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 // We should enhance this to handle negative strides through memory.
35 // Alternatively (and perhaps better) we could rely on an earlier pass to force
36 // forward iteration through memory, which is generally better for cache
37 // behavior. Negative strides *do* happen for memset/memcpy loops.
39 // This could recognize common matrix multiplies and dot product idioms and
40 // replace them with calls to BLAS (if linked in??).
42 //===----------------------------------------------------------------------===//
44 #include "llvm/Transforms/Scalar.h"
45 #include "llvm/ADT/Statistic.h"
46 #include "llvm/Analysis/AliasAnalysis.h"
47 #include "llvm/Analysis/LoopPass.h"
48 #include "llvm/Analysis/ScalarEvolutionExpander.h"
49 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
50 #include "llvm/Analysis/TargetTransformInfo.h"
51 #include "llvm/Analysis/ValueTracking.h"
52 #include "llvm/IR/DataLayout.h"
53 #include "llvm/IR/Dominators.h"
54 #include "llvm/IR/IRBuilder.h"
55 #include "llvm/IR/IntrinsicInst.h"
56 #include "llvm/IR/Module.h"
57 #include "llvm/Support/Debug.h"
58 #include "llvm/Support/raw_ostream.h"
59 #include "llvm/Analysis/TargetLibraryInfo.h"
60 #include "llvm/Transforms/Utils/Local.h"
63 #define DEBUG_TYPE "loop-idiom"
65 STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
66 STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
70 class LoopIdiomRecognize;
72 /// This class defines some utility functions for loop idiom recognization.
75 /// Return true iff the block contains nothing but an uncondition branch
76 /// (aka goto instruction).
77 static bool isAlmostEmpty(BasicBlock *);
79 static BranchInst *getBranch(BasicBlock *BB) {
80 return dyn_cast<BranchInst>(BB->getTerminator());
83 /// Derive the precondition block (i.e the block that guards the loop
84 /// preheader) from the given preheader.
85 static BasicBlock *getPrecondBb(BasicBlock *PreHead);
88 /// This class is to recoginize idioms of population-count conducted in
89 /// a noncountable loop. Currently it only recognizes this pattern:
91 /// while(x) {cnt++; ...; x &= x - 1; ...}
93 class NclPopcountRecognize {
94 LoopIdiomRecognize &LIR;
96 BasicBlock *PreCondBB;
98 typedef IRBuilder<> IRBuilderTy;
101 explicit NclPopcountRecognize(LoopIdiomRecognize &TheLIR);
105 /// Take a glimpse of the loop to see if we need to go ahead recoginizing
107 bool preliminaryScreen();
109 /// Check if the given conditional branch is based on the comparison
110 /// between a variable and zero, and if the variable is non-zero, the
111 /// control yields to the loop entry. If the branch matches the behavior,
112 /// the variable involved in the comparion is returned. This function will
113 /// be called to see if the precondition and postcondition of the loop
114 /// are in desirable form.
115 Value *matchCondition(BranchInst *Br, BasicBlock *NonZeroTarget) const;
117 /// Return true iff the idiom is detected in the loop. and 1) \p CntInst
118 /// is set to the instruction counting the population bit. 2) \p CntPhi
119 /// is set to the corresponding phi node. 3) \p Var is set to the value
120 /// whose population bits are being counted.
122 (Instruction *&CntInst, PHINode *&CntPhi, Value *&Var) const;
124 /// Insert ctpop intrinsic function and some obviously dead instructions.
125 void transform(Instruction *CntInst, PHINode *CntPhi, Value *Var);
127 /// Create llvm.ctpop.* intrinsic function.
128 CallInst *createPopcntIntrinsic(IRBuilderTy &IRB, Value *Val, DebugLoc DL);
131 class LoopIdiomRecognize : public LoopPass {
133 const DataLayout *DL;
136 TargetLibraryInfo *TLI;
137 const TargetTransformInfo *TTI;
140 explicit LoopIdiomRecognize() : LoopPass(ID) {
141 initializeLoopIdiomRecognizePass(*PassRegistry::getPassRegistry());
142 DL = nullptr; DT = nullptr; SE = nullptr; TLI = nullptr; TTI = nullptr;
145 bool runOnLoop(Loop *L, LPPassManager &LPM) override;
146 bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
147 SmallVectorImpl<BasicBlock*> &ExitBlocks);
149 bool processLoopStore(StoreInst *SI, const SCEV *BECount);
150 bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
152 bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
153 unsigned StoreAlignment,
154 Value *SplatValue, Instruction *TheStore,
155 const SCEVAddRecExpr *Ev,
156 const SCEV *BECount);
157 bool processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
158 const SCEVAddRecExpr *StoreEv,
159 const SCEVAddRecExpr *LoadEv,
160 const SCEV *BECount);
162 /// This transformation requires natural loop information & requires that
163 /// loop preheaders be inserted into the CFG.
