From: Paul Schlie <schlie@comcast.net>
To: Robert Dewar <dewar@adacore.com>
Cc: Matthew Woodcraft <mattheww@chiark.greenend.org.uk>, <gcc@gcc.gnu.org>
Subject: Re: Where does the C standard describe overflow of signed integers?
Date: Thu, 14 Jul 2005 19:28:00 -0000 [thread overview]
Message-ID: <BEFC351B.AD1A%schlie@comcast.net> (raw)
In-Reply-To: <42D6B970.1090903@adacore.com>
> From: Robert Dewar <dewar@adacore.com>
>> Paul Schlie wrote:
>>> What about optimising x*2/2 to x?
>>
>> Given that "C" requires the above be evaluated as (x*2)/2, as the language
>> specifies that the syntax defines the precedence of the operations, and that
>> no optimization should alter the behavior as specified by the program; I'd
>> say that unless it was known that the value range of x was between 0
>> and INT_MAX, the optimization is simply invalid.
>
> the optimization is indeed valid
>
> optimizations may most certainly alter behavior of undefined
> code. think about uninitialized local variables.
I don't contest that it may, I simply don't believe it should.
next prev parent reply other threads:[~2005-07-14 19:28 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-07-14 19:09 Paul Schlie
2005-07-14 19:13 ` Robert Dewar
2005-07-14 19:28 ` Paul Schlie [this message]
2005-07-14 19:33 ` Robert Dewar
2005-07-14 20:13 ` Paul Schlie
2005-07-15 13:20 ` