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

From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
To: vincent+gcc at vinc17 dot org
Cc: autoconf-patches at gnu dot org, bug-gnulib at gnu dot org, dewar at adacore dot com, eggert at cs dot ucla dot edu, gcc at gcc dot gnu dot org
Date: Sun, 31 Dec 2006 10:08:32 EST
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
References: <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> <10612310029.AA28910@vlsi1.ultra.nyu.edu> <45970486.9090606@adacore.com> <20061231112419.GR32297@ay.vinc17.org> <10612311403.AA19198@vlsi1.ultra.nyu.edu> <20061231143915.GV32297@ay.vinc17.org>

> Well, that's not equivalent. For instance, MPFR has many conditions
> that evaluate to TRUE or FALSE on some/many implementations (mainly
> because the type sizes depend on the implementation), even without
> the assumption that an overflow cannot occur.

Can you give an example of such a condition and show how an optimization that
assumed overflows were undefined could break that code?

Follow-Ups:
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Vincent Lefevre

References:
- 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: Richard Kenner
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Robert Dewar
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Vincent Lefevre
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Richard Kenner
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
  - From: Vincent Lefevre

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