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+//===- LoopIdiomRecognize.cpp - Loop idiom recognition --------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This pass implements an idiom recognizer that transforms simple loops into a
+// non-loop form. In cases that this kicks in, it can be a significant
+// performance win.
+//
+// If compiling for code size we avoid idiom recognition if the resulting
+// code could be larger than the code for the original loop. One way this could
+// happen is if the loop is not removable after idiom recognition due to the
+// presence of non-idiom instructions. The initial implementation of the
+// heuristics applies to idioms in multi-block loops.
+//
+//===----------------------------------------------------------------------===//
+//
+// TODO List:
+//
+// Future loop memory idioms to recognize:
+// memcmp, memmove, strlen, etc.
+// Future floating point idioms to recognize in -ffast-math mode:
+// fpowi
+// Future integer operation idioms to recognize:
+// ctpop
+//
+// Beware that isel's default lowering for ctpop is highly inefficient for
+// i64 and larger types when i64 is legal and the value has few bits set. It
+// would be good to enhance isel to emit a loop for ctpop in this case.
+//
+// This could recognize common matrix multiplies and dot product idioms and
+// replace them with calls to BLAS (if linked in??).
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Scalar/LoopIdiomRecognize.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/MapVector.h"
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallPtrSet.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Analysis/AliasAnalysis.h"
+#include "llvm/Analysis/LoopAccessAnalysis.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/MemoryLocation.h"
+#include "llvm/Analysis/OptimizationRemarkEmitter.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/ScalarEvolutionExpander.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Attributes.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/Constant.h"
+#include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugLoc.h"
+#include "llvm/IR/DerivedTypes.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/GlobalValue.h"
+#include "llvm/IR/GlobalVariable.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InstrTypes.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/Intrinsics.h"
+#include "llvm/IR/LLVMContext.h"
+#include "llvm/IR/Module.h"
+#include "llvm/IR/PassManager.h"
+#include "llvm/IR/Type.h"
+#include "llvm/IR/User.h"
+#include "llvm/IR/Value.h"
+#include "llvm/IR/ValueHandle.h"
+#include "llvm/Pass.h"
+#include "llvm/Support/Casting.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
+#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BuildLibCalls.h"
+#include "llvm/Transforms/Utils/Local.h"
+#include "llvm/Transforms/Utils/LoopUtils.h"
+#include <algorithm>
+#include <cassert>
+#include <cstdint>
+#include <utility>
+#include <vector>
+
+using namespace llvm;
+
+#define DEBUG_TYPE "loop-idiom"
+
+STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
+STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
+
+static cl::opt<bool> UseLIRCodeSizeHeurs(
+ "use-lir-code-size-heurs",
+ cl::desc("Use loop idiom recognition code size heuristics when compiling"
+ "with -Os/-Oz"),
+ cl::init(true), cl::Hidden);
+
+namespace {
+
+class LoopIdiomRecognize {
+ Loop *CurLoop = nullptr;
+ AliasAnalysis *AA;
+ DominatorTree *DT;
+ LoopInfo *LI;
+ ScalarEvolution *SE;
+ TargetLibraryInfo *TLI;
+ const TargetTransformInfo *TTI;
+ const DataLayout *DL;
+ OptimizationRemarkEmitter &ORE;
+ bool ApplyCodeSizeHeuristics;
+
+public:
+ explicit LoopIdiomRecognize(AliasAnalysis *AA, DominatorTree *DT,
+ LoopInfo *LI, ScalarEvolution *SE,
+ TargetLibraryInfo *TLI,
+ const TargetTransformInfo *TTI,
+ const DataLayout *DL,
+ OptimizationRemarkEmitter &ORE)
+ : AA(AA), DT(DT), LI(LI), SE(SE), TLI(TLI), TTI(TTI), DL(DL), ORE(ORE) {}
+
+ bool runOnLoop(Loop *L);
+
+private:
+ using StoreList = SmallVector<StoreInst *, 8>;
+ using StoreListMap = MapVector<Value *, StoreList>;
+
+ StoreListMap StoreRefsForMemset;
+ StoreListMap StoreRefsForMemsetPattern;
+ StoreList StoreRefsForMemcpy;
+ bool HasMemset;
+ bool HasMemsetPattern;
+ bool HasMemcpy;
+
+ /// Return code for isLegalStore()
+ enum LegalStoreKind {
+ None = 0,
+ Memset,
+ MemsetPattern,
+ Memcpy,
+ UnorderedAtomicMemcpy,
+ DontUse // Dummy retval never to be used. Allows catching errors in retval
+ // handling.
+ };
+
+ /// \name Countable Loop Idiom Handling
+ /// @{
+
+ bool runOnCountableLoop();
+ bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
+ SmallVectorImpl<BasicBlock *> &ExitBlocks);
+
+ void collectStores(BasicBlock *BB);
+ LegalStoreKind isLegalStore(StoreInst *SI);
+ enum class ForMemset { No, Yes };
+ bool processLoopStores(SmallVectorImpl<StoreInst *> &SL, const SCEV *BECount,
+ ForMemset For);
+ bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
+
+ bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
+ unsigned StoreAlignment, Value *StoredVal,
+ Instruction *TheStore,
+ SmallPtrSetImpl<Instruction *> &Stores,
+ const SCEVAddRecExpr *Ev, const SCEV *BECount,
+ bool NegStride, bool IsLoopMemset = false);
+ bool processLoopStoreOfLoopLoad(StoreInst *SI, const SCEV *BECount);
+ bool avoidLIRForMultiBlockLoop(bool IsMemset = false,
+ bool IsLoopMemset = false);
+
+ /// @}
+ /// \name Noncountable Loop Idiom Handling
+ /// @{
+
+ bool runOnNoncountableLoop();
+
+ bool recognizePopcount();
+ void transformLoopToPopcount(BasicBlock *PreCondBB, Instruction *CntInst,
+ PHINode *CntPhi, Value *Var);
+ bool recognizeAndInsertFFS(); /// Find First Set: ctlz or cttz
+ void transformLoopToCountable(Intrinsic::ID IntrinID, BasicBlock *PreCondBB,
+ Instruction *CntInst, PHINode *CntPhi,
+ Value *Var, Instruction *DefX,
+ const DebugLoc &DL, bool ZeroCheck,
+ bool IsCntPhiUsedOutsideLoop);
+
+ /// @}
+};
+
+class LoopIdiomRecognizeLegacyPass : public LoopPass {
+public:
+ static char ID;
+
+ explicit LoopIdiomRecognizeLegacyPass() : LoopPass(ID) {
+ initializeLoopIdiomRecognizeLegacyPassPass(
+ *PassRegistry::getPassRegistry());
+ }
+
+ bool runOnLoop(Loop *L, LPPassManager &LPM) override {
+ if (skipLoop(L))
+ return false;
+
+ AliasAnalysis *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
+ DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
+ LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
+ ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
+ TargetLibraryInfo *TLI =
+ &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
+ const TargetTransformInfo *TTI =
+ &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
+ *L->getHeader()->getParent());
+ const DataLayout *DL = &L->getHeader()->getModule()->getDataLayout();
+
+ // For the old PM, we can't use OptimizationRemarkEmitter as an analysis
+ // pass. Function analyses need to be preserved across loop transformations
+ // but ORE cannot be preserved (see comment before the pass definition).
+ OptimizationRemarkEmitter ORE(L->getHeader()->getParent());
+
+ LoopIdiomRecognize LIR(AA, DT, LI, SE, TLI, TTI, DL, ORE);
+ return LIR.runOnLoop(L);
+ }
+
+ /// This transformation requires natural loop information & requires that
+ /// loop preheaders be inserted into the CFG.
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addRequired<TargetLibraryInfoWrapperPass>();
+ AU.addRequired<TargetTransformInfoWrapperPass>();
+ getLoopAnalysisUsage(AU);
+ }
+};
+
+} // end anonymous namespace
+
+char LoopIdiomRecognizeLegacyPass::ID = 0;
+
+PreservedAnalyses LoopIdiomRecognizePass::run(Loop &L, LoopAnalysisManager &AM,
+ LoopStandardAnalysisResults &AR,
+ LPMUpdater &) {
+ const auto *DL = &L.getHeader()->getModule()->getDataLayout();
+
+ const auto &FAM =
+ AM.getResult<FunctionAnalysisManagerLoopProxy>(L, AR).getManager();
+ Function *F = L.getHeader()->getParent();
+
+ auto *ORE = FAM.getCachedResult<OptimizationRemarkEmitterAnalysis>(*F);
+ // FIXME: This should probably be optional rather than required.
