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Reply-To: tprince@computer.org
Subject: Re: Cygwin 32bit: Can't use gcc -mfpmath=sse
References: <op.x4rlk1hl6wtfvl@orion> <1999691441959416@web12o.yandex.ru> <op.x4srsuxx6wtfvl@orion>
To: cygwin@cygwin.com
From: Tim Prince <n8tm@aol.com>
Message-ID: <55F2D9B7.5030209@aol.com>
Date: Fri, 11 Sep 2015 09:40:07 -0400
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On 9/11/2015 8:03 AM, HK wrote:
> On Fri, 11 Sep 2015 10:16:56 +0200, Evgeny Grin <k2k@yandex.ru> wrote:
>
>> 10.09.2015, 23:52, "HK" <hk1020@t-online.de>:
>>> On Thu, 10 Sep 2015 13:19:04 +0200, V?clav_Haisman wrote:
>>>>  On 10 September 2015 at 01:30, HK wrote:
>>>>>  hello.c:1:0: warning: SSE instruction set disabled, using 387
>>>>>  arithmetics
>>>>
>>>>  Does it help to use `-march=native`? My hunch is that this is because
>>>>  the default CPU type is set to such that does not have SSE.
>>>
>>> Yep, that did the trick. Thanks for the suggestion. Now, is this a gcc
>>> build
>>> build problem? The 64bit version doesn't need -march=native and that
>>> is on
>>> the same computer.
>>
>> It's not a problem as by default GCC generate code compatible with
>> maximum number of CPU models.
>> If you need to generate an SSE instructions, you have to use at lest
>> -march=pentium3.
>> For x86-64 version, SSE is always enabled as all x86-64 CPUs support
>> SSE and SSE2.
>> See http://gcc.gnu.org/onlinedocs/gcc/x86-Options.html#x86-Options
>
> Thanks. While I don't quite agree with the choice of defaults it makes
> sense.
> So does my 32bit window next to the 64bit window on the same computer
> really
> have a different instruction set? Anyway, case closed.
Intel compilers made SSE2 the default even for 32-bit mode, subsequent
to all CPUs which supported 387 but not SSE3 going out of production. 
There's still a lot of interest in 387 mode, however. 
You might argue for making SSE3 the default, but it's generally
important nowadays to set an appropriate option for the target platforms.

-- 
Tim Prince


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