-//===- DCE.cpp - Code to perform dead code elimination --------------------===//
+//===- ADCE.cpp - Code to perform dead code elimination -------------------===//
//
// The LLVM Compiler Infrastructure
//
//
// This file implements the Aggressive Dead Code Elimination pass. This pass
// optimistically assumes that all instructions are dead until proven otherwise,
-// allowing it to eliminate dead computations that other DCE passes do not
+// allowing it to eliminate dead computations that other DCE passes do not
// catch, particularly involving loop computations.
//
//===----------------------------------------------------------------------===//
-#define DEBUG_TYPE "adce"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/BasicBlock.h"
-#include "llvm/Instructions.h"
-#include "llvm/Pass.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Support/Compiler.h"
-#include "llvm/Support/InstIterator.h"
-#include "llvm/ADT/DenseSet.h"
+#include "llvm/Transforms/Scalar/ADCE.h"
#include "llvm/ADT/DepthFirstIterator.h"
-#include "llvm/ADT/Statistic.h"
+#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
-
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/GlobalsModRef.h"
+#include "llvm/IR/BasicBlock.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
+#include "llvm/Pass.h"
+#include "llvm/Transforms/Scalar.h"
using namespace llvm;
-STATISTIC(NumRemoved, "Number of instructions removed");
+#define DEBUG_TYPE "adce"
-namespace {
- struct VISIBILITY_HIDDEN ADCE : public FunctionPass {
- static char ID; // Pass identification, replacement for typeid
- ADCE() : FunctionPass((intptr_t)&ID) {}
-
- DenseSet<Instruction*> alive;
- SmallVector<Instruction*, 1024> worklist;
-
- DenseSet<BasicBlock*> reachable;
- SmallVector<BasicBlock*, 1024> unreachable;
-
- virtual bool runOnFunction(Function& F);
-
- virtual void getAnalysisUsage(AnalysisUsage& AU) const {
- AU.setPreservesCFG();
- }
-
- };
-}
+STATISTIC(NumRemoved, "Number of instructions removed");
-char ADCE::ID = 0;
-static RegisterPass<ADCE> X("adce", "Aggressive Dead Code Elimination");
+static bool aggressiveDCE(Function& F) {
+ SmallPtrSet<Instruction*, 128> Alive;
+ SmallVector<Instruction*, 128> Worklist;
-bool ADCE::runOnFunction(Function& F) {
- alive.clear();
- worklist.clear();
- reachable.clear();
- unreachable.clear();
-
- // First, collect the set of reachable blocks ...
- for (df_iterator<BasicBlock*> DI = df_begin(&F.getEntryBlock()),
- DE = df_end(&F.getEntryBlock()); DI != DE; ++DI)
- reachable.insert(*DI);
-
- // ... and then invert it into the list of unreachable ones. These
- // blocks will be removed from the function.
- for (Function::iterator FI = F.begin(), FE = F.end(); FI != FE; ++FI)
- if (!reachable.count(FI))
- unreachable.push_back(FI);
-
- // Prepare to remove blocks by removing the PHI node entries for those blocks
- // in their successors, and remove them from reference counting.
- for (SmallVector<BasicBlock*, 1024>::iterator UI = unreachable.begin(),
- UE = unreachable.end(); UI != UE; ++UI) {
- BasicBlock* BB = *UI;
- for (succ_iterator SI = succ_begin(BB), SE = succ_end(BB);
- SI != SE; ++SI) {
- BasicBlock* succ = *SI;
- BasicBlock::iterator succ_inst = succ->begin();
- while (PHINode* P = dyn_cast<PHINode>(succ_inst)) {
- P->removeIncomingValue(BB);
- ++succ_inst;
- }
- }
-
- BB->dropAllReferences();
- }
-
- // Finally, erase the unreachable blocks.
- for (SmallVector<BasicBlock*, 1024>::iterator UI = unreachable.begin(),
- UE = unreachable.end(); UI != UE; ++UI)
- (*UI)->eraseFromParent();
-
// Collect the set of "root" instructions that are known live.
- for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
- if (isa<TerminatorInst>(I.getInstructionIterator()) ||
- I->mayWriteToMemory()) {
- alive.insert(I.getInstructionIterator());
- worklist.push_back(I.getInstructionIterator());
+ for (Instruction &I : instructions(F)) {
+ if (isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) || I.isEHPad() ||
+ I.mayHaveSideEffects()) {
+ Alive.insert(&I);
+ Worklist.push_back(&I);
}
-
+ }
+
// Propagate liveness backwards to operands.
- while (!worklist.empty()) {
- Instruction* curr = worklist.back();
- worklist.pop_back();
-
- for (Instruction::op_iterator OI = curr->op_begin(), OE = curr->op_end();
- OI != OE; ++OI)
- if (Instruction* Inst = dyn_cast<Instruction>(OI))
- if (alive.insert(Inst))
- worklist.push_back(Inst);
+ while (!Worklist.empty()) {
+ Instruction *Curr = Worklist.pop_back_val();
+ for (Use &OI : Curr->operands()) {
+ if (Instruction *Inst = dyn_cast<Instruction>(OI))
+ if (Alive.insert(Inst).second)
+ Worklist.push_back(Inst);
+ }
}
-
+
// The inverse of the live set is the dead set. These are those instructions
// which have no side effects and do not influence the control flow or return
// value of the function, and may therefore be deleted safely.
- // NOTE: We reuse the worklist vector here for memory efficiency.
- for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
- if (!alive.count(I.getInstructionIterator())) {
- worklist.push_back(I.getInstructionIterator());
- I->dropAllReferences();
+ // NOTE: We reuse the Worklist vector here for memory efficiency.
+ for (Instruction &I : instructions(F)) {
+ if (!Alive.count(&I)) {
+ Worklist.push_back(&I);
+ I.dropAllReferences();
}
-
- for (SmallVector<Instruction*, 1024>::iterator I = worklist.begin(),
- E = worklist.end(); I != E; ++I) {
- NumRemoved++;
- (*I)->eraseFromParent();
}
-
- return !worklist.empty();
+
+ for (Instruction *&I : Worklist) {
+ ++NumRemoved;
+ I->eraseFromParent();
+ }
+
+ return !Worklist.empty();
+}
+
+PreservedAnalyses ADCEPass::run(Function &F) {
+ if (aggressiveDCE(F))
+ return PreservedAnalyses::none();
+ return PreservedAnalyses::all();
}
-FunctionPass *llvm::createAggressiveDCEPass() {
- return new ADCE();
+namespace {
+struct ADCELegacyPass : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ ADCELegacyPass() : FunctionPass(ID) {
+ initializeADCELegacyPassPass(*PassRegistry::getPassRegistry());
+ }
+
+ bool runOnFunction(Function& F) override {
+ if (skipOptnoneFunction(F))
+ return false;
+ return aggressiveDCE(F);
+ }
+
+ void getAnalysisUsage(AnalysisUsage& AU) const override {
+ AU.setPreservesCFG();
+ AU.addPreserved<GlobalsAAWrapperPass>();
+ }
+};
}
+
+char ADCELegacyPass::ID = 0;
+INITIALIZE_PASS(ADCELegacyPass, "adce", "Aggressive Dead Code Elimination",
+ false, false)
+
+FunctionPass *llvm::createAggressiveDCEPass() { return new ADCELegacyPass(); }
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