[llvm] r244889 - [SystemZ] Support large LLVM IR struct return values

[Hans Wennborg via llvm-commits]

Merged in r244909.

Cheers,
Hans

On Thu, Aug 13, 2015 at 8:58 AM, Ulrich Weigand
<Ulrich.Weigand at de.ibm.com> wrote:
>
> Hi Hans,
>
> if there's still time, I think it would be good to merge this
> patch to the 3.7 branch, since it fixes a crash when running
> current Mesa/llvmpipe and is a relatively straightforward fix.
>
> Thanks,
> Ulrich
>
>>[SystemZ] Support large LLVM IR struct return values
>>
>>Recent mesa/llvmpipe crashes on SystemZ due to a failed assertion when
>>attempting to compile a routine with a return type of
>>  { <4 x float>, <4 x float>, <4 x float>, <4 x float> }
>>on a system without vector instruction support.
>>
>>This is because after legalizing the vector type, we get a return value
>>consisting of 16 floats, which cannot all be returned in registers.
>>
>>Usually, what should happen in this case is that the target's
> CanLowerReturn
>>routine rejects the return type, in which case SelectionDAG falls back to
>>implementing a structure return in memory via implicit reference.
>>
>>However, the SystemZ target never actually implemented any CanLowerReturn
>>routine, and thus would accept any struct return type.
>>
>>This patch fixes the crash by implementing CanLowerReturn.  As a side
> effect,
>>this also handles fp128 return values, fixing a todo that was noted in
>>SystemZCallingConv.td.
>