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LoopIdiomRecognize.cpp
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00001 //===-- LoopIdiomRecognize.cpp - Loop idiom recognition -------------------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file is distributed under the University of Illinois Open Source
00006 // License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This pass implements an idiom recognizer that transforms simple loops into a
00011 // non-loop form.  In cases that this kicks in, it can be a significant
00012 // performance win.
00013 //
00014 //===----------------------------------------------------------------------===//
00015 //
00016 // TODO List:
00017 //
00018 // Future loop memory idioms to recognize:
00019 //   memcmp, memmove, strlen, etc.
00020 // Future floating point idioms to recognize in -ffast-math mode:
00021 //   fpowi
00022 // Future integer operation idioms to recognize:
00023 //   ctpop, ctlz, cttz
00024 //
00025 // Beware that isel's default lowering for ctpop is highly inefficient for
00026 // i64 and larger types when i64 is legal and the value has few bits set.  It
00027 // would be good to enhance isel to emit a loop for ctpop in this case.
00028 //
00029 // We should enhance the memset/memcpy recognition to handle multiple stores in
00030 // the loop.  This would handle things like:
00031 //   void foo(_Complex float *P)
00032 //     for (i) { __real__(*P) = 0;  __imag__(*P) = 0; }
00033 //
00034 // We should enhance this to handle negative strides through memory.
00035 // Alternatively (and perhaps better) we could rely on an earlier pass to force
00036 // forward iteration through memory, which is generally better for cache
00037 // behavior.  Negative strides *do* happen for memset/memcpy loops.
00038 //
00039 // This could recognize common matrix multiplies and dot product idioms and
00040 // replace them with calls to BLAS (if linked in??).
00041 //
00042 //===----------------------------------------------------------------------===//
00043 
00044 #include "llvm/Transforms/Scalar.h"
00045 #include "llvm/ADT/Statistic.h"
00046 #include "llvm/Analysis/AliasAnalysis.h"
00047 #include "llvm/Analysis/LoopPass.h"
00048 #include "llvm/Analysis/ScalarEvolutionExpander.h"
00049 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
00050 #include "llvm/Analysis/TargetTransformInfo.h"
00051 #include "llvm/Analysis/ValueTracking.h"
00052 #include "llvm/IR/DataLayout.h"
00053 #include "llvm/IR/Dominators.h"
00054 #include "llvm/IR/IRBuilder.h"
00055 #include "llvm/IR/IntrinsicInst.h"
00056 #include "llvm/IR/Module.h"
00057 #include "llvm/Support/Debug.h"
00058 #include "llvm/Support/raw_ostream.h"
00059 #include "llvm/Target/TargetLibraryInfo.h"
00060 #include "llvm/Transforms/Utils/Local.h"
00061 using namespace llvm;
00062 
00063 #define DEBUG_TYPE "loop-idiom"
00064 
00065 STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
00066 STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
00067 
00068 namespace {
00069 
00070   class LoopIdiomRecognize;
00071 
00072   /// This class defines some utility functions for loop idiom recognization.
00073   class LIRUtil {
00074   public:
00075     /// Return true iff the block contains nothing but an uncondition branch
00076     /// (aka goto instruction).
00077     static bool isAlmostEmpty(BasicBlock *);
00078 
00079     static BranchInst *getBranch(BasicBlock *BB) {
00080       return dyn_cast<BranchInst>(BB->getTerminator());
00081     }
00082 
00083     /// Derive the precondition block (i.e the block that guards the loop
00084     /// preheader) from the given preheader.
00085     static BasicBlock *getPrecondBb(BasicBlock *PreHead);
00086   };
00087 
00088   /// This class is to recoginize idioms of population-count conducted in
00089   /// a noncountable loop. Currently it only recognizes this pattern:
00090   /// \code
00091   ///   while(x) {cnt++; ...; x &= x - 1; ...}
00092   /// \endcode
00093   class NclPopcountRecognize {
00094     LoopIdiomRecognize &LIR;
00095     Loop *CurLoop;
00096     BasicBlock *PreCondBB;
00097 
00098     typedef IRBuilder<> IRBuilderTy;
00099 
00100   public:
00101     explicit NclPopcountRecognize(LoopIdiomRecognize &TheLIR);
00102     bool recognize();
00103 
00104   private:
00105     /// Take a glimpse of the loop to see if we need to go ahead recoginizing
00106     /// the idiom.
00107     bool preliminaryScreen();
00108 
00109     /// Check if the given conditional branch is based on the comparison
00110     /// between a variable and zero, and if the variable is non-zero, the
00111     /// control yields to the loop entry. If the branch matches the behavior,
00112     /// the variable involved in the comparion is returned. This function will
00113     /// be called to see if the precondition and postcondition of the loop
00114     /// are in desirable form.
00115     Value *matchCondition (BranchInst *Br, BasicBlock *NonZeroTarget) const;
00116 
00117     /// Return true iff the idiom is detected in the loop. and 1) \p CntInst
00118     /// is set to the instruction counting the pupulation bit. 2) \p CntPhi
00119     /// is set to the corresponding phi node. 3) \p Var is set to the value
00120     /// whose population bits are being counted.
00121     bool detectIdiom
00122       (Instruction *&CntInst, PHINode *&CntPhi, Value *&Var) const;
00123 
00124     /// Insert ctpop intrinsic function and some obviously dead instructions.
00125     void transform (Instruction *CntInst, PHINode *CntPhi, Value *Var);
00126 
00127     /// Create llvm.ctpop.* intrinsic function.
