code review 6962043: cmd/dist, cmd/8g: implement GO386=387/sse to choose FPU...

cmd/dist, cmd/8g: implement GO386=387/sse to choose FPU flavour.

A new environment variable GO386 is introduced to choose between
code generation targeting 387 or SSE2. No auto-detection is
performed and the setting defaults to 387 to preserve previous
behaviour.

The patch is a reorganization of CL6549052 by rsc.

Fixes issue 3912.

[remyoudompheng, 2012-12-19 21:16:53]

Hello golang-dev@googlegroups.com (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[remyoudompheng, 2012-12-19 21:18:00]

The CL is a reorganization of http://codereview.appspot.com/6549052/

[minux1, 2012-12-19 21:57:14]

thank you. i will try to implement the auto detection part for cmd/dist.

[rsc, 2012-12-20 19:23:52]

i think you can get it from the cpuid w/ eax=1.

[rsc, 2012-12-22 22:19:46]

Can you create a global use_sse variable instead of the repeated strcmp calls?
It probably doesn't matter but still...

For detecting SSE2 I think this will work with msvc and gcc (msvc provides
__cpuid automatically):

#include <stdio.h>

#ifndef COMPILER_MSVC
static void
__cpuid(int dst[4], int ax)
{
	asm volatile("cpuid"
		: "=a" (dst[0]), "=b" (dst[1]), "=c" (dst[2]), "=d" (dst[3])
		: "a" (ax));
}
#endif

int
main(void)
{
	int info[4];
	
	__cpuid(info, 1);
	printf("%#x\n", info[3] & (1<<26));
	return 0;
}

https://codereview.appspot.com/6962043/diff/5002/src/cmd/8g/ggen.c
File src/cmd/8g/ggen.c (right):

https://codereview.appspot.com/6962043/diff/5002/src/cmd/8g/ggen.c#newcode868
src/cmd/8g/ggen.c:868: // floating-point.  387 (not SSE2) to interoperate with
8c
s/ to interoperate with 8c//
that was never true, just a misunderstanding on my part (sse2 and 387 coexist, i
was thinking of mmx).

[rsc, 2013-01-02 20:44:38]

ping...

[remyoudompheng, 2013-01-02 21:40:23]

Hello minux.ma@gmail.com, rsc@golang.org (cc: golang-dev@googlegroups.com),

Please take another look.

[rsc, 2013-01-02 21:52:04]

LGTM

I'd like to autodetect the default GO386 setting but we can do that in a
separate CL.

https://codereview.appspot.com/6962043/diff/5002/src/cmd/8g/ggen.c
File src/cmd/8g/ggen.c (right):

https://codereview.appspot.com/6962043/diff/5002/src/cmd/8g/ggen.c#newcode868
src/cmd/8g/ggen.c:868: // floating-point.  387 (not SSE2) to interoperate with
8c
On 2012/12/22 22:19:46, rsc wrote:
> s/ to interoperate with 8c//
> that was never true, just a misunderstanding on my part (sse2 and 387 coexist,
i
> was thinking of mmx).

still applies

[remyoudompheng, 2013-01-02 21:54:58]

https://codereview.appspot.com/6962043/diff/5002/src/cmd/8g/ggen.c
File src/cmd/8g/ggen.c (right):

https://codereview.appspot.com/6962043/diff/5002/src/cmd/8g/ggen.c#newcode868
src/cmd/8g/ggen.c:868: // floating-point.  387 (not SSE2) to interoperate with
8c
On 2013/01/02 21:52:04, rsc wrote:
> On 2012/12/22 22:19:46, rsc wrote:
> > s/ to interoperate with 8c//
> > that was never true, just a misunderstanding on my part (sse2 and 387
coexist,
> i
> > was thinking of mmx).
> 
> still applies

Done.

[remyoudompheng, 2013-01-02 21:56:01]

*** Submitted as https://code.google.com/p/go/source/detail?r=be005b410410 ***

cmd/dist, cmd/8g: implement GO386=387/sse to choose FPU flavour.

A new environment variable GO386 is introduced to choose between
code generation targeting 387 or SSE2. No auto-detection is
performed and the setting defaults to 387 to preserve previous
behaviour.

The patch is a reorganization of CL6549052 by rsc.

Fixes issue 3912.

R=minux.ma, rsc
CC=golang-dev
https://codereview.appspot.com/6962043

[rsc, 2013-01-02 22:08:09]

thanks. i started the autodetect in CL 7035055.