165 void getAnalysisUsage(AnalysisUsage &AU) const override {
166 AU.addRequired<LoopInfo>();
167 AU.addPreserved<LoopInfo>();
168 AU.addRequiredID(LoopSimplifyID);
169 AU.addPreservedID(LoopSimplifyID);
170 AU.addRequiredID(LCSSAID);
171 AU.addPreservedID(LCSSAID);
172 AU.addRequired<AliasAnalysis>();
173 AU.addPreserved<AliasAnalysis>();
174 AU.addRequired<ScalarEvolution>();
175 AU.addPreserved<ScalarEvolution>();
176 AU.addPreserved<DominatorTreeWrapperPass>();
177 AU.addRequired<DominatorTreeWrapperPass>();
178 AU.addRequired<TargetLibraryInfoWrapperPass>();
179 AU.addRequired<TargetTransformInfo>();
182 const DataLayout *getDataLayout() {
185 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
186 DL = DLP ? &DLP->getDataLayout() : nullptr;
190 DominatorTree *getDominatorTree() {
192 : (DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree());
195 ScalarEvolution *getScalarEvolution() {
196 return SE ? SE : (SE = &getAnalysis<ScalarEvolution>());
199 TargetLibraryInfo *getTargetLibraryInfo() {
201 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
206 const TargetTransformInfo *getTargetTransformInfo() {
207 return TTI ? TTI : (TTI = &getAnalysis<TargetTransformInfo>());
210 Loop *getLoop() const { return CurLoop; }
213 bool runOnNoncountableLoop();
214 bool runOnCountableLoop();
218 char LoopIdiomRecognize::ID = 0;
219 INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
221 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
222 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
223 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
224 INITIALIZE_PASS_DEPENDENCY(LCSSA)
225 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
226 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
227 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
228 INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
229 INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
232 Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
234 /// deleteDeadInstruction - Delete this instruction. Before we do, go through
235 /// and zero out all the operands of this instruction. If any of them become
236 /// dead, delete them and the computation tree that feeds them.
238 static void deleteDeadInstruction(Instruction *I, ScalarEvolution &SE,
239 const TargetLibraryInfo *TLI) {
240 SmallVector<Instruction*, 32> NowDeadInsts;
242 NowDeadInsts.push_back(I);
244 // Before we touch this instruction, remove it from SE!
246 Instruction *DeadInst = NowDeadInsts.pop_back_val();
248 // This instruction is dead, zap it, in stages. Start by removing it from
250 SE.forgetValue(DeadInst);
252 for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
253 Value *Op = DeadInst->getOperand(op);
254 DeadInst->setOperand(op, nullptr);
256 // If this operand just became dead, add it to the NowDeadInsts list.
257 if (!Op->use_empty()) continue;
259 if (Instruction *OpI = dyn_cast<Instruction>(Op))
260 if (isInstructionTriviallyDead(OpI, TLI))
261 NowDeadInsts.push_back(OpI);
264 DeadInst->eraseFromParent();
266 } while (!NowDeadInsts.empty());
269 /// deleteIfDeadInstruction - If the specified value is a dead instruction,
270 /// delete it and any recursively used instructions.
271 static void deleteIfDeadInstruction(Value *V, ScalarEvolution &SE,
272 const TargetLibraryInfo *TLI) {
273 if (Instruction *I = dyn_cast<Instruction>(V))
274 if (isInstructionTriviallyDead(I, TLI))
275 deleteDeadInstruction(I, SE, TLI);
278 //===----------------------------------------------------------------------===//
280 // Implementation of LIRUtil
282 //===----------------------------------------------------------------------===//
284 // This function will return true iff the given block contains nothing but goto.
285 // A typical usage of this function is to check if the preheader function is
286 // "almost" empty such that generated intrinsic functions can be moved across
287 // the preheader and be placed at the end of the precondition block without
288 // the concern of breaking data dependence.
