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 //===----------------------------------------------------------------------===//
18 // Future loop memory idioms to recognize:
19 // memcmp, memmove, strlen, etc.
20 // Future floating point idioms to recognize in -ffast-math mode:
22 // Future integer operation idioms to recognize:
25 // Beware that isel's default lowering for ctpop is highly inefficient for
26 // i64 and larger types when i64 is legal and the value has few bits set. It
27 // would be good to enhance isel to emit a loop for ctpop in this case.
29 // We should enhance the memset/memcpy recognition to handle multiple stores in
30 // the loop. This would handle things like:
31 // void foo(_Complex float *P)
32 // for (i) { __real__(*P) = 0; __imag__(*P) = 0; }
34 // This could recognize common matrix multiplies and dot product idioms and
35 // replace them with calls to BLAS (if linked in??).
37 //===----------------------------------------------------------------------===//
39 #include "llvm/Transforms/Scalar.h"
40 #include "llvm/ADT/Statistic.h"
41 #include "llvm/Analysis/AliasAnalysis.h"
42 #include "llvm/Analysis/BasicAliasAnalysis.h"
43 #include "llvm/Analysis/GlobalsModRef.h"
44 #include "llvm/Analysis/LoopPass.h"
45 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
46 #include "llvm/Analysis/ScalarEvolutionExpander.h"
47 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
48 #include "llvm/Analysis/TargetLibraryInfo.h"
49 #include "llvm/Analysis/TargetTransformInfo.h"
50 #include "llvm/Analysis/ValueTracking.h"
51 #include "llvm/IR/DataLayout.h"
52 #include "llvm/IR/Dominators.h"
53 #include "llvm/IR/IRBuilder.h"
54 #include "llvm/IR/IntrinsicInst.h"
55 #include "llvm/IR/Module.h"
56 #include "llvm/Support/Debug.h"
57 #include "llvm/Support/raw_ostream.h"
58 #include "llvm/Transforms/Utils/Local.h"
61 #define DEBUG_TYPE "loop-idiom"
63 STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
64 STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
68 class LoopIdiomRecognize : public LoopPass {
74 TargetLibraryInfo *TLI;
75 const TargetTransformInfo *TTI;
80 explicit LoopIdiomRecognize() : LoopPass(ID) {
81 initializeLoopIdiomRecognizePass(*PassRegistry::getPassRegistry());
84 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
86 /// This transformation requires natural loop information & requires that
87 /// loop preheaders be inserted into the CFG.
89 void getAnalysisUsage(AnalysisUsage &AU) const override {
90 AU.addRequired<LoopInfoWrapperPass>();
91 AU.addPreserved<LoopInfoWrapperPass>();
92 AU.addRequiredID(LoopSimplifyID);
93 AU.addPreservedID(LoopSimplifyID);
94 AU.addRequiredID(LCSSAID);
95 AU.addPreservedID(LCSSAID);
96 AU.addRequired<AAResultsWrapperPass>();
97 AU.addPreserved<AAResultsWrapperPass>();
98 AU.addRequired<ScalarEvolutionWrapperPass>();
99 AU.addPreserved<ScalarEvolutionWrapperPass>();
100 AU.addPreserved<SCEVAAWrapperPass>();
101 AU.addRequired<DominatorTreeWrapperPass>();
102 AU.addPreserved<DominatorTreeWrapperPass>();
103 AU.addRequired<TargetLibraryInfoWrapperPass>();
104 AU.addRequired<TargetTransformInfoWrapperPass>();
105 AU.addPreserved<BasicAAWrapperPass>();
106 AU.addPreserved<GlobalsAAWrapperPass>();
110 typedef SmallVector<StoreInst *, 8> StoreList;
113 /// \name Countable Loop Idiom Handling
116 bool runOnCountableLoop();
117 bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
118 SmallVectorImpl<BasicBlock *> &ExitBlocks);
120 void collectStores(BasicBlock *BB);
121 bool isLegalStore(StoreInst *SI);
122 bool processLoopStore(StoreInst *SI, const SCEV *BECount);
123 bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
125 bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
126 unsigned StoreAlignment, Value *SplatValue,
127 Instruction *TheStore, const SCEVAddRecExpr *Ev,
128 const SCEV *BECount, bool NegStride);
129 bool processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
130 const SCEVAddRecExpr *StoreEv,
131 const SCEV *BECount, bool NegStride);
134 /// \name Noncountable Loop Idiom Handling
137 bool runOnNoncountableLoop();
139 bool recognizePopcount();
140 void transformLoopToPopcount(BasicBlock *PreCondBB, Instruction *CntInst,
141 PHINode *CntPhi, Value *Var);
146 } // End anonymous namespace.