00128     CallInst *createPopcntIntrinsic(IRBuilderTy &IRB, Value *Val, DebugLoc DL);
00129   };
00130 
00131   class LoopIdiomRecognize : public LoopPass {
00132     Loop *CurLoop;
00133     const DataLayout *DL;
00134     DominatorTree *DT;
00135     ScalarEvolution *SE;
00136     TargetLibraryInfo *TLI;
00137     const TargetTransformInfo *TTI;
00138   public:
00139     static char ID;
00140     explicit LoopIdiomRecognize() : LoopPass(ID) {
00141       initializeLoopIdiomRecognizePass(*PassRegistry::getPassRegistry());
00142       DL = 0; DT = 0; SE = 0; TLI = 0; TTI = 0;
00143     }
00144 
00145     bool runOnLoop(Loop *L, LPPassManager &LPM) override;
00146     bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
00147                         SmallVectorImpl<BasicBlock*> &ExitBlocks);
00148 
00149     bool processLoopStore(StoreInst *SI, const SCEV *BECount);
00150     bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
00151 
00152     bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
00153                                  unsigned StoreAlignment,
00154                                  Value *SplatValue, Instruction *TheStore,
00155                                  const SCEVAddRecExpr *Ev,
00156                                  const SCEV *BECount);
00157     bool processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
00158                                     const SCEVAddRecExpr *StoreEv,
00159                                     const SCEVAddRecExpr *LoadEv,
00160                                     const SCEV *BECount);
00161 
00162     /// This transformation requires natural loop information & requires that
00163     /// loop preheaders be inserted into the CFG.
00164     ///
00165     void getAnalysisUsage(AnalysisUsage &AU) const override {
00166       AU.addRequired<LoopInfo>();
00167       AU.addPreserved<LoopInfo>();
00168       AU.addRequiredID(LoopSimplifyID);
00169       AU.addPreservedID(LoopSimplifyID);
00170       AU.addRequiredID(LCSSAID);
00171       AU.addPreservedID(LCSSAID);
00172       AU.addRequired<AliasAnalysis>();
00173       AU.addPreserved<AliasAnalysis>();
00174       AU.addRequired<ScalarEvolution>();
00175       AU.addPreserved<ScalarEvolution>();
00176       AU.addPreserved<DominatorTreeWrapperPass>();
00177       AU.addRequired<DominatorTreeWrapperPass>();
00178       AU.addRequired<TargetLibraryInfo>();
00179       AU.addRequired<TargetTransformInfo>();
00180     }
00181 
00182     const DataLayout *getDataLayout() {
00183       if (DL)
00184         return DL;
00185       DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
00186       DL = DLP ? &DLP->getDataLayout() : 0;
00187       return DL;
00188     }
00189 
00190     DominatorTree *getDominatorTree() {
00191       return DT ? DT
00192                 : (DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree());
00193     }
00194 
00195     ScalarEvolution *getScalarEvolution() {
00196       return SE ? SE : (SE = &getAnalysis<ScalarEvolution>());
00197     }
00198 
00199     TargetLibraryInfo *getTargetLibraryInfo() {
00200       return TLI ? TLI : (TLI = &getAnalysis<TargetLibraryInfo>());
00201     }
00202 
00203     const TargetTransformInfo *getTargetTransformInfo() {
00204       return TTI ? TTI : (TTI = &getAnalysis<TargetTransformInfo>());
00205     }
00206 
00207     Loop *getLoop() const { return CurLoop; }
00208 
00209   private:
00210     bool runOnNoncountableLoop();
00211     bool runOnCountableLoop();
00212   };
00213 }
00214 
00215 char LoopIdiomRecognize::ID = 0;
00216 INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
00217                       false, false)
00218 INITIALIZE_PASS_DEPENDENCY(LoopInfo)
00219 INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
00220 INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
00221 INITIALIZE_PASS_DEPENDENCY(LCSSA)
00222 INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
00223 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
00224 INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
00225 INITIALIZE_AG_DEPENDENCY(TargetTransformInfo)
00226 INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
00227                     false, false)
00228 
00229 Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
00230 
00231 /// deleteDeadInstruction - Delete this instruction.  Before we do, go through
00232 /// and zero out all the operands of this instruction.  If any of them become
00233 /// dead, delete them and the computation tree that feeds them.
00234 ///
00235 static void deleteDeadInstruction(Instruction *I, ScalarEvolution &SE,
00236                                   const TargetLibraryInfo *TLI) {
00237   SmallVector<Instruction*, 32> NowDeadInsts;
00238 
00239   NowDeadInsts.push_back(I);
00240 
00241   // Before we touch this instruction, remove it from SE!
00242   do {
00243     Instruction *DeadInst = NowDeadInsts.pop_back_val();
00244 
00245     // This instruction is dead, zap it, in stages.  Start by removing it from
00246     // SCEV.
00247     SE.forgetValue(DeadInst);
00248 
00249     for (unsigned op = 0, e = DeadInst->getNumOperands(); op != e; ++op) {
00250       Value *Op = DeadInst->getOperand(op);
00251       DeadInst->setOperand(op, 0);
00252 
00253       // If this operand just became dead, add it to the NowDeadInsts list.
00254       if (!Op->use_empty()) continue;
00255 
00256       if (Instruction *OpI = dyn_cast<Instruction>(Op))
00257         if (isInstructionTriviallyDead(OpI, TLI))
00258           NowDeadInsts.push_back(OpI);
00259     }
00260 
00261     DeadInst->eraseFromParent();
00262 
00263   } while (!NowDeadInsts.empty());
00264 }
00265 
00266 /// deleteIfDeadInstruction - If the specified value is a dead instruction,
00267 /// delete it and any recursively used instructions.
00268 static void deleteIfDeadInstruction(Value *V, ScalarEvolution &SE,
00269                                     const TargetLibraryInfo *TLI) {
00270   if (Instruction *I = dyn_cast<Instruction>(V))
00271     if (isInstructionTriviallyDead(I, TLI))
00272       deleteDeadInstruction(I, SE, TLI);
00273 }
00274 
00275 //===----------------------------------------------------------------------===//
00276 //
00277 //          Implementation of LIRUtil
00278 //
00279 //===----------------------------------------------------------------------===//
00280 
00281 // This function will return true iff the given block contains nothing but goto.
