GCC does not support *mmintrin.h with function specific opts

[Xinliang David Li]

What is the compile time impact for turning it on? Code not including
the intrinsic headers should not be affected too much.  If the impact
is small, why not turning on this option by default -- which seems to
be the behavior of ICC.

With this option, all functions without the appropriate target options
will be allowed to reference not supported builtins, without warnings
or errors. Is it possible to delay the check till the builtin
expansion time?

thanks,

David

On Thu, Apr 11, 2013 at 12:05 PM, Sriraman Tallam <tmsriram@google.com> wrote:
> Hi,
>
>     *mmintrin headers does not work with function specific opts.
>
> Example 1:
>
>
> #include <smmintrin.h>
>
> __attribute__((target("sse4.1")))
> __m128i foo(__m128i *V)
> {
>     return _mm_stream_load_si128(V);
> }
>
>
> $ g++ test.cc
> smmintrin.h:31:3: error: #error "SSE4.1 instruction set not enabled"
>  # error "SSE4.1 instruction set not enabled"
>
> This error happens even though foo is marked "sse4.1"
>
> There are multiple issues at play here. One, the headers are guarded
> by macros that are switched on only when the target specific options,
> like -msse4.1 in this case, are present in the command line. Also, the
> target specific builtins, like __builtin_ia32_movntdqa called by
> _mm_stream_load_si128, are exposed only in the presence of the
> appropriate target ISA option.
>
>
> I have attached a patch that fixes this. I have added an option
> "-mgenerate-builtins" that will do two things.  It will define a macro
> "__ALL_ISA__" which will expose the *intrin.h functions. It will also
> expose all the target specific builtins.  -mgenerate-builtins will not
> affect code generation.
>
> This feature will greatly benefit the function multiversioning usability too.
>
> Comments?
>
> Thanks
> Sri