amd64/115581: [patch] -mfancy-math-387 has no effect

Simun Mikecin numisemis at
Tue Aug 21 08:10:08 PDT 2007

The following reply was made to PR amd64/115581; it has been noted by GNATS.

From: Simun Mikecin <numisemis at>
To: Bruce Evans <brde at>
Cc: bug-followup at
Subject: Re: amd64/115581: [patch] -mfancy-math-387 has no effect
Date: Tue, 21 Aug 2007 07:37:41 -0700 (PDT)

 --- Bruce Evans <brde at> wrote:
 > > This PR is about -mfancy-math-387 usage when compiling 32-bit compatibility 
 > > libraries that are gone be used on FreeBSD/amd64.
 > > As far as I can see FreeBSD's libm on i386 uses those fancy instructions (for 
 > > example /usr/src.current/lib/msun/i387/s_sin.S), so the same libm will be 
 > > used for running 32-bit apps on FreeBSD/amd64.
 > Well, that's in asm so it is not affected by compiler flags.  Compiler
 > flags can cause the library to be not used at all in some cases where
 > the library is better.
 I'm just wondering will it have a positive impact on performance if FreeBSD/i386 libm is changed
 not to use that asm code with fancy instructions (just like FreeBSD/amd64 does).
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