Wireshark-dev: Re: [Wireshark-dev] How to define HAVE_SSE42 with autotools?
From: Anders Broman <[email protected]>
Date: Wed, 11 Jun 2014 07:22:30 +0000
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Jakub Zawadzki
Sent: den 10 juni 2014 23:55
To: Developer support list for Wireshark
Subject: Re: [Wireshark-dev] How to define HAVE_SSE42 with autotools?

Hello,

On Tue, Jun 10, 2014 at 05:06:24PM +0000, Anders Broman wrote:
>> >From: [email protected] 
>> >[mailto:[email protected]] On Behalf Of Guy Harris
>> >
>> >HAVE_SSE42 is used in two places:
>> >
>> >	1) wsutil/ws_mempbrk_sse42.c, where it controls whether to build 
>> >that file at all;
>> >
>> >	2) wsutil/ws_mempbrk.c, where it controls whether to check whether the CPU has SSE 4.2 and, if it does, call the SSE 4.2 version of the code.
>> >
>> >So what HAVE_SSE42 really seems to mean is "does the compiler support the intrinsics used in wsutil/ws_mempbrk_sse42.c?"
>> >
>> >Should we, instead, check for compiler support for those intrinsics?
>> 
>> Yes I guess...
>> 
>> >And will the compiler generate code for those intrinsics, using the SSE 4.2 instructions, even if you haven't told it, with a command-line option, to generate SSE 4.2 code in general?  Or does the >>compiler not do a good job of supporting choosing whether to use SSE 4.2 instructions at run time rather than at compile time?
>> 
>> I have recently added some macros I found that define HAVE_SSE4_2 so at least the stuff compiles now on all the buildbots(I think).
>> 
>> I'm not sure if there should be a command line option or not. But ideally we should compile ws_mempbrk_sse42.c if the compiler supports it and check cpu_info() at runtime to use it or not.
>
>
>What about using simple standard AC_TRY_COMPILE( )?
>
>something like:
>
>#v+
>
>AC_MSG_CHECKING([whether the compiler support -msse4.2 and if there is nmmintrin.h header])
>
>save_CFLAGS="$CFLAGS"
>CFLAGS="$CFLAGS -msse4.2"
>
>AC_TRY_COMPILE(
>[#include <nmmintrin.h>],
>[return 0;],
>[
>	ac_cv_wireshark_have_sse42=yes
>	AC_DEFINE(HAVE_SSE42,,[Support SSSE4.2 (Streaming SIMD Extensions 4.2) instructions])
>	AC_MSG_RESULT([yes])
>],
>[
>	ac_cv_wireshark_have_sse42=no
>	AC_MSG_RESULT([no])
>])
>
>dnl build libwsutil_sse42 only if there is SSE4.2 AM_CONDITIONAL(SSE42_SUPPORTED, test "x$ac_cv_wireshark_have_sse42" = "xno")
>
>CFLAGS="$save_CFLAGS"
>
>#v-
>
>+ uncommented if SSE42_SUPPORTED in wsutil/Makefile.am
>
>Anders it's ok for you?

Sure, perhaps the macro (ax_check_compile_flag) I imported can be used?

>I like idea to force (don't do runtime detection) SSE4.2 if -msse4.2 is supported & host CPU support can do sse4.2, but I think it's not worth troubles :)
>
>
>With Regards,
>Jakub.

Regards
Anders

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