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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:
http://lists.gnu.org/archive/html/bug-gnulib/2006-12/msg00084.html
Here is a bit more discussion:
http://gcc.gnu.org/ml/gcc/2006-12/msg00607.html
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.
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", (continued)
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Guenther, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Ian Lance Taylor, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Ian Lance Taylor, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- RE: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Dave Korn, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Karl Berry, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Bruce Korb, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Robert Dewar, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...",
Paul Eggert <=
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Ian Lance Taylor, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Daniel Berlin, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Bruce Korb, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Bernd Schmidt, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Gabriel Dos Reis, 2006/12/31
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Joe Buck, 2006/12/30
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2006/12/30
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Joe Buck, 2006/12/31