289 bool LIRUtil::isAlmostEmpty(BasicBlock *BB) {
290 if (BranchInst *Br = getBranch(BB)) {
291 return Br->isUnconditional() && BB->size() == 1;
296 BasicBlock *LIRUtil::getPrecondBb(BasicBlock *PreHead) {
297 if (BasicBlock *BB = PreHead->getSinglePredecessor()) {
298 BranchInst *Br = getBranch(BB);
299 return Br && Br->isConditional() ? BB : nullptr;
304 //===----------------------------------------------------------------------===//
306 // Implementation of NclPopcountRecognize
308 //===----------------------------------------------------------------------===//
310 NclPopcountRecognize::NclPopcountRecognize(LoopIdiomRecognize &TheLIR):
311 LIR(TheLIR), CurLoop(TheLIR.getLoop()), PreCondBB(nullptr) {
314 bool NclPopcountRecognize::preliminaryScreen() {
315 const TargetTransformInfo *TTI = LIR.getTargetTransformInfo();
316 if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
319 // Counting population are usually conducted by few arithmetic instructions.
320 // Such instructions can be easilly "absorbed" by vacant slots in a
321 // non-compact loop. Therefore, recognizing popcount idiom only makes sense
322 // in a compact loop.
324 // Give up if the loop has multiple blocks or multiple backedges.
325 if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
328 BasicBlock *LoopBody = *(CurLoop->block_begin());
329 if (LoopBody->size() >= 20) {
330 // The loop is too big, bail out.
334 // It should have a preheader containing nothing but a goto instruction.
335 BasicBlock *PreHead = CurLoop->getLoopPreheader();
336 if (!PreHead || !LIRUtil::isAlmostEmpty(PreHead))
339 // It should have a precondition block where the generated popcount instrinsic
340 // function will be inserted.
341 PreCondBB = LIRUtil::getPrecondBb(PreHead);
348 Value *NclPopcountRecognize::matchCondition(BranchInst *Br,
349 BasicBlock *LoopEntry) const {
350 if (!Br || !Br->isConditional())
353 ICmpInst *Cond = dyn_cast<ICmpInst>(Br->getCondition());
357 ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
358 if (!CmpZero || !CmpZero->isZero())
361 ICmpInst::Predicate Pred = Cond->getPredicate();
362 if ((Pred == ICmpInst::ICMP_NE && Br->getSuccessor(0) == LoopEntry) ||
363 (Pred == ICmpInst::ICMP_EQ && Br->getSuccessor(1) == LoopEntry))
364 return Cond->getOperand(0);
369 bool NclPopcountRecognize::detectIdiom(Instruction *&CntInst,
372 // Following code tries to detect this idiom:
375 // goto loop-exit // the precondition of the loop
378 // x1 = phi (x0, x2);
379 // cnt1 = phi(cnt0, cnt2);
383 // x2 = x1 & (x1 - 1);
390 // step 1: Check to see if the look-back branch match this pattern:
391 // "if (a!=0) goto loop-entry".
392 BasicBlock *LoopEntry;
393 Instruction *DefX2, *CountInst;
394 Value *VarX1, *VarX0;
395 PHINode *PhiX, *CountPhi;
397 DefX2 = CountInst = nullptr;
398 VarX1 = VarX0 = nullptr;
399 PhiX = CountPhi = nullptr;
400 LoopEntry = *(CurLoop->block_begin());
402 // step 1: Check if the loop-back branch is in desirable form.
404 if (Value *T = matchCondition (LIRUtil::getBranch(LoopEntry), LoopEntry))
405 DefX2 = dyn_cast<Instruction>(T);
410 // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
412 if (!DefX2 || DefX2->getOpcode() != Instruction::And)
415 BinaryOperator *SubOneOp;
417 if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
418 VarX1 = DefX2->getOperand(1);
420 VarX1 = DefX2->getOperand(0);
421 SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
426 Instruction *SubInst = cast<Instruction>(SubOneOp);
427 ConstantInt *Dec = dyn_cast<ConstantInt>(SubInst->getOperand(1));
429 !((SubInst->getOpcode() == Instruction::Sub && Dec->isOne()) ||
430 (SubInst->getOpcode() == Instruction::Add && Dec->isAllOnesValue()))) {
435 // step 3: Check the recurrence of variable X
437 PhiX = dyn_cast<PHINode>(VarX1);
439 (PhiX->getOperand(0) != DefX2 && PhiX->getOperand(1) != DefX2)) {
444 // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
447 for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI(),
448 IterE = LoopEntry->end(); Iter != IterE; Iter++) {
449 Instruction *Inst = Iter;
450 if (Inst->getOpcode() != Instruction::Add)
453 ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
454 if (!Inc || !Inc->isOne())
457 PHINode *Phi = dyn_cast<PHINode>(Inst->getOperand(0));
458 if (!Phi || Phi->getParent() != LoopEntry)
461 // Check if the result of the instruction is live of the loop.
