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

From: Robert Dewar <dewar at adacore dot com>
To: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>
Cc: eggert at cs dot ucla dot edu, autoconf-patches at gnu dot org, bug-gnulib at gnu dot org, gcc at gcc dot gnu dot org
Date: Sun, 31 Dec 2006 08:56:33 -0500
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
References: <200612300047.kBU0lFwk014817@localhost.localdomain> <10612300508.AA08474@vlsi1.ultra.nyu.edu> <87psa1izpc.fsf@penguin.cs.ucla.edu> <45963E6D.5070203@t-online.de> <10612301301.AA14129@vlsi1.ultra.nyu.edu> <871wmht4ab.fsf@penguin.cs.ucla.edu> <10612302258.AA24598@vlsi1.ultra.nyu.edu> <87lkkosz1n.fsf@penguin.cs.ucla.edu> <45970416.80407@adacore.com> <8764bssikm.fsf@penguin.cs.ucla.edu> <571f6b510612310047r3b7ef9acl4a0ab082e88e17a3@mail.gmail.com> <87bqlkmm3r.fsf@penguin.cs.ucla.edu> <10612311350.AA18850@vlsi1.ultra.nyu.edu>

Richard Kenner wrote:

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


There's also a burden of proof that proposed optimizations will actually
"break longstanding code".  So far, all of the examples of code shown
that assumes wrapv semantics are such that it's nearly impossible to see
any useful optimization that would break it!


Also, there are bug reports filed, so we certainly DO have examples
of code breaking, and quite a few reports have discussed the need
to enable -fwrapv for specific code bases.

References:
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Andrew Pinski
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Richard Kenner
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Paul Eggert
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Bernd Schmidt
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Richard Kenner
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Paul Eggert
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Richard Kenner
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Paul Eggert
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Robert Dewar
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Paul Eggert
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Steven Bosscher
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Paul Eggert
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Richard Kenner

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