mirror of
https://github.com/c64scene-ar/llvm-6502.git
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@237624 91177308-0d34-0410-b5e6-96231b3b80d8
1108 lines
41 KiB
C++
1108 lines
41 KiB
C++
//===-- LoopIdiomRecognize.cpp - Loop idiom recognition -------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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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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//===----------------------------------------------------------------------===//
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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, ctlz, cttz
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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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// We should enhance the memset/memcpy recognition to handle multiple stores in
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// the loop. This would handle things like:
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// void foo(_Complex float *P)
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// for (i) { __real__(*P) = 0; __imag__(*P) = 0; }
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//
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// We should enhance this to handle negative strides through memory.
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// Alternatively (and perhaps better) we could rely on an earlier pass to force
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// forward iteration through memory, which is generally better for cache
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// behavior. Negative strides *do* happen for memset/memcpy loops.
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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/Transforms/Scalar.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/LoopPass.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/Analysis/ValueTracking.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/Dominators.h"
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#include "llvm/IR/IRBuilder.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Module.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/Utils/Local.h"
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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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namespace {
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class LoopIdiomRecognize;
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/// This class defines some utility functions for loop idiom recognization.
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class LIRUtil {
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public:
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/// Return true iff the block contains nothing but an uncondition branch
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/// (aka goto instruction).
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static bool isAlmostEmpty(BasicBlock *);
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static BranchInst *getBranch(BasicBlock *BB) {
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return dyn_cast<BranchInst>(BB->getTerminator());
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}
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/// Derive the precondition block (i.e the block that guards the loop
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/// preheader) from the given preheader.
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static BasicBlock *getPrecondBb(BasicBlock *PreHead);
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};
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/// This class is to recoginize idioms of population-count conducted in
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/// a noncountable loop. Currently it only recognizes this pattern:
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/// \code
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/// while(x) {cnt++; ...; x &= x - 1; ...}
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/// \endcode
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class NclPopcountRecognize {
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LoopIdiomRecognize &LIR;
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Loop *CurLoop;
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BasicBlock *PreCondBB;
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typedef IRBuilder<> IRBuilderTy;
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public:
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explicit NclPopcountRecognize(LoopIdiomRecognize &TheLIR);
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bool recognize();
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private:
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/// Take a glimpse of the loop to see if we need to go ahead recoginizing
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/// the idiom.
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bool preliminaryScreen();
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/// Check if the given conditional branch is based on the comparison
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/// between a variable and zero, and if the variable is non-zero, the
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/// control yields to the loop entry. If the branch matches the behavior,
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/// the variable involved in the comparion is returned. This function will
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/// be called to see if the precondition and postcondition of the loop
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/// are in desirable form.
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Value *matchCondition(BranchInst *Br, BasicBlock *NonZeroTarget) const;
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/// Return true iff the idiom is detected in the loop. and 1) \p CntInst
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/// is set to the instruction counting the population bit. 2) \p CntPhi
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/// is set to the corresponding phi node. 3) \p Var is set to the value
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/// whose population bits are being counted.
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bool detectIdiom
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(Instruction *&CntInst, PHINode *&CntPhi, Value *&Var) const;
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/// Insert ctpop intrinsic function and some obviously dead instructions.
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void transform(Instruction *CntInst, PHINode *CntPhi, Value *Var);
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/// Create llvm.ctpop.* intrinsic function.
