1//===------ SimplifyInstructions.cpp - Remove redundant instructions ------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This is a utility pass used for testing the InstructionSimplify analysis. 11// The analysis is applied to every instruction, and if it simplifies then the 12// instruction is replaced by the simplification. If you are looking for a pass 13// that performs serious instruction folding, use the instcombine pass instead. 14// 15//===----------------------------------------------------------------------===// 16 17#include "llvm/Transforms/Scalar.h" 18#include "llvm/ADT/DepthFirstIterator.h" 19#include "llvm/ADT/SmallPtrSet.h" 20#include "llvm/ADT/Statistic.h" 21#include "llvm/Analysis/InstructionSimplify.h" 22#include "llvm/IR/DataLayout.h" 23#include "llvm/IR/Dominators.h" 24#include "llvm/IR/Function.h" 25#include "llvm/IR/Type.h" 26#include "llvm/Pass.h" 27#include "llvm/Target/TargetLibraryInfo.h" 28#include "llvm/Transforms/Utils/Local.h" 29using namespace llvm; 30 31#define DEBUG_TYPE "instsimplify" 32 33STATISTIC(NumSimplified, "Number of redundant instructions removed"); 34 35namespace { 36 struct InstSimplifier : public FunctionPass { 37 static char ID; // Pass identification, replacement for typeid 38 InstSimplifier() : FunctionPass(ID) { 39 initializeInstSimplifierPass(*PassRegistry::getPassRegistry()); 40 } 41 42 void getAnalysisUsage(AnalysisUsage &AU) const override { 43 AU.setPreservesCFG(); 44 AU.addRequired<TargetLibraryInfo>(); 45 } 46 47 /// runOnFunction - Remove instructions that simplify. 48 bool runOnFunction(Function &F) override { 49 const DominatorTreeWrapperPass *DTWP = 50 getAnalysisIfAvailable<DominatorTreeWrapperPass>(); 51 const DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr; 52 DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>(); 53 const DataLayout *DL = DLP ? &DLP->getDataLayout() : nullptr; 54 const TargetLibraryInfo *TLI = &getAnalysis<TargetLibraryInfo>(); 55 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2; 56 bool Changed = false; 57 58 do { 59 for (BasicBlock *BB : depth_first(&F.getEntryBlock())) 60 // Here be subtlety: the iterator must be incremented before the loop 61 // body (not sure why), so a range-for loop won't work here. 62 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) { 63 Instruction *I = BI++; 64 // The first time through the loop ToSimplify is empty and we try to 65 // simplify all instructions. On later iterations ToSimplify is not 66 // empty and we only bother simplifying instructions that are in it. 67 if (!ToSimplify->empty() && !ToSimplify->count(I)) 68 continue; 69 // Don't waste time simplifying unused instructions. 70 if (!I->use_empty()) 71 if (Value *V = SimplifyInstruction(I, DL, TLI, DT)) { 72 // Mark all uses for resimplification next time round the loop. 73 for (User *U : I->users()) 74 Next->insert(cast<Instruction>(U)); 75 I->replaceAllUsesWith(V); 76 ++NumSimplified; 77 Changed = true; 78 } 79 bool res = RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 80 if (res) { 81 // RecursivelyDeleteTriviallyDeadInstruction can remove 82 // more than one instruction, so simply incrementing the 83 // iterator does not work. When instructions get deleted 84 // re-iterate instead. 85 BI = BB->begin(); BE = BB->end(); 86 Changed |= res; 87 } 88 } 89 90 // Place the list of instructions to simplify on the next loop iteration 91 // into ToSimplify. 92 std::swap(ToSimplify, Next); 93 Next->clear(); 94 } while (!ToSimplify->empty()); 95 96 return Changed; 97 } 98 }; 99} 100 101char InstSimplifier::ID = 0; 102INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify", 103 "Remove redundant instructions", false, false) 104INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 105INITIALIZE_PASS_END(InstSimplifier, "instsimplify", 106 "Remove redundant instructions", false, false) 107char &llvm::InstructionSimplifierID = InstSimplifier::ID; 108 109// Public interface to the simplify instructions pass. 110FunctionPass *llvm::createInstructionSimplifierPass() { 111 return new InstSimplifier(); 112} 113