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The pass is really just a means of accessing a cached instance of the TargetLibraryInfo object, and this way we can re-use that object for the new pass manager as its result. Lots of delta, but nothing interesting happening here. This is the common pattern that is developing to allow analyses to live in both the old and new pass manager -- a wrapper pass in the old pass manager emulates the separation intrinsic to the new pass manager between the result and pass for analyses. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@226157 91177308-0d34-0410-b5e6-96231b3b80d8
143 lines
4.6 KiB
C++
143 lines
4.6 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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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/InstIterator.h"
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#include "llvm/IR/Instruction.h"
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#include "llvm/Pass.h"
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#include "llvm/Analysis/TargetLibraryInfo.h"
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#include "llvm/Transforms/Utils/Local.h"
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using namespace llvm;
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#define DEBUG_TYPE "dce"
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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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bool runOnBasicBlock(BasicBlock &BB) override {
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if (skipOptnoneFunction(BB))
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return false;
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auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
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TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI() : nullptr;
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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, TLI)) {
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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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void getAnalysisUsage(AnalysisUsage &AU) const override {
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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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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override {
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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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if (skipOptnoneFunction(F))
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return false;
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auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
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TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI() : nullptr;
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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, TLI)) { // 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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WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
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WorkList.end());
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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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