00282 // A typical usage of this function is to check if the preheader function is
00283 // "almost" empty such that generated intrinsic functions can be moved across
00284 // the preheader and be placed at the end of the precondition block without
00285 // the concern of breaking data dependence.
00286 bool LIRUtil::isAlmostEmpty(BasicBlock *BB) {
00287   if (BranchInst *Br = getBranch(BB)) {
00288     return Br->isUnconditional() && BB->size() == 1;
00289   }
00290   return false;
00291 }
00292 
00293 BasicBlock *LIRUtil::getPrecondBb(BasicBlock *PreHead) {
00294   if (BasicBlock *BB = PreHead->getSinglePredecessor()) {
00295     BranchInst *Br = getBranch(BB);
00296     return Br && Br->isConditional() ? BB : 0;
00297   }
00298   return 0;
00299 }
00300 
00301 //===----------------------------------------------------------------------===//
00302 //
00303 //          Implementation of NclPopcountRecognize
00304 //
00305 //===----------------------------------------------------------------------===//
00306 
00307 NclPopcountRecognize::NclPopcountRecognize(LoopIdiomRecognize &TheLIR):
00308   LIR(TheLIR), CurLoop(TheLIR.getLoop()), PreCondBB(0) {
00309 }
00310 
00311 bool NclPopcountRecognize::preliminaryScreen() {
00312   const TargetTransformInfo *TTI = LIR.getTargetTransformInfo();
00313   if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
00314     return false;
00315 
00316   // Counting population are usually conducted by few arithmetic instructions.
00317   // Such instructions can be easilly "absorbed" by vacant slots in a
00318   // non-compact loop. Therefore, recognizing popcount idiom only makes sense
00319   // in a compact loop.
00320 
00321   // Give up if the loop has multiple blocks or multiple backedges.
00322   if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
00323     return false;
00324 
00325   BasicBlock *LoopBody = *(CurLoop->block_begin());
00326   if (LoopBody->size() >= 20) {
00327     // The loop is too big, bail out.
00328     return false;
00329   }
00330 
00331   // It should have a preheader containing nothing but a goto instruction.
00332   BasicBlock *PreHead = CurLoop->getLoopPreheader();
00333   if (!PreHead || !LIRUtil::isAlmostEmpty(PreHead))
00334     return false;
00335 
00336   // It should have a precondition block where the generated popcount instrinsic
00337   // function will be inserted.
00338   PreCondBB = LIRUtil::getPrecondBb(PreHead);
00339   if (!PreCondBB)
00340     return false;
00341 
00342   return true;
00343 }
00344 
00345 Value *NclPopcountRecognize::matchCondition (BranchInst *Br,
00346                                              BasicBlock *LoopEntry) const {
00347   if (!Br || !Br->isConditional())
00348     return 0;
00349 
00350   ICmpInst *Cond = dyn_cast<ICmpInst>(Br->getCondition());
00351   if (!Cond)
00352     return 0;
00353 
00354   ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
00355   if (!CmpZero || !CmpZero->isZero())
00356     return 0;
00357 
00358   ICmpInst::Predicate Pred = Cond->getPredicate();
00359   if ((Pred == ICmpInst::ICMP_NE && Br->getSuccessor(0) == LoopEntry) ||
00360       (Pred == ICmpInst::ICMP_EQ && Br->getSuccessor(1) == LoopEntry))
00361     return Cond->getOperand(0);
00362 
00363   return 0;
00364 }
00365 
00366 bool NclPopcountRecognize::detectIdiom(Instruction *&CntInst,
00367                                        PHINode *&CntPhi,
00368                                        Value *&Var) const {
00369   // Following code tries to detect this idiom:
00370   //
00371   //    if (x0 != 0)
00372   //      goto loop-exit // the precondition of the loop
00373   //    cnt0 = init-val;
00374   //    do {
00375   //       x1 = phi (x0, x2);
00376   //       cnt1 = phi(cnt0, cnt2);
00377   //
00378   //       cnt2 = cnt1 + 1;
00379   //        ...
00380   //       x2 = x1 & (x1 - 1);
00381   //        ...
00382   //    } while(x != 0);
00383   //
00384   // loop-exit:
00385   //
00386 
00387   // step 1: Check to see if the look-back branch match this pattern:
00388   //    "if (a!=0) goto loop-entry".
00389   BasicBlock *LoopEntry;
00390   Instruction *DefX2, *CountInst;
00391   Value *VarX1, *VarX0;
00392   PHINode *PhiX, *CountPhi;
00393 
00394   DefX2 = CountInst = 0;
00395   VarX1 = VarX0 = 0;
00396   PhiX = CountPhi = 0;
00397   LoopEntry = *(CurLoop->block_begin());
00398 
00399   // step 1: Check if the loop-back branch is in desirable form.
00400   {
00401     if (Value *T = matchCondition (LIRUtil::getBranch(LoopEntry), LoopEntry))
00402       DefX2 = dyn_cast<Instruction>(T);
00403     else
00404       return false;
00405   }
00406 
00407   // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
00408   {
00409     if (!DefX2 || DefX2->getOpcode() != Instruction::And)
00410       return false;
00411 
00412     BinaryOperator *SubOneOp;
00413 
00414     if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
00415       VarX1 = DefX2->getOperand(1);
00416     else {
00417       VarX1 = DefX2->getOperand(0);
00418       SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
00419     }
00420     if (!SubOneOp)
00421       return false;
00422 
00423     Instruction *SubInst = cast<Instruction>(SubOneOp);
00424     ConstantInt *Dec = dyn_cast<ConstantInt>(SubInst->getOperand(1));
00425     if (!Dec ||
00426         !((SubInst->getOpcode() == Instruction::Sub && Dec->isOne()) ||
00427           (SubInst->getOpcode() == Instruction::Add && Dec->isAllOnesValue()))) {
00428       return false;
00429     }
00430   }
00431 
00432   // step 3: Check the recurrence of variable X
00433   {
00434     PhiX = dyn_cast<PHINode>(VarX1);
00435     if (!PhiX ||
00436         (PhiX->getOperand(0) != DefX2 && PhiX->getOperand(1) != DefX2)) {
00437       return false;
00438     }
00439   }
00440 
00441   // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
00442   {
00443     CountInst = NULL;
00444     for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI(),
00445            IterE = LoopEntry->end(); Iter != IterE; Iter++) {
00446       Instruction *Inst = Iter;
00447       if (Inst->getOpcode() != Instruction::Add)
00448         continue;
00449 
00450       ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
00451       if (!Inc || !Inc->isOne())
00452         continue;
00453 
00454       PHINode *Phi = dyn_cast<PHINode>(Inst->getOperand(0));
00455       if (!Phi || Phi->getParent() != LoopEntry)
00456         continue;
00457 
00458       // Check if the result of the instruction is live of the loop.
