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081c34b725
must be called in the pass's constructor. This function uses static dependency declarations to recursively initialize the pass's dependencies. Clients that only create passes through the createFooPass() APIs will require no changes. Clients that want to use the CommandLine options for passes will need to manually call the appropriate initialization functions in PassInitialization.h before parsing commandline arguments. I have tested this with all standard configurations of clang and llvm-gcc on Darwin. It is possible that there are problems with the static dependencies that will only be visible with non-standard options. If you encounter any crash in pass registration/creation, please send the testcase to me directly. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@116820 91177308-0d34-0410-b5e6-96231b3b80d8
92 lines
2.9 KiB
C++
92 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 is distributed under the University of Illinois Open Source
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// 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 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/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 ConstantPropagation : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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ConstantPropagation() : FunctionPass(ID) {
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initializeConstantPropagationPass(*PassRegistry::getPassRegistry());
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}
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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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}
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char ConstantPropagation::ID = 0;
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INITIALIZE_PASS(ConstantPropagation, "constprop",
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"Simple constant propagation", false, false)
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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->eraseFromParent();
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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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