Re: [MLton-commit] r6887

[Matthew Fluet-3]

On Tue, 23 Sep 2008, Wesley Terpstra wrote:
> feround.c and IEEEReal.c carried duplicated fesetround code.
> The IEEEReal i386 version also works on x86_64.

This is not technically true, as it only sets the control word on the x87
unit and not on the SSE unit.  For amd64, we use the SSE instructions
exclusively for floating-point computation, so changing the x87 control
word has no effect.  See
   http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/libc/sysdeps/x86_64/fpu/fesetround.c?rev=1.2&cvsroot=glibc

I doubt that there is any amd64 platform that does not provide
fe{get,set}round in libm, so I don't think it is necesary to provide
assembly for amd64.


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[Matthew Fluet-3]

On Tue, 30 Sep 2008, Matthew Fluet wrote:

> On Tue, 23 Sep 2008, Wesley Terpstra wrote:
>>  feround.c and IEEEReal.c carried duplicated fesetround code.
>>  The IEEEReal i386 version also works on x86_64.
>
> This is not technically true, as it only sets the control word on the x87
> unit and not on the SSE unit.  For amd64, we use the SSE instructions
> exclusively for floating-point computation, so changing the x87 control word
> has no effect.  See
>   http://sources.redhat.com/cgi-bin/cvsweb.cgi/~checkout~/libc/sysdeps/x86_64/fpu/fesetround.c?rev=1.2&cvsroot=glibc
>
> I doubt that there is any amd64 platform that does not provide
> fe{get,set}round in libm, so I don't think it is necesary to provide assembly
> for amd64.

Hmm, I got confused looking at just the patch in the commit log.  I guess
the SSE control word changes were added some time ago.  And, looking at
that commit entry (r6693), it seems that MinGW on Win64 does not provide
(working) fe{get,set}round in libm.

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[Wesley W. Terpstra]

On Tue, Sep 30, 2008 at 11:17 PM, Matthew Fluet <fluet@...> wrote:
> On Tue, 23 Sep 2008, Wesley Terpstra wrote:
>> feround.c and IEEEReal.c carried duplicated fesetround code.
>> The IEEEReal i386 version also works on x86_64.
>
> This is not technically true, as it only sets the control word on the x87
> unit and not on the SSE unit.

An earlier commit by me added the SSE instructions to update the SSE
unit at the same time (check IEEEReal.c -- I added 64 bit assembly) as
the x87 unit. At the time I didn't realize there were two copies so
only updated the one. The commit you saw merged them and removed the
old version.

> For amd64, we use the SSE instructions exclusively for floating-point computation, so changing the x87 control word has no effect.
> I doubt that there is any amd64 platform that does not provide
> fe{get,set}round in libm, so I don't think it is necesary to provide
> assembly for amd64.

Not true. I added that code because it was needed on MinGW/win64. The
"libc" there also uses x87 ops, so we need to set both since MLton
native codegen uses the other. I assume it's supposed to affect
cos/sin/etc? At least it passes the regressions as it is now.

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