00459       bool LiveOutLoop = false;
00460       for (User *U : Inst->users()) {
00461         if ((cast<Instruction>(U))->getParent() != LoopEntry) {
00462           LiveOutLoop = true; break;
00463         }
00464       }
00465 
00466       if (LiveOutLoop) {
00467         CountInst = Inst;
00468         CountPhi = Phi;
00469         break;
00470       }
00471     }
00472 
00473     if (!CountInst)
00474       return false;
00475   }
00476 
00477   // step 5: check if the precondition is in this form:
00478   //   "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
00479   {
00480     BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
00481     Value *T = matchCondition (PreCondBr, CurLoop->getLoopPreheader());
00482     if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
00483       return false;
00484 
00485     CntInst = CountInst;
00486     CntPhi = CountPhi;
00487     Var = T;
00488   }
00489 
00490   return true;
00491 }
00492 
00493 void NclPopcountRecognize::transform(Instruction *CntInst,
00494                                      PHINode *CntPhi, Value *Var) {
00495 
00496   ScalarEvolution *SE = LIR.getScalarEvolution();
00497   TargetLibraryInfo *TLI = LIR.getTargetLibraryInfo();
00498   BasicBlock *PreHead = CurLoop->getLoopPreheader();
00499   BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
00500   const DebugLoc DL = CntInst->getDebugLoc();
00501 
00502   // Assuming before transformation, the loop is following:
00503   //  if (x) // the precondition
00504   //     do { cnt++; x &= x - 1; } while(x);
00505 
00506   // Step 1: Insert the ctpop instruction at the end of the precondition block
00507   IRBuilderTy Builder(PreCondBr);
00508   Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
00509   {
00510     PopCnt = createPopcntIntrinsic(Builder, Var, DL);
00511     NewCount = PopCntZext =
00512       Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
00513 
00514     if (NewCount != PopCnt)
00515       (cast<Instruction>(NewCount))->setDebugLoc(DL);
00516 
00517     // TripCnt is exactly the number of iterations the loop has
00518     TripCnt = NewCount;
00519 
00520     // If the population counter's initial value is not zero, insert Add Inst.
00521     Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
00522     ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
00523     if (!InitConst || !InitConst->isZero()) {
00524       NewCount = Builder.CreateAdd(NewCount, CntInitVal);
00525       (cast<Instruction>(NewCount))->setDebugLoc(DL);
00526     }
00527   }
00528 
00529   // Step 2: Replace the precondition from "if(x == 0) goto loop-exit" to
00530   //   "if(NewCount == 0) loop-exit". Withtout this change, the intrinsic
00531   //   function would be partial dead code, and downstream passes will drag
00532   //   it back from the precondition block to the preheader.
00533   {
00534     ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
00535 
00536     Value *Opnd0 = PopCntZext;
00537     Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
00538     if (PreCond->getOperand(0) != Var)
00539       std::swap(Opnd0, Opnd1);
00540 
00541     ICmpInst *NewPreCond =
00542       cast<ICmpInst>(Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
00543     PreCond->replaceAllUsesWith(NewPreCond);
00544 
00545     deleteDeadInstruction(PreCond, *SE, TLI);
00546   }
00547 
00548   // Step 3: Note that the population count is exactly the trip count of the
00549   // loop in question, which enble us to to convert the loop from noncountable
00550   // loop into a countable one. The benefit is twofold:
00551   //
00552   //  - If the loop only counts population, the entire loop become dead after
00553   //    the transformation. It is lots easier to prove a countable loop dead
00554   //    than to prove a noncountable one. (In some C dialects, a infite loop
00555   //    isn't dead even if it computes nothing useful. In general, DCE needs
00556   //    to prove a noncountable loop finite before safely delete it.)
00557   //
00558   //  - If the loop also performs something else, it remains alive.
00559   //    Since it is transformed to countable form, it can be aggressively
00560   //    optimized by some optimizations which are in general not applicable
00561   //    to a noncountable loop.
00562   //
00563   // After this step, this loop (conceptually) would look like following:
00564   //   newcnt = __builtin_ctpop(x);
00565   //   t = newcnt;
00566   //   if (x)
00567   //     do { cnt++; x &= x-1; t--) } while (t > 0);
00568   BasicBlock *Body = *(CurLoop->block_begin());
00569   {
00570     BranchInst *LbBr = LIRUtil::getBranch(Body);
00571     ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
00572     Type *Ty = TripCnt->getType();
00573 
00574     PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", Body->begin());
00575 
00576     Builder.SetInsertPoint(LbCond);
00577     Value *Opnd1 = cast<Value>(TcPhi);
00578     Value *Opnd2 = cast<Value>(ConstantInt::get(Ty, 1));
00579     Instruction *TcDec =
00580       cast<Instruction>(Builder.CreateSub(Opnd1, Opnd2, "tcdec", false, true));
00581 
00582     TcPhi->addIncoming(TripCnt, PreHead);
00583     TcPhi->addIncoming(TcDec, Body);
00584 
00585     CmpInst::Predicate Pred = (LbBr->getSuccessor(0) == Body) ?
00586       CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
00587     LbCond->setPredicate(Pred);
00588     LbCond->setOperand(0, TcDec);
00589     LbCond->setOperand(1, cast<Value>(ConstantInt::get(Ty, 0)));
00590   }
00591 
00592   // Step 4: All the references to the original population counter outside
00593   //  the loop are replaced with the NewCount -- the value returned from
00594   //  __builtin_ctpop().