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CallInst *createPopcntIntrinsic(IRBuilderTy &IRB, Value *Val, DebugLoc DL);
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};
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class LoopIdiomRecognize : public LoopPass {
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Loop *CurLoop;
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DominatorTree *DT;
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ScalarEvolution *SE;
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TargetLibraryInfo *TLI;
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const TargetTransformInfo *TTI;
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public:
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static char ID;
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explicit LoopIdiomRecognize() : LoopPass(ID) {
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initializeLoopIdiomRecognizePass(*PassRegistry::getPassRegistry());
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DT = nullptr;
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SE = nullptr;
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TLI = nullptr;
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TTI = nullptr;
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}
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bool runOnLoop(Loop *L, LPPassManager &LPM) override;
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bool runOnLoopBlock(BasicBlock *BB, const SCEV *BECount,
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SmallVectorImpl<BasicBlock*> &ExitBlocks);
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bool processLoopStore(StoreInst *SI, const SCEV *BECount);
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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,
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Value *SplatValue, Instruction *TheStore,
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const SCEVAddRecExpr *Ev,
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const SCEV *BECount);
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bool processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
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const SCEVAddRecExpr *StoreEv,
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const SCEVAddRecExpr *LoadEv,
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const SCEV *BECount);
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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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///
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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AU.addRequired<LoopInfoWrapperPass>();
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AU.addPreserved<LoopInfoWrapperPass>();
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AU.addRequiredID(LoopSimplifyID);
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AU.addPreservedID(LoopSimplifyID);
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AU.addRequiredID(LCSSAID);
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AU.addPreservedID(LCSSAID);
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AU.addRequired<AliasAnalysis>();
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AU.addPreserved<AliasAnalysis>();
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AU.addRequired<ScalarEvolution>();
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AU.addPreserved<ScalarEvolution>();
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AU.addPreserved<DominatorTreeWrapperPass>();
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AU.addRequired<DominatorTreeWrapperPass>();
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AU.addRequired<TargetLibraryInfoWrapperPass>();
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AU.addRequired<TargetTransformInfoWrapperPass>();
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}
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DominatorTree *getDominatorTree() {
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return DT ? DT
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: (DT = &getAnalysis<DominatorTreeWrapperPass>().getDomTree());
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}
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ScalarEvolution *getScalarEvolution() {
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return SE ? SE : (SE = &getAnalysis<ScalarEvolution>());
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}
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TargetLibraryInfo *getTargetLibraryInfo() {
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if (!TLI)
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TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
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return TLI;
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}
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const TargetTransformInfo *getTargetTransformInfo() {
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return TTI ? TTI
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: (TTI = &getAnalysis<TargetTransformInfoWrapperPass>().getTTI(
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*CurLoop->getHeader()->getParent()));
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}
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Loop *getLoop() const { return CurLoop; }
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private:
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bool runOnNoncountableLoop();
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bool runOnCountableLoop();
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};
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}
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char LoopIdiomRecognize::ID = 0;
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INITIALIZE_PASS_BEGIN(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
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false, false)
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INITIALIZE_PASS_DEPENDENCY(LoopInfoWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(DominatorTreeWrapperPass)
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INITIALIZE_PASS_DEPENDENCY(LoopSimplify)
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INITIALIZE_PASS_DEPENDENCY(LCSSA)
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INITIALIZE_PASS_DEPENDENCY(ScalarEvolution)
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INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
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INITIALIZE_AG_DEPENDENCY(AliasAnalysis)
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INITIALIZE_PASS_DEPENDENCY(TargetTransformInfoWrapperPass)
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INITIALIZE_PASS_END(LoopIdiomRecognize, "loop-idiom", "Recognize loop idioms",
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false, false)
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Pass *llvm::createLoopIdiomPass() { return new LoopIdiomRecognize(); }
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/// deleteDeadInstruction - Delete this instruction. Before we do, go through
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/// and zero out all the operands of this instruction. If any of them become
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/// dead, delete them and the computation tree that feeds them.
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///
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static void deleteDeadInstruction(Instruction *I,
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const TargetLibraryInfo *TLI) {
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SmallVector<Value *, 16> Operands(I->value_op_begin(), I->value_op_end());
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I->replaceAllUsesWith(UndefValue::get(I->getType()));
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I->eraseFromParent();
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for (Value *Op : Operands)
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RecursivelyDeleteTriviallyDeadInstructions(Op, TLI);
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}
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//===----------------------------------------------------------------------===//
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//
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// Implementation of LIRUtil
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//
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//===----------------------------------------------------------------------===//
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// This function will return true iff the given block contains nothing but goto.
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// A typical usage of this function is to check if the preheader function is
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// "almost" empty such that generated intrinsic functions can be moved across
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// the preheader and be placed at the end of the precondition block without
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// the concern of breaking data dependence.
