| //===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file was developed by the LLVM research group and is distributed under |
| // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file implements constant propagation and merging: |
| // |
| // Specifically, this: |
| // * Converts instructions like "add int 1, 2" into 3 |
| // |
| // Notice that: |
| // * This pass has a habit of making definitions be dead. It is a good idea |
| // to to run a DIE pass sometime after running this pass. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "llvm/Transforms/Scalar.h" |
| #include "llvm/Transforms/Utils/Local.h" |
| #include "llvm/ConstantHandling.h" |
| #include "llvm/Instruction.h" |
| #include "llvm/Pass.h" |
| #include "llvm/Support/InstIterator.h" |
| #include "Support/Statistic.h" |
| #include <set> |
| |
| namespace llvm { |
| |
| namespace { |
| Statistic<> NumInstKilled("constprop", "Number of instructions killed"); |
| |
| struct ConstantPropagation : public FunctionPass { |
| bool runOnFunction(Function &F); |
| |
| virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
| AU.setPreservesCFG(); |
| } |
| }; |
| |
| RegisterOpt<ConstantPropagation> X("constprop","Simple constant propagation"); |
| } |
| |
| Pass *createConstantPropagationPass() { |
| return new ConstantPropagation(); |
| } |
| |
| |
| bool ConstantPropagation::runOnFunction(Function &F) { |
| // Initialize the worklist to all of the instructions ready to process... |
| std::set<Instruction*> WorkList(inst_begin(F), inst_end(F)); |
| bool Changed = false; |
| |
| while (!WorkList.empty()) { |
| Instruction *I = *WorkList.begin(); |
| WorkList.erase(WorkList.begin()); // Get an element from the worklist... |
| |
| if (!I->use_empty()) // Don't muck with dead instructions... |
| if (Constant *C = ConstantFoldInstruction(I)) { |
| // Add all of the users of this instruction to the worklist, they might |
| // be constant propagatable now... |
| for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); |
| UI != UE; ++UI) |
| WorkList.insert(cast<Instruction>(*UI)); |
| |
| // Replace all of the uses of a variable with uses of the constant. |
| I->replaceAllUsesWith(C); |
| |
| // We made a change to the function... |
| Changed = true; |
| ++NumInstKilled; |
| } |
| } |
| return Changed; |
| } |
| |
| } // End llvm namespace |