00595   {
00596     SmallVector<Value *, 4> CntUses;
00597     for (User *U : CntInst->users())
00598       if (cast<Instruction>(U)->getParent() != Body)
00599         CntUses.push_back(U);
00600     for (unsigned Idx = 0; Idx < CntUses.size(); Idx++) {
00601       (cast<Instruction>(CntUses[Idx]))->replaceUsesOfWith(CntInst, NewCount);
00602     }
00603   }
00604 
00605   // step 5: Forget the "non-computable" trip-count SCEV associated with the
00606   //   loop. The loop would otherwise not be deleted even if it becomes empty.
00607   SE->forgetLoop(CurLoop);
00608 }
00609 
00610 CallInst *NclPopcountRecognize::createPopcntIntrinsic(IRBuilderTy &IRBuilder,
00611                                                       Value *Val, DebugLoc DL) {
00612   Value *Ops[] = { Val };
00613   Type *Tys[] = { Val->getType() };
00614 
00615   Module *M = (*(CurLoop->block_begin()))->getParent()->getParent();
00616   Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
00617   CallInst *CI = IRBuilder.CreateCall(Func, Ops);
00618   CI->setDebugLoc(DL);
00619 
00620   return CI;
00621 }
00622 
00623 /// recognize - detect population count idiom in a non-countable loop. If
00624 ///   detected, transform the relevant code to popcount intrinsic function
00625 ///   call, and return true; otherwise, return false.
00626 bool NclPopcountRecognize::recognize() {
00627 
00628   if (!LIR.getTargetTransformInfo())
00629     return false;
00630 
00631   LIR.getScalarEvolution();
00632 
00633   if (!preliminaryScreen())
00634     return false;
00635 
00636   Instruction *CntInst;
00637   PHINode *CntPhi;
00638   Value *Val;
00639   if (!detectIdiom(CntInst, CntPhi, Val))
00640     return false;
00641 
00642   transform(CntInst, CntPhi, Val);
00643   return true;
00644 }
00645 
00646 //===----------------------------------------------------------------------===//
00647 //
00648 //          Implementation of LoopIdiomRecognize
00649 //
00650 //===----------------------------------------------------------------------===//
00651 
00652 bool LoopIdiomRecognize::runOnCountableLoop() {
00653   const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
00654   if (isa<SCEVCouldNotCompute>(BECount)) return false;
00655 
00656   // If this loop executes exactly one time, then it should be peeled, not
00657   // optimized by this pass.
00658   if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
00659     if (BECst->getValue()->getValue() == 0)
00660       return false;
00661 
00662   // We require target data for now.
00663   if (!getDataLayout())
00664     return false;
00665 
00666   // set DT
00667   (void)getDominatorTree();
00668 
00669   LoopInfo &LI = getAnalysis<LoopInfo>();
00670   TLI = &getAnalysis<TargetLibraryInfo>();
00671 
00672   // set TLI
00673   (void)getTargetLibraryInfo();
00674 
00675   SmallVector<BasicBlock*, 8> ExitBlocks;
00676   CurLoop->getUniqueExitBlocks(ExitBlocks);
00677 
00678   DEBUG(dbgs() << "loop-idiom Scanning: F["
00679                << CurLoop->getHeader()->getParent()->getName()
00680                << "] Loop %" << CurLoop->getHeader()->getName() << "\n");
00681 
00682   bool MadeChange = false;
00683   // Scan all the blocks in the loop that are not in subloops.
00684   for (Loop::block_iterator BI = CurLoop->block_begin(),
00685          E = CurLoop->block_end(); BI != E; ++BI) {
00686     // Ignore blocks in subloops.
00687     if (LI.getLoopFor(*BI) != CurLoop)
00688       continue;
00689 
00690     MadeChange |= runOnLoopBlock(*BI, BECount, ExitBlocks);
00691   }
00692   return MadeChange;
00693 }
00694 
00695 bool LoopIdiomRecognize::runOnNoncountableLoop() {
00696   NclPopcountRecognize Popcount(*this);
00697   if (Popcount.recognize())
00698     return true;
00699 
00700   return false;
00701 }
00702 
00703 bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
00704   if (skipOptnoneFunction(L))
00705     return false;
00706 
00707   CurLoop = L;
00708 
00709   // If the loop could not be converted to canonical form, it must have an
00710   // indirectbr in it, just give up.
00711   if (!L->getLoopPreheader())
00712     return false;
00713 
00714   // Disable loop idiom recognition if the function's name is a common idiom.
00715   StringRef Name = L->getHeader()->getParent()->getName();
00716   if (Name == "memset" || Name == "memcpy")
00717     return false;
00718 
00719   SE = &getAnalysis<ScalarEvolution>();
00720   if (SE->hasLoopInvariantBackedgeTakenCount(L))
00721     return runOnCountableLoop();
00722   return runOnNoncountableLoop();
00723 }
00724 
00725 /// runOnLoopBlock - Process the specified block, which lives in a counted loop
00726 /// with the specified backedge count.  This block is known to be in the current
00727 /// loop and not in any subloops.
00728 bool LoopIdiomRecognize::runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
00729                                      SmallVectorImpl<BasicBlock*> &ExitBlocks) {
00730   // We can only promote stores in this block if they are unconditionally
00731   // executed in the loop.  For a block to be unconditionally executed, it has
00732   // to dominate all the exit blocks of the loop.  Verify this now.