+ if (!ORE)
+ report_fatal_error(
+ "LoopIdiomRecognizePass: OptimizationRemarkEmitterAnalysis not cached "
+ "at a higher level");
+
+ LoopIdiomRecognize LIR(&AR.AA, &AR.DT, &AR.LI, &AR.SE, &AR.TLI, &AR.TTI, DL,
+ *ORE);
+ if (!LIR.runOnLoop(&L))
+ return PreservedAnalyses::all();
+
+ return getLoopPassPreservedAnalyses();
+}
+
+INITIALIZE_PASS_BEGIN(LoopIdiomRecognizeLegacyPass, "loop-idiom",
+ "Recognize loop idioms", false, false)
+INITIALIZE_PASS_DEPENDENCY(LoopPass)
+INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
+INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
+INITIALIZE_PASS_END(LoopIdiomRecognizeLegacyPass, "loop-idiom",
+ "Recognize loop idioms", false, false)
+
+Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognizeLegacyPass(); }
+
+static void deleteDeadInstruction(Instruction *I) {
+ I->replaceAllUsesWith(UndefValue::get(I->getType()));
+ I->eraseFromParent();
+}
+
+//===----------------------------------------------------------------------===//
+//
+// Implementation of LoopIdiomRecognize
+//
+//===----------------------------------------------------------------------===//
+
+bool LoopIdiomRecognize::runOnLoop(Loop *L) {
+ CurLoop = L;
+ // If the loop could not be converted to canonical form, it must have an
+ // indirectbr in it, just give up.
+ if (!L->getLoopPreheader())
+ return false;
+
+ // Disable loop idiom recognition if the function's name is a common idiom.
+ StringRef Name = L->getHeader()->getParent()->getName();
+ if (Name == "memset" || Name == "memcpy")
+ return false;
+
+ // Determine if code size heuristics need to be applied.
+ ApplyCodeSizeHeuristics =
+ L->getHeader()->getParent()->hasOptSize() && UseLIRCodeSizeHeurs;
+
+ HasMemset = TLI->has(LibFunc_memset);
+ HasMemsetPattern = TLI->has(LibFunc_memset_pattern16);
+ HasMemcpy = TLI->has(LibFunc_memcpy);
+
+ if (HasMemset || HasMemsetPattern || HasMemcpy)
+ if (SE->hasLoopInvariantBackedgeTakenCount(L))
+ return runOnCountableLoop();
+
+ return runOnNoncountableLoop();
+}
+
+bool LoopIdiomRecognize::runOnCountableLoop() {
+ const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
+ assert(!isa<SCEVCouldNotCompute>(BECount) &&
+ "runOnCountableLoop() called on a loop without a predictable"
+ "backedge-taken count");
+
+ // If this loop executes exactly one time, then it should be peeled, not
+ // optimized by this pass.
+ if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
+ if (BECst->getAPInt() == 0)
+ return false;
+
+ SmallVector<BasicBlock *, 8> ExitBlocks;
+ CurLoop->getUniqueExitBlocks(ExitBlocks);
+
+ LLVM_DEBUG(dbgs() << DEBUG_TYPE " Scanning: F["
+ << CurLoop->getHeader()->getParent()->getName()
+ << "] Countable Loop %" << CurLoop->getHeader()->getName()
+ << "\n");
+
+ bool MadeChange = false;
+
+ // The following transforms hoist stores/memsets into the loop pre-header.
+ // Give up if the loop has instructions may throw.
+ SimpleLoopSafetyInfo SafetyInfo;
+ SafetyInfo.computeLoopSafetyInfo(CurLoop);
+ if (SafetyInfo.anyBlockMayThrow())
+ return MadeChange;
+
+ // Scan all the blocks in the loop that are not in subloops.
+ for (auto *BB : CurLoop->getBlocks()) {
+ // Ignore blocks in subloops.
+ if (LI->getLoopFor(BB) != CurLoop)
+ continue;
+
+ MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
+ }
+ return MadeChange;
+}
+
+static APInt getStoreStride(const SCEVAddRecExpr *StoreEv) {
+ const SCEVConstant *ConstStride = cast<SCEVConstant>(StoreEv->getOperand(1));
+ return ConstStride->getAPInt();
+}
+
+/// getMemSetPatternValue - If a strided store of the specified value is safe to
+/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
+/// be passed in. Otherwise, return null.
+///
+/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
+/// just replicate their input array and then pass on to memset_pattern16.
+static Constant *getMemSetPatternValue(Value *V, const DataLayout *DL) {
+ // FIXME: This could check for UndefValue because it can be merged into any
+ // other valid pattern.
+
+ // If the value isn't a constant, we can't promote it to being in a constant
+ // array. We could theoretically do a store to an alloca or something, but
+ // that doesn't seem worthwhile.
+ Constant *C = dyn_cast<Constant>(V);
+ if (!C)
+ return nullptr;
+
+ // Only handle simple values that are a power of two bytes in size.
+ uint64_t Size = DL->getTypeSizeInBits(V->getType());
+ if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
+ return nullptr;
+
+ // Don't care enough about darwin/ppc to implement this.
+ if (DL->isBigEndian())
+ return nullptr;
+
+ // Convert to size in bytes.
+ Size /= 8;
+
+ // TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
+ // if the top and bottom are the same (e.g. for vectors and large integers).
+ if (Size > 16)
+ return nullptr;
+
+ // If the constant is exactly 16 bytes, just use it.
+ if (Size == 16)
+ return C;
+
+ // Otherwise, we'll use an array of the constants.
+ unsigned ArraySize = 16 / Size;
+ ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
+ return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
+}
+
+LoopIdiomRecognize::LegalStoreKind
+LoopIdiomRecognize::isLegalStore(StoreInst *SI) {
+ // Don't touch volatile stores.
+ if (SI->isVolatile())
+ return LegalStoreKind::None;
+ // We only want simple or unordered-atomic stores.
+ if (!SI->isUnordered())
+ return LegalStoreKind::None;
+
+ // Don't convert stores of non-integral pointer types to memsets (which stores
+ // integers).
+ if (DL->isNonIntegralPointerType(SI->getValueOperand()->getType()))
+ return LegalStoreKind::None;
+
+ // Avoid merging nontemporal stores.
+ if (SI->getMetadata(LLVMContext::MD_nontemporal))
+ return LegalStoreKind::None;
+
+ Value *StoredVal = SI->getValueOperand();
+ Value *StorePtr = SI->getPointerOperand();
+
+ // Reject stores that are so large that they overflow an unsigned.
+ uint64_t SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
+ if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
+ return LegalStoreKind::None;
+
+ // See if the pointer expression is an AddRec like {base,+,1} on the current
+ // loop, which indicates a strided store. If we have something else, it's a
+ // random store we can't handle.
+ const SCEVAddRecExpr *StoreEv =
+ dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
+ if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
+ return LegalStoreKind::None;
+
+ // Check to see if we have a constant stride.
+ if (!isa<SCEVConstant>(StoreEv->getOperand(1)))
+ return LegalStoreKind::None;
+
+ // See if the store can be turned into a memset.
+
+ // If the stored value is a byte-wise value (like i32 -1), then it may be
+ // turned into a memset of i8 -1, assuming that all the consecutive bytes
+ // are stored. A store of i32 0x01020304 can never be turned into a memset,
+ // but it can be turned into memset_pattern if the target supports it.
+ Value *SplatValue = isBytewiseValue(StoredVal, *DL);
+ Constant *PatternValue = nullptr;
+
+ // Note: memset and memset_pattern on unordered-atomic is yet not supported
+ bool UnorderedAtomic = SI->isUnordered() && !SI->isSimple();
+
+ // If we're allowed to form a memset, and the stored value would be
+ // acceptable for memset, use it.
+ if (!UnorderedAtomic && HasMemset && SplatValue &&
+ // Verify that the stored value is loop invariant. If not, we can't
+ // promote the memset.
+ CurLoop->isLoopInvariant(SplatValue)) {
+ // It looks like we can use SplatValue.
+ return LegalStoreKind::Memset;
+ } else if (!UnorderedAtomic && HasMemsetPattern &&
+ // Don't create memset_pattern16s with address spaces.
+ StorePtr->getType()->getPointerAddressSpace() == 0 &&
+ (PatternValue = getMemSetPatternValue(StoredVal, DL))) {
+ // It looks like we can use PatternValue!
+ return LegalStoreKind::MemsetPattern;
+ }
+
+ // Otherwise, see if the store can be turned into a memcpy.
+ if (HasMemcpy) {
+ // Check to see if the stride matches the size of the store. If so, then we
+ // know that every byte is touched in the loop.
+ APInt Stride = getStoreStride(StoreEv);
+ unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
+ if (StoreSize != Stride && StoreSize != -Stride)
+ return LegalStoreKind::None;
+
+ // The store must be feeding a non-volatile load.
+ LoadInst *LI = dyn_cast<LoadInst>(SI->getValueOperand());
+
+ // Only allow non-volatile loads
+ if (!LI || LI->isVolatile())
+ return LegalStoreKind::None;
+ // Only allow simple or unordered-atomic loads
+ if (!LI->isUnordered())
+ return LegalStoreKind::None;
+
+ // See if the pointer expression is an AddRec like {base,+,1} on the current
+ // loop, which indicates a strided load. If we have something else, it's a
+ // random load we can't handle.
+ const SCEVAddRecExpr *LoadEv =
+ dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getPointerOperand()));
+ if (!LoadEv || LoadEv->getLoop() != CurLoop || !LoadEv->isAffine())
+ return LegalStoreKind::None;
+
+ // The store and load must share the same stride.
+ if (StoreEv->getOperand(1) != LoadEv->getOperand(1))
+ return LegalStoreKind::None;
+
+ // Success. This store can be converted into a memcpy.
