Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Jonathan Gray]

On Sat, Dec 12, 2015 at 06:41:56PM +, Emil Velikov wrote:
> On 10 December 2015 at 08:42, Oded Gabbay  wrote:
> > On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner  wrote:
> >> On Tue, Dec 8, 2015 at 9:37 PM, Jonathan Gray  wrote:
> >>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
> >>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
> >>> still get optimised out but now there is at least one SSE4.1 instruction
> >>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
> >>> got optimised out the configure test would incorrectly pass when the
> >>> compiler supported the intrinsics and the assembler didn't support the
> >>> instructions.
> >>>
> >>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
> >>> Signed-off-by: Jonathan Gray 
> >>> Cc: "11.0 11.1" 
> >>> ---
> >>>  configure.ac | 2 +-
> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
> >>>
> >>> diff --git a/configure.ac b/configure.ac
> >>> index 260934d..1d82e47 100644
> >>> --- a/configure.ac
> >>> +++ b/configure.ac
> >>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS"
> >>>  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
> >>>  #include 
> >>>  int main () {
> >>> -__m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
> >>> +volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
> >>>  c = _mm_max_epu32(a, b);
> >>>  return 0;
> >>
> >> I would have extracted an int from the result of _mm_max_epu32 and
> >> returned that instead of 0.
> >
> > Instead of the volatile I assume ?
> >
> Precisely. If anyone wants to follow on Matt's suggestion we can pick
> that one as well. I'd like to get a patch for the next stable releases
> (next Friday for 11.0.x and just after new year for 11.1.1) so I'll
> take whatever's around :-)
> 
> -Emil

I avoided that as I wasn't sure if there was a case where autoconf
cared about the return code.  If someone wants to create a new diff
feel free, I have limited connectivity till the middle of next week.
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Oded Gabbay]

On Sun, Dec 13, 2015 at 11:56 AM, Jonathan Gray  wrote:
> On Sat, Dec 12, 2015 at 06:41:56PM +, Emil Velikov wrote:
>> On 10 December 2015 at 08:42, Oded Gabbay  wrote:
>> > On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner  wrote:
>> >> On Tue, Dec 8, 2015 at 9:37 PM, Jonathan Gray  wrote:
>> >>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>> >>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>> >>> still get optimised out but now there is at least one SSE4.1 instruction
>> >>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>> >>> got optimised out the configure test would incorrectly pass when the
>> >>> compiler supported the intrinsics and the assembler didn't support the
>> >>> instructions.
>> >>>
>> >>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>> >>> Signed-off-by: Jonathan Gray 
>> >>> Cc: "11.0 11.1" 
>> >>> ---
>> >>>  configure.ac | 2 +-
>> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> >>>
>> >>> diff --git a/configure.ac b/configure.ac
>> >>> index 260934d..1d82e47 100644
>> >>> --- a/configure.ac
>> >>> +++ b/configure.ac
>> >>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS"
>> >>>  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>> >>>  #include 
>> >>>  int main () {
>> >>> -__m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>> >>> +volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>> >>>  c = _mm_max_epu32(a, b);
>> >>>  return 0;
>> >>
>> >> I would have extracted an int from the result of _mm_max_epu32 and
>> >> returned that instead of 0.
>> >
>> > Instead of the volatile I assume ?
>> >
>> Precisely. If anyone wants to follow on Matt's suggestion we can pick
>> that one as well. I'd like to get a patch for the next stable releases
>> (next Friday for 11.0.x and just after new year for 11.1.1) so I'll
>> take whatever's around :-)
>>
>> -Emil
>
> I avoided that as I wasn't sure if there was a case where autoconf
> cared about the return code.  If someone wants to create a new diff
> feel free, I have limited connectivity till the middle of next week.

So I'm not a huge SSE expert, but I tried doing this (remove volatile
and return _mm_cvtsi128_si32 of c):


#include 
#include 
#include 

int main () {
__m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
c = _mm_xor_si128 (a, b);
return _mm_cvtsi128_si32(c);
}
-

When compiling with "gcc -O1 -msse2", gcc is 4.8.5 (from RHEL 7.2), I got:

-
main:
.LFB521:
.cfi_startproc
movl $0, %eax
ret
.cfi_endproc
---

So unless I misunderstood matt's suggestion, I think we *have* to use
the volatile as it forces the compiler to produce pxor and movdqa
assembly commands.