148 char LoopIdiomRecognize::ID = 0;
149 INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
151 INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
152 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
153 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
154 INITIALIZE_PASS_DEPENDENCY(LCSSA)
155 INITIALIZE_PASS_DEPENDENCY(ScalarEvolutionWrapperPass)
156 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
157 INITIALIZE_PASS_DEPENDENCY(BasicAAWrapperPass)
158 INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
159 INITIALIZE_PASS_DEPENDENCY(GlobalsAAWrapperPass)
160 INITIALIZE_PASS_DEPENDENCY(SCEVAAWrapperPass)
161 INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
162 INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
165 Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
167 /// deleteDeadInstruction - Delete this instruction. Before we do, go through
168 /// and zero out all the operands of this instruction. If any of them become
169 /// dead, delete them and the computation tree that feeds them.
171 static void deleteDeadInstruction(Instruction *I,
172 const TargetLibraryInfo *TLI) {
173 SmallVector<Value *, 16> Operands(I->value_op_begin(), I->value_op_end());
174 I->replaceAllUsesWith(UndefValue::get(I->getType()));
175 I->eraseFromParent();
176 for (Value *Op : Operands)
177 RecursivelyDeleteTriviallyDeadInstructions(Op, TLI);
180 //===----------------------------------------------------------------------===//
182 // Implementation of LoopIdiomRecognize
184 //===----------------------------------------------------------------------===//
186 bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
187 if (skipOptnoneFunction(L))
191 // If the loop could not be converted to canonical form, it must have an
192 // indirectbr in it, just give up.
193 if (!L->getLoopPreheader())
196 // Disable loop idiom recognition if the function's name is a common idiom.
197 StringRef Name = L->getHeader()->getParent()->getName();
198 if (Name == "memset" || Name == "memcpy")
201 AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
202 DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
203 LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
204 SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
205 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
206 TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
207 *CurLoop->getHeader()->getParent());
208 DL = &CurLoop->getHeader()->getModule()->getDataLayout();
210 if (SE->hasLoopInvariantBackedgeTakenCount(L))
211 return runOnCountableLoop();
213 return runOnNoncountableLoop();
216 bool LoopIdiomRecognize::runOnCountableLoop() {
217 const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
218 assert(!isa<SCEVCouldNotCompute>(BECount) &&
219 "runOnCountableLoop() called on a loop without a predictable"
220 "backedge-taken count");
222 // If this loop executes exactly one time, then it should be peeled, not
223 // optimized by this pass.
224 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
225 if (BECst->getValue()->getValue() == 0)
228 SmallVector<BasicBlock *, 8> ExitBlocks;
229 CurLoop->getUniqueExitBlocks(ExitBlocks);
231 DEBUG(dbgs() << "loop-idiom Scanning: F["
232 << CurLoop->getHeader()->getParent()->getName() << "] Loop %"
233 << CurLoop->getHeader()->getName() << "\n");
235 bool MadeChange = false;
236 // Scan all the blocks in the loop that are not in subloops.
237 for (auto *BB : CurLoop->getBlocks()) {
238 // Ignore blocks in subloops.
239 if (LI->getLoopFor(BB) != CurLoop)
242 MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
247 static unsigned getStoreSizeInBytes(StoreInst *SI, const DataLayout *DL) {
248 uint64_t SizeInBits = DL->getTypeSizeInBits(SI->getValueOperand()->getType());
249 assert(((SizeInBits & 7) || (SizeInBits >> 32) == 0) &&
250 "Don't overflow unsigned.");
251 return (unsigned)SizeInBits >> 3;
254 static unsigned getStoreStride(const SCEVAddRecExpr *StoreEv) {
255 const SCEVConstant *ConstStride = cast<SCEVConstant>(StoreEv->getOperand(1));
256 return ConstStride->getValue()->getValue().getZExtValue();
259 bool LoopIdiomRecognize::isLegalStore(StoreInst *SI) {
260 // Don't touch volatile stores.
