1 //===------ SimplifyInstructions.cpp - Remove redundant instructions ------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
15 //===----------------------------------------------------------------------===//
17 #define DEBUG_TYPE "instsimplify"
18 #include "llvm/Function.h"
19 #include "llvm/Pass.h"
20 #include "llvm/Type.h"
21 #include "llvm/ADT/Statistic.h"
22 #include "llvm/Analysis/Dominators.h"
23 #include "llvm/Analysis/InstructionSimplify.h"
24 #include "llvm/Target/TargetData.h"
25 #include "llvm/Transforms/Scalar.h"
26 #include "llvm/Transforms/Utils/Local.h"
30 STATISTIC(NumSimplified, "Number of redundant instructions removed");
33 struct InstSimplifier : public FunctionPass {
34 static char ID; // Pass identification, replacement for typeid
35 InstSimplifier() : FunctionPass(ID) {
36 initializeInstSimplifierPass(*PassRegistry::getPassRegistry());
39 void getAnalysisUsage(AnalysisUsage &AU) const {
43 /// runOnFunction - Remove instructions that simplify.
44 bool runOnFunction(Function &F) {
45 const TargetData *TD = getAnalysisIfAvailable<TargetData>();
46 const DominatorTree *DT = getAnalysisIfAvailable<DominatorTree>();
49 // Add all interesting instructions to the worklist. These are processed
50 // in FIFO order, so instructions are usually visited before their uses.
51 std::queue<Instruction*> Worklist;
52 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
53 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
54 Instruction *I = BI++;
55 // Zap any dead instructions.
56 if (isInstructionTriviallyDead(I)) {
61 // Add all others to the worklist.
65 // Simplify everything in the worklist until the cows come home.
66 while (!Worklist.empty()) {
67 Instruction *I = Worklist.front();
69 // Don't bother simplifying unused instructions.
70 if (I->use_empty()) continue;
71 Value *V = SimplifyInstruction(I, TD, DT);
74 // This instruction simplifies! Replace it with its simplification and
75 // add all uses to the worklist, since they may now simplify.
77 I->replaceAllUsesWith(V);
78 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
80 Worklist.push(cast<Instruction>(*UI));
84 // Finally, run over the function zapping any dead instructions.
85 for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
86 for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE;) {
87 Instruction *I = BI++;
88 if (isInstructionTriviallyDead(I)) {
99 char InstSimplifier::ID = 0;
100 INITIALIZE_PASS(InstSimplifier, "instsimplify", "Remove redundant instructions",
102 char &llvm::InstructionSimplifierID = InstSimplifier::ID;
104 // Public interface to the simplify instructions pass.
105 FunctionPass *llvm::createInstructionSimplifierPass() {
106 return new InstSimplifier();