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Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

From: Paul Eggert
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: Sun, 31 Dec 2006 10:47:27 -0800
User-agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.4 (gnu/linux)

"Daniel Berlin" <address@hidden> writes:

> These are not performance needing applications.

No, I chose gzip -9 and sha512sum precisely because they are
CPU-bound (integer arithmetic only).  On my platform, if the
input file is cached sha512sum is approximately 300 times
slower than 'cat', and gzip -9 is approximately 1000 times

> The burden ought to be (and IMHO is) on those who propose we change
> optimizer behavior in order to support something non-standard.

Please, let's move beyond this "non-standard" rhetoric.
There's nothing weird or unusual about assuming wrapv
semantics.  As we've seen it is common practice dating back
to Unix source code in the 1970s, and (if you want to be
pedantic) C99 Annex H with LIA-1 wrapping semantics gives a
standard for it.

The question is not whether GCC should support wrapv
semantics; it already does, if you specify -fwrapv.
The question is merely whether wrapv should be the default
with optimization levels -O0 through -O2.

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