264 Value *StoredVal = SI->getValueOperand();
265 Value *StorePtr = SI->getPointerOperand();
267 // Reject stores that are so large that they overflow an unsigned.
268 uint64_t SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
269 if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
272 // See if the pointer expression is an AddRec like {base,+,1} on the current
273 // loop, which indicates a strided store. If we have something else, it's a
274 // random store we can't handle.
275 const SCEVAddRecExpr *StoreEv =
276 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
277 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
280 // Check to see if we have a constant stride.
281 if (!isa<SCEVConstant>(StoreEv->getOperand(1)))
287 void LoopIdiomRecognize::collectStores(BasicBlock *BB) {
289 for (Instruction &I : *BB) {
290 StoreInst *SI = dyn_cast<StoreInst>(&I);
294 // Make sure this is a strided store with a constant stride.
295 if (!isLegalStore(SI))
298 // Save the store locations.
299 StoreRefs.push_back(SI);
303 /// runOnLoopBlock - Process the specified block, which lives in a counted loop
304 /// with the specified backedge count. This block is known to be in the current
305 /// loop and not in any subloops.
306 bool LoopIdiomRecognize::runOnLoopBlock(
307 BasicBlock *BB, const SCEV *BECount,
308 SmallVectorImpl<BasicBlock *> &ExitBlocks) {
309 // We can only promote stores in this block if they are unconditionally
310 // executed in the loop. For a block to be unconditionally executed, it has
311 // to dominate all the exit blocks of the loop. Verify this now.
312 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
313 if (!DT->dominates(BB, ExitBlocks[i]))
316 bool MadeChange = false;
317 // Look for store instructions, which may be optimized to memset/memcpy.
319 for (auto &SI : StoreRefs)
320 MadeChange |= processLoopStore(SI, BECount);
322 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
323 Instruction *Inst = &*I++;
324 // Look for memset instructions, which may be optimized to a larger memset.
325 if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst)) {
327 if (!processLoopMemSet(MSI, BECount))
331 // If processing the memset invalidated our iterator, start over from the
342 /// processLoopStore - See if this store can be promoted to a memset or memcpy.
343 bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
344 assert(SI->isSimple() && "Expected only non-volatile stores.");
346 Value *StoredVal = SI->getValueOperand();
347 Value *StorePtr = SI->getPointerOperand();
349 // Check to see if the stride matches the size of the store. If so, then we
350 // know that every byte is touched in the loop.
351 const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
352 unsigned Stride = getStoreStride(StoreEv);
353 unsigned StoreSize = getStoreSizeInBytes(SI, DL);
354 if (StoreSize != Stride && StoreSize != -Stride)
357 bool NegStride = StoreSize == -Stride;
359 // See if we can optimize just this store in isolation.
360 if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
361 StoredVal, SI, StoreEv, BECount, NegStride))
364 // Optimize the store into a memcpy, if it feeds an similarly strided load.
365 return processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, BECount, NegStride);
368 /// processLoopMemSet - See if this memset can be promoted to a large memset.
369 bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
370 const SCEV *BECount) {
371 // We can only handle non-volatile memsets with a constant size.
372 if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength()))
375 // If we're not allowed to hack on memset, we fail.
376 if (!TLI->has(LibFunc::memset))
379 Value *Pointer = MSI->getDest();
381 // See if the pointer expression is an AddRec like {base,+,1} on the current
382 // loop, which indicates a strided store. If we have something else, it's a
383 // random store we can't handle.
384 const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
385 if (!Ev || Ev->getLoop() != CurLoop || !Ev->isAffine())
388 // Reject memsets that are so large that they overflow an unsigned.
389 uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
390 if ((SizeInBytes >> 32) != 0)
393 // Check to see if the stride matches the size of the memset. If so, then we
394 // know that every byte is touched in the loop.
395 const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
397 // TODO: Could also handle negative stride here someday, that will require the
398 // validity check in mayLoopAccessLocation to be updated though.
