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Date: Fri, 12 May 2017 07:22:00 -0000
From: Richard Biener <rguenther@suse.de>
To: Uros Bizjak <ubizjak@gmail.com>
cc: Rainer Orth <ro@cebitec.uni-bielefeld.de>,     "gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] Fix PR79201 (half-way)
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On Thu, 11 May 2017, Uros Bizjak wrote:

> On Thu, May 11, 2017 at 4:02 PM, Richard Biener <rguenther@suse.de> wrote:
> 
> >> > Uros added the testcase in 2008 -- I think if we want to have a testcase
> >> > for the original issue we need a different one.  Or simply remove
> >> > the testcase.
> >>
> >> No, there is something going on in the testcase:
> >>
> >> .L3:
> >>         movq    (%ecx,%eax,8), %mm1
> >>         paddq   (%ebx,%eax,8), %mm1
> >>         addl    $1, %eax
> >>         movq    %mm1, %mm0
> >>         cmpl    %eax, %edx
> >>         jne     .L3
> >>
> >>
> >> The compiler should allocate %mm0 to movq and paddq to avoid %mm1 ->
> >> %mm0 move. These are all movv1di patterns (they shouldn't interfere
> >> with movdi), and it is not clear to me why RA allocates %mm1 instead
> >> of %mm0.
> >
> > In any case the testcase is no longer testing what it tested as the
> > input to RA is now different.  The testcase doesn't make much sense:
> 
> Following is the cleaned testcase:
> 
> --cut here--
> /* { dg-do compile { target ia32 } } */
> /* { dg-options "-O2 -msse2 -mtune=core2" } */
> /* { dg-additional-options "-mno-vect8-ret-in-mem" { target *-*-vxworks* } } */
> /* { dg-additional-options "-mabi=sysv" { target x86_64-*-mingw* } } */
> 
> #include <mmintrin.h>
> 
> typedef __SIZE_TYPE__ size_t;
> 
> __m64
> unsigned_add3 (const __m64 * a, const __m64 * b, size_t count)
> {
>   __m64 sum = { 0, 0 };
> 
>   if (count > 0)
>     sum = _mm_add_si64 (a[count-1], b[count-1]);
> 
>   return sum;
> }
> 
> /* { dg-final { scan-assembler-times "movq\[ \\t\]+\[^\n\]*%mm" 1 } } */
> -- cut here--
> 
> The testcase still tests that only one movq is generated (gcc-4.1
> generated three). However, I have disabled the test on x86_64, since
> x86_64 returns mmx values in XMM registers, and MMX -> XMM moves
> always go through memory.

Thank you very much.

Richard.