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bool LIRUtil::isAlmostEmpty(BasicBlock *BB) {
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if (BranchInst *Br = getBranch(BB)) {
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return Br->isUnconditional() && Br == BB->begin();
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}
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return false;
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}
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BasicBlock *LIRUtil::getPrecondBb(BasicBlock *PreHead) {
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if (BasicBlock *BB = PreHead->getSinglePredecessor()) {
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BranchInst *Br = getBranch(BB);
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return Br && Br->isConditional() ? BB : nullptr;
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}
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return nullptr;
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}
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//===----------------------------------------------------------------------===//
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//
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// Implementation of NclPopcountRecognize
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//
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//===----------------------------------------------------------------------===//
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NclPopcountRecognize::NclPopcountRecognize(LoopIdiomRecognize &TheLIR):
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LIR(TheLIR), CurLoop(TheLIR.getLoop()), PreCondBB(nullptr) {
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}
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bool NclPopcountRecognize::preliminaryScreen() {
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const TargetTransformInfo *TTI = LIR.getTargetTransformInfo();
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if (TTI->getPopcntSupport(32) != TargetTransformInfo::PSK_FastHardware)
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return false;
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// Counting population are usually conducted by few arithmetic instructions.
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// Such instructions can be easilly "absorbed" by vacant slots in a
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// non-compact loop. Therefore, recognizing popcount idiom only makes sense
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// in a compact loop.
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// Give up if the loop has multiple blocks or multiple backedges.
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if (CurLoop->getNumBackEdges() != 1 || CurLoop->getNumBlocks() != 1)
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return false;
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BasicBlock *LoopBody = *(CurLoop->block_begin());
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if (LoopBody->size() >= 20) {
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// The loop is too big, bail out.
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return false;
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}
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// It should have a preheader containing nothing but a goto instruction.
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BasicBlock *PreHead = CurLoop->getLoopPreheader();
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if (!PreHead || !LIRUtil::isAlmostEmpty(PreHead))
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return false;
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// It should have a precondition block where the generated popcount instrinsic
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// function will be inserted.
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PreCondBB = LIRUtil::getPrecondBb(PreHead);
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if (!PreCondBB)
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return false;
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return true;
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}
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Value *NclPopcountRecognize::matchCondition(BranchInst *Br,
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BasicBlock *LoopEntry) const {
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if (!Br || !Br->isConditional())
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return nullptr;
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ICmpInst *Cond = dyn_cast<ICmpInst>(Br->getCondition());
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if (!Cond)
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return nullptr;
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ConstantInt *CmpZero = dyn_cast<ConstantInt>(Cond->getOperand(1));
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if (!CmpZero || !CmpZero->isZero())
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return nullptr;
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ICmpInst::Predicate Pred = Cond->getPredicate();
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if ((Pred == ICmpInst::ICMP_NE && Br->getSuccessor(0) == LoopEntry) ||
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(Pred == ICmpInst::ICMP_EQ && Br->getSuccessor(1) == LoopEntry))
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return Cond->getOperand(0);
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return nullptr;
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}
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bool NclPopcountRecognize::detectIdiom(Instruction *&CntInst,
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PHINode *&CntPhi,
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Value *&Var) const {
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// Following code tries to detect this idiom:
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//
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// if (x0 != 0)
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// goto loop-exit // the precondition of the loop
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// cnt0 = init-val;
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// do {
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// x1 = phi (x0, x2);
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// cnt1 = phi(cnt0, cnt2);
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//
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// cnt2 = cnt1 + 1;
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// ...
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// x2 = x1 & (x1 - 1);
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// ...
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// } while(x != 0);
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//
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// loop-exit:
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//
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// step 1: Check to see if the look-back branch match this pattern:
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// "if (a!=0) goto loop-entry".
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BasicBlock *LoopEntry;
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Instruction *DefX2, *CountInst;
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Value *VarX1, *VarX0;
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PHINode *PhiX, *CountPhi;
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DefX2 = CountInst = nullptr;
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VarX1 = VarX0 = nullptr;
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PhiX = CountPhi = nullptr;
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LoopEntry = *(CurLoop->block_begin());
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// step 1: Check if the loop-back branch is in desirable form.
