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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
137 lines
4.2 KiB
C++
137 lines
4.2 KiB
C++
//===- DCE.cpp - Code to perform dead code elimination --------------------===//
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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 dead inst elimination and dead code elimination.
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//
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// Dead Inst Elimination performs a single pass over the function removing
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// instructions that are obviously dead. Dead Code Elimination is similar, but
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// it rechecks instructions that were used by removed instructions to see if
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// they are newly dead.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "dce"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/Transforms/Utils/Local.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(DIEEliminated, "Number of insts removed by DIE pass");
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STATISTIC(DCEEliminated, "Number of insts removed");
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namespace {
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//===--------------------------------------------------------------------===//
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// DeadInstElimination pass implementation
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//
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struct DeadInstElimination : public BasicBlockPass {
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static char ID; // Pass identification, replacement for typeid
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DeadInstElimination() : BasicBlockPass(ID) {
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initializeDeadInstEliminationPass(*PassRegistry::getPassRegistry());
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}
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virtual bool runOnBasicBlock(BasicBlock &BB) {
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bool Changed = false;
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for (BasicBlock::iterator DI = BB.begin(); DI != BB.end(); ) {
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Instruction *Inst = DI++;
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if (isInstructionTriviallyDead(Inst)) {
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Inst->eraseFromParent();
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Changed = true;
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++DIEEliminated;
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}
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}
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return Changed;
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}
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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 DeadInstElimination::ID = 0;
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INITIALIZE_PASS(DeadInstElimination, "die",
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"Dead Instruction Elimination", false, false)
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Pass *llvm::createDeadInstEliminationPass() {
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return new DeadInstElimination();
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}
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namespace {
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//===--------------------------------------------------------------------===//
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// DeadCodeElimination pass implementation
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//
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struct DCE : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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DCE() : FunctionPass(ID) {
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initializeDCEPass(*PassRegistry::getPassRegistry());
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}
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virtual 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 DCE::ID = 0;
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INITIALIZE_PASS(DCE, "dce", "Dead Code Elimination", false, false)
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bool DCE::runOnFunction(Function &F) {
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// Start out with all of the instructions in the worklist...
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std::vector<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.push_back(&*i);
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// Loop over the worklist finding instructions that are dead. If they are
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// dead make them drop all of their uses, making other instructions
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// potentially dead, and work until the worklist is empty.
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//
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bool MadeChange = false;
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while (!WorkList.empty()) {
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Instruction *I = WorkList.back();
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WorkList.pop_back();
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if (isInstructionTriviallyDead(I)) { // If the instruction is dead.
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// Loop over all of the values that the instruction uses, if there are
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// instructions being used, add them to the worklist, because they might
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// go dead after this one is removed.
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//
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for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
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if (Instruction *Used = dyn_cast<Instruction>(*OI))
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WorkList.push_back(Used);
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// Remove the instruction.
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I->eraseFromParent();
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// Remove the instruction from the worklist if it still exists in it.
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for (std::vector<Instruction*>::iterator WI = WorkList.begin();
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WI != WorkList.end(); ) {
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if (*WI == I)
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WI = WorkList.erase(WI);
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else
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++WI;
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}
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MadeChange = true;
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++DCEEliminated;
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}
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}
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return MadeChange;
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}
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FunctionPass *llvm::createDeadCodeEliminationPass() {
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return new DCE();
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}
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