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

From: Gabriel Dos Reis
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: 31 Dec 2006 18:23:23 +0100

Robert Dewar <address@hidden> writes:

| Gerald Pfeifer wrote:
| > On Sun, 31 Dec 2006, Robert Dewar wrote:
| >> If you do it in signed expecting wrapping, then the optimization
| >> destroys your code. Yes, it is technically your fault, but this
| >> business of telling users
| >>
| >> "sorry, your code is non-standard, gcc won't handle it as you
| >> expect, go fix your code"
| > My understanding of previous messages in this thread was that other
| > compilers (like ICC) do enable the optimization we are talking about
| > here by default.
| Well that's not such a clear criterion. "the optimization" here is
| misleading, what we really have is a whole class of optimizations
| enabled by taking advantage of signed overflow being undefined.

We need more precise collection of data than "I've heard xxx does the
same optimization", because it is not clear when xxx does it and under
what conditions.  For example, Sun (which has been cited in this
thread) spends lot of resources on ensuring backward compability,
whether anachronistic or downright illegal codes[1] or existing
pratice even if not blessed by the standards, that I would like
to see more precise reports than hear-say. 

[1] at recent C++ committee meetings, Sun representative objected to the
new meaning of C++ keyword auto on the ground that they still supports
implicit "int", which has been banned from mode than a decade ago.

-- Gaby

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