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{
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if (Value *T = matchCondition (LIRUtil::getBranch(LoopEntry), LoopEntry))
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DefX2 = dyn_cast<Instruction>(T);
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else
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return false;
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}
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// step 2: detect instructions corresponding to "x2 = x1 & (x1 - 1)"
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{
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if (!DefX2 || DefX2->getOpcode() != Instruction::And)
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return false;
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BinaryOperator *SubOneOp;
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if ((SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(0))))
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VarX1 = DefX2->getOperand(1);
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else {
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VarX1 = DefX2->getOperand(0);
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SubOneOp = dyn_cast<BinaryOperator>(DefX2->getOperand(1));
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}
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if (!SubOneOp)
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return false;
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Instruction *SubInst = cast<Instruction>(SubOneOp);
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ConstantInt *Dec = dyn_cast<ConstantInt>(SubInst->getOperand(1));
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if (!Dec ||
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!((SubInst->getOpcode() == Instruction::Sub && Dec->isOne()) ||
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(SubInst->getOpcode() == Instruction::Add && Dec->isAllOnesValue()))) {
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return false;
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}
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}
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// step 3: Check the recurrence of variable X
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{
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PhiX = dyn_cast<PHINode>(VarX1);
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if (!PhiX ||
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(PhiX->getOperand(0) != DefX2 && PhiX->getOperand(1) != DefX2)) {
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return false;
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}
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}
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// step 4: Find the instruction which count the population: cnt2 = cnt1 + 1
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{
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CountInst = nullptr;
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for (BasicBlock::iterator Iter = LoopEntry->getFirstNonPHI(),
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IterE = LoopEntry->end(); Iter != IterE; Iter++) {
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Instruction *Inst = Iter;
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if (Inst->getOpcode() != Instruction::Add)
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continue;
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ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
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if (!Inc || !Inc->isOne())
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continue;
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PHINode *Phi = dyn_cast<PHINode>(Inst->getOperand(0));
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if (!Phi || Phi->getParent() != LoopEntry)
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continue;
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// Check if the result of the instruction is live of the loop.
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bool LiveOutLoop = false;
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for (User *U : Inst->users()) {
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if ((cast<Instruction>(U))->getParent() != LoopEntry) {
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LiveOutLoop = true; break;
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}
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}
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if (LiveOutLoop) {
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CountInst = Inst;
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CountPhi = Phi;
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break;
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}
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}
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if (!CountInst)
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return false;
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}
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// step 5: check if the precondition is in this form:
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// "if (x != 0) goto loop-head ; else goto somewhere-we-don't-care;"
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{
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BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
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Value *T = matchCondition (PreCondBr, CurLoop->getLoopPreheader());
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if (T != PhiX->getOperand(0) && T != PhiX->getOperand(1))
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return false;
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CntInst = CountInst;
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CntPhi = CountPhi;
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Var = T;
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}
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return true;
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}
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void NclPopcountRecognize::transform(Instruction *CntInst,
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PHINode *CntPhi, Value *Var) {
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ScalarEvolution *SE = LIR.getScalarEvolution();
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TargetLibraryInfo *TLI = LIR.getTargetLibraryInfo();
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BasicBlock *PreHead = CurLoop->getLoopPreheader();
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BranchInst *PreCondBr = LIRUtil::getBranch(PreCondBB);
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const DebugLoc DL = CntInst->getDebugLoc();
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// Assuming before transformation, the loop is following:
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// if (x) // the precondition
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// do { cnt++; x &= x - 1; } while(x);
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// Step 1: Insert the ctpop instruction at the end of the precondition block
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IRBuilderTy Builder(PreCondBr);
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Value *PopCnt, *PopCntZext, *NewCount, *TripCnt;
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{
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PopCnt = createPopcntIntrinsic(Builder, Var, DL);
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NewCount = PopCntZext =
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Builder.CreateZExtOrTrunc(PopCnt, cast<IntegerType>(CntPhi->getType()));
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if (NewCount != PopCnt)
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(cast<Instruction>(NewCount))->setDebugLoc(DL);
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// TripCnt is exactly the number of iterations the loop has
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TripCnt = NewCount;
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// If the population counter's initial value is not zero, insert Add Inst.