   Oded
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Matt Turner]

On Sun, Dec 13, 2015 at 5:23 AM, Oded Gabbay  wrote:
> On Sun, Dec 13, 2015 at 11:56 AM, Jonathan Gray  wrote:
>> On Sat, Dec 12, 2015 at 06:41:56PM +, Emil Velikov wrote:
>>> On 10 December 2015 at 08:42, Oded Gabbay  wrote:
>>> > On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner  wrote:
>>> >> On Tue, Dec 8, 2015 at 9:37 PM, Jonathan Gray  wrote:
>>> >>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>>> >>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>>> >>> still get optimised out but now there is at least one SSE4.1 instruction
>>> >>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>>> >>> got optimised out the configure test would incorrectly pass when the
>>> >>> compiler supported the intrinsics and the assembler didn't support the
>>> >>> instructions.
>>> >>>
>>> >>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>>> >>> Signed-off-by: Jonathan Gray 
>>> >>> Cc: "11.0 11.1" 
>>> >>> ---
>>> >>>  configure.ac | 2 +-
>>> >>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>> >>>
>>> >>> diff --git a/configure.ac b/configure.ac
>>> >>> index 260934d..1d82e47 100644
>>> >>> --- a/configure.ac
>>> >>> +++ b/configure.ac
>>> >>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS"
>>> >>>  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>>> >>>  #include 
>>> >>>  int main () {
>>> >>> -__m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>>> >>> +volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>>> >>>  c = _mm_max_epu32(a, b);
>>> >>>  return 0;
>>> >>
>>> >> I would have extracted an int from the result of _mm_max_epu32 and
>>> >> returned that instead of 0.
>>> >
>>> > Instead of the volatile I assume ?
>>> >
>>> Precisely. If anyone wants to follow on Matt's suggestion we can pick
>>> that one as well. I'd like to get a patch for the next stable releases
>>> (next Friday for 11.0.x and just after new year for 11.1.1) so I'll
>>> take whatever's around :-)
>>>
>>> -Emil
>>
>> I avoided that as I wasn't sure if there was a case where autoconf
>> cared about the return code.  If someone wants to create a new diff
>> feel free, I have limited connectivity till the middle of next week.
>
> So I'm not a huge SSE expert, but I tried doing this (remove volatile
> and return _mm_cvtsi128_si32 of c):
>
> 
> #include 
> #include 
> #include 
>
> int main () {
> __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
> c = _mm_xor_si128 (a, b);
> return _mm_cvtsi128_si32(c);
> }
> -
>
> When compiling with "gcc -O1 -msse2", gcc is 4.8.5 (from RHEL 7.2), I got:
>
> -
> main:
> .LFB521:
> .cfi_startproc
> movl $0, %eax
> ret
> .cfi_endproc
> ---
>
> So unless I misunderstood matt's suggestion, I think we *have* to use
> the volatile as it forces the compiler to produce pxor and movdqa
> assembly commands.

Since all the arguments to the intrinsics are constants, GCC is
constant-evaluating them.

I expect all you'd need to do is pass some global variables to the
intrinsics or similar.
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Oded Gabbay]

