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Re: What is acceptable for -ffast-math? (Was: associative law in combine)
- To: dewar at gnat dot com
- Subject: Re: What is acceptable for -ffast-math? (Was: associative law in combine)
- From: Tim Hollebeek <tim at hollebeek dot com>
- Date: Mon, 30 Jul 2001 10:08:54 -0400
- Cc: torvalds at transmeta dot com, gcc at gcc dot gnu dot org, moshier at moshier dot ne dot mediaone dot net, tprince at computer dot org
- References: <20010730130117.CB0DEF2B53@nile.gnat.com>
- Reply-To: tim at hollebeek dot com
On Mon, Jul 30, 2001 at 09:01:17AM -0400, dewar@gnat.com wrote:
> It certainly would be interesting to hear from someone with extensive
> experience in writing numerical codes supporting Linus' position (I have
> that extensive experience, but for sure I do not support the position that
> a compiler should by default do completely different things from what it
> is told.
His position is even worse: the compiler should abandon well specified
semantics in favor of less predictable ones (where what result you get
depends on which optimizations were applied).
When people suggest similar things regarding inlining and assembly
fragments, which certainly are understood by far less than 1% of the
users, Linus flames the list for breaking his code which depends on
very subtle aspects of the behavior of those features.
So hopefully he'll reverse his position, and take a position
consistent with his previous positions: optimization should not
transform working code into code that produces different results,
no matter how fast it does so.
-Tim