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

From: Bernd Schmidt
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: Sun, 31 Dec 2006 20:08:35 +0100
User-agent: Thunderbird (X11/20061229)

Paul Eggert wrote:
But so far, benchmark scores are the only scores given by the people
who oppose having -O2 imply -fwrapv.

And you expect real-world results will be different because...?

You say you doubt it affects performance.  Based on what?  Facts
please, not guesses and hand-waiving...

The burden of proof ought to be on the guys proposing -O2
optimizations that break longstanding code, not on the skeptics.

IMHO the burden of proof should be on the people who are surprised that interesting things happen when they write in a language that isn't C and then try to pass it through a C compiler.

Has an example of code that actually breaks with a new gcc but not an old one been posted in this thread yet? With -fstrict-aliasing we at least had examples of code that really broke with a new optimization before we disabled it (in the compiler, not in autoconf, mind you). Code got fixed, -fstrict-aliasing got enabled a release later, everyone moved on.


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