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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 17:32:40 -0800
User-agent: Gnus/5.1008 (Gnus v5.10.8) Emacs/21.4 (gnu/linux)

Robert Dewar <address@hidden> writes:

> We have not seen ONE imaginary example, let
> alone a real example, where the optimziation of loop invariants
> (by far the most important optimization in the class we are
> discussing) would break existing code.

But didn't this thread get started by a real program that was broken
by an optimization of loop invariants?  Certainly I got a real bug
report of a real problem, which you can see here:

Here is a bit more discussion:

If this doesn't count as "optimization of loop invariants"
then what would count?

This particular example was just a test program run by "configure", so
the penalty for getting it wrong wasn't that severe -- the application
compiled its own version of mktime rather than using the system
mktime.  But I daresay I can find an example of real-world production
code that does something similar.

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