399 if (!Stride || MSI->getLength() != Stride->getValue())
402 return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
403 MSI->getAlignment(), MSI->getValue(), MSI, Ev,
404 BECount, /*NegStride=*/false);
407 /// mayLoopAccessLocation - Return true if the specified loop might access the
408 /// specified pointer location, which is a loop-strided access. The 'Access'
409 /// argument specifies what the verboten forms of access are (read or write).
410 static bool mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
411 const SCEV *BECount, unsigned StoreSize,
413 Instruction *IgnoredStore) {
414 // Get the location that may be stored across the loop. Since the access is
415 // strided positively through memory, we say that the modified location starts
416 // at the pointer and has infinite size.
417 uint64_t AccessSize = MemoryLocation::UnknownSize;
419 // If the loop iterates a fixed number of times, we can refine the access size
420 // to be exactly the size of the memset, which is (BECount+1)*StoreSize
421 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
422 AccessSize = (BECst->getValue()->getZExtValue() + 1) * StoreSize;
424 // TODO: For this to be really effective, we have to dive into the pointer
425 // operand in the store. Store to &A[i] of 100 will always return may alias
426 // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
427 // which will then no-alias a store to &A[100].
428 MemoryLocation StoreLoc(Ptr, AccessSize);
430 for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
432 for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
433 if (&*I != IgnoredStore && (AA.getModRefInfo(&*I, StoreLoc) & Access))
439 /// getMemSetPatternValue - If a strided store of the specified value is safe to
440 /// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
441 /// be passed in. Otherwise, return null.
443 /// Note that we don't ever attempt to use memset_pattern8 or 4, because these
444 /// just replicate their input array and then pass on to memset_pattern16.
445 static Constant *getMemSetPatternValue(Value *V, const DataLayout *DL) {
446 // If the value isn't a constant, we can't promote it to being in a constant
447 // array. We could theoretically do a store to an alloca or something, but
448 // that doesn't seem worthwhile.
449 Constant *C = dyn_cast<Constant>(V);
453 // Only handle simple values that are a power of two bytes in size.
454 uint64_t Size = DL->getTypeSizeInBits(V->getType());
455 if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
458 // Don't care enough about darwin/ppc to implement this.
459 if (DL->isBigEndian())
462 // Convert to size in bytes.
465 // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
466 // if the top and bottom are the same (e.g. for vectors and large integers).
470 // If the constant is exactly 16 bytes, just use it.
474 // Otherwise, we'll use an array of the constants.
475 unsigned ArraySize = 16 / Size;
476 ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
477 return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
480 // If we have a negative stride, Start refers to the end of the memory location
481 // we're trying to memset. Therefore, we need to recompute the base pointer,
482 // which is just Start - BECount*Size.
483 static const SCEV *getStartForNegStride(const SCEV *Start, const SCEV *BECount,
484 Type *IntPtr, unsigned StoreSize,
485 ScalarEvolution *SE) {
486 const SCEV *Index = SE->getTruncateOrZeroExtend(BECount, IntPtr);
488 Index = SE->getMulExpr(Index, SE->getConstant(IntPtr, StoreSize),
490 return SE->getMinusSCEV(Start, Index);
493 /// processLoopStridedStore - We see a strided store of some value. If we can
494 /// transform this into a memset or memset_pattern in the loop preheader, do so.
495 bool LoopIdiomRecognize::processLoopStridedStore(
496 Value *DestPtr, unsigned StoreSize, unsigned StoreAlignment,
497 Value *StoredVal, Instruction *TheStore, const SCEVAddRecExpr *Ev,
498 const SCEV *BECount, bool NegStride) {
500 // If the stored value is a byte-wise value (like i32 -1), then it may be
501 // turned into a memset of i8 -1, assuming that all the consecutive bytes
502 // are stored. A store of i32 0x01020304 can never be turned into a memset,
503 // but it can be turned into memset_pattern if the target supports it.
504 Value *SplatValue = isBytewiseValue(StoredVal);
505 Constant *PatternValue = nullptr;
506 unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
508 // If we're allowed to form a memset, and the stored value would be acceptable
509 // for memset, use it.
510 if (SplatValue && TLI->has(LibFunc::memset) &&
511 // Verify that the stored value is loop invariant. If not, we can't
512 // promote the memset.
