SimplifyInstructions.cpp revision 276479
1218885Sdim//===------ SimplifyInstructions.cpp - Remove redundant instructions ------===// 2218885Sdim// 3218885Sdim// The LLVM Compiler Infrastructure 4218885Sdim// 5218885Sdim// This file is distributed under the University of Illinois Open Source 6218885Sdim// License. See LICENSE.TXT for details. 7218885Sdim// 8218885Sdim//===----------------------------------------------------------------------===// 9218885Sdim// 10218885Sdim// This is a utility pass used for testing the InstructionSimplify analysis. 11218885Sdim// The analysis is applied to every instruction, and if it simplifies then the 12218885Sdim// instruction is replaced by the simplification. If you are looking for a pass 13218885Sdim// that performs serious instruction folding, use the instcombine pass instead. 14218885Sdim// 15218885Sdim//===----------------------------------------------------------------------===// 16218885Sdim 17249423Sdim#include "llvm/Transforms/Scalar.h" 18218885Sdim#include "llvm/ADT/DepthFirstIterator.h" 19218885Sdim#include "llvm/ADT/SmallPtrSet.h" 20218885Sdim#include "llvm/ADT/Statistic.h" 21218885Sdim#include "llvm/Analysis/InstructionSimplify.h" 22249423Sdim#include "llvm/IR/DataLayout.h" 23276479Sdim#include "llvm/IR/Dominators.h" 24249423Sdim#include "llvm/IR/Function.h" 25249423Sdim#include "llvm/IR/Type.h" 26249423Sdim#include "llvm/Pass.h" 27234353Sdim#include "llvm/Target/TargetLibraryInfo.h" 28218885Sdim#include "llvm/Transforms/Utils/Local.h" 29218885Sdimusing namespace llvm; 30218885Sdim 31276479Sdim#define DEBUG_TYPE "instsimplify" 32276479Sdim 33218885SdimSTATISTIC(NumSimplified, "Number of redundant instructions removed"); 34218885Sdim 35218885Sdimnamespace { 36218885Sdim struct InstSimplifier : public FunctionPass { 37218885Sdim static char ID; // Pass identification, replacement for typeid 38218885Sdim InstSimplifier() : FunctionPass(ID) { 39218885Sdim initializeInstSimplifierPass(*PassRegistry::getPassRegistry()); 40218885Sdim } 41218885Sdim 42276479Sdim void getAnalysisUsage(AnalysisUsage &AU) const override { 43218885Sdim AU.setPreservesCFG(); 44234353Sdim AU.addRequired<TargetLibraryInfo>(); 45218885Sdim } 46218885Sdim 47218885Sdim /// runOnFunction - Remove instructions that simplify. 48276479Sdim bool runOnFunction(Function &F) override { 49276479Sdim const DominatorTreeWrapperPass *DTWP = 50276479Sdim getAnalysisIfAvailable<DominatorTreeWrapperPass>(); 51276479Sdim const DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr; 52276479Sdim DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); 53276479Sdim const DataLayout *DL = DLP ? &DLP->getDataLayout() : nullptr; 54234353Sdim const TargetLibraryInfo *TLI = &getAnalysis<TargetLibraryInfo>(); 55218885Sdim SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2; 56218885Sdim bool Changed = false; 57218885Sdim 58218885Sdim do { 59276479Sdim for (BasicBlock *BB : depth_first(&F.getEntryBlock())) 60276479Sdim // Here be subtlety: the iterator must be incremented before the loop 61276479Sdim // body (not sure why), so a range-for loop won't work here. 62276479Sdim for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) { 63218885Sdim Instruction *I = BI++; 64218885Sdim // The first time through the loop ToSimplify is empty and we try to 65218885Sdim // simplify all instructions. On later iterations ToSimplify is not 66218885Sdim // empty and we only bother simplifying instructions that are in it. 67218885Sdim if (!ToSimplify->empty() && !ToSimplify->count(I)) 68218885Sdim continue; 69218885Sdim // Don't waste time simplifying unused instructions. 70218885Sdim if (!I->use_empty()) 71276479Sdim if (Value *V = SimplifyInstruction(I, DL, TLI, DT)) { 72218885Sdim // Mark all uses for resimplification next time round the loop. 73276479Sdim for (User *U : I->users()) 74276479Sdim Next->insert(cast<Instruction>(U)); 75218885Sdim I->replaceAllUsesWith(V); 76218885Sdim ++NumSimplified; 77218885Sdim Changed = true; 78218885Sdim } 79276479Sdim bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 80276479Sdim if (res) { 81276479Sdim // RecursivelyDeleteTriviallyDeadInstruction can remove 82276479Sdim // more than one instruction, so simply incrementing the 83276479Sdim // iterator does not work. When instructions get deleted 84276479Sdim // re-iterate instead. 85276479Sdim BI = BB->begin(); BE = BB->end(); 86276479Sdim Changed |= res; 87276479Sdim } 88218885Sdim } 89218885Sdim 90218885Sdim // Place the list of instructions to simplify on the next loop iteration 91218885Sdim // into ToSimplify. 92218885Sdim std::swap(ToSimplify, Next); 93218885Sdim Next->clear(); 94218885Sdim } while (!ToSimplify->empty()); 95218885Sdim 96218885Sdim return Changed; 97218885Sdim } 98218885Sdim }; 99218885Sdim} 100218885Sdim 101218885Sdimchar InstSimplifier::ID = 0; 102234353SdimINITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify", 103234353Sdim "Remove redundant instructions", false, false) 104234353SdimINITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 105234353SdimINITIALIZE_PASS_END(InstSimplifier, "instsimplify", 106234353Sdim "Remove redundant instructions", false, false) 107218885Sdimchar &llvm::InstructionSimplifierID = InstSimplifier::ID; 108218885Sdim 109218885Sdim// Public interface to the simplify instructions pass. 110218885SdimFunctionPass *llvm::createInstructionSimplifierPass() { 111218885Sdim return new InstSimplifier(); 112218885Sdim} 113