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Re: What is acceptable for -ffast-math? (Was: associative law incombine)
- To: Linus Torvalds <torvalds at transmeta dot com>
- Subject: Re: What is acceptable for -ffast-math? (Was: associative law incombine)
- From: Gabriel Dos_Reis <gdosreis at sophia dot inria dot fr>
- Date: Wed, 1 Aug 2001 19:45:18 +0200 (MEST)
- Cc: Gabriel Dos_Reis <Gabriel dot Dos_Reis at sophia dot inria dot fr>, Tim Hollebeek <tim at hollebeek dot com>, Theodore Papadopoulo <Theodore dot Papadopoulo at sophia dot inria dot fr>, Gabriel Dos Reis <gdr at codesourcery dot com>, <dewar at gnat dot com>, <amylaar at redhat dot com>, <aoliva at redhat dot com>, <gcc at gcc dot gnu dot org>, <moshier at moshier dot ne dot mediaone dot net>, <tprince at computer dot org>
- References: <15208.15111.761855.922613@perceval.inria.fr><Pine.LNX.4.33.0108011029190.20912-100000@penguin.transmeta.com>
| On Wed, 1 Aug 2001, Gabriel Dos_Reis wrote:
| >
| > | Now, show me a case where a/b/c -> a/(b*c) is significantly less accurate?
| >
| > On a 64-bit double processor just take
|
| Oooh.. Quoting me out-of-context.
You requested an example. I gave one.
Then for your the purpose of your rhetorics, you said
Let's confine this to x86 - it is the most common case by far, and hey,
especially when it comes to games etc I doubt it matters what HP-PA does,
for example. We can easily make the optimizations be enabled on a
per-architecture basis.
I gave a pretty much fair example to illustrate the point that the
transformation does affect the result on 64-bit double processors
example -- they are quite common.
Be honest and admit that you're getting to the point of requesting a
feature for a very specific target where you know the transformation
is safe. Which is pretty much different from the previous "it won't
matter" stance.
-- Gaby