513 CurLoop->isLoopInvariant(SplatValue)) {
514 // Keep and use SplatValue.
515 PatternValue = nullptr;
516 } else if (DestAS == 0 && TLI->has(LibFunc::memset_pattern16) &&
517 (PatternValue = getMemSetPatternValue(StoredVal, DL))) {
518 // Don't create memset_pattern16s with address spaces.
519 // It looks like we can use PatternValue!
520 SplatValue = nullptr;
522 // Otherwise, this isn't an idiom we can transform. For example, we can't
523 // do anything with a 3-byte store.
527 // The trip count of the loop and the base pointer of the addrec SCEV is
528 // guaranteed to be loop invariant, which means that it should dominate the
529 // header. This allows us to insert code for it in the preheader.
530 BasicBlock *Preheader = CurLoop->getLoopPreheader();
531 IRBuilder<> Builder(Preheader->getTerminator());
532 SCEVExpander Expander(*SE, *DL, "loop-idiom");
534 Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
535 Type *IntPtr = Builder.getIntPtrTy(*DL, DestAS);
537 const SCEV *Start = Ev->getStart();
538 // Handle negative strided loops.
540 Start = getStartForNegStride(Start, BECount, IntPtr, StoreSize, SE);
542 // Okay, we have a strided store "p[i]" of a splattable value. We can turn
543 // this into a memset in the loop preheader now if we want. However, this
544 // would be unsafe to do if there is anything else in the loop that may read
545 // or write to the aliased location. Check for any overlap by generating the
546 // base pointer and checking the region.
548 Expander.expandCodeFor(Start, DestInt8PtrTy, Preheader->getTerminator());
549 if (mayLoopAccessLocation(BasePtr, MRI_ModRef, CurLoop, BECount, StoreSize,
552 // If we generated new code for the base pointer, clean up.
553 RecursivelyDeleteTriviallyDeadInstructions(BasePtr, TLI);
557 // Okay, everything looks good, insert the memset.
559 // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
560 // pointer size if it isn't already.
561 BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);
563 const SCEV *NumBytesS =
564 SE->getAddExpr(BECount, SE->getOne(IntPtr), SCEV::FlagNUW);
565 if (StoreSize != 1) {
566 NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
571 Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
576 Builder.CreateMemSet(BasePtr, SplatValue, NumBytes, StoreAlignment);
578 // Everything is emitted in default address space
579 Type *Int8PtrTy = DestInt8PtrTy;
581 Module *M = TheStore->getModule();
583 M->getOrInsertFunction("memset_pattern16", Builder.getVoidTy(),
584 Int8PtrTy, Int8PtrTy, IntPtr, (void *)nullptr);
586 // Otherwise we should form a memset_pattern16. PatternValue is known to be
587 // an constant array of 16-bytes. Plop the value into a mergable global.
588 GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
589 GlobalValue::PrivateLinkage,
590 PatternValue, ".memset_pattern");
591 GV->setUnnamedAddr(true); // Ok to merge these.
592 GV->setAlignment(16);
593 Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
594 NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
597 DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"
598 << " from store to: " << *Ev << " at: " << *TheStore << "\n");
599 NewCall->setDebugLoc(TheStore->getDebugLoc());
601 // Okay, the memset has been formed. Zap the original store and anything that
603 deleteDeadInstruction(TheStore, TLI);
608 /// If the stored value is a strided load in the same loop with the same stride
609 /// this may be transformable into a memcpy. This kicks in for stuff like
610 /// for (i) A[i] = B[i];
611 bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(
612 StoreInst *SI, unsigned StoreSize, const SCEVAddRecExpr *StoreEv,
613 const SCEV *BECount, bool NegStride) {
614 // If we're not allowed to form memcpy, we fail.
615 if (!TLI->has(LibFunc::memcpy))
618 // The store must be feeding a non-volatile load.
619 LoadInst *LI = dyn_cast<LoadInst>(SI->getValueOperand());
620 if (!LI || !LI->isSimple())
623 // See if the pointer expression is an AddRec like {base,+,1} on the current
624 // loop, which indicates a strided load. If we have something else, it's a
625 // random load we can't handle.
626 const SCEVAddRecExpr *LoadEv =
627 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getPointerOperand()));
628 if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
631 // The store and load must share the same stride.