462 bool LiveOutLoop = false;
463 for (User *U : Inst->users()) {
464 if ((cast<Instruction>(U))->getParent() != LoopEntry) {
465 LiveOutLoop = true; break;
480 // step 5: check if the precondition is in this form:
481 // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
483 BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
484 Value *T = matchCondition (PreCondBr, CurLoop->getLoopPreheader());
485 if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
496 void NclPopcountRecognize::transform(Instruction *CntInst,
497 PHINode *CntPhi, Value *Var) {
499 ScalarEvolution *SE = LIR.getScalarEvolution();
500 TargetLibraryInfo *TLI = LIR.getTargetLibraryInfo();
501 BasicBlock *PreHead = CurLoop->getLoopPreheader();
502 BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
503 const DebugLoc DL = CntInst->getDebugLoc();
505 // Assuming before transformation, the loop is following:
506 // if (x) // the precondition
507 // do { cnt++; x &= x - 1; } while(x);
509 // Step 1: Insert the ctpop instruction at the end of the precondition block
510 IRBuilderTy Builder(PreCondBr);
511 Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
513 PopCnt = createPopcntIntrinsic(Builder, Var, DL);
514 NewCount = PopCntZext =
515 Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
517 if (NewCount != PopCnt)
518 (cast<Instruction>(NewCount))->setDebugLoc(DL);
520 // TripCnt is exactly the number of iterations the loop has
523 // If the population counter's initial value is not zero, insert Add Inst.
524 Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
525 ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
526 if (!InitConst || !InitConst->isZero()) {
527 NewCount = Builder.CreateAdd(NewCount, CntInitVal);
528 (cast<Instruction>(NewCount))->setDebugLoc(DL);
532 // Step 2: Replace the precondition from "if(x == 0) goto loop-exit" to
533 // "if(NewCount == 0) loop-exit". Withtout this change, the intrinsic
534 // function would be partial dead code, and downstream passes will drag
535 // it back from the precondition block to the preheader.
537 ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
539 Value *Opnd0 = PopCntZext;
540 Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
541 if (PreCond->getOperand(0) != Var)
542 std::swap(Opnd0, Opnd1);
544 ICmpInst *NewPreCond =
545 cast<ICmpInst>(Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
546 PreCond->replaceAllUsesWith(NewPreCond);
548 deleteDeadInstruction(PreCond, *SE, TLI);
551 // Step 3: Note that the population count is exactly the trip count of the
552 // loop in question, which enble us to to convert the loop from noncountable
553 // loop into a countable one. The benefit is twofold:
555 // - If the loop only counts population, the entire loop become dead after
556 // the transformation. It is lots easier to prove a countable loop dead
557 // than to prove a noncountable one. (In some C dialects, a infite loop
558 // isn't dead even if it computes nothing useful. In general, DCE needs
559 // to prove a noncountable loop finite before safely delete it.)
561 // - If the loop also performs something else, it remains alive.
562 // Since it is transformed to countable form, it can be aggressively
563 // optimized by some optimizations which are in general not applicable
564 // to a noncountable loop.
566 // After this step, this loop (conceptually) would look like following:
567 // newcnt = __builtin_ctpop(x);
570 // do { cnt++; x &= x-1; t--) } while (t > 0);
571 BasicBlock *Body = *(CurLoop->block_begin());
573 BranchInst *LbBr = LIRUtil::getBranch(Body);
574 ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
575 Type *Ty = TripCnt->getType();
577 PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", Body->begin());
579 Builder.SetInsertPoint(LbCond);
580 Value *Opnd1 = cast<Value>(TcPhi);
581 Value *Opnd2 = cast<Value>(ConstantInt::get(Ty, 1));
583 cast<Instruction>(Builder.CreateSub(Opnd1, Opnd2, "tcdec", false, true));
585 TcPhi->addIncoming(TripCnt, PreHead);
586 TcPhi->addIncoming(TcDec, Body);
588 CmpInst::Predicate Pred = (LbBr->getSuccessor(0) == Body) ?
589 CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
590 LbCond->setPredicate(Pred);
591 LbCond->setOperand(0, TcDec);
592 LbCond->setOperand(1, cast<Value>(ConstantInt::get(Ty, 0)));
595 // Step 4: All the references to the original population counter outside
596 // the loop are replaced with the NewCount -- the value returned from
597 // __builtin_ctpop().