+ UnorderedAtomic = UnorderedAtomic || LI->isAtomic();
+ return UnorderedAtomic ? LegalStoreKind::UnorderedAtomicMemcpy
+ : LegalStoreKind::Memcpy;
+ }
+ // This store can't be transformed into a memset/memcpy.
+ return LegalStoreKind::None;
+}
+
+void LoopIdiomRecognize::collectStores(BasicBlock *BB) {
+ StoreRefsForMemset.clear();
+ StoreRefsForMemsetPattern.clear();
+ StoreRefsForMemcpy.clear();
+ for (Instruction &I : *BB) {
+ StoreInst *SI = dyn_cast<StoreInst>(&I);
+ if (!SI)
+ continue;
+
+ // Make sure this is a strided store with a constant stride.
+ switch (isLegalStore(SI)) {
+ case LegalStoreKind::None:
+ // Nothing to do
+ break;
+ case LegalStoreKind::Memset: {
+ // Find the base pointer.
+ Value *Ptr = GetUnderlyingObject(SI->getPointerOperand(), *DL);
+ StoreRefsForMemset[Ptr].push_back(SI);
+ } break;
+ case LegalStoreKind::MemsetPattern: {
+ // Find the base pointer.
+ Value *Ptr = GetUnderlyingObject(SI->getPointerOperand(), *DL);
+ StoreRefsForMemsetPattern[Ptr].push_back(SI);
+ } break;
+ case LegalStoreKind::Memcpy:
+ case LegalStoreKind::UnorderedAtomicMemcpy:
+ StoreRefsForMemcpy.push_back(SI);
+ break;
+ default:
+ assert(false && "unhandled return value");
+ break;
+ }
+ }
+}
+
+/// runOnLoopBlock - Process the specified block, which lives in a counted loop
+/// with the specified backedge count. This block is known to be in the current
+/// loop and not in any subloops.
+bool LoopIdiomRecognize::runOnLoopBlock(
+ BasicBlock *BB, const SCEV *BECount,
+ SmallVectorImpl<BasicBlock *> &ExitBlocks) {
+ // We can only promote stores in this block if they are unconditionally
+ // executed in the loop. For a block to be unconditionally executed, it has
+ // to dominate all the exit blocks of the loop. Verify this now.
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i)
+ if (!DT->dominates(BB, ExitBlocks[i]))
+ return false;
+
+ bool MadeChange = false;
+ // Look for store instructions, which may be optimized to memset/memcpy.
+ collectStores(BB);
+
+ // Look for a single store or sets of stores with a common base, which can be
+ // optimized into a memset (memset_pattern). The latter most commonly happens
+ // with structs and handunrolled loops.
+ for (auto &SL : StoreRefsForMemset)
+ MadeChange |= processLoopStores(SL.second, BECount, ForMemset::Yes);
+
+ for (auto &SL : StoreRefsForMemsetPattern)
+ MadeChange |= processLoopStores(SL.second, BECount, ForMemset::No);
+
+ // Optimize the store into a memcpy, if it feeds an similarly strided load.
+ for (auto &SI : StoreRefsForMemcpy)
+ MadeChange |= processLoopStoreOfLoopLoad(SI, BECount);
+
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E;) {
+ Instruction *Inst = &*I++;
+ // Look for memset instructions, which may be optimized to a larger memset.
+ if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst)) {
+ WeakTrackingVH InstPtr(&*I);
+ if (!processLoopMemSet(MSI, BECount))
+ continue;
+ MadeChange = true;
+
+ // If processing the memset invalidated our iterator, start over from the
+ // top of the block.
+ if (!InstPtr)
+ I = BB->begin();
+ continue;
+ }
+ }
+
+ return MadeChange;
+}
+
+/// See if this store(s) can be promoted to a memset.
+bool LoopIdiomRecognize::processLoopStores(SmallVectorImpl<StoreInst *> &SL,
+ const SCEV *BECount, ForMemset For) {
+ // Try to find consecutive stores that can be transformed into memsets.
+ SetVector<StoreInst *> Heads, Tails;
+ SmallDenseMap<StoreInst *, StoreInst *> ConsecutiveChain;
+
+ // Do a quadratic search on all of the given stores and find
+ // all of the pairs of stores that follow each other.
+ SmallVector<unsigned, 16> IndexQueue;
+ for (unsigned i = 0, e = SL.size(); i < e; ++i) {
+ assert(SL[i]->isSimple() && "Expected only non-volatile stores.");
+
+ Value *FirstStoredVal = SL[i]->getValueOperand();
+ Value *FirstStorePtr = SL[i]->getPointerOperand();
+ const SCEVAddRecExpr *FirstStoreEv =
+ cast<SCEVAddRecExpr>(SE->getSCEV(FirstStorePtr));
+ APInt FirstStride = getStoreStride(FirstStoreEv);
+ unsigned FirstStoreSize = DL->getTypeStoreSize(SL[i]->getValueOperand()->getType());
+
+ // See if we can optimize just this store in isolation.
+ if (FirstStride == FirstStoreSize || -FirstStride == FirstStoreSize) {
+ Heads.insert(SL[i]);
+ continue;
+ }
+
+ Value *FirstSplatValue = nullptr;
+ Constant *FirstPatternValue = nullptr;
+
+ if (For == ForMemset::Yes)
+ FirstSplatValue = isBytewiseValue(FirstStoredVal, *DL);
+ else
+ FirstPatternValue = getMemSetPatternValue(FirstStoredVal, DL);
+
+ assert((FirstSplatValue || FirstPatternValue) &&
+ "Expected either splat value or pattern value.");
+
+ IndexQueue.clear();
+ // If a store has multiple consecutive store candidates, search Stores
+ // array according to the sequence: from i+1 to e, then from i-1 to 0.
+ // This is because usually pairing with immediate succeeding or preceding
+ // candidate create the best chance to find memset opportunity.
+ unsigned j = 0;
+ for (j = i + 1; j < e; ++j)
+ IndexQueue.push_back(j);
+ for (j = i; j > 0; --j)
+ IndexQueue.push_back(j - 1);
+
+ for (auto &k : IndexQueue) {
+ assert(SL[k]->isSimple() && "Expected only non-volatile stores.");
+ Value *SecondStorePtr = SL[k]->getPointerOperand();
+ const SCEVAddRecExpr *SecondStoreEv =
+ cast<SCEVAddRecExpr>(SE->getSCEV(SecondStorePtr));
+ APInt SecondStride = getStoreStride(SecondStoreEv);
+
+ if (FirstStride != SecondStride)
+ continue;
+
+ Value *SecondStoredVal = SL[k]->getValueOperand();
+ Value *SecondSplatValue = nullptr;
+ Constant *SecondPatternValue = nullptr;
+
+ if (For == ForMemset::Yes)
+ SecondSplatValue = isBytewiseValue(SecondStoredVal, *DL);
+ else
+ SecondPatternValue = getMemSetPatternValue(SecondStoredVal, DL);
+
+ assert((SecondSplatValue || SecondPatternValue) &&
+ "Expected either splat value or pattern value.");
+
+ if (isConsecutiveAccess(SL[i], SL[k], *DL, *SE, false)) {
+ if (For == ForMemset::Yes) {
+ if (isa<UndefValue>(FirstSplatValue))
+ FirstSplatValue = SecondSplatValue;
+ if (FirstSplatValue != SecondSplatValue)
+ continue;
+ } else {
+ if (isa<UndefValue>(FirstPatternValue))
+ FirstPatternValue = SecondPatternValue;
+ if (FirstPatternValue != SecondPatternValue)
+ continue;
+ }
+ Tails.insert(SL[k]);
+ Heads.insert(SL[i]);
+ ConsecutiveChain[SL[i]] = SL[k];
+ break;
+ }
+ }
+ }
+
+ // We may run into multiple chains that merge into a single chain. We mark the
+ // stores that we transformed so that we don't visit the same store twice.
+ SmallPtrSet<Value *, 16> TransformedStores;
+ bool Changed = false;
+
+ // For stores that start but don't end a link in the chain:
+ for (SetVector<StoreInst *>::iterator it = Heads.begin(), e = Heads.end();
+ it != e; ++it) {
+ if (Tails.count(*it))
+ continue;
+
+ // We found a store instr that starts a chain. Now follow the chain and try
+ // to transform it.
+ SmallPtrSet<Instruction *, 8> AdjacentStores;
+ StoreInst *I = *it;
+
+ StoreInst *HeadStore = I;
+ unsigned StoreSize = 0;
+
+ // Collect the chain into a list.
+ while (Tails.count(I) || Heads.count(I)) {
+ if (TransformedStores.count(I))
+ break;
+ AdjacentStores.insert(I);
+
+ StoreSize += DL->getTypeStoreSize(I->getValueOperand()->getType());
+ // Move to the next value in the chain.
+ I = ConsecutiveChain[I];
+ }
+
+ Value *StoredVal = HeadStore->getValueOperand();
+ Value *StorePtr = HeadStore->getPointerOperand();
+ const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
+ APInt Stride = getStoreStride(StoreEv);
+
+ // Check to see if the stride matches the size of the stores. If so, then
+ // we know that every byte is touched in the loop.
