[Mesa-dev] [PATCH 1/2] configure.ac: roll up a program for the sse4.1 check

[Emil Velikov]

On 17/11/14 14:44, Erik Faye-Lund wrote:
> On Sat, Nov 15, 2014 at 7:18 PM, Matt Turner <mattst88 at gmail.com> wrote:
>> On Sat, Nov 15, 2014 at 10:13 AM, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>>> On Sat, Nov 15, 2014 at 12:04 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>>>> So when checking/building sse code we have three possibilities:
>>>>  1 Old compiler, throws an error when using -msse*
>>>>  2 New compiler, user disables sse* (-mno-sse*)
>>>>  3 New compiler, user doesn't disable sse
>>>>
>>>> The original code, added code for #1 but not #2. Later on we patched
>>>> around the lack of handling #2 by wrapping the code in __SSE4_1__.
>>>> Yet it lead to a missing/undefined symbol in case of #1 or #2, which
>>>> might cause an issue for #2 when using the i965 driver.
>>>>
>>>> A bit later we "fixed" the undefined symbol by using #1, rather than
>>>> updating it to handle #2. With this commit we set things straight :)
>>>>
>>>> To top it all up, conventions state that in case of conflicting
>>>> (-enable-foo -disable-foo) options, the latter one takes precedence.
>>>> Thus we need to make sure to prepend -msse4.1 to CFLAGS in our test.
>>>>
>>>> Cc: Siavash Eliasi <siavashserver at gmail.com>
>>>> Cc: Matt Turner <mattst88 at gmail.com>
>>>> Signed-off-by: Emil Velikov <emil.l.velikov at gmail.com>
>>>> ---
>>>>
>>>> Man this thing is _very_ messy.
>>>> Matt from the last hunk it seems that pixman might need fixing. Should
>>>> be bother with that, or let people have fun when they hit it :P
>>>>
>>>> -Emil
>>>>
>>>>  configure.ac | 14 +++++++++++++-
>>>>  1 file changed, 13 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/configure.ac b/configure.ac
>>>> index 91e111b..9d1835e 100644
>>>> --- a/configure.ac
>>>> +++ b/configure.ac
>>>> @@ -252,7 +252,19 @@ AC_SUBST([VISIBILITY_CXXFLAGS])
>>>>  dnl
>>>>  dnl Optional flags, check for compiler support
>>>>  dnl
>>>> -AX_CHECK_COMPILE_FLAG([-msse4.1], [SSE41_SUPPORTED=1], [SSE41_SUPPORTED=0])
>>>> +save_CFLAGS="$CFLAGS"
>>>> +CFLAGS="-msse4.1 $CFLAGS"
>>>> +AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>>>> +#include <mmintrin.h>
>>>> +#include <xmmintrin.h>
>>>> +#include <emmintrin.h>
>>>> +#include <smmintrin.h>
>>>> +int main () {
>>>> +    __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>>>> +    c = _mm_max_epu32(a, b);
>>>> +    return 0;
>>>
>>> This seems complicated.
>>>
>>> (a) Just #include <immintrin.h>
>>> (b) Is any of this even necessary? how about
>>>
>>> int main() { return !__SSE_4_1__; }
>>
>> Checking that you can actually using the intrinsics seens like a good
>> plan. Pixman's configure.ac has been doing that for a long time. I'd
>> rather copy that. It's not like we'd save much by not doing it.
> 
> ...But then we cannot cross-compile with run-time SSE 4.1 support from
> a machine without SSE 4.1 support, no?
> 
Autohell should be smart enough to use the correct (cross-compilation)
tool-chain while building that code. Must admit that I have not checked
if that is truly the case.

-Emil