//===- 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.
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "dce"
#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 "Support/Statistic.h"
+#include "llvm/ADT/Statistic.h"
#include <set>
using namespace llvm;
-namespace {
- Statistic<> DIEEliminated("die", "Number of insts removed");
- Statistic<> DCEEliminated("dce", "Number of insts removed");
+STATISTIC(DIEEliminated, "Number of insts removed by DIE pass");
+STATISTIC(DCEEliminated, "Number of insts removed");
+namespace {
//===--------------------------------------------------------------------===//
// DeadInstElimination pass implementation
//
-
struct DeadInstElimination : public BasicBlockPass {
+ static char ID; // Pass identification, replacement for typeid
+ DeadInstElimination() : BasicBlockPass(ID) {}
virtual bool runOnBasicBlock(BasicBlock &BB) {
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)) {
+ Inst->eraseFromParent();
Changed = true;
++DIEEliminated;
- } else
- ++DI;
+ }
+ }
return Changed;
}
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 {
+ static char ID; // Pass identification, replacement for typeid
+ DCE() : FunctionPass(ID) {}
+
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
};
-
- RegisterOpt<DCE> Y("dce", "Dead Code Elimination");
}
+char DCE::ID = 0;
+INITIALIZE_PASS(DCE, "dce", "Dead Code Elimination", false, false);
+
bool DCE::runOnFunction(Function &F) {
// Start out with all of the instructions in the worklist...
- std::vector<Instruction*> WorkList(inst_begin(F), inst_end(F));
- std::set<Instruction*> DeadInsts;
-
+ std::vector<Instruction*> WorkList;
+ for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
+ WorkList.push_back(&*i);
+
// 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.
//
+ bool MadeChange = false;
while (!WorkList.empty()) {
Instruction *I = WorkList.back();
WorkList.pop_back();
-
- if (isInstructionTriviallyDead(I)) { // If the instruction is dead...
+
+ 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::use_iterator UI = I->use_begin(), UE = I->use_end();
- UI != UE; ++UI)
- if (Instruction *Used = dyn_cast<Instruction>(*UI))
+ 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();
+ // Remove the instruction.
+ I->eraseFromParent();
- // Keep track of this instruction, because we are going to delete it later
- DeadInsts.insert(I);
- }
- }
-
- // 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...
+ // Remove the instruction from the worklist if it still exists in it.
+ for (std::vector<Instruction*>::iterator WI = WorkList.begin();
+ WI != WorkList.end(); ) {
+ if (*WI == I)
+ WI = WorkList.erase(WI);
+ else
+ ++WI;
}
- return true;
+ MadeChange = true;
+ ++DCEEliminated;
+ }
+ }
+ return MadeChange;
}
-Pass *llvm::createDeadCodeEliminationPass() {
+FunctionPass *llvm::createDeadCodeEliminationPass() {
return new DCE();
}
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