+ if (StoreSize != Stride && StoreSize != -Stride)
+ continue;
+
+ bool NegStride = StoreSize == -Stride;
+
+ if (processLoopStridedStore(StorePtr, StoreSize, HeadStore->getAlignment(),
+ StoredVal, HeadStore, AdjacentStores, StoreEv,
+ BECount, NegStride)) {
+ TransformedStores.insert(AdjacentStores.begin(), AdjacentStores.end());
+ Changed = true;
+ }
+ }
+
+ return Changed;
+}
+
+/// processLoopMemSet - See if this memset can be promoted to a large memset.
+bool LoopIdiomRecognize::processLoopMemSet(MemSetInst *MSI,
+ const SCEV *BECount) {
+ // We can only handle non-volatile memsets with a constant size.
+ if (MSI->isVolatile() || !isa<ConstantInt>(MSI->getLength()))
+ return false;
+
+ // If we're not allowed to hack on memset, we fail.
+ if (!HasMemset)
+ return false;
+
+ Value *Pointer = MSI->getDest();
+
+ // See if the pointer expression is an AddRec like {base,+,1} on the current
+ // loop, which indicates a strided store. If we have something else, it's a
+ // random store we can't handle.
+ const SCEVAddRecExpr *Ev = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Pointer));
+ if (!Ev || Ev->getLoop() != CurLoop || !Ev->isAffine())
+ return false;
+
+ // Reject memsets that are so large that they overflow an unsigned.
+ uint64_t SizeInBytes = cast<ConstantInt>(MSI->getLength())->getZExtValue();
+ if ((SizeInBytes >> 32) != 0)
+ return false;
+
+ // Check to see if the stride matches the size of the memset. If so, then we
+ // know that every byte is touched in the loop.
+ const SCEVConstant *ConstStride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
+ if (!ConstStride)
+ return false;
+
+ APInt Stride = ConstStride->getAPInt();
+ if (SizeInBytes != Stride && SizeInBytes != -Stride)
+ return false;
+
+ // Verify that the memset value is loop invariant. If not, we can't promote
+ // the memset.
+ Value *SplatValue = MSI->getValue();
+ if (!SplatValue || !CurLoop->isLoopInvariant(SplatValue))
+ return false;
+
+ SmallPtrSet<Instruction *, 1> MSIs;
+ MSIs.insert(MSI);
+ bool NegStride = SizeInBytes == -Stride;
+ return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
+ MSI->getDestAlignment(), SplatValue, MSI, MSIs,
+ Ev, BECount, NegStride, /*IsLoopMemset=*/true);
+}
+
+/// mayLoopAccessLocation - Return true if the specified loop might access the
+/// specified pointer location, which is a loop-strided access. The 'Access'
+/// argument specifies what the verboten forms of access are (read or write).
+static bool
+mayLoopAccessLocation(Value *Ptr, ModRefInfo Access, Loop *L,
+ const SCEV *BECount, unsigned StoreSize,
+ AliasAnalysis &AA,
+ SmallPtrSetImpl<Instruction *> &IgnoredStores) {
+ // Get the location that may be stored across the loop. Since the access is
+ // strided positively through memory, we say that the modified location starts
+ // at the pointer and has infinite size.
+ LocationSize AccessSize = LocationSize::unknown();
+
+ // If the loop iterates a fixed number of times, we can refine the access size
+ // to be exactly the size of the memset, which is (BECount+1)*StoreSize
+ if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
+ AccessSize = LocationSize::precise((BECst->getValue()->getZExtValue() + 1) *
+ StoreSize);
+
+ // TODO: For this to be really effective, we have to dive into the pointer
+ // operand in the store. Store to &A[i] of 100 will always return may alias
+ // with store of &A[100], we need to StoreLoc to be "A" with size of 100,
+ // which will then no-alias a store to &A[100].
+ MemoryLocation StoreLoc(Ptr, AccessSize);
+
+ for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
+ ++BI)
+ for (Instruction &I : **BI)
+ if (IgnoredStores.count(&I) == 0 &&
+ isModOrRefSet(
+ intersectModRef(AA.getModRefInfo(&I, StoreLoc), Access)))
+ return true;
+
+ return false;
+}
+
+// If we have a negative stride, Start refers to the end of the memory location
+// we're trying to memset. Therefore, we need to recompute the base pointer,
+// which is just Start - BECount*Size.
+static const SCEV *getStartForNegStride(const SCEV *Start, const SCEV *BECount,
+ Type *IntPtr, unsigned StoreSize,
+ ScalarEvolution *SE) {
+ const SCEV *Index = SE->getTruncateOrZeroExtend(BECount, IntPtr);
+ if (StoreSize != 1)
+ Index = SE->getMulExpr(Index, SE->getConstant(IntPtr, StoreSize),
+ SCEV::FlagNUW);
+ return SE->getMinusSCEV(Start, Index);
+}
+
+/// Compute the number of bytes as a SCEV from the backedge taken count.
+///
+/// This also maps the SCEV into the provided type and tries to handle the
+/// computation in a way that will fold cleanly.
+static const SCEV *getNumBytes(const SCEV *BECount, Type *IntPtr,
+ unsigned StoreSize, Loop *CurLoop,
+ const DataLayout *DL, ScalarEvolution *SE) {
+ const SCEV *NumBytesS;
+ // The # stored bytes is (BECount+1)*Size. Expand the trip count out to
+ // pointer size if it isn't already.
+ //
+ // If we're going to need to zero extend the BE count, check if we can add
+ // one to it prior to zero extending without overflow. Provided this is safe,
+ // it allows better simplification of the +1.
+ if (DL->getTypeSizeInBits(BECount->getType()) <
+ DL->getTypeSizeInBits(IntPtr) &&
+ SE->isLoopEntryGuardedByCond(
+ CurLoop, ICmpInst::ICMP_NE, BECount,
+ SE->getNegativeSCEV(SE->getOne(BECount->getType())))) {
+ NumBytesS = SE->getZeroExtendExpr(
+ SE->getAddExpr(BECount, SE->getOne(BECount->getType()), SCEV::FlagNUW),
+ IntPtr);
+ } else {
+ NumBytesS = SE->getAddExpr(SE->getTruncateOrZeroExtend(BECount, IntPtr),
+ SE->getOne(IntPtr), SCEV::FlagNUW);
+ }
+
+ // And scale it based on the store size.
+ if (StoreSize != 1) {
+ NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
+ SCEV::FlagNUW);
+ }
+ return NumBytesS;
+}
+
+/// processLoopStridedStore - We see a strided store of some value. If we can
+/// transform this into a memset or memset_pattern in the loop preheader, do so.
+bool LoopIdiomRecognize::processLoopStridedStore(
+ Value *DestPtr, unsigned StoreSize, unsigned StoreAlignment,
+ Value *StoredVal, Instruction *TheStore,
+ SmallPtrSetImpl<Instruction *> &Stores, const SCEVAddRecExpr *Ev,
+ const SCEV *BECount, bool NegStride, bool IsLoopMemset) {
+ Value *SplatValue = isBytewiseValue(StoredVal, *DL);
+ Constant *PatternValue = nullptr;
+
+ if (!SplatValue)
+ PatternValue = getMemSetPatternValue(StoredVal, DL);
+
+ assert((SplatValue || PatternValue) &&
+ "Expected either splat value or pattern value.");
+
+ // The trip count of the loop and the base pointer of the addrec SCEV is
+ // guaranteed to be loop invariant, which means that it should dominate the
+ // header. This allows us to insert code for it in the preheader.
+ unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
+ BasicBlock *Preheader = CurLoop->getLoopPreheader();
+ IRBuilder<> Builder(Preheader->getTerminator());
+ SCEVExpander Expander(*SE, *DL, "loop-idiom");
+
+ Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
+ Type *IntPtr = Builder.getIntPtrTy(*DL, DestAS);
+
+ const SCEV *Start = Ev->getStart();
+ // Handle negative strided loops.
+ if (NegStride)
+ Start = getStartForNegStride(Start, BECount, IntPtr, StoreSize, SE);
+
+ // TODO: ideally we should still be able to generate memset if SCEV expander
+ // is taught to generate the dependencies at the latest point.
+ if (!isSafeToExpand(Start, *SE))
+ return false;
+
+ // Okay, we have a strided store "p[i]" of a splattable value. We can turn
+ // this into a memset in the loop preheader now if we want. However, this
+ // would be unsafe to do if there is anything else in the loop that may read
+ // or write to the aliased location. Check for any overlap by generating the
+ // base pointer and checking the region.
+ Value *BasePtr =
+ Expander.expandCodeFor(Start, DestInt8PtrTy, Preheader->getTerminator());
+ if (mayLoopAccessLocation(BasePtr, ModRefInfo::ModRef, CurLoop, BECount,
+ StoreSize, *AA, Stores)) {
+ Expander.clear();
+ // If we generated new code for the base pointer, clean up.
+ RecursivelyDeleteTriviallyDeadInstructions(BasePtr, TLI);
+ return false;
+ }
+
+ if (avoidLIRForMultiBlockLoop(/*IsMemset=*/true, IsLoopMemset))
+ return false;
+
+ // Okay, everything looks good, insert the memset.