599 SmallVector<Value *, 4> CntUses;
600 for (User *U : CntInst->users())
601 if (cast<Instruction>(U)->getParent() != Body)
602 CntUses.push_back(U);
603 for (unsigned Idx = 0; Idx < CntUses.size(); Idx++) {
604 (cast<Instruction>(CntUses[Idx]))->replaceUsesOfWith(CntInst, NewCount);
608 // step 5: Forget the "non-computable" trip-count SCEV associated with the
609 // loop. The loop would otherwise not be deleted even if it becomes empty.
610 SE->forgetLoop(CurLoop);
613 CallInst *NclPopcountRecognize::createPopcntIntrinsic(IRBuilderTy &IRBuilder,
614 Value *Val, DebugLoc DL) {
615 Value *Ops[] = { Val };
616 Type *Tys[] = { Val->getType() };
618 Module *M = (*(CurLoop->block_begin()))->getParent()->getParent();
619 Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
620 CallInst *CI = IRBuilder.CreateCall(Func, Ops);
626 /// recognize - detect population count idiom in a non-countable loop. If
627 /// detected, transform the relevant code to popcount intrinsic function
628 /// call, and return true; otherwise, return false.
629 bool NclPopcountRecognize::recognize() {
631 if (!LIR.getTargetTransformInfo())
634 LIR.getScalarEvolution();
636 if (!preliminaryScreen())
639 Instruction *CntInst;
642 if (!detectIdiom(CntInst, CntPhi, Val))
645 transform(CntInst, CntPhi, Val);
649 //===----------------------------------------------------------------------===//
651 // Implementation of LoopIdiomRecognize
653 //===----------------------------------------------------------------------===//
655 bool LoopIdiomRecognize::runOnCountableLoop() {
656 const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
657 if (isa<SCEVCouldNotCompute>(BECount)) return false;
659 // If this loop executes exactly one time, then it should be peeled, not
660 // optimized by this pass.
661 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
662 if (BECst->getValue()->getValue() == 0)
665 // We require target data for now.
666 if (!getDataLayout())
670 (void)getDominatorTree();
672 LoopInfo &LI = getAnalysis<LoopInfo>();
673 TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
676 (void)getTargetLibraryInfo();
678 SmallVector<BasicBlock*, 8> ExitBlocks;
679 CurLoop->getUniqueExitBlocks(ExitBlocks);
681 DEBUG(dbgs() << "loop-idiom Scanning: F["
682 << CurLoop->getHeader()->getParent()->getName()
683 << "] Loop %" << CurLoop->getHeader()->getName() << "\n");
685 bool MadeChange = false;
686 // Scan all the blocks in the loop that are not in subloops.
687 for (Loop::block_iterator BI = CurLoop->block_begin(),
688 E = CurLoop->block_end(); BI != E; ++BI) {
689 // Ignore blocks in subloops.
690 if (LI.getLoopFor(*BI) != CurLoop)
693 MadeChange |= runOnLoopBlock(*BI, BECount, ExitBlocks);
698 bool LoopIdiomRecognize::runOnNoncountableLoop() {
699 NclPopcountRecognize Popcount(*this);
700 if (Popcount.recognize())
706 bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
707 if (skipOptnoneFunction(L))
712 // If the loop could not be converted to canonical form, it must have an
713 // indirectbr in it, just give up.
714 if (!L->getLoopPreheader())
717 // Disable loop idiom recognition if the function's name is a common idiom.
718 StringRef Name = L->getHeader()->getParent()->getName();
719 if (Name == "memset" || Name == "memcpy")
722 SE = &getAnalysis<ScalarEvolution>();
723 if (SE->hasLoopInvariantBackedgeTakenCount(L))
724 return runOnCountableLoop();
725 return runOnNoncountableLoop();
728 /// runOnLoopBlock - Process the specified block, which lives in a counted loop
729 /// with the specified backedge count. This block is known to be in the current
730 /// loop and not in any subloops.
731 bool LoopIdiomRecognize::runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
732 SmallVectorImpl<BasicBlock*> &ExitBlocks) {
733 // We can only promote stores in this block if they are unconditionally
734 // executed in the loop. For a block to be unconditionally executed, it has
735 // to dominate all the exit blocks of the loop. Verify this now.
736 for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
737 if (!DT->dominates(BB, ExitBlocks[i]))
740 bool MadeChange = false;
741 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
742 Instruction *Inst = I++;
743 // Look for store instructions, which may be optimized to memset/memcpy.
744 if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
746 if (!processLoopStore(SI, BECount)) continue;
749 // If processing the store invalidated our iterator, start over from the
756 // Look for memset instructions, which may be optimized to a larger memset.
