#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.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"
using namespace llvm;
#define DEBUG_TYPE "adce"
STATISTIC(NumRemoved, "Number of instructions removed");
namespace {
struct ADCE : public FunctionPass {
static char ID; ADCE() : FunctionPass(ID) {
initializeADCEPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function& F) override;
void getAnalysisUsage(AnalysisUsage& AU) const override {
AU.setPreservesCFG();
}
};
}
char ADCE::ID = 0;
INITIALIZE_PASS(ADCE, "adce", "Aggressive Dead Code Elimination", false, false)
bool ADCE::runOnFunction(Function& F) {
if (skipOptnoneFunction(F))
return false;
SmallPtrSet<Instruction*, 128> alive;
SmallVector<Instruction*, 128> worklist;
for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I)
if (isa<TerminatorInst>(I.getInstructionIterator()) ||
isa<DbgInfoIntrinsic>(I.getInstructionIterator()) ||
isa<LandingPadInst>(I.getInstructionIterator()) ||
I->mayHaveSideEffects()) {
alive.insert(I.getInstructionIterator());
worklist.push_back(I.getInstructionIterator());
}
while (!worklist.empty()) {
Instruction* curr = worklist.pop_back_val();
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);
}
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();
}
for (SmallVectorImpl<Instruction *>::iterator I = worklist.begin(),
E = worklist.end(); I != E; ++I) {
++NumRemoved;
(*I)->eraseFromParent();
}
return !worklist.empty();
}
FunctionPass *llvm::createAggressiveDCEPass() {
return new ADCE();
}