632 if (StoreEv->getOperand(1) != LoadEv->getOperand(1))
635 // The trip count of the loop and the base pointer of the addrec SCEV is
636 // guaranteed to be loop invariant, which means that it should dominate the
637 // header. This allows us to insert code for it in the preheader.
638 BasicBlock *Preheader = CurLoop->getLoopPreheader();
639 IRBuilder<> Builder(Preheader->getTerminator());
640 SCEVExpander Expander(*SE, *DL, "loop-idiom");
642 const SCEV *StrStart = StoreEv->getStart();
643 unsigned StrAS = SI->getPointerAddressSpace();
644 Type *IntPtrTy = Builder.getIntPtrTy(*DL, StrAS);
646 // Handle negative strided loops.
648 StrStart = getStartForNegStride(StrStart, BECount, IntPtrTy, StoreSize, SE);
650 // Okay, we have a strided store "p[i]" of a loaded value. We can turn
651 // this into a memcpy in the loop preheader now if we want. However, this
652 // would be unsafe to do if there is anything else in the loop that may read
653 // or write the memory region we're storing to. This includes the load that
654 // feeds the stores. Check for an alias by generating the base address and
655 // checking everything.
656 Value *StoreBasePtr = Expander.expandCodeFor(
657 StrStart, Builder.getInt8PtrTy(StrAS), Preheader->getTerminator());
659 if (mayLoopAccessLocation(StoreBasePtr, MRI_ModRef, CurLoop, BECount,
660 StoreSize, *AA, SI)) {
662 // If we generated new code for the base pointer, clean up.
663 RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
667 const SCEV *LdStart = LoadEv->getStart();
668 unsigned LdAS = LI->getPointerAddressSpace();
670 // Handle negative strided loops.
672 LdStart = getStartForNegStride(LdStart, BECount, IntPtrTy, StoreSize, SE);
674 // For a memcpy, we have to make sure that the input array is not being
675 // mutated by the loop.
676 Value *LoadBasePtr = Expander.expandCodeFor(
677 LdStart, Builder.getInt8PtrTy(LdAS), Preheader->getTerminator());
679 if (mayLoopAccessLocation(LoadBasePtr, MRI_Mod, CurLoop, BECount, StoreSize,
682 // If we generated new code for the base pointer, clean up.
683 RecursivelyDeleteTriviallyDeadInstructions(LoadBasePtr, TLI);
684 RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
688 // Okay, everything is safe, we can transform this!
690 // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
691 // pointer size if it isn't already.
692 BECount = SE->getTruncateOrZeroExtend(BECount, IntPtrTy);
694 const SCEV *NumBytesS =
695 SE->getAddExpr(BECount, SE->getOne(IntPtrTy), SCEV::FlagNUW);
697 NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtrTy, StoreSize),
701 Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
704 Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
705 std::min(SI->getAlignment(), LI->getAlignment()));
706 NewCall->setDebugLoc(SI->getDebugLoc());
708 DEBUG(dbgs() << " Formed memcpy: " << *NewCall << "\n"
709 << " from load ptr=" << *LoadEv << " at: " << *LI << "\n"
710 << " from store ptr=" << *StoreEv << " at: " << *SI << "\n");
712 // Okay, the memcpy has been formed. Zap the original store and anything that
714 deleteDeadInstruction(SI, TLI);
719 bool LoopIdiomRecognize::runOnNoncountableLoop() {
720 return recognizePopcount();
723 /// Check if the given conditional branch is based on the comparison between
724 /// a variable and zero, and if the variable is non-zero, the control yields to
725 /// the loop entry. If the branch matches the behavior, the variable involved
726 /// in the comparion is returned. This function will be called to see if the
727 /// precondition and postcondition of the loop are in desirable form.
728 static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry) {
729 if (!BI || !BI->isConditional())
732 ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
736 ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
737 if (!CmpZero || !CmpZero->isZero())
740 ICmpInst::Predicate Pred = Cond->getPredicate();
741 if ((Pred == ICmpInst::ICMP_NE && BI->getSuccessor(0) == LoopEntry) ||
742 (Pred == ICmpInst::ICMP_EQ && BI->getSuccessor(1) == LoopEntry))
743 return Cond->getOperand(0);
748 /// Return true iff the idiom is detected in the loop.