+
+ const SCEV *NumBytesS =
+ getNumBytes(BECount, IntPtr, StoreSize, CurLoop, DL, SE);
+
+ // TODO: ideally we should still be able to generate memset if SCEV expander
+ // is taught to generate the dependencies at the latest point.
+ if (!isSafeToExpand(NumBytesS, *SE))
+ return false;
+
+ Value *NumBytes =
+ Expander.expandCodeFor(NumBytesS, IntPtr, Preheader->getTerminator());
+
+ CallInst *NewCall;
+ if (SplatValue) {
+ NewCall =
+ Builder.CreateMemSet(BasePtr, SplatValue, NumBytes, StoreAlignment);
+ } else {
+ // Everything is emitted in default address space
+ Type *Int8PtrTy = DestInt8PtrTy;
+
+ Module *M = TheStore->getModule();
+ StringRef FuncName = "memset_pattern16";
+ FunctionCallee MSP = M->getOrInsertFunction(FuncName, Builder.getVoidTy(),
+ Int8PtrTy, Int8PtrTy, IntPtr);
+ inferLibFuncAttributes(M, FuncName, *TLI);
+
+ // Otherwise we should form a memset_pattern16. PatternValue is known to be
+ // an constant array of 16-bytes. Plop the value into a mergable global.
+ GlobalVariable *GV = new GlobalVariable(*M, PatternValue->getType(), true,
+ GlobalValue::PrivateLinkage,
+ PatternValue, ".memset_pattern");
+ GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global); // Ok to merge these.
+ GV->setAlignment(16);
+ Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
+ NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
+ }
+
+ LLVM_DEBUG(dbgs() << " Formed memset: " << *NewCall << "\n"
+ << " from store to: " << *Ev << " at: " << *TheStore
+ << "\n");
+ NewCall->setDebugLoc(TheStore->getDebugLoc());
+
+ ORE.emit([&]() {
+ return OptimizationRemark(DEBUG_TYPE, "ProcessLoopStridedStore",
+ NewCall->getDebugLoc(), Preheader)
+ << "Transformed loop-strided store into a call to "
+ << ore::NV("NewFunction", NewCall->getCalledFunction())
+ << "() function";
+ });
+
+ // Okay, the memset has been formed. Zap the original store and anything that
+ // feeds into it.
+ for (auto *I : Stores)
+ deleteDeadInstruction(I);
+ ++NumMemSet;
+ return true;
+}
+
+/// If the stored value is a strided load in the same loop with the same stride
+/// this may be transformable into a memcpy. This kicks in for stuff like
+/// for (i) A[i] = B[i];
+bool LoopIdiomRecognize::processLoopStoreOfLoopLoad(StoreInst *SI,
+ const SCEV *BECount) {
+ assert(SI->isUnordered() && "Expected only non-volatile non-ordered stores.");
+
+ Value *StorePtr = SI->getPointerOperand();
+ const SCEVAddRecExpr *StoreEv = cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
+ APInt Stride = getStoreStride(StoreEv);
+ unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
+ bool NegStride = StoreSize == -Stride;
+
+ // The store must be feeding a non-volatile load.
+ LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
+ assert(LI->isUnordered() && "Expected only non-volatile non-ordered loads.");
+
+ // See if the pointer expression is an AddRec like {base,+,1} on the current
+ // loop, which indicates a strided load. If we have something else, it's a
+ // random load we can't handle.
+ const SCEVAddRecExpr *LoadEv =
+ cast<SCEVAddRecExpr>(SE->getSCEV(LI->getPointerOperand()));
+
+ // The trip count of the loop and the base pointer of the addrec SCEV is
+ // guaranteed to be loop invariant, which means that it should dominate the
+ // header. This allows us to insert code for it in the preheader.
+ BasicBlock *Preheader = CurLoop->getLoopPreheader();
+ IRBuilder<> Builder(Preheader->getTerminator());
+ SCEVExpander Expander(*SE, *DL, "loop-idiom");
+
+ const SCEV *StrStart = StoreEv->getStart();
+ unsigned StrAS = SI->getPointerAddressSpace();
+ Type *IntPtrTy = Builder.getIntPtrTy(*DL, StrAS);
+
+ // Handle negative strided loops.
+ if (NegStride)
+ StrStart = getStartForNegStride(StrStart, BECount, IntPtrTy, StoreSize, SE);
+
+ // Okay, we have a strided store "p[i]" of a loaded value. We can turn
+ // this into a memcpy in the loop preheader now if we want. However, this
+ // would be unsafe to do if there is anything else in the loop that may read
+ // or write the memory region we're storing to. This includes the load that
+ // feeds the stores. Check for an alias by generating the base address and
+ // checking everything.
+ Value *StoreBasePtr = Expander.expandCodeFor(
+ StrStart, Builder.getInt8PtrTy(StrAS), Preheader->getTerminator());
+
+ SmallPtrSet<Instruction *, 1> Stores;
+ Stores.insert(SI);
+ if (mayLoopAccessLocation(StoreBasePtr, ModRefInfo::ModRef, CurLoop, BECount,
+ StoreSize, *AA, Stores)) {
+ Expander.clear();
+ // If we generated new code for the base pointer, clean up.
+ RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
+ return false;
+ }
+
+ const SCEV *LdStart = LoadEv->getStart();
+ unsigned LdAS = LI->getPointerAddressSpace();
+
+ // Handle negative strided loops.
+ if (NegStride)
+ LdStart = getStartForNegStride(LdStart, BECount, IntPtrTy, StoreSize, SE);
+
+ // For a memcpy, we have to make sure that the input array is not being
+ // mutated by the loop.
+ Value *LoadBasePtr = Expander.expandCodeFor(
+ LdStart, Builder.getInt8PtrTy(LdAS), Preheader->getTerminator());
+
+ if (mayLoopAccessLocation(LoadBasePtr, ModRefInfo::Mod, CurLoop, BECount,
+ StoreSize, *AA, Stores)) {
+ Expander.clear();
+ // If we generated new code for the base pointer, clean up.
+ RecursivelyDeleteTriviallyDeadInstructions(LoadBasePtr, TLI);
+ RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
+ return false;
+ }
+
+ if (avoidLIRForMultiBlockLoop())
+ return false;
+
+ // Okay, everything is safe, we can transform this!
+
+ const SCEV *NumBytesS =
+ getNumBytes(BECount, IntPtrTy, StoreSize, CurLoop, DL, SE);
+
+ Value *NumBytes =
+ Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
+
+ CallInst *NewCall = nullptr;
+ // Check whether to generate an unordered atomic memcpy:
+ // If the load or store are atomic, then they must necessarily be unordered
+ // by previous checks.
+ if (!SI->isAtomic() && !LI->isAtomic())
+ NewCall = Builder.CreateMemCpy(StoreBasePtr, SI->getAlignment(),
+ LoadBasePtr, LI->getAlignment(), NumBytes);
+ else {
+ // We cannot allow unaligned ops for unordered load/store, so reject
+ // anything where the alignment isn't at least the element size.
+ unsigned Align = std::min(SI->getAlignment(), LI->getAlignment());
+ if (Align < StoreSize)
+ return false;
+
+ // If the element.atomic memcpy is not lowered into explicit
+ // loads/stores later, then it will be lowered into an element-size
+ // specific lib call. If the lib call doesn't exist for our store size, then
+ // we shouldn't generate the memcpy.
+ if (StoreSize > TTI->getAtomicMemIntrinsicMaxElementSize())
+ return false;
+
+ // Create the call.
+ // Note that unordered atomic loads/stores are *required* by the spec to
+ // have an alignment but non-atomic loads/stores may not.
+ NewCall = Builder.CreateElementUnorderedAtomicMemCpy(
+ StoreBasePtr, SI->getAlignment(), LoadBasePtr, LI->getAlignment(),
+ NumBytes, StoreSize);
+ }
+ NewCall->setDebugLoc(SI->getDebugLoc());
+
+ LLVM_DEBUG(dbgs() << " Formed memcpy: " << *NewCall << "\n"
+ << " from load ptr=" << *LoadEv << " at: " << *LI << "\n"
+ << " from store ptr=" << *StoreEv << " at: " << *SI
+ << "\n");
+
+ ORE.emit([&]() {
+ return OptimizationRemark(DEBUG_TYPE, "ProcessLoopStoreOfLoopLoad",
+ NewCall->getDebugLoc(), Preheader)
+ << "Formed a call to "
+ << ore::NV("NewFunction", NewCall->getCalledFunction())
+ << "() function";
+ });
+
+ // Okay, the memcpy has been formed. Zap the original store and anything that
+ // feeds into it.
+ deleteDeadInstruction(SI);
+ ++NumMemCpy;
+ return true;
+}
+
+// When compiling for codesize we avoid idiom recognition for a multi-block loop
+// unless it is a loop_memset idiom or a memset/memcpy idiom in a nested loop.
