mirror of
https://github.com/RPCS3/llvm-mirror.git
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fbea601694
Split off from D61144 llvm-svn: 362022
1790 lines
66 KiB
C++
1790 lines
66 KiB
C++
//===- LoopIdiomRecognize.cpp - Loop idiom recognition --------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass implements an idiom recognizer that transforms simple loops into a
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// non-loop form. In cases that this kicks in, it can be a significant
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// performance win.
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//
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// If compiling for code size we avoid idiom recognition if the resulting
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// code could be larger than the code for the original loop. One way this could
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// happen is if the loop is not removable after idiom recognition due to the
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// presence of non-idiom instructions. The initial implementation of the
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// heuristics applies to idioms in multi-block loops.
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//
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//===----------------------------------------------------------------------===//
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//
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// TODO List:
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//
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// Future loop memory idioms to recognize:
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// memcmp, memmove, strlen, etc.
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// Future floating point idioms to recognize in -ffast-math mode:
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// fpowi
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// Future integer operation idioms to recognize:
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// ctpop
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//
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// Beware that isel's default lowering for ctpop is highly inefficient for
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// i64 and larger types when i64 is legal and the value has few bits set. It
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// would be good to enhance isel to emit a loop for ctpop in this case.
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//
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// This could recognize common matrix multiplies and dot product idioms and
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// replace them with calls to BLAS (if linked in??).
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/APInt.h"
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/MapVector.h"
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#include "llvm/ADT/SetVector.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/LoopAccessAnalysis.h"
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#include "llvm/Analysis/LoopInfo.h"
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#include "llvm/Analysis/LoopPass.h"
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#include "llvm/Analysis/MemoryLocation.h"
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#include "llvm/Analysis/ScalarEvolution.h"
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#include "llvm/Analysis/ScalarEvolutionExpander.h"
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#include "llvm/Analysis/ScalarEvolutionExpressions.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Analysis/TargetTransformInfo.h"
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#include "llvm/Transforms/Utils/Local.h"
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#include "llvm/Analysis/ValueTracking.h"
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#include "llvm/IR/Attributes.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Constant.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DebugLoc.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/GlobalValue.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/InstrTypes.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/PassManager.h"
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#include "llvm/IR/Type.h"
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#include "llvm/IR/User.h"
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#include "llvm/IR/Value.h"
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#include "llvm/IR/ValueHandle.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/Support/raw_ostream.h"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Scalar/LoopIdiomRecognize.h"
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#include "llvm/Transforms/Utils/BuildLibCalls.h"
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#include "llvm/Transforms/Utils/LoopUtils.h"
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#include <algorithm>
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#include <cassert>
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#include <cstdint>
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#include <utility>
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#include <vector>
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using namespace llvm;
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#define DEBUG_TYPE "loop-idiom"
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STATISTIC(NumMemSet, "Number of memset's formed from loop stores");
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STATISTIC(NumMemCpy, "Number of memcpy's formed from loop load+stores");
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static cl::opt<bool> UseLIRCodeSizeHeurs(
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"use-lir-code-size-heurs",
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cl::desc("Use loop idiom recognition code size heuristics when compiling"
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"with -Os/-Oz"),
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cl::init(true), cl::Hidden);
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namespace {
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class LoopIdiomRecognize {
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Loop *CurLoop = nullptr;
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AliasAnalysis *AA;
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DominatorTree *DT;
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LoopInfo *LI;
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ScalarEvolution *SE;
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TargetLibraryInfo *TLI;
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const TargetTransformInfo *TTI;
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const DataLayout *DL;
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bool ApplyCodeSizeHeuristics;
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public:
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explicit LoopIdiomRecognize(AliasAnalysis *AA, DominatorTree *DT,
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LoopInfo *LI, ScalarEvolution *SE,
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TargetLibraryInfo *TLI,
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const TargetTransformInfo *TTI,
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const DataLayout *DL)
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: AA(AA), DT(DT), LI(LI), SE(SE), TLI(TLI), TTI(TTI), DL(DL) {}
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bool runOnLoop(Loop *L);
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private:
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using StoreList = SmallVector<StoreInst *, 8>;
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using StoreListMap = MapVector<Value *, StoreList>;
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StoreListMap StoreRefsForMemset;
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StoreListMap StoreRefsForMemsetPattern;
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StoreList StoreRefsForMemcpy;
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bool HasMemset;
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bool HasMemsetPattern;
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bool HasMemcpy;
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/// Return code for isLegalStore()
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enum LegalStoreKind {
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None = 0,
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Memset,
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MemsetPattern,
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Memcpy,
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UnorderedAtomicMemcpy,
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DontUse // Dummy retval never to be used. Allows catching errors in retval
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// handling.
