//===- DCE.cpp - Code to perform dead code elimination --------------------===//
-//
+//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
//===----------------------------------------------------------------------===//
//
// This file implements dead inst elimination and dead code elimination.
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Scalar.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/Instruction.h"
-#include "llvm/Pass.h"
-#include "llvm/Support/InstIterator.h"
+#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/Statistic.h"
-#include <set>
+#include "llvm/IR/InstIterator.h"
+#include "llvm/IR/Instruction.h"
+#include "llvm/Pass.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/Transforms/Utils/Local.h"
using namespace llvm;
-namespace {
- Statistic<> DIEEliminated("die", "Number of insts removed");
- Statistic<> DCEEliminated("dce", "Number of insts removed");
+#define DEBUG_TYPE "dce"
+
+STATISTIC(DIEEliminated, "Number of insts removed by DIE pass");
+STATISTIC(DCEEliminated, "Number of insts removed");
+namespace {
//===--------------------------------------------------------------------===//
// DeadInstElimination pass implementation
//
-
struct DeadInstElimination : public BasicBlockPass {
- virtual bool runOnBasicBlock(BasicBlock &BB) {
+ static char ID; // Pass identification, replacement for typeid
+ DeadInstElimination() : BasicBlockPass(ID) {
+ initializeDeadInstEliminationPass(*PassRegistry::getPassRegistry());
+ }
+ bool runOnBasicBlock(BasicBlock &BB) override {
+ if (skipOptnoneFunction(BB))
+ return false;
+ auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
+ TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI() : nullptr;
bool Changed = false;
- for (BasicBlock::iterator DI = BB.begin(); DI != BB.end(); )
- if (dceInstruction(DI)) {
+ for (BasicBlock::iterator DI = BB.begin(); DI != BB.end(); ) {
+ Instruction *Inst = &*DI++;
+ if (isInstructionTriviallyDead(Inst, TLI)) {
+ Inst->eraseFromParent();
Changed = true;
++DIEEliminated;
- } else
- ++DI;
+ }
+ }
return Changed;
}
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
}
};
-
- RegisterOpt<DeadInstElimination> X("die", "Dead Instruction Elimination");
}
+char DeadInstElimination::ID = 0;
+INITIALIZE_PASS(DeadInstElimination, "die",
+ "Dead Instruction Elimination", false, false)
+
Pass *llvm::createDeadInstEliminationPass() {
return new DeadInstElimination();
}
-//===----------------------------------------------------------------------===//
-// DeadCodeElimination pass implementation
-//
-
namespace {
+ //===--------------------------------------------------------------------===//
+ // DeadCodeElimination pass implementation
+ //
struct DCE : public FunctionPass {
- virtual bool runOnFunction(Function &F);
+ static char ID; // Pass identification, replacement for typeid
+ DCE() : FunctionPass(ID) {
+ initializeDCEPass(*PassRegistry::getPassRegistry());
+ }
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+ bool runOnFunction(Function &F) override;
+
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.setPreservesCFG();
}
};
+}
+
+char DCE::ID = 0;
+INITIALIZE_PASS(DCE, "dce", "Dead Code Elimination", false, false)
+
+static bool DCEInstruction(Instruction *I,
+ SmallSetVector<Instruction *, 16> &WorkList,
+ const TargetLibraryInfo *TLI) {
+ if (isInstructionTriviallyDead(I, TLI)) {
+ // Null out all of the instruction's operands to see if any operand becomes
+ // dead as we go.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
+ Value *OpV = I->getOperand(i);
+ I->setOperand(i, nullptr);
+
+ if (!OpV->use_empty() || I == OpV)
+ continue;
+
+ // If the operand is an instruction that became dead as we nulled out the
+ // operand, and if it is 'trivially' dead, delete it in a future loop
+ // iteration.
+ if (Instruction *OpI = dyn_cast<Instruction>(OpV))
+ if (isInstructionTriviallyDead(OpI, TLI))
+ WorkList.insert(OpI);
+ }
- RegisterOpt<DCE> Y("dce", "Dead Code Elimination");
+ I->eraseFromParent();
+ ++DCEEliminated;
+ return true;
+ }
+ return false;
}
bool DCE::runOnFunction(Function &F) {
- // Start out with all of the instructions in the worklist...
- std::vector<Instruction*> WorkList;
- for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i) {
- WorkList.push_back(&*i);
+ if (skipOptnoneFunction(F))
+ return false;
+
+ auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
+ TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI() : nullptr;
+
+ bool MadeChange = false;
+ SmallSetVector<Instruction *, 16> WorkList;
+ // Iterate over the original function, only adding insts to the worklist
+ // if they actually need to be revisited. This avoids having to pre-init
+ // the worklist with the entire function's worth of instructions.
+ for (inst_iterator FI = inst_begin(F), FE = inst_end(F); FI != FE;) {
+ Instruction *I = &*FI;
+ ++FI;
+
+ // We're visiting this instruction now, so make sure it's not in the
+ // worklist from an earlier visit.
+ if (!WorkList.count(I))
+ MadeChange |= DCEInstruction(I, WorkList, TLI);
}
- std::set<Instruction*> DeadInsts;
-
- // Loop over the worklist finding instructions that are dead. If they are
- // dead make them drop all of their uses, making other instructions
- // potentially dead, and work until the worklist is empty.
- //
+
while (!WorkList.empty()) {
- Instruction *I = WorkList.back();
- WorkList.pop_back();
-
- if (isInstructionTriviallyDead(I)) { // If the instruction is dead...
- // Loop over all of the values that the instruction uses, if there are
- // instructions being used, add them to the worklist, because they might
- // go dead after this one is removed.
- //
- for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
- if (Instruction *Used = dyn_cast<Instruction>(*OI))
- WorkList.push_back(Used);
-
- // Tell the instruction to let go of all of the values it uses...
- I->dropAllReferences();
-
- // Keep track of this instruction, because we are going to delete it later
- DeadInsts.insert(I);
- }
+ Instruction *I = WorkList.pop_back_val();
+ MadeChange |= DCEInstruction(I, WorkList, TLI);
}
-
- // If we found no dead instructions, we haven't changed the function...
- if (DeadInsts.empty()) return false;
-
- // Otherwise, loop over the program, removing and deleting the instructions...
- for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
- for (BasicBlock::iterator BI = I->begin(); BI != I->end(); )
- if (DeadInsts.count(BI)) { // Is this instruction dead?
- BI = I->getInstList().erase(BI); // Yup, remove and delete inst
- ++DCEEliminated;
- } else { // This instruction is not dead
- ++BI; // Continue on to the next one...
- }
-
- return true;
+ return MadeChange;
}
FunctionPass *llvm::createDeadCodeEliminationPass() {
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