+//
+bool LoopIdiomRecognize::avoidLIRForMultiBlockLoop(bool IsMemset,
+ bool IsLoopMemset) {
+ if (ApplyCodeSizeHeuristics && CurLoop->getNumBlocks() > 1) {
+ if (!CurLoop->getParentLoop() && (!IsMemset || !IsLoopMemset)) {
+ LLVM_DEBUG(dbgs() << " " << CurLoop->getHeader()->getParent()->getName()
+ << " : LIR " << (IsMemset ? "Memset" : "Memcpy")
+ << " avoided: multi-block top-level loop\n");
+ return true;
+ }
+ }
+
+ return false;
+}
+
+bool LoopIdiomRecognize::runOnNoncountableLoop() {
+ LLVM_DEBUG(dbgs() << DEBUG_TYPE " Scanning: F["
+ << CurLoop->getHeader()->getParent()->getName()
+ << "] Noncountable Loop %"
+ << CurLoop->getHeader()->getName() << "\n");
+
+ return recognizePopcount() || recognizeAndInsertFFS();
+}
+
+/// Check if the given conditional branch is based on the comparison between
+/// a variable and zero, and if the variable is non-zero or zero (JmpOnZero is
+/// true), the control yields to the loop entry. If the branch matches the
+/// behavior, the variable involved in the comparison is returned. This function
+/// will be called to see if the precondition and postcondition of the loop are
+/// in desirable form.
+static Value *matchCondition(BranchInst *BI, BasicBlock *LoopEntry,
+ bool JmpOnZero = false) {
+ if (!BI || !BI->isConditional())
+ return nullptr;
+
+ ICmpInst *Cond = dyn_cast<ICmpInst>(BI->getCondition());
+ if (!Cond)
+ return nullptr;
+
+ ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
+ if (!CmpZero || !CmpZero->isZero())
+ return nullptr;
+
+ BasicBlock *TrueSucc = BI->getSuccessor(0);
+ BasicBlock *FalseSucc = BI->getSuccessor(1);
+ if (JmpOnZero)
+ std::swap(TrueSucc, FalseSucc);
+
+ ICmpInst::Predicate Pred = Cond->getPredicate();
+ if ((Pred == ICmpInst::ICMP_NE && TrueSucc == LoopEntry) ||
+ (Pred == ICmpInst::ICMP_EQ && FalseSucc == LoopEntry))
+ return Cond->getOperand(0);
+
+ return nullptr;
+}
+
+// Check if the recurrence variable `VarX` is in the right form to create
+// the idiom. Returns the value coerced to a PHINode if so.
+static PHINode *getRecurrenceVar(Value *VarX, Instruction *DefX,
+ BasicBlock *LoopEntry) {
+ auto *PhiX = dyn_cast<PHINode>(VarX);
+ if (PhiX && PhiX->getParent() == LoopEntry &&
+ (PhiX->getOperand(0) == DefX || PhiX->getOperand(1) == DefX))
+ return PhiX;
+ return nullptr;
+}
+
+/// Return true iff the idiom is detected in the loop.
+///
+/// Additionally:
+/// 1) \p CntInst is set to the instruction counting the population bit.
+/// 2) \p CntPhi is set to the corresponding phi node.
+/// 3) \p Var is set to the value whose population bits are being counted.
+///
+/// The core idiom we are trying to detect is:
+/// \code
+/// if (x0 != 0)
+/// goto loop-exit // the precondition of the loop
+/// cnt0 = init-val;
+/// do {
+/// x1 = phi (x0, x2);
+/// cnt1 = phi(cnt0, cnt2);
+///
+/// cnt2 = cnt1 + 1;
+/// ...
+/// x2 = x1 & (x1 - 1);
+/// ...
+/// } while(x != 0);
+///
+/// loop-exit:
+/// \endcode
+static bool detectPopcountIdiom(Loop *CurLoop, BasicBlock *PreCondBB,
+ Instruction *&CntInst, PHINode *&CntPhi,
+ Value *&Var) {
+ // step 1: Check to see if the look-back branch match this pattern:
+ // "if (a!=0) goto loop-entry".
+ BasicBlock *LoopEntry;
+ Instruction *DefX2, *CountInst;
+ Value *VarX1, *VarX0;
+ PHINode *PhiX, *CountPhi;
+
+ DefX2 = CountInst = nullptr;
+ VarX1 = VarX0 = nullptr;
+ PhiX = CountPhi = nullptr;
+ LoopEntry = *(CurLoop->block_begin());
+
+ // step 1: Check if the loop-back branch is in desirable form.
+ {
+ if (Value *T = matchCondition(
+ dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
+ DefX2 = dyn_cast<Instruction>(T);
+ else
+ return false;
+ }
+
+ // step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
+ {
+ if (!DefX2 || DefX2->getOpcode() != Instruction::And)
+ return false;
+
+ BinaryOperator *SubOneOp;
+
+ if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
+ VarX1 = DefX2->getOperand(1);
+ else {
+ VarX1 = DefX2->getOperand(0);
+ SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
+ }
+ if (!SubOneOp || SubOneOp->getOperand(0) != VarX1)
+ return false;
+
+ ConstantInt *Dec = dyn_cast<ConstantInt>(SubOneOp->getOperand(1));
+ if (!Dec ||
+ !((SubOneOp->getOpcode() == Instruction::Sub && Dec->isOne()) ||
+ (SubOneOp->getOpcode() == Instruction::Add &&
+ Dec->isMinusOne()))) {
+ return false;
+ }
+ }
+
+ // step 3: Check the recurrence of variable X
+ PhiX = getRecurrenceVar(VarX1, DefX2, LoopEntry);
+ if (!PhiX)
+ return false;
+
+ // step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
+ {
+ CountInst = nullptr;
+ for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI()->getIterator(),
+ IterE = LoopEntry->end();
+ Iter != IterE; Iter++) {
+ Instruction *Inst = &*Iter;
+ if (Inst->getOpcode() != Instruction::Add)
+ continue;
+
+ ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
+ if (!Inc || !Inc->isOne())
+ continue;
+
+ PHINode *Phi = getRecurrenceVar(Inst->getOperand(0), Inst, LoopEntry);
+ if (!Phi)
+ continue;
+
+ // Check if the result of the instruction is live of the loop.
+ bool LiveOutLoop = false;
+ for (User *U : Inst->users()) {
+ if ((cast<Instruction>(U))->getParent() != LoopEntry) {
+ LiveOutLoop = true;
+ break;
+ }
+ }
+
+ if (LiveOutLoop) {
+ CountInst = Inst;
+ CountPhi = Phi;
+ break;
+ }
+ }
+
+ if (!CountInst)
+ return false;
+ }
+
+ // step 5: check if the precondition is in this form:
+ // "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
+ {
+ auto *PreCondBr = dyn_cast<BranchInst>(PreCondBB->getTerminator());
+ Value *T = matchCondition(PreCondBr, CurLoop->getLoopPreheader());
+ if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
+ return false;
+
+ CntInst = CountInst;
+ CntPhi = CountPhi;
+ Var = T;
+ }
+
+ return true;
+}
+
+/// Return true if the idiom is detected in the loop.
+///
+/// Additionally:
+/// 1) \p CntInst is set to the instruction Counting Leading Zeros (CTLZ)
+/// or nullptr if there is no such.
+/// 2) \p CntPhi is set to the corresponding phi node
+/// or nullptr if there is no such.
+/// 3) \p Var is set to the value whose CTLZ could be used.
+/// 4) \p DefX is set to the instruction calculating Loop exit condition.
+///
+/// The core idiom we are trying to detect is:
+/// \code
+/// if (x0 == 0)
+/// goto loop-exit // the precondition of the loop
+/// cnt0 = init-val;
+/// do {
+/// x = phi (x0, x.next); //PhiX
+/// cnt = phi(cnt0, cnt.next);
+///
+/// cnt.next = cnt + 1;
+/// ...
+/// x.next = x >> 1; // DefX
+/// ...
+/// } while(x.next != 0);
+///
+/// loop-exit:
+/// \endcode
+static bool detectShiftUntilZeroIdiom(Loop *CurLoop, const DataLayout &DL,
+ Intrinsic::ID &IntrinID, Value *&InitX,
+ Instruction *&CntInst, PHINode *&CntPhi,
+ Instruction *&DefX) {
+ BasicBlock *LoopEntry;
+ Value *VarX = nullptr;
+
+ DefX = nullptr;
+ CntInst = nullptr;
+ CntPhi = nullptr;
+ LoopEntry = *(CurLoop->block_begin());
+
+ // step 1: Check if the loop-back branch is in desirable form.
+ if (Value *T = matchCondition(
+ dyn_cast<BranchInst>(LoopEntry->getTerminator()), LoopEntry))
+ DefX = dyn_cast<Instruction>(T);
+ else
+ return false;
+
+ // step 2: detect instructions corresponding to "x.next = x >> 1 or x << 1"
+ if (!DefX || !DefX->isShift())
+ return false;
+ IntrinID = DefX->getOpcode() == Instruction::Shl ? Intrinsic::cttz :
+ Intrinsic::ctlz;
+ ConstantInt *Shft = dyn_cast<ConstantInt>(DefX->getOperand(1));
+ if (!Shft || !Shft->isOne())
+ return false;
+ VarX = DefX->getOperand(0);
+
+ // step 3: Check the recurrence of variable X
+ PHINode *PhiX = getRecurrenceVar(VarX, DefX, LoopEntry);
+ if (!PhiX)
+ return false;
+
+ InitX = PhiX->getIncomingValueForBlock(CurLoop->getLoopPreheader());
+
+ // Make sure the initial value can't be negative otherwise the ashr in the
+ // loop might never reach zero which would make the loop infinite.