On Sun, Dec 13, 2015 at 10:34 PM, Matt Turner  wrote:
> On Sun, Dec 13, 2015 at 5:23 AM, Oded Gabbay  wrote:
>> On Sun, Dec 13, 2015 at 11:56 AM, Jonathan Gray  wrote:
>>> On Sat, Dec 12, 2015 at 06:41:56PM +, Emil Velikov wrote:
 On 10 December 2015 at 08:42, Oded Gabbay  wrote:
 > On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner  wrote:
 >> On Tue, Dec 8, 2015 at 9:37 PM, Jonathan Gray  wrote:
 >>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
 >>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
 >>> still get optimised out but now there is at least one SSE4.1 
 >>> instruction
 >>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 
 >>> instructions
 >>> got optimised out the configure test would incorrectly pass when the
 >>> compiler supported the intrinsics and the assembler didn't support the
 >>> instructions.
 >>>
 >>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
 >>> Signed-off-by: Jonathan Gray 
 >>> Cc: "11.0 11.1" 
 >>> ---
 >>>  configure.ac | 2 +-
 >>>  1 file changed, 1 insertion(+), 1 deletion(-)
 >>>
 >>> diff --git a/configure.ac b/configure.ac
 >>> index 260934d..1d82e47 100644
 >>> --- a/configure.ac
 >>> +++ b/configure.ac
 >>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS"
 >>>  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 >>>  #include 
 >>>  int main () {
 >>> -__m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
 >>> +volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), 
 >>> c;
 >>>  c = _mm_max_epu32(a, b);
 >>>  return 0;
 >>
 >> I would have extracted an int from the result of _mm_max_epu32 and
 >> returned that instead of 0.
 >
 > Instead of the volatile I assume ?
 >
 Precisely. If anyone wants to follow on Matt's suggestion we can pick
 that one as well. I'd like to get a patch for the next stable releases
 (next Friday for 11.0.x and just after new year for 11.1.1) so I'll
 take whatever's around :-)

 -Emil
>>>
>>> I avoided that as I wasn't sure if there was a case where autoconf
>>> cared about the return code.  If someone wants to create a new diff
>>> feel free, I have limited connectivity till the middle of next week.
>>
>> So I'm not a huge SSE expert, but I tried doing this (remove volatile
>> and return _mm_cvtsi128_si32 of c):
>>
>> 
>> #include 
>> #include 
>> #include 
>>
>> int main () {
>> __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>> c = _mm_xor_si128 (a, b);
>> return _mm_cvtsi128_si32(c);
>> }
>> -
>>
>> When compiling with "gcc -O1 -msse2", gcc is 4.8.5 (from RHEL 7.2), I got:
>>
>> -
>> main:
>> .LFB521:
>> .cfi_startproc
>> movl $0, %eax
>> ret
>> .cfi_endproc
>> ---
>>
>> So unless I misunderstood matt's suggestion, I think we *have* to use
>> the volatile as it forces the compiler to produce pxor and movdqa
>> assembly commands.
>
> Since all the arguments to the intrinsics are constants, GCC is
> constant-evaluating them.
>
> I expect all you'd need to do is pass some global variables to the
> intrinsics or similar.

ok, so what helped was this:

int param;

int main () {
__m128i a = _mm_set1_epi32 (param), b = _mm_set1_epi32 (param+1), c;

Notice the (param+1) - if using just (param), the compiler will
optimize it. And it is quite understandable, as xoring a value with
itself gives 0.

Oded
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Emil Velikov]

On 10 December 2015 at 08:42, Oded Gabbay  wrote:
> On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner  wrote:
>> On Tue, Dec 8, 2015 at 9:37 PM, Jonathan Gray  wrote:
>>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>>> still get optimised out but now there is at least one SSE4.1 instruction
>>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>>> got optimised out the configure test would incorrectly pass when the
>>> compiler supported the intrinsics and the assembler didn't support the
>>> instructions.
>>>
>>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>>> Signed-off-by: Jonathan Gray 
>>> Cc: "11.0 11.1" 
>>> ---
>>>  configure.ac | 2 +-
>>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/configure.ac b/configure.ac
>>> index 260934d..1d82e47 100644
>>> --- a/configure.ac
>>> +++ b/configure.ac
>>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS"
>>>  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>>>  #include 
>>>  int main () {
>>> -__m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>>> +volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>>>  c = _mm_max_epu32(a, b);
>>>  return 0;
>>
>> I would have extracted an int from the result of _mm_max_epu32 and
>> returned that instead of 0.
>
> Instead of the volatile I assume ?
>
Precisely. If anyone wants to follow on Matt's suggestion we can pick
that one as well. I'd like to get a patch for the next stable releases
(next Friday for 11.0.x and just after new year for 11.1.1) so I'll
take whatever's around :-)