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};
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/// \name Countable Loop Idiom Handling
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/// @{
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bool runOnCountableLoop();
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bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
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SmallVectorImpl<BasicBlock *> &ExitBlocks);
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void collectStores(BasicBlock *BB);
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LegalStoreKind isLegalStore(StoreInst *SI);
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enum class ForMemset { No, Yes };
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bool processLoopStores(SmallVectorImpl<StoreInst *> &SL, const SCEV *BECount,
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ForMemset For);
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bool processLoopMemSet(MemSetInst *MSI, const SCEV *BECount);
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bool processLoopStridedStore(Value *DestPtr, unsigned StoreSize,
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unsigned StoreAlignment, Value *StoredVal,
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Instruction *TheStore,
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SmallPtrSetImpl<Instruction *> &Stores,
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const SCEVAddRecExpr *Ev, const SCEV *BECount,
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bool NegStride, bool IsLoopMemset = false);
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bool processLoopStoreOfLoopLoad(StoreInst *SI, const SCEV *BECount);
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bool avoidLIRForMultiBlockLoop(bool IsMemset = false,
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bool IsLoopMemset = false);
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/// @}
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/// \name Noncountable Loop Idiom Handling
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/// @{
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bool runOnNoncountableLoop();
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bool recognizePopcount();
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void transformLoopToPopcount(BasicBlock *PreCondBB, Instruction *CntInst,
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PHINode *CntPhi, Value *Var);
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bool recognizeAndInsertFFS(); /// Find First Set: ctlz or cttz
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void transformLoopToCountable(Intrinsic::ID IntrinID, BasicBlock *PreCondBB,
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Instruction *CntInst, PHINode *CntPhi,
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Value *Var, Instruction *DefX,
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const DebugLoc &DL, bool ZeroCheck,
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bool IsCntPhiUsedOutsideLoop);
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/// @}
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};
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class LoopIdiomRecognizeLegacyPass : public LoopPass {
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public:
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static char ID;
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explicit LoopIdiomRecognizeLegacyPass() : LoopPass(ID) {
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initializeLoopIdiomRecognizeLegacyPassPass(
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*PassRegistry::getPassRegistry());
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}
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bool runOnLoop(Loop *L, LPPassManager &LPM) override {
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if (skipLoop(L))
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return false;
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AliasAnalysis *AA = &getAnalysis<AAResultsWrapperPass>().getAAResults();
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DominatorTree *DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree();
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LoopInfo *LI = &getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
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ScalarEvolution *SE = &getAnalysis<ScalarEvolutionWrapperPass>().getSE();
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TargetLibraryInfo *TLI =
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&getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
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const TargetTransformInfo *TTI =
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&getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
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*L->getHeader()->getParent());
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const DataLayout *DL = &L->getHeader()->getModule()->getDataLayout();
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LoopIdiomRecognize LIR(AA, DT, LI, SE, TLI, TTI, DL);
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return LIR.runOnLoop(L);
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}
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/// This transformation requires natural loop information & requires that
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/// loop preheaders be inserted into the CFG.
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<TargetLibraryInfoWrapperPass>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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getLoopAnalysisUsage(AU);
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}
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};
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} // end anonymous namespace
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char LoopIdiomRecognizeLegacyPass::ID = 0;
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PreservedAnalyses LoopIdiomRecognizePass::run(Loop &L, LoopAnalysisManager &AM,
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LoopStandardAnalysisResults &AR,
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LPMUpdater &) {
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const auto *DL = &L.getHeader()->getModule()->getDataLayout();
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LoopIdiomRecognize LIR(&AR.AA, &AR.DT, &AR.LI, &AR.SE, &AR.TLI, &AR.TTI, DL);
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if (!LIR.runOnLoop(&L))
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return PreservedAnalyses::all();
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return getLoopPassPreservedAnalyses();
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}
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INITIALIZE_PASS_BEGIN(LoopIdiomRecognizeLegacyPass, "loop-idiom",
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"Recognize loop idioms", false, false)
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INITIALIZE_PASS_DEPENDENCY(LoopPass)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_PASS_END(LoopIdiomRecognizeLegacyPass, "loop-idiom",
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"Recognize loop idioms", false, false)
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Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognizeLegacyPass(); }
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static void deleteDeadInstruction(Instruction *I) {
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I->replaceAllUsesWith(UndefValue::get(I->getType()));
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I->eraseFromParent();
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}
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//===----------------------------------------------------------------------===//
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//
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// Implementation of LoopIdiomRecognize
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//
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//===----------------------------------------------------------------------===//
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bool LoopIdiomRecognize::runOnLoop(Loop *L) {
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CurLoop = L;
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// If the loop could not be converted to canonical form, it must have an
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// indirectbr in it, just give up.