+ if (DefX->getOpcode() == Instruction::AShr && !isKnownNonNegative(InitX, DL))
+ return false;
+
+ // step 4: Find the instruction which count the CTLZ: cnt.next = cnt + 1
+ // TODO: We can skip the step. If loop trip count is known (CTLZ),
+ // then all uses of "cnt.next" could be optimized to the trip count
+ // plus "cnt0". Currently it is not optimized.
+ // This step could be used to detect POPCNT instruction:
+ // cnt.next = cnt + (x.next & 1)
+ for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI()->getIterator(),
+ IterE = LoopEntry->end();
+ Iter != IterE; Iter++) {
+ Instruction *Inst = &*Iter;
+ if (Inst->getOpcode() != Instruction::Add)
+ continue;
+
+ ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
+ if (!Inc || !Inc->isOne())
+ continue;
+
+ PHINode *Phi = getRecurrenceVar(Inst->getOperand(0), Inst, LoopEntry);
+ if (!Phi)
+ continue;
+
+ CntInst = Inst;
+ CntPhi = Phi;
+ break;
+ }
+ if (!CntInst)
+ return false;
+
+ return true;
+}
+
+/// Recognize CTLZ or CTTZ idiom in a non-countable loop and convert the loop
+/// to countable (with CTLZ / CTTZ trip count). If CTLZ / CTTZ inserted as a new
+/// trip count returns true; otherwise, returns false.
+bool LoopIdiomRecognize::recognizeAndInsertFFS() {
+ // Give up if the loop has multiple blocks or multiple backedges.
+ if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
+ return false;
+
+ Intrinsic::ID IntrinID;
+ Value *InitX;
+ Instruction *DefX = nullptr;
+ PHINode *CntPhi = nullptr;
+ Instruction *CntInst = nullptr;
+ // Help decide if transformation is profitable. For ShiftUntilZero idiom,
+ // this is always 6.
+ size_t IdiomCanonicalSize = 6;
+
+ if (!detectShiftUntilZeroIdiom(CurLoop, *DL, IntrinID, InitX,
+ CntInst, CntPhi, DefX))
+ return false;
+
+ bool IsCntPhiUsedOutsideLoop = false;
+ for (User *U : CntPhi->users())
+ if (!CurLoop->contains(cast<Instruction>(U))) {
+ IsCntPhiUsedOutsideLoop = true;
+ break;
+ }
+ bool IsCntInstUsedOutsideLoop = false;
+ for (User *U : CntInst->users())
+ if (!CurLoop->contains(cast<Instruction>(U))) {
+ IsCntInstUsedOutsideLoop = true;
+ break;
+ }
+ // If both CntInst and CntPhi are used outside the loop the profitability
+ // is questionable.
+ if (IsCntInstUsedOutsideLoop && IsCntPhiUsedOutsideLoop)
+ return false;
+
+ // For some CPUs result of CTLZ(X) intrinsic is undefined
+ // when X is 0. If we can not guarantee X != 0, we need to check this
+ // when expand.
+ bool ZeroCheck = false;
+ // It is safe to assume Preheader exist as it was checked in
+ // parent function RunOnLoop.
+ BasicBlock *PH = CurLoop->getLoopPreheader();
+
+ // If we are using the count instruction outside the loop, make sure we
+ // have a zero check as a precondition. Without the check the loop would run
+ // one iteration for before any check of the input value. This means 0 and 1
+ // would have identical behavior in the original loop and thus
+ if (!IsCntPhiUsedOutsideLoop) {
+ auto *PreCondBB = PH->getSinglePredecessor();
+ if (!PreCondBB)
+ return false;
+ auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
+ if (!PreCondBI)
+ return false;
+ if (matchCondition(PreCondBI, PH) != InitX)
+ return false;
+ ZeroCheck = true;
+ }
+
+ // Check if CTLZ / CTTZ intrinsic is profitable. Assume it is always
+ // profitable if we delete the loop.
+
+ // the loop has only 6 instructions:
+ // %n.addr.0 = phi [ %n, %entry ], [ %shr, %while.cond ]
+ // %i.0 = phi [ %i0, %entry ], [ %inc, %while.cond ]
+ // %shr = ashr %n.addr.0, 1
+ // %tobool = icmp eq %shr, 0
+ // %inc = add nsw %i.0, 1
+ // br i1 %tobool
+
+ const Value *Args[] =
+ {InitX, ZeroCheck ? ConstantInt::getTrue(InitX->getContext())
+ : ConstantInt::getFalse(InitX->getContext())};
+
+ // @llvm.dbg doesn't count as they have no semantic effect.
+ auto InstWithoutDebugIt = CurLoop->getHeader()->instructionsWithoutDebug();
+ uint32_t HeaderSize =
+ std::distance(InstWithoutDebugIt.begin(), InstWithoutDebugIt.end());
+
+ if (HeaderSize != IdiomCanonicalSize &&
+ TTI->getIntrinsicCost(IntrinID, InitX->getType(), Args) >
+ TargetTransformInfo::TCC_Basic)
+ return false;
+
+ transformLoopToCountable(IntrinID, PH, CntInst, CntPhi, InitX, DefX,
+ DefX->getDebugLoc(), ZeroCheck,
+ IsCntPhiUsedOutsideLoop);
+ return true;
+}
+
+/// Recognizes a population count idiom in a non-countable loop.
+///
+/// If detected, transforms the relevant code to issue the popcount intrinsic
+/// function call, and returns true; otherwise, returns false.
+bool LoopIdiomRecognize::recognizePopcount() {
+ if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
+ return false;
+
+ // Counting population are usually conducted by few arithmetic instructions.
+ // Such instructions can be easily "absorbed" by vacant slots in a
+ // non-compact loop. Therefore, recognizing popcount idiom only makes sense
+ // in a compact loop.
+
+ // Give up if the loop has multiple blocks or multiple backedges.
+ if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
+ return false;
+
+ BasicBlock *LoopBody = *(CurLoop->block_begin());
+ if (LoopBody->size() >= 20) {
+ // The loop is too big, bail out.
+ return false;
+ }
+
+ // It should have a preheader containing nothing but an unconditional branch.
+ BasicBlock *PH = CurLoop->getLoopPreheader();
+ if (!PH || &PH->front() != PH->getTerminator())
+ return false;
+ auto *EntryBI = dyn_cast<BranchInst>(PH->getTerminator());
+ if (!EntryBI || EntryBI->isConditional())
+ return false;
+
+ // It should have a precondition block where the generated popcount intrinsic
+ // function can be inserted.
+ auto *PreCondBB = PH->getSinglePredecessor();
+ if (!PreCondBB)
+ return false;
+ auto *PreCondBI = dyn_cast<BranchInst>(PreCondBB->getTerminator());
+ if (!PreCondBI || PreCondBI->isUnconditional())
+ return false;
+
+ Instruction *CntInst;
+ PHINode *CntPhi;
+ Value *Val;
+ if (!detectPopcountIdiom(CurLoop, PreCondBB, CntInst, CntPhi, Val))
+ return false;
+
+ transformLoopToPopcount(PreCondBB, CntInst, CntPhi, Val);
+ return true;
+}
+
+static CallInst *createPopcntIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
+ const DebugLoc &DL) {
+ Value *Ops[] = {Val};
+ Type *Tys[] = {Val->getType()};
+
+ Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
+ Function *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
+ CallInst *CI = IRBuilder.CreateCall(Func, Ops);
+ CI->setDebugLoc(DL);
+
+ return CI;
+}
+
+static CallInst *createFFSIntrinsic(IRBuilder<> &IRBuilder, Value *Val,
+ const DebugLoc &DL, bool ZeroCheck,
+ Intrinsic::ID IID) {
+ Value *Ops[] = {Val, ZeroCheck ? IRBuilder.getTrue() : IRBuilder.getFalse()};
+ Type *Tys[] = {Val->getType()};
+
+ Module *M = IRBuilder.GetInsertBlock()->getParent()->getParent();
+ Function *Func = Intrinsic::getDeclaration(M, IID, Tys);
+ CallInst *CI = IRBuilder.CreateCall(Func, Ops);
+ CI->setDebugLoc(DL);
+
+ return CI;
+}
+
+/// Transform the following loop (Using CTLZ, CTTZ is similar):
+/// loop:
+/// CntPhi = PHI [Cnt0, CntInst]
+/// PhiX = PHI [InitX, DefX]
+/// CntInst = CntPhi + 1
+/// DefX = PhiX >> 1
+/// LOOP_BODY
+/// Br: loop if (DefX != 0)
+/// Use(CntPhi) or Use(CntInst)
+///
+/// Into:
+/// If CntPhi used outside the loop:
+/// CountPrev = BitWidth(InitX) - CTLZ(InitX >> 1)
+/// Count = CountPrev + 1
+/// else
+/// Count = BitWidth(InitX) - CTLZ(InitX)
+/// loop:
+/// CntPhi = PHI [Cnt0, CntInst]
+/// PhiX = PHI [InitX, DefX]
+/// PhiCount = PHI [Count, Dec]
+/// CntInst = CntPhi + 1
+/// DefX = PhiX >> 1
+/// Dec = PhiCount - 1
+/// LOOP_BODY
+/// Br: loop if (Dec != 0)
+/// Use(CountPrev + Cnt0) // Use(CntPhi)
+/// or
+/// Use(Count + Cnt0) // Use(CntInst)
+///
+/// If LOOP_BODY is empty the loop will be deleted.