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Value *CntInitVal = CntPhi->getIncomingValueForBlock(PreHead);
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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". Withtout 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));
|
|
PreCond->replaceAllUsesWith(NewPreCond);
|
|
|
|
RecursivelyDeleteTriviallyDeadInstructions(PreCond, TLI);
|
|
}
|
|
|
|
// Step 3: Note that the population count is exactly the trip count of the
|
|
// loop in question, which enble us to to convert the loop from noncountable
|
|
// loop into a countable one. The benefit is twofold:
|
|
//
|
|
// - If the loop only counts population, the entire loop become dead after
|
|
// the transformation. It is lots easier to prove a countable loop dead
|
|
// than to prove a noncountable one. (In some C dialects, a infite 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());
|
|
{
|
|
BranchInst *LbBr = LIRUtil::getBranch(Body);
|
|
ICmpInst *LbCond = cast<ICmpInst>(LbBr->getCondition());
|
|
Type *Ty = TripCnt->getType();
|
|
|
|
PHINode *TcPhi = PHINode::Create(Ty, 2, "tcphi", Body->begin());
|
|
|
|
Builder.SetInsertPoint(LbCond);
|
|
Value *Opnd1 = cast<Value>(TcPhi);
|
|
Value *Opnd2 = cast<Value>(ConstantInt::get(Ty, 1));
|
|
Instruction *TcDec =
|
|
cast<Instruction>(Builder.CreateSub(Opnd1, Opnd2, "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, cast<Value>(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);
|
|
}
|
|
|
|
CallInst *NclPopcountRecognize::createPopcntIntrinsic(IRBuilderTy &IRBuilder,
|
|
Value *Val, DebugLoc DL) {
|
|
Value *Ops[] = { Val };
|
|
Type *Tys[] = { Val->getType() };
|
|
|
|
Module *M = (*(CurLoop->block_begin()))->getParent()->getParent();
|
|
Value *Func = Intrinsic::getDeclaration(M, Intrinsic::ctpop, Tys);
|
|
CallInst *CI = IRBuilder.CreateCall(Func, Ops);
|
|
CI->setDebugLoc(DL);
|
|
|
|
return CI;
|
|
}
|
|
|
|
/// recognize - detect population count idiom in a non-countable loop. If
|
|
/// detected, transform the relevant code to popcount intrinsic function
|
|
/// call, and return true; otherwise, return false.
|
|
bool NclPopcountRecognize::recognize() {
|
|
|
|
if (!LIR.getTargetTransformInfo())
|
|
return false;
|
|
|
|
LIR.getScalarEvolution();
|
|
|
|
if (!preliminaryScreen())
|
|
return false;
|
|
|
|
Instruction *CntInst;
|
|
PHINode *CntPhi;
|
|
Value *Val;
|
|
if (!detectIdiom(CntInst, CntPhi, Val))
|
|
return false;
|
|
|
|
transform(CntInst, CntPhi, Val);
|
|
return true;
|
|
}
|
|
|
|
//===----------------------------------------------------------------------===//
|
|
//
|
|
// Implementation of LoopIdiomRecognize
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
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->getValue()->getValue() == 0)
|
|
return false;
|
|
|
|
// set DT
|
|
(void)getDominatorTree();
|
|
|
|
LoopInfo &LI = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
|
|
TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
|
|
|
|
// set TLI
|
|
(void)getTargetLibraryInfo();
|
|
|
|
SmallVector<BasicBlock*, 8> ExitBlocks;
|
|
CurLoop->getUniqueExitBlocks(ExitBlocks);
|
|
|
|
DEBUG(dbgs() << "loop-idiom Scanning: F["
|
|
<< CurLoop->getHeader()->getParent()->getName()
|
|
<< "] Loop %" << CurLoop->getHeader()->getName() << "\n");
|
|
|
|
bool MadeChange = false;
|
|
// 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;
|
|
}
|
|
|
|
bool LoopIdiomRecognize::runOnNoncountableLoop() {
|
|
NclPopcountRecognize Popcount(*this);
|
|
if (Popcount.recognize())
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
bool LoopIdiomRecognize::runOnLoop(Loop *L, LPPassManager &LPM) {
|
|
if (skipOptnoneFunction(L))
|
|
return false;
|
|
|
|
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;
|
|
|
|
SE = &getAnalysis<ScalarEvolution>();
|
|
if (SE->hasLoopInvariantBackedgeTakenCount(L))
|
|
return runOnCountableLoop();
|
|
return runOnNoncountableLoop();
|
|
}
|
|
|
|
/// 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;
|
|
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
|
|
Instruction *Inst = I++;
|
|
// Look for store instructions, which may be optimized to memset/memcpy.
