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"
33 Statistic<> NumInstKilled("constprop", "Number of instructions killed");
35 struct ConstantPropagation : public FunctionPass {
36 bool runOnFunction(Function &F);
38 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
43 RegisterOpt<ConstantPropagation> X("constprop","Simple constant propagation");
46 Pass *createConstantPropagationPass() {
47 return new ConstantPropagation();
51 bool ConstantPropagation::runOnFunction(Function &F) {
52 // Initialize the worklist to all of the instructions ready to process...
53 std::set<Instruction*> WorkList(inst_begin(F), inst_end(F));
56 while (!WorkList.empty()) {
57 Instruction *I = *WorkList.begin();
58 WorkList.erase(WorkList.begin()); // Get an element from the worklist...
60 if (!I->use_empty()) // Don't muck with dead instructions...
61 if (Constant *C = ConstantFoldInstruction(I)) {
62 // Add all of the users of this instruction to the worklist, they might
63 // be constant propagatable now...
64 for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
66 WorkList.insert(cast<Instruction>(*UI));
68 // Replace all of the uses of a variable with uses of the constant.
69 I->replaceAllUsesWith(C);
71 // We made a change to the function...
79 } // End llvm namespace