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