|
|
if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
|
|
WeakVH InstPtr(I);
|
|
if (!processLoopStore(SI, BECount)) continue;
|
|
MadeChange = true;
|
|
|
|
// If processing the store invalidated our iterator, start over from the
|
|
// top of the block.
|
|
if (!InstPtr)
|
|
I = BB->begin();
|
|
continue;
|
|
}
|
|
|
|
// Look for memset instructions, which may be optimized to a larger memset.
|
|
if (MemSetInst *MSI = dyn_cast<MemSetInst>(Inst)) {
|
|
WeakVH 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;
|
|
}
|
|
|
|
|
|
/// processLoopStore - See if this store can be promoted to a memset or memcpy.
|
|
bool LoopIdiomRecognize::processLoopStore(StoreInst *SI, const SCEV *BECount) {
|
|
if (!SI->isSimple()) return false;
|
|
|
|
Value *StoredVal = SI->getValueOperand();
|
|
Value *StorePtr = SI->getPointerOperand();
|
|
|
|
// Reject stores that are so large that they overflow an unsigned.
|
|
auto &DL = CurLoop->getHeader()->getModule()->getDataLayout();
|
|
uint64_t SizeInBits = DL.getTypeSizeInBits(StoredVal->getType());
|
|
if ((SizeInBits & 7) || (SizeInBits >> 32) != 0)
|
|
return false;
|
|
|
|
// 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 false;
|
|
|
|
// 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.
|
|
unsigned StoreSize = (unsigned)SizeInBits >> 3;
|
|
const SCEVConstant *Stride = dyn_cast<SCEVConstant>(StoreEv->getOperand(1));
|
|
|
|
if (!Stride || StoreSize != Stride->getValue()->getValue()) {
|
|
// TODO: Could also handle negative stride here someday, that will require
|
|
// the validity check in mayLoopAccessLocation to be updated though.
|
|
// Enable this to print exact negative strides.
|
|
if (0 && Stride && StoreSize == -Stride->getValue()->getValue()) {
|
|
dbgs() << "NEGATIVE STRIDE: " << *SI << "\n";
|
|
dbgs() << "BB: " << *SI->getParent();
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
// See if we can optimize just this store in isolation.
|
|
if (processLoopStridedStore(StorePtr, StoreSize, SI->getAlignment(),
|
|
StoredVal, SI, StoreEv, BECount))
|
|
return true;
|
|
|
|
// If the stored value is a strided load in the same loop with the same stride
|
|
// this this may be transformable into a memcpy. This kicks in for stuff like
|
|
// for (i) A[i] = B[i];
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(StoredVal)) {
|
|
const SCEVAddRecExpr *LoadEv =
|
|
dyn_cast<SCEVAddRecExpr>(SE->getSCEV(LI->getOperand(0)));
|
|
if (LoadEv && LoadEv->getLoop() == CurLoop && LoadEv->isAffine() &&
|
|
StoreEv->getOperand(1) == LoadEv->getOperand(1) && LI->isSimple())
|
|
if (processLoopStoreOfLoopLoad(SI, StoreSize, StoreEv, LoadEv, BECount))
|
|
return true;
|
|
}
|
|
//errs() << "UNHANDLED strided store: " << *StoreEv << " - " << *SI << "\n";
|
|
|
|
return false;
|
|
}
|
|
|
|
/// 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 (!TLI->has(LibFunc::memset))
|
|
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 *Stride = dyn_cast<SCEVConstant>(Ev->getOperand(1));
|
|
|
|
// TODO: Could also handle negative stride here someday, that will require the
|
|
// validity check in mayLoopAccessLocation to be updated though.
|
|
if (!Stride || MSI->getLength() != Stride->getValue())
|
|
return false;
|
|
|
|
return processLoopStridedStore(Pointer, (unsigned)SizeInBytes,
|
|
MSI->getAlignment(), MSI->getValue(),
|
|
MSI, Ev, BECount);
|
|
}
|
|
|
|
|
|
/// 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,AliasAnalysis::ModRefResult Access,
|
|
Loop *L, const SCEV *BECount,
|
|
unsigned StoreSize, AliasAnalysis &AA,
|
|
Instruction *IgnoredStore) {
|
|
// 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.
