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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. llvm-svn: 116820
98 lines
3.3 KiB
C++
98 lines
3.3 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 the Aggressive Dead Code Elimination pass. This pass
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// optimistically assumes that all instructions are dead until proven otherwise,
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// allowing it to eliminate dead computations that other DCE passes do not
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// catch, particularly involving loop computations.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "adce"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/BasicBlock.h"
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#include "llvm/Instructions.h"
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#include "llvm/IntrinsicInst.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/InstIterator.h"
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#include "llvm/ADT/DepthFirstIterator.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/Statistic.h"
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using namespace llvm;
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STATISTIC(NumRemoved, "Number of instructions removed");
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namespace {
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struct ADCE : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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ADCE() : FunctionPass(ID) {
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initializeADCEPass(*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 ADCE::ID = 0;
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INITIALIZE_PASS(ADCE, "adce", "Aggressive Dead Code Elimination", false, false)
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bool ADCE::runOnFunction(Function& F) {
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SmallPtrSet<Instruction*, 128> alive;
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SmallVector<Instruction*, 128> worklist;
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// Collect the set of "root" instructions that are known live.
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for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
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if (isa<TerminatorInst>(I.getInstructionIterator()) ||
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isa<DbgInfoIntrinsic>(I.getInstructionIterator()) ||
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I->mayHaveSideEffects()) {
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alive.insert(I.getInstructionIterator());
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worklist.push_back(I.getInstructionIterator());
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}
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// Propagate liveness backwards to operands.
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while (!worklist.empty()) {
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Instruction* curr = worklist.pop_back_val();
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for (Instruction::op_iterator OI = curr->op_begin(), OE = curr->op_end();
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OI != OE; ++OI)
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if (Instruction* Inst = dyn_cast<Instruction>(OI))
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if (alive.insert(Inst))
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worklist.push_back(Inst);
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}
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// The inverse of the live set is the dead set. These are those instructions
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// which have no side effects and do not influence the control flow or return
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// value of the function, and may therefore be deleted safely.
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// NOTE: We reuse the worklist vector here for memory efficiency.
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for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
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if (!alive.count(I.getInstructionIterator())) {
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worklist.push_back(I.getInstructionIterator());
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I->dropAllReferences();
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}
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for (SmallVector<Instruction*, 1024>::iterator I = worklist.begin(),
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E = worklist.end(); I != E; ++I) {
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++NumRemoved;
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(*I)->eraseFromParent();
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}
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return !worklist.empty();
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}
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FunctionPass *llvm::createAggressiveDCEPass() {
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return new ADCE();
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}
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