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

[Erik Faye-Lund]

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?