[llvm-commits] [llvm] r146357 - in /llvm/trunk: include/llvm/Intrinsics.td lib/Analysis/ConstantFolding.cpp lib/Transforms/Scalar/SimplifyLibCalls.cpp lib/VMCore/AutoUpgrade.cpp

[Duncan Sands]

Hi Chandler,

> Switch llvm.cttz and llvm.ctlz to accept a second i1 parameter which
> indicates whether the intrinsic has a defined result for a first
> argument equal to zero.

is this flag really useful, i.e. isn't the undef form enough?  To get the
other form you can test the parameter against zero and use a select.  Then
codegen can zap the select on targets where the processor instruction does
the right thing for an argument of zero.

> --- llvm/trunk/lib/Analysis/ConstantFolding.cpp (original)
> +++ llvm/trunk/lib/Analysis/ConstantFolding.cpp Sun Dec 11 22:26:04 2011
> @@ -1418,6 +1414,14 @@
>             };
>             return ConstantStruct::get(cast<StructType>(F->getReturnType()), Ops);
>           }
> +        case Intrinsic::cttz:
> +          // FIXME: This should check for Op2 == 1, and become unreachable if

Don't you mean "undef" rather than "unreachable"?

> +          // Op1 == 0.
> +          return ConstantInt::get(Ty, Op1->getValue().countTrailingZeros());
> +        case Intrinsic::ctlz:
> +          // FIXME: This should check for Op2 == 1, and become unreachable if
> +          // Op1 == 0.
> +          return ConstantInt::get(Ty, Op1->getValue().countLeadingZeros());
>           }
>         }
>
>
> --- llvm/trunk/lib/VMCore/AutoUpgrade.cpp (original)
> +++ llvm/trunk/lib/VMCore/AutoUpgrade.cpp Sun Dec 11 22:26:04 2011
> @@ -40,7 +40,20 @@
>
>     switch (Name[0]) {
>     default: break;
> -  // SOMEDAY: Add some.
> +  case 'c': {
> +    Type *Tys[] = { F->arg_begin()->getType() };

If one day there is an llvm intrinsic with a name starting with "c" with no
arguments, won't this explode?

> +    if (Name.startswith("ctlz.")&&  F->arg_size() == 1) {
> +      F->setName(Name + ".old");
> +      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::ctlz, Tys);
> +      return true;
> +    }
> +    if (Name.startswith("cttz.")&&  F->arg_size() == 1) {
> +      F->setName(Name + ".old");
> +      NewFn = Intrinsic::getDeclaration(F->getParent(), Intrinsic::cttz, Tys);
> +      return true;
> +    }
> +    break;
> +  }
>     }
>
>     //  This may not belong here. This function is effectively being overloaded

Ciao, Duncan.