-Emil
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Oded Gabbay]

On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner  wrote:
> On Tue, Dec 8, 2015 at 9:37 PM, Jonathan Gray  wrote:
>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>> still get optimised out but now there is at least one SSE4.1 instruction
>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>> got optimised out the configure test would incorrectly pass when the
>> compiler supported the intrinsics and the assembler didn't support the
>> instructions.
>>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>> Signed-off-by: Jonathan Gray 
>> Cc: "11.0 11.1" 
>> ---
>>  configure.ac | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/configure.ac b/configure.ac
>> index 260934d..1d82e47 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS"
>>  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>>  #include 
>>  int main () {
>> -__m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>> +volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>>  c = _mm_max_epu32(a, b);
>>  return 0;
>
> I would have extracted an int from the result of _mm_max_epu32 and
> returned that instead of 0.

Instead of the volatile I assume ?

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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Oded Gabbay]

On Wed, Dec 9, 2015 at 1:09 PM, Emil Velikov  wrote:
> On 9 December 2015 at 05:37, Jonathan Gray  wrote:
>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>> still get optimised out but now there is at least one SSE4.1 instruction
>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>> got optimised out the configure test would incorrectly pass when the
>> compiler supported the intrinsics and the assembler didn't support the
>> instructions.
>>
> Must admit that I was not expecting that one. Looks like pixman (the
> inspiration for this check) is missing volatile as well. Does that one
> build/run fine on OpenBSD ?
>
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>> Signed-off-by: Jonathan Gray 
>> Cc: "11.0 11.1" 
> Reviewed-by: Emil Velikov 
>
> I'll pick this in a couple of days (barring any objections).
>
> Thanks
> Emil

Adding pixman ML.
I must admit ignorance on this one.
I looked at configure.ac of pixman and I don't see any SSE4.1
reference, and AFAIK, we don't use those instructions (only SSE2 and
SSSE3).
Is the above patch relevant for those as well ? because the tests in
configure.ac does *not* contain volatile.

Oded
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Oded Gabbay]

On Wed, Dec 9, 2015 at 2:34 PM, Jonathan Gray  wrote:
> On Wed, Dec 09, 2015 at 01:39:30PM +0200, Oded Gabbay wrote:
>> On Wed, Dec 9, 2015 at 1:09 PM, Emil Velikov  
>> wrote:
>> > On 9 December 2015 at 05:37, Jonathan Gray  wrote:
>> >> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>> >> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>> >> still get optimised out but now there is at least one SSE4.1 instruction
>> >> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>> >> got optimised out the configure test would incorrectly pass when the
>> >> compiler supported the intrinsics and the assembler didn't support the
>> >> instructions.
>> >>
>> > Must admit that I was not expecting that one. Looks like pixman (the
>> > inspiration for this check) is missing volatile as well. Does that one
>> > build/run fine on OpenBSD ?
>> >
>> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>> >> Signed-off-by: Jonathan Gray 
>> >> Cc: "11.0 11.1" 
>> > Reviewed-by: Emil Velikov 
>> >
>> > I'll pick this in a couple of days (barring any objections).
>> >
>> > Thanks
>> > Emil
>>
>> Adding pixman ML.
>> I must admit ignorance on this one.
>> I looked at configure.ac of pixman and I don't see any SSE4.1
>> reference, and AFAIK, we don't use those instructions (only SSE2 and
>> SSSE3).
>> Is the above patch relevant for those as well ? because the tests in
>> configure.ac does *not* contain volatile.
>>
>> Oded
>
> It looks like this is indeed a problem in pixman as well with at least
> gcc 4.2 and 4.9.  Running the pixman sse2 test on amd64 I only
> see xmm register use and movdqa in the generated assembly with -O0.
>
> The pixman configure tests passes on OpenBSD but the toolchain
> recognises sse2 instructions just not sse 4.1.
>
> Introducing volatile to the pixman test stops the xmm/movdqa
> use from being optimised out.

I adapted the patch to pixman's configure.ac and sent it to the ML.
Jonathan, thanks for the patch.

