bool storeIsNoop(MemoryDef *Def, const MemoryLocation &DefLoc, Value *DefUO) {
    StoreInst *Store = dyn_cast<StoreInst>(Def->getMemoryInst());
    MemSetInst *MemSet = dyn_cast<MemSetInst>(Def->getMemoryInst());
    Constant *StoredConstant = nullptr;
    if (Store)
      StoredConstant = dyn_cast<Constant>(Store->getOperand(0));
    if (MemSet)
      StoredConstant = dyn_cast<Constant>(MemSet->getValue());

    if (StoredConstant && StoredConstant->isNullValue()) {
      auto *DefUOInst = dyn_cast<Instruction>(DefUO);
      DefUOInst->dump();
      if (DefUOInst) {
        if (isCallocLikeFn(DefUOInst, &TLI)) {
          auto *UnderlyingDef =
              cast<MemoryDef>(MSSA.getMemoryAccess(DefUOInst));
          // If UnderlyingDef is the clobbering access of Def, no instructions
          // between them can modify the memory location.
          auto *ClobberDef =
              MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def);
          return UnderlyingDef == ClobberDef;
        }

        if (isMallocLikeFn(DefUOInst, &TLI) && MemSet &&
            cast<CallBase>(DefUOInst)->getOperand(0) == MemSet->getLength()) {
          auto *Malloc = cast<CallBase>(DefUOInst);
          IRBuilder<> IRB(Malloc);
          auto *UnderlyingDef =
              cast<MemoryDef>(MSSA.getMemoryAccess(DefUOInst));
          // If UnderlyingDef is the clobbering access of Def, no instructions
          // between them can modify the memory location.
          auto *ClobberDef =
              MSSA.getSkipSelfWalker()->getClobberingMemoryAccess(Def);
          if (UnderlyingDef == ClobberDef) {
            // malloc + memset => calloc
            if (Value *Calloc = emitCalloc(
                    ConstantInt::get(DL.getIntPtrType(IRB.getContext()), 1),
                    Malloc->getOperand(0), IRB, TLI)) {
              Malloc->replaceAllUsesWith(Calloc);
              // Remove memset.
              return true;
            }
          }
        }
      }
    }

    if (!Store)
      return false;