751 /// 1) \p CntInst is set to the instruction counting the population bit.
752 /// 2) \p CntPhi is set to the corresponding phi node.
753 /// 3) \p Var is set to the value whose population bits are being counted.
755 /// The core idiom we are trying to detect is:
758 /// goto loop-exit // the precondition of the loop
761 /// x1 = phi (x0, x2);
762 /// cnt1 = phi(cnt0, cnt2);
766 /// x2 = x1 & (x1 - 1);
772 static bool detectPopcountIdiom(Loop *CurLoop, BasicBlock *PreCondBB,
773 Instruction *&CntInst, PHINode *&CntPhi,
775 // step 1: Check to see if the look-back branch match this pattern:
776 // "if (a!=0) goto loop-entry".
777 BasicBlock *LoopEntry;
778 Instruction *DefX2, *CountInst;
779 Value *VarX1, *VarX0;
780 PHINode *PhiX, *CountPhi;
782 DefX2 = CountInst = nullptr;
783 VarX1 = VarX0 = nullptr;
784 PhiX = CountPhi = nullptr;
785 LoopEntry = *(CurLoop->block_begin());
787 // step 1: Check if the loop-back branch is in desirable form.
789 if (Value *T = matchCondition(
790 dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
791 DefX2 = dyn_cast<Instruction>(T);
796 // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
798 if (!DefX2 || DefX2->getOpcode() != Instruction::And)
801 BinaryOperator *SubOneOp;
803 if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
804 VarX1 = DefX2->getOperand(1);
806 VarX1 = DefX2->getOperand(0);
807 SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
812 Instruction *SubInst = cast<Instruction>(SubOneOp);
813 ConstantInt *Dec = dyn_cast<ConstantInt>(SubInst->getOperand(1));
815 !((SubInst->getOpcode() == Instruction::Sub && Dec->isOne()) ||
816 (SubInst->getOpcode() == Instruction::Add &&
817 Dec->isAllOnesValue()))) {
822 // step 3: Check the recurrence of variable X
824 PhiX = dyn_cast<PHINode>(VarX1);
826 (PhiX->getOperand(0) != DefX2 && PhiX->getOperand(1) != DefX2)) {
831 // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
834 for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI()->getIterator(),
835 IterE = LoopEntry->end();
836 Iter != IterE; Iter++) {
837 Instruction *Inst = &*Iter;
838 if (Inst->getOpcode() != Instruction::Add)
841 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
842 if (!Inc || !Inc->isOne())
845 PHINode *Phi = dyn_cast<PHINode>(Inst->getOperand(0));
846 if (!Phi || Phi->getParent() != LoopEntry)
849 // Check if the result of the instruction is live of the loop.
850 bool LiveOutLoop = false;
851 for (User *U : Inst->users()) {
852 if ((cast<Instruction>(U))->getParent() != LoopEntry) {
869 // step 5: check if the precondition is in this form:
870 // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
872 auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
873 Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
874 if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
885 /// Recognizes a population count idiom in a non-countable loop.
887 /// If detected, transforms the relevant code to issue the popcount intrinsic
888 /// function call, and returns true; otherwise, returns false.
889 bool LoopIdiomRecognize::recognizePopcount() {
890 if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
893 // Counting population are usually conducted by few arithmetic instructions.
894 // Such instructions can be easily "absorbed" by vacant slots in a
895 // non-compact loop. Therefore, recognizing popcount idiom only makes sense
896 // in a compact loop.
898 // Give up if the loop has multiple blocks or multiple backedges.
899 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
902 BasicBlock *LoopBody = *(CurLoop->block_begin());
903 if (LoopBody->size() >= 20) {
904 // The loop is too big, bail out.
908 // It should have a preheader containing nothing but an unconditional branch.
909 BasicBlock *PH = CurLoop->getLoopPreheader();
912 if (&PH->front() != PH->getTerminator())
914 auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
915 if (!EntryBI || EntryBI->isConditional())
918 // It should have a precondition block where the generated popcount instrinsic
919 // function can be inserted.
