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Re: GCC does not support *mmintrin.h with function specific opts
- From: Sriraman Tallam <tmsriram at google dot com>
- To: Xinliang David Li <davidxl at google dot com>
- Cc: GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Thu, 11 Apr 2013 13:05:40 -0700
- Subject: Re: GCC does not support *mmintrin.h with function specific opts
- References: <CAAs8HmwMYGGB80J1-YxSK4tY_hn7i65Tw4DGbaq9RpA9M4vPRQ at mail dot gmail dot com> <CAAkRFZJQCDEMJM6mKAM2RB5OKGYBA5CJcotNR0ok8n8vvsiofw at mail dot gmail dot com>
On Thu, Apr 11, 2013 at 12:43 PM, Xinliang David Li <email@example.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.
> On Thu, Apr 11, 2013 at 12:05 PM, Sriraman Tallam <firstname.lastname@example.org> wrote:
>> *mmintrin headers does not work with function specific opts.
>> Example 1:
>> #include <smmintrin.h>
>> __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.