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

[Xinliang David Li <davidxl at google dot com>]

Great that it is already covered.

David

On Thu, Apr 11, 2013 at 1:09 PM, Sriraman Tallam <tmsriram@google.com> wrote:
> On Thu, Apr 11, 2013 at 1:05 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>> On Thu, Apr 11, 2013 at 12:43 PM, Xinliang David Li <davidxl@google.com> wrote:
>>> 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.
>>
>> I will get back with data on this.
>>
>>>
>>> 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?
>>
>> Right now, an error is generated if a function accesses an unsupported
>> builtin. Since the intrinsic functions are marked inline and call some
>> target builtin, this will always be caught.
>
> To be clear, same example without the target attribute and with
> -mgenerate-builtins results in an error:
>
> #include <smmintrin.h>
>
> __m128i foo(__m128i *V)
> {
>     return _mm_stream_load_si128(V);
> }
>
> $ g++ test.cc -mgenerate-builtins
>
> smmintrin.h:582:59: error: ‘__builtin_ia32_movntdqa’ needs isa option
> -m32 -msse4.1
>    return (__m128i) __builtin_ia32_movntdqa ((__v2di *) __X);
>
>
>>
>> Sri
>>
>>>
>>> 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