Re: [PATCH] i386: Fix emissing of __builtin_cpu_supports.

[Jakub Jelinek <jakub@redhat.com>]

On Tue, Dec 14, 2021 at 10:55:01AM +0100, Martin Liška wrote:
> The patch fixes __builtin_cpu_supports("avx512vbmi2") which returns a negative
> value (that's not allowed in the documentation).
> 
> I also checked ppc target that does the same, and __builtin_cpu_is, which
> are fine.
> 
> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
> 
> Ready to be installed?
> Thanks,
> Martin	
> 
> 	PR target/103661
> 
> gcc/ChangeLog:
> 
> 	* config/i386/i386-builtins.c (fold_builtin_cpu): Compare to 0
> 	as API expects that non-zero values are returned.  For
> 	"avx512vbmi2" argument, we return now 1 << 31, which is a
> 	negative integer value.
> ---
>  gcc/config/i386/i386-builtins.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/gcc/config/i386/i386-builtins.c b/gcc/config/i386/i386-builtins.c
> index 0fb14b55712..7e57b665c1e 100644
> --- a/gcc/config/i386/i386-builtins.c
> +++ b/gcc/config/i386/i386-builtins.c
> @@ -2353,7 +2353,8 @@ fold_builtin_cpu (tree fndecl, tree *args)
>        /* Return __cpu_model.__cpu_features[0] & field_val  */
>        final = build2 (BIT_AND_EXPR, unsigned_type_node, array_elt,
>  		      build_int_cstu (unsigned_type_node, field_val));
> -      return build1 (CONVERT_EXPR, integer_type_node, final);
> +      return build2 (NE_EXPR, integer_type_node, final,
> +		     build_int_cst (unsigned_type_node, 0));
>      }
>    gcc_unreachable ();
>  }

Wouldn't this be better done only if field_val has the msb set
and keep the CONVERT_EXPR otherwise (why isn't it NOP_EXPR?)?

	Jakub