#include "llvm/Transforms/Scalar.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/GlobalsModRef.h"
#include "llvm/Analysis/DemandedBits.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Operator.h"
#include "llvm/Pass.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
using namespace llvm;
#define DEBUG_TYPE "bdce"
STATISTIC(NumRemoved, "Number of instructions removed (unused)");
STATISTIC(NumSimplified, "Number of instructions trivialized (dead bits)");
namespace {
struct BDCE : public FunctionPass {
static char ID; BDCE() : FunctionPass(ID) {
initializeBDCEPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function& F) override;
void getAnalysisUsage(AnalysisUsage& AU) const override {
AU.setPreservesCFG();
AU.addRequired<DemandedBits>();
AU.addPreserved<GlobalsAAWrapperPass>();
}
};
}
char BDCE::ID = 0;
INITIALIZE_PASS_BEGIN(BDCE, "bdce", "Bit-Tracking Dead Code Elimination",
false, false)
INITIALIZE_PASS_DEPENDENCY(DemandedBits)
INITIALIZE_PASS_END(BDCE, "bdce", "Bit-Tracking Dead Code Elimination",
false, false)
bool BDCE::runOnFunction(Function& F) {
if (skipOptnoneFunction(F))
return false;
DemandedBits &DB = getAnalysis<DemandedBits>();
SmallVector<Instruction*, 128> Worklist;
bool Changed = false;
for (Instruction &I : instructions(F)) {
if (I.getType()->isIntegerTy() &&
!DB.getDemandedBits(&I).getBoolValue()) {
DEBUG(dbgs() << "BDCE: Trivializing: " << I << " (all bits dead)\n");
Value *Zero = ConstantInt::get(I.getType(), 0);
++NumSimplified;
I.replaceAllUsesWith(Zero);
Changed = true;
}
if (!DB.isInstructionDead(&I))
continue;
Worklist.push_back(&I);
I.dropAllReferences();
Changed = true;
}
for (Instruction *&I : Worklist) {
++NumRemoved;
I->eraseFromParent();
}
return Changed;
}
FunctionPass *llvm::createBitTrackingDCEPass() {
return new BDCE();
}