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

Bruce Evans brde at
Wed Aug 22 03:00:08 PDT 2007

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

From: Bruce Evans <brde at>
To: Simun Mikecin <numisemis at>
Cc: Bruce Evans <brde at>, bug-followup at
Subject: Re: amd64/115581: [patch] -mfancy-math-387 has no effect
Date: Wed, 22 Aug 2007 19:50:17 +1000 (EST)

 On Tue, 21 Aug 2007, Simun Mikecin wrote:
 > --- 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).
 Maybe someday.  The easy cases have already been looked at and resulted in
 removing the asm implementations of functions like sinf() and asin().

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