920 auto *PreCondBB = PH->getSinglePredecessor();
923 auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
924 if (!PreCondBI || PreCondBI->isUnconditional())
927 Instruction *CntInst;
930 if (!detectPopcountIdiom(CurLoop, PreCondBB, CntInst, CntPhi, Val))
933 transformLoopToPopcount(PreCondBB, CntInst, CntPhi, Val);
937 static CallInst *createPopcntIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
939 Value *Ops[] = {Val};
940 Type *Tys[] = {Val->getType()};
942 Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
943 Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
944 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
950 void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
951 Instruction *CntInst,
952 PHINode *CntPhi, Value *Var) {
953 BasicBlock *PreHead = CurLoop->getLoopPreheader();
954 auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
955 const DebugLoc DL = CntInst->getDebugLoc();
957 // Assuming before transformation, the loop is following:
958 // if (x) // the precondition
959 // do { cnt++; x &= x - 1; } while(x);
961 // Step 1: Insert the ctpop instruction at the end of the precondition block
962 IRBuilder<> Builder(PreCondBr);
963 Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
965 PopCnt = createPopcntIntrinsic(Builder, Var, DL);
966 NewCount = PopCntZext =
967 Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
969 if (NewCount != PopCnt)
970 (cast<Instruction>(NewCount))->setDebugLoc(DL);
972 // TripCnt is exactly the number of iterations the loop has
975 // If the population counter's initial value is not zero, insert Add Inst.
976 Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
977 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
978 if (!InitConst || !InitConst->isZero()) {
979 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
980 (cast<Instruction>(NewCount))->setDebugLoc(DL);
984 // Step 2: Replace the precondition from "if (x == 0) goto loop-exit" to
985 // "if (NewCount == 0) loop-exit". Without this change, the intrinsic
986 // function would be partial dead code, and downstream passes will drag
987 // it back from the precondition block to the preheader.
989 ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
991 Value *Opnd0 = PopCntZext;
992 Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
993 if (PreCond->getOperand(0) != Var)
994 std::swap(Opnd0, Opnd1);
996 ICmpInst *NewPreCond = cast<ICmpInst>(
997 Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
998 PreCondBr->setCondition(NewPreCond);
1000 RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
1003 // Step 3: Note that the population count is exactly the trip count of the
1004 // loop in question, which enable us to to convert the loop from noncountable
1005 // loop into a countable one. The benefit is twofold:
1007 // - If the loop only counts population, the entire loop becomes dead after
1008 // the transformation. It is a lot easier to prove a countable loop dead
1009 // than to prove a noncountable one. (In some C dialects, an infinite loop
1010 // isn't dead even if it computes nothing useful. In general, DCE needs
1011 // to prove a noncountable loop finite before safely delete it.)
1013 // - If the loop also performs something else, it remains alive.
1014 // Since it is transformed to countable form, it can be aggressively
1015 // optimized by some optimizations which are in general not applicable
1016 // to a noncountable loop.
1018 // After this step, this loop (conceptually) would look like following:
1019 // newcnt = __builtin_ctpop(x);
1022 // do { cnt++; x &= x-1; t--) } while (t > 0);
1023 BasicBlock *Body = *(CurLoop->block_begin());
1025 auto *LbBr = dyn_cast<BranchInst>(Body->getTerminator());
1026 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
1027 Type *Ty = TripCnt->getType();
1029 PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
1031 Builder.SetInsertPoint(LbCond);
1032 Instruction *TcDec = cast<Instruction>(
1033 Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
1034 "tcdec", false, true));
1036 TcPhi->addIncoming(TripCnt, PreHead);
1037 TcPhi->addIncoming(TcDec, Body);
1039 CmpInst::Predicate Pred =
1040 (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
1041 LbCond->setPredicate(Pred);
1042 LbCond->setOperand(0, TcDec);
1043 LbCond->setOperand(1, ConstantInt::get(Ty, 0));
1046 // Step 4: All the references to the original population counter outside
1047 // the loop are replaced with the NewCount -- the value returned from
1048 // __builtin_ctpop().
1049 CntInst->replaceUsesOutsideBlock(NewCount, Body);
1051 // step 5: Forget the "non-computable" trip-count SCEV associated with the
1052 // loop. The loop would otherwise not be deleted even if it becomes empty.
1053 SE->forgetLoop(CurLoop);