CodeGenPrepare.cpp

      if (isa<Constant>(CI->getOperand(0)))
        continue;

      bool Change = false;
      if (TLI) {
        Change = OptimizeNoopCopyExpression(CI, *TLI);
        MadeChange |= Change;
      }

      if (!Change && (isa<ZExtInst>(I) || isa<SExtInst>(I))) {
        MadeChange |= MoveExtToFormExtLoad(I);
        MadeChange |= OptimizeExtUses(I);
      }
    } else if (CmpInst *CI = dyn_cast<CmpInst>(I)) {
      MadeChange |= OptimizeCmpExpression(CI);
    } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
      if (TLI)
        MadeChange |= OptimizeMemoryInst(I, I->getOperand(0), LI->getType(),
                                         SunkAddrs);
    } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
      if (TLI)
        MadeChange |= OptimizeMemoryInst(I, SI->getOperand(1),
                                         SI->getOperand(0)->getType(),
                                         SunkAddrs);
    } else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(I)) {
      if (GEPI->hasAllZeroIndices()) {
        /// The GEP operand must be a pointer, so must its result -> BitCast
        Instruction *NC = new BitCastInst(GEPI->getOperand(0), GEPI->getType(),
                                          GEPI->getName(), GEPI);
        GEPI->replaceAllUsesWith(NC);
        GEPI->eraseFromParent();
        ++NumGEPsElim;
        MadeChange = true;
        BBI = NC;
      }
    } else if (CallInst *CI = dyn_cast<CallInst>(I)) {
      // If we found an inline asm expession, and if the target knows how to
      // lower it to normal LLVM code, do so now.
      if (TLI && isa<InlineAsm>(CI->getCalledValue())) {
        if (TLI->ExpandInlineAsm(CI)) {
          BBI = BB.begin();
          // Avoid processing instructions out of order, which could cause
          // reuse before a value is defined.
          SunkAddrs.clear();
        } else
          // Sink address computing for memory operands into the block.
          MadeChange |= OptimizeInlineAsmInst(I, &(*CI), SunkAddrs);
      } else {
        // Other CallInst optimizations that don't need to muck with the
        // enclosing iterator here.
        MadeChange |= OptimizeCallInst(CI);
      }
    }
  }

  return MadeChange;
}