Re: [PATCH v6 2/2] refs.c: SSE4.2 optimizations for check_refname_component

From: Duy Nguyen <pclouds@gmail.com>
Date: Jun 4, 2014, 11:21 UTC
Message-ID: <CACsJy8CK3LNaPVNv=EfFX06uOgpujAz364ZDFL3HBPicDNF57w@mail.gmail.com>
In-Reply-To: <538ED2F1.9030003@web.de>

On Wed, Jun 4, 2014 at 3:04 PM, Torsten Bögershausen <tboegi@web.de> wrote:

Show 23 quoted lines

>
> On 2014-06-04 05.38, David Turner wrote:
> []
>> []
>> diff --git a/Makefile b/Makefile
>> index a53f3a8..dd2127a 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -1326,6 +1326,11 @@ else
>>               COMPAT_OBJS += compat/win32mmap.o
>>       endif
>>  endif
>> +ifdef NO_SSE42
>> +     BASIC_CFLAGS += -DNO_SSE42
>> +else
>> +     BASIC_CFLAGS += -msse4.2
>> +endif
> This does work for some people, but break for others, like the systems in my test-lab.
> On 2 different systems the gcc has support for -msse4.2, but the processor has not,
> and t5511 fails with "Illegal instruction".
> How can that be?
> The maintainer of a Linux distro wants to ship gcc with all possible features,
> an the end-user can compile the code with all the features his very processor has.

I think glibc code uses cpuid instruction to decide whether to use optimized version. May be we can do the same? If we go that route and have a way to detect sse support from compiler, then we can drop NO_SSE42, enable all and pick one at runtime.

-- 
Duy