00733   for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
00734     if (!DT->dominates(BB, ExitBlocks[i]))
00735       return false;
00736 
00737   bool MadeChange = false;
00738   for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
00739     Instruction *Inst = I++;
00740     // Look for store instructions, which may be optimized to memset/memcpy.
00741     if (StoreInst *SI = dyn_cast<StoreInst>(Inst))  {
00742       WeakVH InstPtr(I);
00743       if (!processLoopStore(SI, BECount)) continue;
00744       MadeChange = true;
00745 
00746       // If processing the store invalidated our iterator, start over from the
00747       // top of the block.
00748       if (InstPtr == 0)
00749         I = BB->begin();
00750       continue;
00751     }
00752 
00753     // Look for memset instructions, which may be optimized to a larger memset.
00754     if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst))  {
00755       WeakVH InstPtr(I);
00756       if (!processLoopMemSet(MSI, BECount)) continue;
00757       MadeChange = true;
00758 
00759       // If processing the memset invalidated our iterator, start over from the
00760       // top of the block.
00761       if (InstPtr == 0)
00762         I = BB->begin();
00763       continue;
00764     }
00765   }
00766 
00767   return MadeChange;
00768 }
00769 
00770 
00771 /// processLoopStore - See if this store can be promoted to a memset or memcpy.
00772 bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
00773   if (!SI->isSimple()) return false;
00774 
00775   Value *StoredVal = SI->getValueOperand();
00776   Value *StorePtr = SI->getPointerOperand();
00777 
00778   // Reject stores that are so large that they overflow an unsigned.
00779   uint64_t SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
00780   if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
00781     return false;
00782 
00783   // See if the pointer expression is an AddRec like {base,+,1} on the current
00784   // loop, which indicates a strided store.  If we have something else, it's a
00785   // random store we can't handle.
00786   const SCEVAddRecExpr *StoreEv =
00787     dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
00788   if (StoreEv == 0 || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
00789     return false;
00790 
00791   // Check to see if the stride matches the size of the store.  If so, then we
00792   // know that every byte is touched in the loop.
00793   unsigned StoreSize = (unsigned)SizeInBits >> 3;
00794   const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
00795 
00796   if (Stride == 0 || StoreSize != Stride->getValue()->getValue()) {
00797     // TODO: Could also handle negative stride here someday, that will require
00798     // the validity check in mayLoopAccessLocation to be updated though.
00799     // Enable this to print exact negative strides.
00800     if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
00801       dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
00802       dbgs() << "BB: " << *SI->getParent();
00803     }
00804 
00805     return false;
00806   }
00807 
00808   // See if we can optimize just this store in isolation.
00809   if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
00810                               StoredVal, SI, StoreEv, BECount))
00811     return true;
00812 
00813   // If the stored value is a strided load in the same loop with the same stride
00814   // this this may be transformable into a memcpy.  This kicks in for stuff like
00815   //   for (i) A[i] = B[i];
00816   if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
00817     const SCEVAddRecExpr *LoadEv =
00818       dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getOperand(0)));
00819     if (LoadEv && LoadEv->getLoop() == CurLoop && LoadEv->isAffine() &&
00820         StoreEv->getOperand(1) == LoadEv->getOperand(1) && LI->isSimple())
00821       if (processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, LoadEv, BECount))
00822         return true;
00823   }
00824   //errs() << "UNHANDLED strided store: " << *StoreEv << " - " << *SI << "\n";
00825 
00826   return false;
00827 }
00828 
00829 /// processLoopMemSet - See if this memset can be promoted to a large memset.
00830 bool LoopIdiomRecognize::
00831 processLoopMemSet(MemSetInst *MSI, const SCEV *BECount) {
00832   // We can only handle non-volatile memsets with a constant size.
00833   if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength())) return false;
00834 
00835   // If we're not allowed to hack on memset, we fail.
00836   if (!TLI->has(LibFunc::memset))
00837     return false;
00838 
00839   Value *Pointer = MSI->getDest();
00840 
00841   // See if the pointer expression is an AddRec like {base,+,1} on the current
00842   // loop, which indicates a strided store.  If we have something else, it's a
00843   // random store we can't handle.
00844   const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
00845   if (Ev == 0 || Ev->getLoop() != CurLoop || !Ev->isAffine())
00846     return false;
00847 
00848   // Reject memsets that are so large that they overflow an unsigned.
00849   uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
00850   if ((SizeInBytes >> 32) != 0)
00851     return false;
00852 
00853   // Check to see if the stride matches the size of the memset.  If so, then we
00854   // know that every byte is touched in the loop.
00855   const SCEVConstant *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
00856 
00857   // TODO: Could also handle negative stride here someday, that will require the
00858   // validity check in mayLoopAccessLocation to be updated though.
00859   if (Stride == 0 || MSI->getLength() != Stride->getValue())
00860     return false;
00861 
00862   return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
00863                                  MSI->getAlignment(), MSI->getValue(),
00864                                  MSI, Ev, BECount);
00865 }
00866 
00867 
00868 /// mayLoopAccessLocation - Return true if the specified loop might access the
00869 /// specified pointer location, which is a loop-strided access.  The 'Access'
00870 /// argument specifies what the verboten forms of access are (read or write).
00871 static bool mayLoopAccessLocation(Value *Ptr,AliasAnalysis::ModRefResult Access,
00872                                   Loop *L, const SCEV *BECount,
00873                                   unsigned StoreSize, AliasAnalysis &AA,
00874                                   Instruction *IgnoredStore) {
00875   // Get the location that may be stored across the loop.  Since the access is
00876   // strided positively through memory, we say that the modified location starts
00877   // at the pointer and has infinite size.
