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Re: [PATCH] x86: Define _mm*_undefined_*
- From: Ulrich Drepper <drepper at gmail dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: Ilya Tocar <tocarip dot intel at gmail dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 18 Mar 2014 11:03:00 -0400
- Subject: Re: [PATCH] x86: Define _mm*_undefined_*
- Authentication-results: sourceware.org; auth=none
- References: <87bnx6z9at dot fsf at x240 dot local dot i-did-not-set--mail-host-address--so-tickle-me> <20140317113921 dot GA71172 at msticlxl7 dot ims dot intel dot com> <CAOPLpQebBsPYU_eRLmkVtFJixGg8Kx33sMyZg9n_X8MKJNfV_A at mail dot gmail dot com> <20140318093428 dot GB71172 at msticlxl7 dot ims dot intel dot com> <CAFiYyc1NTh-CV8f1e=9xJBhDx3esZEBtPHWHRiJnAyUWzzhS0Q at mail dot gmail dot com>
On Tue, Mar 18, 2014 at 7:13 AM, Richard Biener
<richard.guenther@gmail.com> wrote:
> extern __inline __m512
> __attribute__ ((__gnu_inline__, __always_inline__, __artificial__))
> _mm512_undefined_ps (void)
> {
> __m512 __Y = __Y;
> return __Y;
> }
This provokes no warnings (as you wrote) and it doesn't clobber flags,
but it doesn't avoid loading. The code below creates a pxor for the
parameter. That's what I think compiler support should help to get
rid of. If the compiler has some magic to recognize -1 masks then
this will help in some situations but it seems to be a specific
implementation for the intrinsics while I've been looking at generic
solution.
typedef double __m128d __attribute__ ((__vector_size__ (16), __may_alias__));
void g(__m128d);
extern __inline __m128d
__attribute__((__gnu_inline__, __always_inline__, __artificial__, const))
_mm_undefined_pd(void) {
__m128d v = v;
return v;
}
void
f()
{
g(_mm_undefined_pd());
}