757 if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst)) {
759 if (!processLoopMemSet(MSI, BECount)) continue;
762 // If processing the memset invalidated our iterator, start over from the
774 /// processLoopStore - See if this store can be promoted to a memset or memcpy.
775 bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
776 if (!SI->isSimple()) return false;
778 Value *StoredVal = SI->getValueOperand();
779 Value *StorePtr = SI->getPointerOperand();
781 // Reject stores that are so large that they overflow an unsigned.
782 uint64_t SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
783 if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
786 // See if the pointer expression is an AddRec like {base,+,1} on the current
787 // loop, which indicates a strided store. If we have something else, it's a
788 // random store we can't handle.
789 const SCEVAddRecExpr *StoreEv =
790 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
791 if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
794 // Check to see if the stride matches the size of the store. If so, then we
795 // know that every byte is touched in the loop.
796 unsigned StoreSize = (unsigned)SizeInBits >> 3;
797 const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
799 if (!Stride || StoreSize != Stride->getValue()->getValue()) {
800 // TODO: Could also handle negative stride here someday, that will require
801 // the validity check in mayLoopAccessLocation to be updated though.
802 // Enable this to print exact negative strides.
803 if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
804 dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
805 dbgs() << "BB: " << *SI->getParent();
811 // See if we can optimize just this store in isolation.
812 if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
813 StoredVal, SI, StoreEv, BECount))
816 // If the stored value is a strided load in the same loop with the same stride
817 // this this may be transformable into a memcpy. This kicks in for stuff like
818 // for (i) A[i] = B[i];
819 if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
820 const SCEVAddRecExpr *LoadEv =
821 dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getOperand(0)));
822 if (LoadEv && LoadEv->getLoop() == CurLoop && LoadEv->isAffine() &&
823 StoreEv->getOperand(1) == LoadEv->getOperand(1) && LI->isSimple())
824 if (processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, LoadEv, BECount))
827 //errs() << "UNHANDLED strided store: " << *StoreEv << " - " << *SI << "\n";
832 /// processLoopMemSet - See if this memset can be promoted to a large memset.
833 bool LoopIdiomRecognize::
834 processLoopMemSet(MemSetInst *MSI, const SCEV *BECount) {
835 // We can only handle non-volatile memsets with a constant size.
836 if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength())) return false;
838 // If we're not allowed to hack on memset, we fail.
839 if (!TLI->has(LibFunc::memset))
842 Value *Pointer = MSI->getDest();
844 // See if the pointer expression is an AddRec like {base,+,1} on the current
845 // loop, which indicates a strided store. If we have something else, it's a
846 // random store we can't handle.
847 const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
848 if (!Ev || Ev->getLoop() != CurLoop || !Ev->isAffine())
851 // Reject memsets that are so large that they overflow an unsigned.
852 uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
853 if ((SizeInBytes >> 32) != 0)
856 // Check to see if the stride matches the size of the memset. If so, then we
857 // know that every byte is touched in the loop.
858 const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
860 // TODO: Could also handle negative stride here someday, that will require the
861 // validity check in mayLoopAccessLocation to be updated though.
862 if (!Stride || MSI->getLength() != Stride->getValue())
865 return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
866 MSI->getAlignment(), MSI->getValue(),
871 /// mayLoopAccessLocation - Return true if the specified loop might access the
872 /// specified pointer location, which is a loop-strided access. The 'Access'
873 /// argument specifies what the verboten forms of access are (read or write).
874 static bool mayLoopAccessLocation(Value *Ptr,AliasAnalysis::ModRefResult Access,
875 Loop *L, const SCEV *BECount,
876 unsigned StoreSize, AliasAnalysis &AA,
877 Instruction *IgnoredStore) {
878 // Get the location that may be stored across the loop. Since the access is
879 // strided positively through memory, we say that the modified location starts
880 // at the pointer and has infinite size.
881 uint64_t AccessSize = AliasAnalysis::UnknownSize;
883 // If the loop iterates a fixed number of times, we can refine the access size
884 // to be exactly the size of the memset, which is (BECount+1)*StoreSize
885 if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
886 AccessSize = (BECst->getValue()->getZExtValue()+1)*StoreSize;
888 // TODO: For this to be really effective, we have to dive into the pointer
889 // operand in the store. Store to &A[i] of 100 will always return may alias
890 // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
891 // which will then no-alias a store to &A[100].
892 AliasAnalysis::Location StoreLoc(Ptr, AccessSize);
894 for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
896 for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
897 if (&*I != IgnoredStore &&
898 (AA.getModRefInfo(I, StoreLoc) & Access))
904 /// getMemSetPatternValue - If a strided store of the specified value is safe to
905 /// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
906 /// be passed in. Otherwise, return null.