+/// If CntInst and DefX are not used in LOOP_BODY they will be removed.
+void LoopIdiomRecognize::transformLoopToCountable(
+ Intrinsic::ID IntrinID, BasicBlock *Preheader, Instruction *CntInst,
+ PHINode *CntPhi, Value *InitX, Instruction *DefX, const DebugLoc &DL,
+ bool ZeroCheck, bool IsCntPhiUsedOutsideLoop) {
+ BranchInst *PreheaderBr = cast<BranchInst>(Preheader->getTerminator());
+
+ // Step 1: Insert the CTLZ/CTTZ instruction at the end of the preheader block
+ IRBuilder<> Builder(PreheaderBr);
+ Builder.SetCurrentDebugLocation(DL);
+ Value *FFS, *Count, *CountPrev, *NewCount, *InitXNext;
+
+ // Count = BitWidth - CTLZ(InitX);
+ // If there are uses of CntPhi create:
+ // CountPrev = BitWidth - CTLZ(InitX >> 1);
+ if (IsCntPhiUsedOutsideLoop) {
+ if (DefX->getOpcode() == Instruction::AShr)
+ InitXNext =
+ Builder.CreateAShr(InitX, ConstantInt::get(InitX->getType(), 1));
+ else if (DefX->getOpcode() == Instruction::LShr)
+ InitXNext =
+ Builder.CreateLShr(InitX, ConstantInt::get(InitX->getType(), 1));
+ else if (DefX->getOpcode() == Instruction::Shl) // cttz
+ InitXNext =
+ Builder.CreateShl(InitX, ConstantInt::get(InitX->getType(), 1));
+ else
+ llvm_unreachable("Unexpected opcode!");
+ } else
+ InitXNext = InitX;
+ FFS = createFFSIntrinsic(Builder, InitXNext, DL, ZeroCheck, IntrinID);
+ Count = Builder.CreateSub(
+ ConstantInt::get(FFS->getType(),
+ FFS->getType()->getIntegerBitWidth()),
+ FFS);
+ if (IsCntPhiUsedOutsideLoop) {
+ CountPrev = Count;
+ Count = Builder.CreateAdd(
+ CountPrev,
+ ConstantInt::get(CountPrev->getType(), 1));
+ }
+
+ NewCount = Builder.CreateZExtOrTrunc(
+ IsCntPhiUsedOutsideLoop ? CountPrev : Count,
+ cast<IntegerType>(CntInst->getType()));
+
+ // If the counter's initial value is not zero, insert Add Inst.
+ Value *CntInitVal = CntPhi->getIncomingValueForBlock(Preheader);
+ ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
+ if (!InitConst || !InitConst->isZero())
+ NewCount = Builder.CreateAdd(NewCount, CntInitVal);
+
+ // Step 2: Insert new IV and loop condition:
+ // loop:
+ // ...
+ // PhiCount = PHI [Count, Dec]
+ // ...
+ // Dec = PhiCount - 1
+ // ...
+ // Br: loop if (Dec != 0)
+ BasicBlock *Body = *(CurLoop->block_begin());
+ auto *LbBr = cast<BranchInst>(Body->getTerminator());
+ ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
+ Type *Ty = Count->getType();
+
+ PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
+
+ Builder.SetInsertPoint(LbCond);
+ Instruction *TcDec = cast<Instruction>(
+ Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
+ "tcdec", false, true));
+
+ TcPhi->addIncoming(Count, Preheader);
+ TcPhi->addIncoming(TcDec, Body);
+
+ CmpInst::Predicate Pred =
+ (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_NE : CmpInst::ICMP_EQ;
+ LbCond->setPredicate(Pred);
+ LbCond->setOperand(0, TcDec);
+ LbCond->setOperand(1, ConstantInt::get(Ty, 0));
+
+ // Step 3: All the references to the original counter outside
+ // the loop are replaced with the NewCount
+ if (IsCntPhiUsedOutsideLoop)
+ CntPhi->replaceUsesOutsideBlock(NewCount, Body);
+ else
+ CntInst->replaceUsesOutsideBlock(NewCount, Body);
+
+ // step 4: Forget the "non-computable" trip-count SCEV associated with the
+ // loop. The loop would otherwise not be deleted even if it becomes empty.
+ SE->forgetLoop(CurLoop);
+}
+
+void LoopIdiomRecognize::transformLoopToPopcount(BasicBlock *PreCondBB,
+ Instruction *CntInst,
+ PHINode *CntPhi, Value *Var) {
+ BasicBlock *PreHead = CurLoop->getLoopPreheader();
+ auto *PreCondBr = cast<BranchInst>(PreCondBB->getTerminator());
+ const DebugLoc &DL = CntInst->getDebugLoc();
+
+ // Assuming before transformation, the loop is following:
+ // if (x) // the precondition
+ // do { cnt++; x &= x - 1; } while(x);
+
+ // Step 1: Insert the ctpop instruction at the end of the precondition block
+ IRBuilder<> Builder(PreCondBr);
+ Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
+ {
+ PopCnt = createPopcntIntrinsic(Builder, Var, DL);
+ NewCount = PopCntZext =
+ Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
+
+ if (NewCount != PopCnt)
+ (cast<Instruction>(NewCount))->setDebugLoc(DL);
+
+ // TripCnt is exactly the number of iterations the loop has
+ TripCnt = NewCount;
+
+ // If the population counter's initial value is not zero, insert Add Inst.
+ Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
+ ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
+ if (!InitConst || !InitConst->isZero()) {
+ NewCount = Builder.CreateAdd(NewCount, CntInitVal);
+ (cast<Instruction>(NewCount))->setDebugLoc(DL);
+ }
+ }
+
+ // Step 2: Replace the precondition from "if (x == 0) goto loop-exit" to
+ // "if (NewCount == 0) loop-exit". Without this change, the intrinsic
+ // function would be partial dead code, and downstream passes will drag
+ // it back from the precondition block to the preheader.
+ {
+ ICmpInst *PreCond = cast<ICmpInst>(PreCondBr->getCondition());
+
+ Value *Opnd0 = PopCntZext;
+ Value *Opnd1 = ConstantInt::get(PopCntZext->getType(), 0);
+ if (PreCond->getOperand(0) != Var)
+ std::swap(Opnd0, Opnd1);
+
+ ICmpInst *NewPreCond = cast<ICmpInst>(
+ Builder.CreateICmp(PreCond->getPredicate(), Opnd0, Opnd1));
+ PreCondBr->setCondition(NewPreCond);
+
+ RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
+ }
+
+ // Step 3: Note that the population count is exactly the trip count of the
+ // loop in question, which enable us to convert the loop from noncountable
+ // loop into a countable one. The benefit is twofold:
+ //
+ // - If the loop only counts population, the entire loop becomes dead after
+ // the transformation. It is a lot easier to prove a countable loop dead
+ // than to prove a noncountable one. (In some C dialects, an infinite loop
+ // isn't dead even if it computes nothing useful. In general, DCE needs
+ // to prove a noncountable loop finite before safely delete it.)
+ //
+ // - If the loop also performs something else, it remains alive.
+ // Since it is transformed to countable form, it can be aggressively
+ // optimized by some optimizations which are in general not applicable
+ // to a noncountable loop.
+ //
+ // After this step, this loop (conceptually) would look like following:
+ // newcnt = __builtin_ctpop(x);
+ // t = newcnt;
+ // if (x)
+ // do { cnt++; x &= x-1; t--) } while (t > 0);
+ BasicBlock *Body = *(CurLoop->block_begin());
+ {
+ auto *LbBr = cast<BranchInst>(Body->getTerminator());
+ ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
+ Type *Ty = TripCnt->getType();
+
+ PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", &Body->front());
+
+ Builder.SetInsertPoint(LbCond);
+ Instruction *TcDec = cast<Instruction>(
+ Builder.CreateSub(TcPhi, ConstantInt::get(Ty, 1),
+ "tcdec", false, true));
+
+ TcPhi->addIncoming(TripCnt, PreHead);
+ TcPhi->addIncoming(TcDec, Body);
+
+ CmpInst::Predicate Pred =
+ (LbBr->getSuccessor(0) == Body) ? CmpInst::ICMP_UGT : CmpInst::ICMP_SLE;
+ LbCond->setPredicate(Pred);
+ LbCond->setOperand(0, TcDec);
+ LbCond->setOperand(1, ConstantInt::get(Ty, 0));
+ }
+
+ // Step 4: All the references to the original population counter outside
+ // the loop are replaced with the NewCount -- the value returned from
+ // __builtin_ctpop().
+ CntInst->replaceUsesOutsideBlock(NewCount, Body);
+
+ // step 5: Forget the "non-computable" trip-count SCEV associated with the
+ // loop. The loop would otherwise not be deleted even if it becomes empty.
+ SE->forgetLoop(CurLoop);
+}
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