|
|
uint64_t AccessSize = AliasAnalysis::UnknownSize;
|
|
|
|
// 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 = (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].
|
|
AliasAnalysis::Location StoreLoc(Ptr, AccessSize);
|
|
|
|
for (Loop::block_iterator BI = L->block_begin(), E = L->block_end(); BI != E;
|
|
++BI)
|
|
for (BasicBlock::iterator I = (*BI)->begin(), E = (*BI)->end(); I != E; ++I)
|
|
if (&*I != IgnoredStore &&
|
|
(AA.getModRefInfo(I, StoreLoc) & Access))
|
|
return true;
|
|
|
|
return false;
|
|
}
|
|
|
|
/// 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) {
|
|
// 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));
|
|
}
|
|
|
|
|
|
/// 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, const SCEVAddRecExpr *Ev,
|
|
const SCEV *BECount) {
|
|
|
|
// 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);
|
|
Constant *PatternValue = nullptr;
|
|
auto &DL = CurLoop->getHeader()->getModule()->getDataLayout();
|
|
unsigned DestAS = DestPtr->getType()->getPointerAddressSpace();
|
|
|
|
// If we're allowed to form a memset, and the stored value would be acceptable
|
|
// for memset, use it.
|
|
if (SplatValue && TLI->has(LibFunc::memset) &&
|
|
// Verify that the stored value is loop invariant. If not, we can't
|
|
// promote the memset.
|
|
CurLoop->isLoopInvariant(SplatValue)) {
|
|
// Keep and use SplatValue.
|
|
PatternValue = nullptr;
|
|
} else if (DestAS == 0 && TLI->has(LibFunc::memset_pattern16) &&
|
|
(PatternValue = getMemSetPatternValue(StoredVal, DL))) {
|
|
// Don't create memset_pattern16s with address spaces.
|
|
// It looks like we can use PatternValue!
|
|
SplatValue = nullptr;
|
|
} else {
|
|
// Otherwise, this isn't an idiom we can transform. For example, we can't
|
|
// do anything with a 3-byte store.
|
|
return false;
|
|
}
|
|
|
|
// 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");
|
|
|
|
Type *DestInt8PtrTy = Builder.getInt8PtrTy(DestAS);
|
|
|
|
// 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(Ev->getStart(), DestInt8PtrTy,
|
|
Preheader->getTerminator());
|
|
|
|
if (mayLoopAccessLocation(BasePtr, AliasAnalysis::ModRef,
|
|
CurLoop, BECount,
|
|
StoreSize, getAnalysis<AliasAnalysis>(), TheStore)) {
|
|
Expander.clear();
|
|
// If we generated new code for the base pointer, clean up.
|
|
RecursivelyDeleteTriviallyDeadInstructions(BasePtr, TLI);
|
|
return false;
|
|
}
|
|
|
|
// Okay, everything looks good, insert the memset.
|
|
|
|
// The # stored bytes is (BECount+1)*Size. Expand the trip count out to
|
|
// pointer size if it isn't already.
|
|
Type *IntPtr = Builder.getIntPtrTy(DL, DestAS);
|
|
BECount = SE->getTruncateOrZeroExtend(BECount, IntPtr);
|
|
|
|
const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtr, 1),
|
|
SCEV::FlagNUW);
|
|
if (StoreSize != 1) {
|
|
NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtr, StoreSize),
|
|
SCEV::FlagNUW);
|
|
}
|
|
|
|
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->getParent()->getParent()->getParent();
|
|
Value *MSP = M->getOrInsertFunction("memset_pattern16",
|
|
Builder.getVoidTy(),
|
|
Int8PtrTy,
|
|
Int8PtrTy,
|
|
IntPtr,
|
|
(void*)nullptr);
|
|
|
|
// 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(true); // Ok to merge these.
|
|
GV->setAlignment(16);
|
|
Value *PatternPtr = ConstantExpr::getBitCast(GV, Int8PtrTy);
|
|
NewCall = Builder.CreateCall(MSP, {BasePtr, PatternPtr, NumBytes});
|
|
}
|
|
|
|
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.
