[PATCH] D23134: Make cltz and cttz zero undef when the operand cannot be zero in InstCombine

[Sanjay Patel via llvm-commits]

spatel added inline comments.

================
Comment at: lib/Transforms/InstCombine/InstCombineCalls.cpp:1283-1296
@@ -1268,16 +1282,16 @@
 
 /// CallInst simplification. This mostly only handles folding of intrinsic
 /// instructions. For normal calls, it allows visitCallSite to do the heavy
 /// lifting.
 Instruction *InstCombiner::visitCallInst(CallInst &CI) {
   auto Args = CI.arg_operands();
   if (Value *V = SimplifyCall(CI.getCalledValue(), Args.begin(), Args.end(), DL,
                               &TLI, &DT, &AC))
     return replaceInstUsesWith(CI, V);
 
   if (isFreeCall(&CI, &TLI))
     return visitFree(CI);
 
   // If the caller function is nounwind, mark the call as nounwind, even if the
   // callee isn't.
   if (CI.getParent()->getParent()->doesNotThrow() &&
----------------
Sorry for still not seeing it...can you add test case to show the difference?

AFAICT, the undef param of these intrinsics must be an i1 true/false constant?

  case Intrinsic::ctlz:  // llvm.ctlz
  case Intrinsic::cttz:  // llvm.cttz
    Assert(isa<ConstantInt>(CS.getArgOperand(1)),
           "is_zero_undef argument of bit counting intrinsics must be a "
           "constant int",
           CS);



https://reviews.llvm.org/D23134