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 #define DEBUG_TYPE "instsimplify" 18 #include "llvm/Transforms/Scalar.h" 19 #include "llvm/ADT/DepthFirstIterator.h" 20 #include "llvm/ADT/SmallPtrSet.h" 21 #include "llvm/ADT/Statistic.h" 22 #include "llvm/Analysis/Dominators.h" 23 #include "llvm/Analysis/InstructionSimplify.h" 24 #include "llvm/IR/DataLayout.h" 25 #include "llvm/IR/Function.h" 26 #include "llvm/IR/Type.h" 27 #include "llvm/Pass.h" 28 #include "llvm/Target/TargetLibraryInfo.h" 29 #include "llvm/Transforms/Utils/Local.h" 30 using namespace llvm; 31 32 STATISTIC(NumSimplified, "Number of redundant instructions removed"); 33 34 namespace { 35 struct InstSimplifier : public FunctionPass { 36 static char ID; // Pass identification, replacement for typeid 37 InstSimplifier() : FunctionPass(ID) { 38 initializeInstSimplifierPass(*PassRegistry::getPassRegistry()); 39 } 40 41 void getAnalysisUsage(AnalysisUsage &AU) const { 42 AU.setPreservesCFG(); 43 AU.addRequired<TargetLibraryInfo>(); 44 } 45 46 /// runOnFunction - Remove instructions that simplify. 47 bool runOnFunction(Function &F) { 48 const DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>(); 49 const DataLayout *TD = getAnalysisIfAvailable<DataLayout>(); 50 const TargetLibraryInfo *TLI = &getAnalysis<TargetLibraryInfo>(); 51 SmallPtrSet<const Instruction*, 8> S1, S2, *ToSimplify = &S1, *Next = &S2; 52 bool Changed = false; 53 54 do { 55 for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()), 56 DE = df_end(&F.getEntryBlock()); DI != DE; ++DI) 57 for (BasicBlock::iterator BI = DI->begin(), BE = DI->end(); BI != BE;) { 58 Instruction *I = BI++; 59 // The first time through the loop ToSimplify is empty and we try to 60 // simplify all instructions. On later iterations ToSimplify is not 61 // empty and we only bother simplifying instructions that are in it. 62 if (!ToSimplify->empty() && !ToSimplify->count(I)) 63 continue; 64 // Don't waste time simplifying unused instructions. 65 if (!I->use_empty()) 66 if (Value *V = SimplifyInstruction(I, TD, TLI, DT)) { 67 // Mark all uses for resimplification next time round the loop. 68 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); 69 UI != UE; ++UI) 70 Next->insert(cast<Instruction>(*UI)); 71 I->replaceAllUsesWith(V); 72 ++NumSimplified; 73 Changed = true; 74 } 75 Changed |= RecursivelyDeleteTriviallyDeadInstructions(I, TLI); 76 } 77 78 // Place the list of instructions to simplify on the next loop iteration 79 // into ToSimplify. 80 std::swap(ToSimplify, Next); 81 Next->clear(); 82 } while (!ToSimplify->empty()); 83 84 return Changed; 85 } 86 }; 87 } 88 89 char InstSimplifier::ID = 0; 90 INITIALIZE_PASS_BEGIN(InstSimplifier, "instsimplify", 91 "Remove redundant instructions", false, false) 92 INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo) 93 INITIALIZE_PASS_END(InstSimplifier, "instsimplify", 94 "Remove redundant instructions", false, false) 95 char &llvm::InstructionSimplifierID = InstSimplifier::ID; 96 97 // Public interface to the simplify instructions pass. 98 FunctionPass *llvm::createInstructionSimplifierPass() { 99 return new InstSimplifier(); 100 } 101
