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From: Hongtao Liu <crazylht@gmail.com>
Date: Thu, 13 Oct 2022 09:43:27 +0800
Message-ID: <CAMZc-bztxKBow-bxsbUWq4x6axfDDhRjpKEmHS3V=-hG-1bvcQ@mail.gmail.com>
Subject: Re: Ignoring 'target specific option mismatch' on inline
To: "J.W. Jagersma" <jwjagersma@gmail.com>
Cc: gcc-help <gcc-help@gcc.gnu.org>
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On Thu, Oct 13, 2022 at 5:45 AM J.W. Jagersma via Gcc-help
<gcc-help@gcc.gnu.org> wrote:
>
> Consider the following (incomplete) code:
>
>     enum simd { mmx = 1, sse = 2 /* , ... */ };
>
>     template<simd flags>
>     void simd_func()
>     {
>         if constexpr (flags & simd::mmx)
>         {
>             // MMX code here
>         }
>         else if constexpr (flags & simd::sse)
>         {
>             // SSE code here
>         }
>         // etc ...
>     }
>
> The idea is to instantiate function templates with optimized SIMD routines
> multiple times, then I can compile all my code with -march=i386, and select the
> best implementation at runtime.
It looks like you want to use function multi-versioning.
>
> However, after already spending a lot of time restructuring my code around this
> idea, I discover that gcc refuses to compile this without having the
> corresponding target options enabled:
>
>     error: inlining failed in call to 'always_inline' '__m64 _mm_unpacklo_pi8(__m64, __m64)': target specific option mismatch
>
> That makes no sense to me.  I want gcc to emit those SIMD instructions verbatim
> in my code, regardless of what compiler options the user specified.  What then
> is the point of feature-test macros (__SSE__, etc)?  I don't get it.
>
> Is there any option or attribute I can use to make gcc ignore these target
> option mismatches when inlining?  Or any other way to make this work?
maybe you can try
#pragma GCC push_options
#pragma GCC target("sse2")
your codes..
 #pragma GCC pop_options

https://gcc.gnu.org/onlinedocs/gcc/Function-Specific-Option-Pragmas.html#Function-Specific-Option-Pragmas


-- 
BR,
Hongtao