00878   uint64_t AccessSize = AliasAnalysis::UnknownSize;
00879 
00880   // If the loop iterates a fixed number of times, we can refine the access size
00881   // to be exactly the size of the memset, which is (BECount+1)*StoreSize
00882   if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
00883     AccessSize = (BECst->getValue()->getZExtValue()+1)*StoreSize;
00884 
00885   // TODO: For this to be really effective, we have to dive into the pointer
00886   // operand in the store.  Store to &A[i] of 100 will always return may alias
00887   // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
00888   // which will then no-alias a store to &A[100].
00889   AliasAnalysis::Location StoreLoc(Ptr, AccessSize);
00890 
00891   for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
00892        ++BI)
00893     for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
00894       if (&*I != IgnoredStore &&
00895           (AA.getModRefInfo(I, StoreLoc) & Access))
00896         return true;
00897 
00898   return false;
00899 }
00900 
00901 /// getMemSetPatternValue - If a strided store of the specified value is safe to
00902 /// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
00903 /// be passed in.  Otherwise, return null.
00904 ///
00905 /// Note that we don't ever attempt to use memset_pattern8 or 4, because these
00906 /// just replicate their input array and then pass on to memset_pattern16.
00907 static Constant *getMemSetPatternValue(Value *V, const DataLayout &DL) {
00908   // If the value isn't a constant, we can't promote it to being in a constant
00909   // array.  We could theoretically do a store to an alloca or something, but
00910   // that doesn't seem worthwhile.
00911   Constant *C = dyn_cast<Constant>(V);
00912   if (C == 0) return 0;
00913 
00914   // Only handle simple values that are a power of two bytes in size.
00915   uint64_t Size = DL.getTypeSizeInBits(V->getType());
00916   if (Size == 0 || (Size & 7) || (Size & (Size-1)))
00917     return 0;
00918 
00919   // Don't care enough about darwin/ppc to implement this.
00920   if (DL.isBigEndian())
00921     return 0;
00922 
00923   // Convert to size in bytes.
00924   Size /= 8;
00925 
00926   // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
00927   // if the top and bottom are the same (e.g. for vectors and large integers).
00928   if (Size > 16) return 0;
00929 
00930   // If the constant is exactly 16 bytes, just use it.
00931   if (Size == 16) return C;
00932 
00933   // Otherwise, we'll use an array of the constants.
00934   unsigned ArraySize = 16/Size;
00935   ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
00936   return ConstantArray::get(AT, std::vector<Constant*>(ArraySize, C));
00937 }
00938 
00939 
00940 /// processLoopStridedStore - We see a strided store of some value.  If we can
00941 /// transform this into a memset or memset_pattern in the loop preheader, do so.
00942 bool LoopIdiomRecognize::
00943 processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
00944                         unsigned StoreAlignment, Value *StoredVal,
00945                         Instruction *TheStore, const SCEVAddRecExpr *Ev,
00946                         const SCEV *BECount) {
00947 
00948   // If the stored value is a byte-wise value (like i32 -1), then it may be
00949   // turned into a memset of i8 -1, assuming that all the consecutive bytes
00950   // are stored.  A store of i32 0x01020304 can never be turned into a memset,
00951   // but it can be turned into memset_pattern if the target supports it.
00952   Value *SplatValue = isBytewiseValue(StoredVal);
00953   Constant *PatternValue = 0;
00954 
00955   unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
00956 
00957   // If we're allowed to form a memset, and the stored value would be acceptable
00958   // for memset, use it.
00959   if (SplatValue && TLI->has(LibFunc::memset) &&
00960       // Verify that the stored value is loop invariant.  If not, we can't
00961       // promote the memset.
00962       CurLoop->isLoopInvariant(SplatValue)) {
00963     // Keep and use SplatValue.
00964     PatternValue = 0;
00965   } else if (DestAS == 0 &&
00966              TLI->has(LibFunc::memset_pattern16) &&
00967              (PatternValue = getMemSetPatternValue(StoredVal, *DL))) {
00968     // Don't create memset_pattern16s with address spaces.
00969     // It looks like we can use PatternValue!
00970     SplatValue = 0;
00971   } else {
00972     // Otherwise, this isn't an idiom we can transform.  For example, we can't
00973     // do anything with a 3-byte store.
00974     return false;
00975   }
00976 
00977   // The trip count of the loop and the base pointer of the addrec SCEV is
00978   // guaranteed to be loop invariant, which means that it should dominate the
00979   // header.  This allows us to insert code for it in the preheader.
00980   BasicBlock *Preheader = CurLoop->getLoopPreheader();
00981   IRBuilder<> Builder(Preheader->getTerminator());
00982   SCEVExpander Expander(*SE, "loop-idiom");
00983 
00984   Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
00985 
00986   // Okay, we have a strided store "p[i]" of a splattable value.  We can turn
00987   // this into a memset in the loop preheader now if we want.  However, this
00988   // would be unsafe to do if there is anything else in the loop that may read
00989   // or write to the aliased location.  Check for any overlap by generating the
00990   // base pointer and checking the region.
00991   Value *BasePtr =
00992     Expander.expandCodeFor(Ev->getStart(), DestInt8PtrTy,
00993                            Preheader->getTerminator());
00994 
00995   if (mayLoopAccessLocation(BasePtr, AliasAnalysis::ModRef,
00996                             CurLoop, BECount,
00997                             StoreSize, getAnalysis<AliasAnalysis>(), TheStore)) {
00998     Expander.clear();
00999     // If we generated new code for the base pointer, clean up.
01000     deleteIfDeadInstruction(BasePtr, *SE, TLI);
01001     return false;
01002   }
01003 
01004   // Okay, everything looks good, insert the memset.
01005 
01006   // The # stored bytes is (BECount+1)*Size.  Expand the trip count out to
01007   // pointer size if it isn't already.
