Re: [RFC C++ / PR51033 ] Handle __builtin_shuffle in constexpr properly in the C++ frontend.

[Marc Glisse <marc.glisse@inria.fr>]

On Sat, 28 Jul 2012, Marc Glisse wrote:

> On Mon, 18 Jun 2012, Ramana Radhakrishnan wrote:
>
>> This patch following on from the fix for turning on __builtin_shuffle
>> for c++ , enables folding of vec_perm_exprs in the front-end for
>> constexpr and constructor style values.
>
> Hello,
>
> I took a look, and the example I gave in
> http://gcc.gnu.org/ml/gcc-patches/2012-06/msg01066.html
> although it doesn't crash the compiler anymore, still fails to compile. I am 
> not sure: were you just trying to remove the ICE, or actually support this 
> use?
>
> #include <x86intrin.h>
> int main(){
>  constexpr __m128d x={1.,2.};
>  constexpr __m128i y={1,0};
>  constexpr __m128d z=__builtin_shuffle(x,y);
> }
>
> $ g++ -std=gnu++11 m.cc
> m.cc: In function 'int main()':
> m.cc:5:23: error: '#'vec_perm_expr' not supported by dump_expr#<expression 
> error>' is not a constant expression
>   constexpr __m128d z=__builtin_shuffle(x,y);
>                       ^

The issue seems to be that we call fold_ternary_loc with a last argument 
that is a CONSTRUCTOR whereas the VEC_PERM_EXPR case expects a VECTOR_CST.

-- 
Marc Glisse