1 //===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements constant propagation and merging:
12 // Specifically, this:
13 // * Converts instructions like "add int 1, 2" into 3
16 // * This pass has a habit of making definitions be dead. It is a good idea
17 // to to run a DIE pass sometime after running this pass.
19 //===----------------------------------------------------------------------===//
21 #include "llvm/Transforms/Scalar.h"
22 #include "llvm/Transforms/Utils/Local.h"
23 #include "llvm/ConstantHandling.h"
24 #include "llvm/Instruction.h"
25 #include "llvm/Pass.h"
26 #include "llvm/Support/InstIterator.h"
27 #include "Support/Statistic.h"
31 Statistic<> NumInstKilled("constprop", "Number of instructions killed");
33 struct ConstantPropagation : public FunctionPass {
34 bool runOnFunction(Function &F);
36 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
41 RegisterOpt<ConstantPropagation> X("constprop","Simple constant propagation");
44 Pass *createConstantPropagationPass() {
45 return new ConstantPropagation();
49 bool ConstantPropagation::runOnFunction(Function &F) {
50 // Initialize the worklist to all of the instructions ready to process...
51 std::set<Instruction*> WorkList(inst_begin(F), inst_end(F));
54 while (!WorkList.empty()) {
55 Instruction *I = *WorkList.begin();
56 WorkList.erase(WorkList.begin()); // Get an element from the worklist...
58 if (!I->use_empty()) // Don't muck with dead instructions...
59 if (Constant *C = ConstantFoldInstruction(I)) {
60 // Add all of the users of this instruction to the worklist, they might
61 // be constant propagatable now...
62 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
64 WorkList.insert(cast<Instruction>(*UI));
66 // Replace all of the uses of a variable with uses of the constant.
67 I->replaceAllUsesWith(C);
69 // We made a change to the function...