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91 lines
2.9 KiB
C++
91 lines
2.9 KiB
C++
//===- ConstantProp.cpp - Code to perform Simple Constant Propagation -----===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements constant propagation and merging:
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//
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// Specifically, this:
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// * Converts instructions like "add int 1, 2" into 3
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//
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// Notice that:
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// * This pass has a habit of making definitions be dead. It is a good idea
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// to to run a DIE pass sometime after running this pass.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "constprop"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Analysis/ConstantFolding.h"
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#include "llvm/Constant.h"
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#include "llvm/Instruction.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/InstIterator.h"
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#include "llvm/ADT/Statistic.h"
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#include <set>
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using namespace llvm;
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STATISTIC(NumInstKilled, "Number of instructions killed");
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namespace {
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struct VISIBILITY_HIDDEN ConstantPropagation : public FunctionPass {
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static char ID; // Pass identifcation, replacement for typeid
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ConstantPropagation() : FunctionPass((intptr_t)&ID) {}
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bool runOnFunction(Function &F);
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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}
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};
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char ConstantPropagation::ID = 0;
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RegisterPass<ConstantPropagation> X("constprop",
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"Simple constant propagation");
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}
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FunctionPass *llvm::createConstantPropagationPass() {
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return new ConstantPropagation();
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}
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bool ConstantPropagation::runOnFunction(Function &F) {
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// Initialize the worklist to all of the instructions ready to process...
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std::set<Instruction*> WorkList;
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for(inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
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WorkList.insert(&*i);
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}
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bool Changed = false;
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while (!WorkList.empty()) {
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Instruction *I = *WorkList.begin();
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WorkList.erase(WorkList.begin()); // Get an element from the worklist...
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if (!I->use_empty()) // Don't muck with dead instructions...
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if (Constant *C = ConstantFoldInstruction(I)) {
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// Add all of the users of this instruction to the worklist, they might
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// be constant propagatable now...
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for (Value::use_iterator UI = I->use_begin(), UE = I->use_end();
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UI != UE; ++UI)
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WorkList.insert(cast<Instruction>(*UI));
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// Replace all of the uses of a variable with uses of the constant.
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I->replaceAllUsesWith(C);
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// Remove the dead instruction.
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WorkList.erase(I);
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I->getParent()->getInstList().erase(I);
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// We made a change to the function...
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Changed = true;
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++NumInstKilled;
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}
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}
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return Changed;
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}
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