Oded
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Jonathan Gray]

On Wed, Dec 09, 2015 at 01:39:30PM +0200, Oded Gabbay wrote:
> On Wed, Dec 9, 2015 at 1:09 PM, Emil Velikov  wrote:
> > On 9 December 2015 at 05:37, Jonathan Gray  wrote:
> >> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
> >> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
> >> still get optimised out but now there is at least one SSE4.1 instruction
> >> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
> >> got optimised out the configure test would incorrectly pass when the
> >> compiler supported the intrinsics and the assembler didn't support the
> >> instructions.
> >>
> > Must admit that I was not expecting that one. Looks like pixman (the
> > inspiration for this check) is missing volatile as well. Does that one
> > build/run fine on OpenBSD ?
> >
> >> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
> >> Signed-off-by: Jonathan Gray 
> >> Cc: "11.0 11.1" 
> > Reviewed-by: Emil Velikov 
> >
> > I'll pick this in a couple of days (barring any objections).
> >
> > Thanks
> > Emil
> 
> Adding pixman ML.
> I must admit ignorance on this one.
> I looked at configure.ac of pixman and I don't see any SSE4.1
> reference, and AFAIK, we don't use those instructions (only SSE2 and
> SSSE3).
> Is the above patch relevant for those as well ? because the tests in
> configure.ac does *not* contain volatile.
> 
> Oded

It looks like this is indeed a problem in pixman as well with at least
gcc 4.2 and 4.9.  Running the pixman sse2 test on amd64 I only
see xmm register use and movdqa in the generated assembly with -O0.

The pixman configure tests passes on OpenBSD but the toolchain
recognises sse2 instructions just not sse 4.1.

Introducing volatile to the pixman test stops the xmm/movdqa
use from being optimised out.
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Emil Velikov]

On 9 December 2015 at 05:37, Jonathan Gray  wrote:
> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
> still get optimised out but now there is at least one SSE4.1 instruction
> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
> got optimised out the configure test would incorrectly pass when the
> compiler supported the intrinsics and the assembler didn't support the
> instructions.
>
Must admit that I was not expecting that one. Looks like pixman (the
inspiration for this check) is missing volatile as well. Does that one
build/run fine on OpenBSD ?

> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
> Signed-off-by: Jonathan Gray 
> Cc: "11.0 11.1" 
Reviewed-by: Emil Velikov 

I'll pick this in a couple of days (barring any objections).

Thanks
Emil
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Re: [Mesa-dev] [Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Emil Velikov]

On 9 December 2015 at 11:39, Oded Gabbay  wrote:
> On Wed, Dec 9, 2015 at 1:09 PM, Emil Velikov  wrote:
>> On 9 December 2015 at 05:37, Jonathan Gray  wrote:
>>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>>> still get optimised out but now there is at least one SSE4.1 instruction
>>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>>> got optimised out the configure test would incorrectly pass when the
>>> compiler supported the intrinsics and the assembler didn't support the
>>> instructions.
>>>
>> Must admit that I was not expecting that one. Looks like pixman (the
>> inspiration for this check) is missing volatile as well. Does that one
>> build/run fine on OpenBSD ?
>>
>>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>>> Signed-off-by: Jonathan Gray 
>>> Cc: "11.0 11.1" 
>> Reviewed-by: Emil Velikov 
>>
>> I'll pick this in a couple of days (barring any objections).
>>
>> Thanks
>> Emil
>
> Adding pixman ML.
> I must admit ignorance on this one.
> I looked at configure.ac of pixman and I don't see any SSE4.1
> reference, and AFAIK, we don't use those instructions (only SSE2 and
> SSSE3).
> Is the above patch relevant for those as well ? because the tests in
> configure.ac does *not* contain volatile.
>
True, there is no SSE4.1 detection in pixman but the logic should
still holds. .Unless ... it is exclusive to SSE4.1, which I rather
doubt. Unfortunately there is no easy way to get older GCC on Arch
otherwise I would have tried it.

The full patch for reference http://patchwork.freedesktop.org/patch/67449/

-Emil
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