 Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
1652 "tcdec", false, true));
1654 TcPhi->addIncoming(Count, Preheader);
1655 TcPhi->addIncoming(TcDec, Body);
1657 CmpInst::Predicate Pred =
1658 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_NE : CmpInst::ICMP_EQ;
1659 LbCond->setPredicate(Pred);
1660 LbCond->setOperand(0, TcDec);
1661 LbCond->setOperand(1, ConstantInt::get(Ty, 0));
1663 // Step 3: All the references to the original counter outside
1664 // the loop are replaced with the NewCount
1665 if (IsCntPhiUsedOutsideLoop)
1666 CntPhi->replaceUsesOutsideBlock(NewCount, Body);
1668 CntInst->replaceUsesOutsideBlock(NewCount, Body);
1670 // step 4: Forget the "non-computable" trip-count SCEV associated with the
1671 // loop. The loop would otherwise not be deleted even if it becomes empty.
1672 SE->forgetLoop(CurLoop);
1675 void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
1676 Instruction *CntInst,
1677 PHINode *CntPhi, Value *Var) {
1678 BasicBlock *PreHead = CurLoop->getLoopPreheader();
1679 auto *PreCondBr = cast<BranchInst>(PreCondBB->getTerminator());
1680 const DebugLoc &DL = CntInst->getDebugLoc();
1682 // Assuming before transformation, the loop is following:
1683 // if (x) // the precondition
1684 // do { cnt++; x &= x - 1; } while(x);
1686 // Step 1: Insert the ctpop instruction at the end of the precondition block
1687 IRBuilder<> Builder(PreCondBr);
1688 Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
1690 PopCnt = createPopcntIntrinsic(Builder, Var, DL);
1691 NewCount = PopCntZext =
1692 Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
1694 if (NewCount != PopCnt)
1695 (cast<Instruction>(NewCount))->setDebugLoc(DL);
1697 // TripCnt is exactly the number of iterations the loop has
1700 // If the population counter's initial value is not zero, insert Add Inst.
1701 Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
1702 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
1703 if (!InitConst || !InitConst->isZero()) {
1704 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
1705 (cast<Instruction>(NewCount))->setDebugLoc(DL);
1709 // Step 2: Replace the precondition from "if (x == 0) goto loop-exit" to
1710 // "if (NewCount == 0) loop-exit". Without this change, the intrinsic
1711 // function would be partial dead code, and downstream passes will drag
1712 // it back from the precondition block to the preheader.
1714 ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
1716 Value *Opnd0 = PopCntZext;
1717 Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
1718 if (PreCond->getOperand(0) != Var)
1719 std::swap(Opnd0, Opnd1);
1721 ICmpInst *NewPreCond = cast<ICmpInst>(
1722 Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
1723 PreCondBr->setCondition(NewPreCond);
1725 RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
1728 // Step 3: Note that the population count is exactly the trip count of the
1729 // loop in question, which enable us to convert the loop from noncountable
1730 // loop into a countable one. The benefit is twofold:
1732 // - If the loop only counts population, the entire loop becomes dead after
1733 // the transformation. It is a lot easier to prove a countable loop dead
1734 // than to prove a noncountable one. (In some C dialects, an infinite loop
1735 // isn't dead even if it computes nothing useful. In general, DCE needs
1736 // to prove a noncountable loop finite before safely delete it.)
1738 // - If the loop also performs something else, it remains alive.
1739 // Since it is transformed to countable form, it can be aggressively
1740 // optimized by some optimizations which are in general not applicable
1741 // to a noncountable loop.
1743 // After this step, this loop (conceptually) would look like following:
1744 // newcnt = __builtin_ctpop(x);
1747 // do { cnt++; x &= x-1; t--) } while (t > 0);
1748 BasicBlock *Body = *(CurLoop->block_begin());
1750 auto *LbBr = cast<BranchInst>(Body->getTerminator());
1751 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
1752 Type *Ty = TripCnt->getType();
1754 PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
1756 Builder.SetInsertPoint(LbCond);
1757 Instruction *TcDec = cast<Instruction>(
1758 Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
1759 "tcdec", false, true));
1761 TcPhi->addIncoming(TripCnt, PreHead);
1762 TcPhi->addIncoming(TcDec, Body);
1764 CmpInst::Predicate Pred =
1765 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
1766 LbCond->setPredicate(Pred);
1767 LbCond->setOperand(0, TcDec);
1768 LbCond->setOperand(1, ConstantInt::get(Ty, 0));
1771 // Step 4: All the references to the original population counter outside
1772 // the loop are replaced with the NewCount -- the value returned from
1773 // __builtin_ctpop().
1774 CntInst->replaceUsesOutsideBlock(NewCount, Body);
1776 // step 5: Forget the "non-computable" trip-count SCEV associated with the
1777 // loop. The loop would otherwise not be deleted even if it becomes empty.
1778 SE->forgetLoop(CurLoop);