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

From: Robert Dewar
Subject: Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
Date: Tue, 02 Jan 2007 10:37:07 -0500
User-agent: Thunderbird (Windows/20061207)

Richard Guenther wrote:
On 1/2/07, Richard Kenner <address@hidden> wrote:
We do that with -fstrict-aliasing, which also changes language semantics.
Well, yes, but not quite in the same way.  Indeed it's rather hard to
describe in what way it changes the language semantics but easier to
describe the effect it has on optimization.  I think -fwrapv is the other
way around.

Well, while the effect of -fstrict-aliasing is hard to describe (TBAA
_is_ a complex
part of the standard), -fno-strict-aliasing rules are simple.  All
loads and stores
alias each other if they cannot be proven not to alias by points-to analysis.

That's an implementation oriented analysis, and indeed it is easy
to say at the implementation level what this means. What is not
easy is to describe the formal semantics of the resulting language
at the level of the standard.


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