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.
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?
