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Re: -O* Gives Different Results than Individual Optimizations?

From: Alexey Salmin <alexey dot salmin at gmail dot com>
To: Ian Lance Taylor <iant at google dot com>
Cc: Mike Sullivan <mbsullivan at gmail dot com>, gcc-help at gcc dot gnu dot org
Date: Mon, 12 Oct 2009 14:43:17 +0700
Subject: Re: -O* Gives Different Results than Individual Optimizations?
References: <ca8f01c20910112116l735427cak5a43aad31b8ee3fb@mail.gmail.com> <mcrpr8txemw.fsf@dhcp-172-17-9-151.mtv.corp.google.com>

On Mon, Oct 12, 2009 at 2:20 PM, Ian Lance Taylor <iant@google.com> wrote:
> Mike Sullivan <mbsullivan@gmail.com> writes:
>
>> A co-worker of mine is having some odd floating-point issues that are
>> related to the compilation options passed to GCC v4.3.3.
>
> There are many instability issues with gcc floating point when using
> the 80387 FP stack on x86. ?This is the classic bug report
> http://gcc.gnu.org/PR323 , which has finally been fixed for the
> upcoming gcc 4.5 by adding a new option -fexcess-precision=standard.
>
> If your processor is newer than a Pentium 3, then you can avoid the
> problem by using option such as -march=pentium4 -mtune=generic
> -mfpmath=sse.
>
> Ian
>

There was another interesting question in that mail: is "-O1" flag
something different from just combination of "-fsomething" flags?

Alexey

References:
- -O* Gives Different Results than Individual Optimizations?
  - From: Mike Sullivan
- Re: -O* Gives Different Results than Individual Optimizations?
  - From: Ian Lance Taylor

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