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if (!L->getLoopPreheader())
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return false;
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// Disable loop idiom recognition if the function's name is a common idiom.
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StringRef Name = L->getHeader()->getParent()->getName();
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if (Name == "memset" || Name == "memcpy")
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return false;
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// Determine if code size heuristics need to be applied.
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ApplyCodeSizeHeuristics =
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L->getHeader()->getParent()->hasOptSize() && UseLIRCodeSizeHeurs;
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HasMemset = TLI->has(LibFunc_memset);
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HasMemsetPattern = TLI->has(LibFunc_memset_pattern16);
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HasMemcpy = TLI->has(LibFunc_memcpy);
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if (HasMemset || HasMemsetPattern || HasMemcpy)
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if (SE->hasLoopInvariantBackedgeTakenCount(L))
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return runOnCountableLoop();
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return runOnNoncountableLoop();
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}
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bool LoopIdiomRecognize::runOnCountableLoop() {
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const SCEV *BECount = SE->getBackedgeTakenCount(CurLoop);
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assert(!isa<SCEVCouldNotCompute>(BECount) &&
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"runOnCountableLoop() called on a loop without a predictable"
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"backedge-taken count");
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// If this loop executes exactly one time, then it should be peeled, not
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// optimized by this pass.
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if (const SCEVConstant *BECst = dyn_cast<SCEVConstant>(BECount))
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if (BECst->getAPInt() == 0)
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return false;
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SmallVector<BasicBlock *, 8> ExitBlocks;
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CurLoop->getUniqueExitBlocks(ExitBlocks);
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LLVM_DEBUG(dbgs() << DEBUG_TYPE " Scanning: F["
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<< CurLoop->getHeader()->getParent()->getName()
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<< "] Countable Loop %" << CurLoop->getHeader()->getName()
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<< "\n");
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bool MadeChange = false;
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// The following transforms hoist stores/memsets into the loop pre-header.
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// Give up if the loop has instructions may throw.
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SimpleLoopSafetyInfo SafetyInfo;
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SafetyInfo.computeLoopSafetyInfo(CurLoop);
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if (SafetyInfo.anyBlockMayThrow())
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return MadeChange;
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// Scan all the blocks in the loop that are not in subloops.
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for (auto *BB : CurLoop->getBlocks()) {
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// Ignore blocks in subloops.
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if (LI->getLoopFor(BB) != CurLoop)
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continue;
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MadeChange |= runOnLoopBlock(BB, BECount, ExitBlocks);
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}
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return MadeChange;
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}
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static APInt getStoreStride(const SCEVAddRecExpr *StoreEv) {
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const SCEVConstant *ConstStride = cast<SCEVConstant>(StoreEv->getOperand(1));
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return ConstStride->getAPInt();
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}
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/// getMemSetPatternValue - If a strided store of the specified value is safe to
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/// turn into a memset_pattern16, return a ConstantArray of 16 bytes that should
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/// be passed in. Otherwise, return null.
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///
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/// Note that we don't ever attempt to use memset_pattern8 or 4, because these
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/// just replicate their input array and then pass on to memset_pattern16.
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static Constant *getMemSetPatternValue(Value *V, const DataLayout *DL) {
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// FIXME: This could check for UndefValue because it can be merged into any
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// other valid pattern.
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// If the value isn't a constant, we can't promote it to being in a constant
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// array. We could theoretically do a store to an alloca or something, but
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// that doesn't seem worthwhile.
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Constant *C = dyn_cast<Constant>(V);
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if (!C)
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return nullptr;
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// Only handle simple values that are a power of two bytes in size.
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uint64_t Size = DL->getTypeSizeInBits(V->getType());
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if (Size == 0 || (Size & 7) || (Size & (Size - 1)))
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return nullptr;
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// Don't care enough about darwin/ppc to implement this.
