On Thu, Oct 13, 2022 at 5:45 AM J.W. Jagersma via Gcc-help
<gcc-help@xxxxxxxxxxx> 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
