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Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."
From: |
Richard Kenner |
Subject: |
Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..." |
Date: |
Tue, 02 Jan 2007 10:43:05 EST |
> 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.
Yes, the rules are "simple", but are written in terms of OPTIMIZATIONS, not
of language concepts: you can't talk about "points-to-analysis" in a language
standard!
In other words, -fwrapv says that we are modifying the language semantics to
define signed overflows as wrapping and this will have effects on the
optimizer (so the language effect is primary), while -fno-strict-aliasing
says what the optimizer will do and hence how we're modifying the language
(meaning the optimizer effect is primary).
There's isn't that big a difference here, admittedly and I agree that it's
unfortunate that we do this for strict aliasing, but I doing it for -fwrapv
would be even worse for the above reason.
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", (continued)
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Guenther, 2007/01/02
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Guenther, 2007/01/02
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Robert Dewar, 2007/01/02
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2007/01/02
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Guenther, 2007/01/02
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Robert Dewar, 2007/01/02
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...",
Richard Kenner <=
Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Mark Mitchell, 2007/01/01
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Paul Eggert, 2007/01/01
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Daniel Berlin, 2007/01/01
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Mark Mitchell, 2007/01/01
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Paul Eggert, 2007/01/01
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Kenner, 2007/01/01
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Joe Buck, 2007/01/02
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Sandiford, 2007/01/04
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Guenther, 2007/01/04
- Re: changing "configure" to default to "gcc -g -O2 -fwrapv ...", Richard Sandiford, 2007/01/04