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if (DL->isBigEndian())
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return nullptr;
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// Convert to size in bytes.
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Size /= 8;
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// TODO: If CI is larger than 16-bytes, we can try slicing it in half to see
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// if the top and bottom are the same (e.g. for vectors and large integers).
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if (Size > 16)
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return nullptr;
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// If the constant is exactly 16 bytes, just use it.
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if (Size == 16)
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return C;
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// Otherwise, we'll use an array of the constants.
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unsigned ArraySize = 16 / Size;
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ArrayType *AT = ArrayType::get(V->getType(), ArraySize);
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return ConstantArray::get(AT, std::vector<Constant *>(ArraySize, C));
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}
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LoopIdiomRecognize::LegalStoreKind
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LoopIdiomRecognize::isLegalStore(StoreInst *SI) {
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// Don't touch volatile stores.
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if (SI->isVolatile())
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return LegalStoreKind::None;
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// We only want simple or unordered-atomic stores.
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if (!SI->isUnordered())
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return LegalStoreKind::None;
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// Don't convert stores of non-integral pointer types to memsets (which stores
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// integers).
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if (DL->isNonIntegralPointerType(SI->getValueOperand()->getType()))
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return LegalStoreKind::None;
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// Avoid merging nontemporal stores.
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if (SI->getMetadata(LLVMContext::MD_nontemporal))
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return LegalStoreKind::None;
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Value *StoredVal = SI->getValueOperand();
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Value *StorePtr = SI->getPointerOperand();
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// Reject stores that are so large that they overflow an unsigned.
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uint64_t SizeInBits = DL->getTypeSizeInBits(StoredVal->getType());
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if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
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return LegalStoreKind::None;
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// See if the pointer expression is an AddRec like {base,+,1} on the current
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// loop, which indicates a strided store. If we have something else, it's a
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// random store we can't handle.
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const SCEVAddRecExpr *StoreEv =
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dyn_cast<SCEVAddRecExpr>(SE->getSCEV(StorePtr));
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if (!StoreEv || StoreEv->getLoop() != CurLoop || !StoreEv->isAffine())
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return LegalStoreKind::None;
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// Check to see if we have a constant stride.
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if (!isa<SCEVConstant>(StoreEv->getOperand(1)))
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return LegalStoreKind::None;
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// See if the store can be turned into a memset.
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// If the stored value is a byte-wise value (like i32 -1), then it may be
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// turned into a memset of i8 -1, assuming that all the consecutive bytes
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// are stored. A store of i32 0x01020304 can never be turned into a memset,
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// but it can be turned into memset_pattern if the target supports it.
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Value *SplatValue = isBytewiseValue(StoredVal);
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Constant *PatternValue = nullptr;
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// Note: memset and memset_pattern on unordered-atomic is yet not supported
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bool UnorderedAtomic = SI->isUnordered() && !SI->isSimple();
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// If we're allowed to form a memset, and the stored value would be
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// acceptable for memset, use it.
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if (!UnorderedAtomic && HasMemset && SplatValue &&
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// Verify that the stored value is loop invariant. If not, we can't
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// promote the memset.
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CurLoop->isLoopInvariant(SplatValue)) {
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// It looks like we can use SplatValue.
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return LegalStoreKind::Memset;
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} else if (!UnorderedAtomic && HasMemsetPattern &&
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// Don't create memset_pattern16s with address spaces.
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StorePtr->getType()->getPointerAddressSpace() == 0 &&
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(PatternValue = getMemSetPatternValue(StoredVal, DL))) {
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// It looks like we can use PatternValue!
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return LegalStoreKind::MemsetPattern;
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}
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// Otherwise, see if the store can be turned into a memcpy.
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if (HasMemcpy) {
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// Check to see if the stride matches the size of the store. If so, then we
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// know that every byte is touched in the loop.
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APInt Stride = getStoreStride(StoreEv);
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unsigned StoreSize = DL->getTypeStoreSize(SI->getValueOperand()->getType());
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if (StoreSize != Stride && StoreSize != -Stride)
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return LegalStoreKind::None;
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// The store must be feeding a non-volatile load.
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LoadInst *LI = dyn_cast<LoadInst>(SI->getValueOperand());
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// Only allow non-volatile loads
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|
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);
|
|
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);
|
|
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);
|
|
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());
|
|
|
|
// 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");
|
|
|
|
// 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);
|
|
}
|