[LLVMdev] should AlwaysInliner inline this case?

[Chandler Carruth]

On Mon, Jan 5, 2015 at 3:09 AM, David Majnemer <david.majnemer at gmail.com>
wrote:

>
>> The idea of improving the inliner is also great, but you may find that
>> it's needed for cases other than this one if i'm right about the
>> instcombine.
>>
>
> Sadly, the combine fails because InstCombine
> queries CastInst::isBitCastable to determine the castable-ness of the
> parameter type and the argument type.  It isn't bitcastable though, it's
> ptrtoint/inttoptr castable.
>
> The following patch opens up the optimization:
> --- a/lib/Transforms/InstCombine/InstCombineCalls.cpp
> +++ b/lib/Transforms/InstCombine/InstCombineCalls.cpp
> @@ -1456,7 +1456,7 @@ bool
> InstCombiner::transformConstExprCastCall(CallSite CS) {
>      Type *ParamTy = FT->getParamType(i);
>      Type *ActTy = (*AI)->getType();
>
> -    if (!CastInst::isBitCastable(ActTy, ParamTy))
> +    if (!CastInst::isBitOrNoopPointerCastable(ActTy, ParamTy, DL))
>        return false;   // Cannot transform this parameter value.
>
>      if (AttrBuilder(CallerPAL.getParamAttributes(i + 1), i + 1).
> @@ -1551,7 +1551,7 @@ bool
> InstCombiner::transformConstExprCastCall(CallSite CS) {
>      if ((*AI)->getType() == ParamTy) {
>        Args.push_back(*AI);
>      } else {
> -      Args.push_back(Builder->CreateBitCast(*AI, ParamTy));
> +      Args.push_back(Builder->CreateBitOrPointerCast(*AI, ParamTy));
>      }
>
>      // Add any parameter attributes.
>

This is exactly why I added those casting utilities. With sufficient
testing, this patch LGTM as a way to effectively canonicalize these cases.
Need to make sure this handles all the cases of ptr->int and int->ptr with
too large, too small, and just right integer sizes. If all goes well, this
seems like a really nice improvement.
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