908 /// Note that we don't ever attempt to use memset_pattern8 or 4, because these
909 /// just replicate their input array and then pass on to memset_pattern16.
910 static Constant *getMemSetPatternValue(Value *V, const DataLayout &DL) {
911 // If the value isn't a constant, we can't promote it to being in a constant
912 // array. We could theoretically do a store to an alloca or something, but
913 // that doesn't seem worthwhile.
914 Constant *C = dyn_cast<Constant>(V);
915 if (!C) return nullptr;
917 // Only handle simple values that are a power of two bytes in size.
918 uint64_t Size = DL.getTypeSizeInBits(V->getType());
919 if (Size == 0 || (Size & 7) || (Size & (Size-1)))
922 // Don't care enough about darwin/ppc to implement this.
923 if (DL.isBigEndian())
926 // Convert to size in bytes.
929 // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
930 // if the top and bottom are the same (e.g. for vectors and large integers).
931 if (Size > 16) return nullptr;
933 // If the constant is exactly 16 bytes, just use it.
934 if (Size == 16) return C;
936 // Otherwise, we'll use an array of the constants.
937 unsigned ArraySize = 16/Size;
938 ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
939 return ConstantArray::get(AT, std::vector<Constant*>(ArraySize, C));
943 /// processLoopStridedStore - We see a strided store of some value. If we can
944 /// transform this into a memset or memset_pattern in the loop preheader, do so.
945 bool LoopIdiomRecognize::
946 processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
947 unsigned StoreAlignment, Value *StoredVal,
948 Instruction *TheStore, const SCEVAddRecExpr *Ev,
949 const SCEV *BECount) {
951 // If the stored value is a byte-wise value (like i32 -1), then it may be
952 // turned into a memset of i8 -1, assuming that all the consecutive bytes
953 // are stored. A store of i32 0x01020304 can never be turned into a memset,
954 // but it can be turned into memset_pattern if the target supports it.
955 Value *SplatValue = isBytewiseValue(StoredVal);
956 Constant *PatternValue = nullptr;
958 unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
960 // If we're allowed to form a memset, and the stored value would be acceptable
961 // for memset, use it.
962 if (SplatValue && TLI->has(LibFunc::memset) &&
963 // Verify that the stored value is loop invariant. If not, we can't
964 // promote the memset.
965 CurLoop->isLoopInvariant(SplatValue)) {
966 // Keep and use SplatValue.
967 PatternValue = nullptr;
968 } else if (DestAS == 0 &&
969 TLI->has(LibFunc::memset_pattern16) &&
970 (PatternValue = getMemSetPatternValue(StoredVal, *DL))) {
971 // Don't create memset_pattern16s with address spaces.
972 // It looks like we can use PatternValue!
973 SplatValue = nullptr;
975 // Otherwise, this isn't an idiom we can transform. For example, we can't
976 // do anything with a 3-byte store.
980 // The trip count of the loop and the base pointer of the addrec SCEV is
981 // guaranteed to be loop invariant, which means that it should dominate the
982 // header. This allows us to insert code for it in the preheader.
983 BasicBlock *Preheader = CurLoop->getLoopPreheader();
984 IRBuilder<> Builder(Preheader->getTerminator());
985 SCEVExpander Expander(*SE, "loop-idiom");
987 Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
989 // Okay, we have a strided store "p[i]" of a splattable value. We can turn
990 // this into a memset in the loop preheader now if we want. However, this
991 // would be unsafe to do if there is anything else in the loop that may read
992 // or write to the aliased location. Check for any overlap by generating the
993 // base pointer and checking the region.
995 Expander.expandCodeFor(Ev->getStart(), DestInt8PtrTy,
996 Preheader->getTerminator());
998 if (mayLoopAccessLocation(BasePtr, AliasAnalysis::ModRef,
1000 StoreSize, getAnalysis<AliasAnalysis>(), TheStore)) {
1002 // If we generated new code for the base pointer, clean up.
1003 deleteIfDeadInstruction(BasePtr, *SE, TLI);
1007 // Okay, everything looks good, insert the memset.
1009 // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
1010 // pointer size if it isn't already.