|
|
deleteDeadInstruction(TheStore, TLI);
|
|
++NumMemSet;
|
|
return true;
|
|
}
|
|
|
|
/// processLoopStoreOfLoopLoad - We see a strided store whose value is a
|
|
/// same-strided load.
|
|
bool LoopIdiomRecognize::
|
|
processLoopStoreOfLoopLoad(StoreInst *SI, unsigned StoreSize,
|
|
const SCEVAddRecExpr *StoreEv,
|
|
const SCEVAddRecExpr *LoadEv,
|
|
const SCEV *BECount) {
|
|
// If we're not allowed to form memcpy, we fail.
|
|
if (!TLI->has(LibFunc::memcpy))
|
|
return false;
|
|
|
|
LoadInst *LI = cast<LoadInst>(SI->getValueOperand());
|
|
|
|
// 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());
|
|
const DataLayout &DL = Preheader->getModule()->getDataLayout();
|
|
SCEVExpander Expander(*SE, DL, "loop-idiom");
|
|
|
|
// 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(StoreEv->getStart(),
|
|
Builder.getInt8PtrTy(SI->getPointerAddressSpace()),
|
|
Preheader->getTerminator());
|
|
|
|
if (mayLoopAccessLocation(StoreBasePtr, AliasAnalysis::ModRef,
|
|
CurLoop, BECount, StoreSize,
|
|
getAnalysis<AliasAnalysis>(), SI)) {
|
|
Expander.clear();
|
|
// If we generated new code for the base pointer, clean up.
|
|
RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
|
|
return false;
|
|
}
|
|
|
|
// For a memcpy, we have to make sure that the input array is not being
|
|
// mutated by the loop.
|
|
Value *LoadBasePtr =
|
|
Expander.expandCodeFor(LoadEv->getStart(),
|
|
Builder.getInt8PtrTy(LI->getPointerAddressSpace()),
|
|
Preheader->getTerminator());
|
|
|
|
if (mayLoopAccessLocation(LoadBasePtr, AliasAnalysis::Mod, CurLoop, BECount,
|
|
StoreSize, getAnalysis<AliasAnalysis>(), SI)) {
|
|
Expander.clear();
|
|
// If we generated new code for the base pointer, clean up.
|
|
RecursivelyDeleteTriviallyDeadInstructions(LoadBasePtr, TLI);
|
|
RecursivelyDeleteTriviallyDeadInstructions(StoreBasePtr, TLI);
|
|
return false;
|
|
}
|
|
|
|
// Okay, everything is safe, we can transform this!
|
|
|
|
|
|
// The # stored bytes is (BECount+1)*Size. Expand the trip count out to
|
|
// pointer size if it isn't already.
|
|
Type *IntPtrTy = Builder.getIntPtrTy(DL, SI->getPointerAddressSpace());
|
|
BECount = SE->getTruncateOrZeroExtend(BECount, IntPtrTy);
|
|
|
|
const SCEV *NumBytesS = SE->getAddExpr(BECount, SE->getConstant(IntPtrTy, 1),
|
|
SCEV::FlagNUW);
|
|
if (StoreSize != 1)
|
|
NumBytesS = SE->getMulExpr(NumBytesS, SE->getConstant(IntPtrTy, StoreSize),
|
|
SCEV::FlagNUW);
|
|
|
|
Value *NumBytes =
|
|
Expander.expandCodeFor(NumBytesS, IntPtrTy, Preheader->getTerminator());
|
|
|
|
CallInst *NewCall =
|
|
Builder.CreateMemCpy(StoreBasePtr, LoadBasePtr, NumBytes,
|
|
std::min(SI->getAlignment(), LI->getAlignment()));
|
|
NewCall->setDebugLoc(SI->getDebugLoc());
|
|
|
|
DEBUG(dbgs() << " Formed memcpy: " << *NewCall << "\n"
|
|
<< " from load ptr=" << *LoadEv << " at: " << *LI << "\n"
|
|
<< " from store ptr=" << *StoreEv << " at: " << *SI << "\n");
|
|
|
|
|
|
// Okay, the memset has been formed. Zap the original store and anything that
|
|
// feeds into it.
|
|
deleteDeadInstruction(SI, TLI);
|
|
++NumMemCpy;
|
|
return true;
|
|
}
|