#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 "llvm/ADT/Statistic.h"
using namespace llvm;
STATISTIC(DIEEliminated, "Number of insts removed by DIE pass");
STATISTIC(DCEEliminated, "Number of insts removed");
namespace {
struct DeadInstElimination : public BasicBlockPass {
static char ID; DeadInstElimination() : BasicBlockPass(ID) {
initializeDeadInstEliminationPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnBasicBlock(BasicBlock &BB) {
bool Changed = false;
for (BasicBlock::iterator DI = BB.begin(); DI != BB.end(); ) {
Instruction *Inst = DI++;
if (isInstructionTriviallyDead(Inst)) {
Inst->eraseFromParent();
Changed = true;
++DIEEliminated;
}
}
return Changed;
}
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
};
}
char DeadInstElimination::ID = 0;
INITIALIZE_PASS(DeadInstElimination, "die",
"Dead Instruction Elimination", false, false)
Pass *llvm::createDeadInstEliminationPass() {
return new DeadInstElimination();
}
namespace {
struct DCE : public FunctionPass {
static char ID; DCE() : FunctionPass(ID) {
initializeDCEPass(*PassRegistry::getPassRegistry());
}
virtual bool runOnFunction(Function &F);
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesCFG();
}
};
}
char DCE::ID = 0;
INITIALIZE_PASS(DCE, "dce", "Dead Code Elimination", false, false)
bool DCE::runOnFunction(Function &F) {
std::vector<Instruction*> WorkList;
for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
WorkList.push_back(&*i);
bool MadeChange = false;
while (!WorkList.empty()) {
Instruction *I = WorkList.back();
WorkList.pop_back();
if (isInstructionTriviallyDead(I)) { 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);
I->eraseFromParent();
for (std::vector<Instruction*>::iterator WI = WorkList.begin();
WI != WorkList.end(); ) {
if (*WI == I)
WI = WorkList.erase(WI);
else
++WI;
}
MadeChange = true;
++DCEEliminated;
}
}
return MadeChange;
}
FunctionPass *llvm::createDeadCodeEliminationPass() {
return new DCE();
}