1011 Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
1012 BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);
1014 const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1),
1016 if (StoreSize != 1) {
1017 NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
1022 Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
1026 NewCall = Builder.CreateMemSet(BasePtr,
1031 // Everything is emitted in default address space
1032 Type *Int8PtrTy = DestInt8PtrTy;
1034 Module *M = TheStore->getParent()->getParent()->getParent();
1035 Value *MSP = M->getOrInsertFunction("memset_pattern16",
1036 Builder.getVoidTy(),
1042 // Otherwise we should form a memset_pattern16. PatternValue is known to be
1043 // an constant array of 16-bytes. Plop the value into a mergable global.
1044 GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
1045 GlobalValue::InternalLinkage,
1046 PatternValue, ".memset_pattern");
1047 GV->setUnnamedAddr(true); // Ok to merge these.
1048 GV->setAlignment(16);
1049 Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
1050 NewCall = Builder.CreateCall3(MSP, BasePtr, PatternPtr, NumBytes);
1053 DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"
1054 << " from store to: " << *Ev << " at: " << *TheStore << "\n");
1055 NewCall->setDebugLoc(TheStore->getDebugLoc());
1057 // Okay, the memset has been formed. Zap the original store and anything that
1059 deleteDeadInstruction(TheStore, *SE, TLI);
1064 /// processLoopStoreOfLoopLoad - We see a strided store whose value is a
1065 /// same-strided load.
1066 bool LoopIdiomRecognize::
1067 processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
1068 const SCEVAddRecExpr *StoreEv,
1069 const SCEVAddRecExpr *LoadEv,
1070 const SCEV *BECount) {
1071 // If we're not allowed to form memcpy, we fail.
1072 if (!TLI->has(LibFunc::memcpy))
1075 LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
1077 // The trip count of the loop and the base pointer of the addrec SCEV is
1078 // guaranteed to be loop invariant, which means that it should dominate the
1079 // header. This allows us to insert code for it in the preheader.
1080 BasicBlock *Preheader = CurLoop->getLoopPreheader();
1081 IRBuilder<> Builder(Preheader->getTerminator());
1082 SCEVExpander Expander(*SE, "loop-idiom");
1084 // Okay, we have a strided store "p[i]" of a loaded value. We can turn
1085 // this into a memcpy in the loop preheader now if we want. However, this
1086 // would be unsafe to do if there is anything else in the loop that may read
1087 // or write the memory region we're storing to. This includes the load that
1088 // feeds the stores. Check for an alias by generating the base address and
1089 // checking everything.
1090 Value *StoreBasePtr =
1091 Expander.expandCodeFor(StoreEv->getStart(),
1092 Builder.getInt8PtrTy(SI->getPointerAddressSpace()),
1093 Preheader->getTerminator());
1095 if (mayLoopAccessLocation(StoreBasePtr, AliasAnalysis::ModRef,
1096 CurLoop, BECount, StoreSize,
1097 getAnalysis<AliasAnalysis>(), SI)) {
1099 // If we generated new code for the base pointer, clean up.
1100 deleteIfDeadInstruction(StoreBasePtr, *SE, TLI);
1104 // For a memcpy, we have to make sure that the input array is not being
1105 // mutated by the loop.
1106 Value *LoadBasePtr =
1107 Expander.expandCodeFor(LoadEv->getStart(),
1108 Builder.getInt8PtrTy(LI->getPointerAddressSpace()),
1109 Preheader->getTerminator());
1111 if (mayLoopAccessLocation(LoadBasePtr, AliasAnalysis::Mod, CurLoop, BECount,
1112 StoreSize, getAnalysis<AliasAnalysis>(), SI)) {
1114 // If we generated new code for the base pointer, clean up.
1115 deleteIfDeadInstruction(LoadBasePtr, *SE, TLI);
1116 deleteIfDeadInstruction(StoreBasePtr, *SE, TLI);
1120 // Okay, everything is safe, we can transform this!
1123 // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
1124 // pointer size if it isn't already.
1125 Type *IntPtrTy = Builder.getIntPtrTy(DL, SI->getPointerAddressSpace());
1126 BECount = SE->getTruncateOrZeroExtend(BECount, IntPtrTy);
1128 const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtrTy, 1),
1131 NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtrTy, StoreSize),
1135 Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
1138 Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
1139 std::min(SI->getAlignment(), LI->getAlignment()));
1140 NewCall->setDebugLoc(SI->getDebugLoc());
1142 DEBUG(dbgs() << " Formed memcpy: " << *NewCall << "\n"
1143 << " from load ptr=" << *LoadEv << " at: " << *LI << "\n"
1144 << " from store ptr=" << *StoreEv << " at: " << *SI << "\n");
1147 // Okay, the memset has been formed. Zap the original store and anything that
1149 deleteDeadInstruction(SI, *SE, TLI);