01008   Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
01009   BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);
01010 
01011   const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1),
01012                                          SCEV::FlagNUW);
01013   if (StoreSize != 1) {
01014     NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
01015                                SCEV::FlagNUW);
01016   }
01017 
01018   Value *NumBytes =
01019     Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
01020 
01021   CallInst *NewCall;
01022   if (SplatValue) {
01023     NewCall = Builder.CreateMemSet(BasePtr,
01024                                    SplatValue,
01025                                    NumBytes,
01026                                    StoreAlignment);
01027   } else {
01028     // Everything is emitted in default address space
01029     Type *Int8PtrTy = DestInt8PtrTy;
01030 
01031     Module *M = TheStore->getParent()->getParent()->getParent();
01032     Value *MSP = M->getOrInsertFunction("memset_pattern16",
01033                                         Builder.getVoidTy(),
01034                                         Int8PtrTy,
01035                                         Int8PtrTy,
01036                                         IntPtr,
01037                                         (void*)0);
01038 
01039     // Otherwise we should form a memset_pattern16.  PatternValue is known to be
01040     // an constant array of 16-bytes.  Plop the value into a mergable global.
01041     GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
01042                                             GlobalValue::InternalLinkage,
01043                                             PatternValue, ".memset_pattern");
01044     GV->setUnnamedAddr(true); // Ok to merge these.
01045     GV->setAlignment(16);
01046     Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
01047     NewCall = Builder.CreateCall3(MSP, BasePtr, PatternPtr, NumBytes);
01048   }
01049 
01050   DEBUG(dbgs() << "  Formed memset: " << *NewCall << "\n"
01051                << "    from store to: " << *Ev << " at: " << *TheStore << "\n");
01052   NewCall->setDebugLoc(TheStore->getDebugLoc());
01053 
01054   // Okay, the memset has been formed.  Zap the original store and anything that
01055   // feeds into it.
01056   deleteDeadInstruction(TheStore, *SE, TLI);
01057   ++NumMemSet;
01058   return true;
01059 }
01060 
01061 /// processLoopStoreOfLoopLoad - We see a strided store whose value is a
01062 /// same-strided load.
01063 bool LoopIdiomRecognize::
01064 processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
01065                            const SCEVAddRecExpr *StoreEv,
01066                            const SCEVAddRecExpr *LoadEv,
01067                            const SCEV *BECount) {
01068   // If we're not allowed to form memcpy, we fail.
01069   if (!TLI->has(LibFunc::memcpy))
01070     return false;
01071 
01072   LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
01073 
01074   // The trip count of the loop and the base pointer of the addrec SCEV is
01075   // guaranteed to be loop invariant, which means that it should dominate the
01076   // header.  This allows us to insert code for it in the preheader.
01077   BasicBlock *Preheader = CurLoop->getLoopPreheader();
01078   IRBuilder<> Builder(Preheader->getTerminator());
01079   SCEVExpander Expander(*SE, "loop-idiom");
01080 
01081   // Okay, we have a strided store "p[i]" of a loaded value.  We can turn
01082   // this into a memcpy in the loop preheader now if we want.  However, this
01083   // would be unsafe to do if there is anything else in the loop that may read
01084   // or write the memory region we're storing to.  This includes the load that
01085   // feeds the stores.  Check for an alias by generating the base address and
01086   // checking everything.
01087   Value *StoreBasePtr =
01088     Expander.expandCodeFor(StoreEv->getStart(),
01089                            Builder.getInt8PtrTy(SI->getPointerAddressSpace()),
01090                            Preheader->getTerminator());
01091 
01092   if (mayLoopAccessLocation(StoreBasePtr, AliasAnalysis::ModRef,
01093                             CurLoop, BECount, StoreSize,
01094                             getAnalysis<AliasAnalysis>(), SI)) {
01095     Expander.clear();
01096     // If we generated new code for the base pointer, clean up.
01097     deleteIfDeadInstruction(StoreBasePtr, *SE, TLI);
01098     return false;
01099   }
01100 
01101   // For a memcpy, we have to make sure that the input array is not being
01102   // mutated by the loop.
01103   Value *LoadBasePtr =
01104     Expander.expandCodeFor(LoadEv->getStart(),
01105                            Builder.getInt8PtrTy(LI->getPointerAddressSpace()),
01106                            Preheader->getTerminator());
01107 
01108   if (mayLoopAccessLocation(LoadBasePtr, AliasAnalysis::Mod, CurLoop, BECount,
01109                             StoreSize, getAnalysis<AliasAnalysis>(), SI)) {
01110     Expander.clear();
01111     // If we generated new code for the base pointer, clean up.
01112     deleteIfDeadInstruction(LoadBasePtr, *SE, TLI);
01113     deleteIfDeadInstruction(StoreBasePtr, *SE, TLI);
01114     return false;
01115   }
01116 
01117   // Okay, everything is safe, we can transform this!
01118 
01119 
01120   // The # stored bytes is (BECount+1)*Size.  Expand the trip count out to
01121   // pointer size if it isn't already.
01122   Type *IntPtrTy = Builder.getIntPtrTy(DL, SI->getPointerAddressSpace());
01123   BECount = SE->getTruncateOrZeroExtend(BECount, IntPtrTy);
01124 
01125   const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtrTy, 1),
01126                                          SCEV::FlagNUW);
01127   if (StoreSize != 1)
01128     NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtrTy, StoreSize),
01129                                SCEV::FlagNUW);
01130 
01131   Value *NumBytes =
01132     Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
01133 
01134   CallInst *NewCall =
01135     Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
01136                          std::min(SI->getAlignment(), LI->getAlignment()));
01137   NewCall->setDebugLoc(SI->getDebugLoc());
01138 
01139   DEBUG(dbgs() << "  Formed memcpy: " << *NewCall << "\n"
01140                << "    from load ptr=" << *LoadEv << " at: " << *LI << "\n"
01141                << "    from store ptr=" << *StoreEv << " at: " << *SI << "\n");
01142 
01143 
01144   // Okay, the memset has been formed.  Zap the original store and anything that
01145   // feeds into it.
01146   deleteDeadInstruction(SI, *SE, TLI);
01147   ++NumMemCpy;
01148   return true;
01149 }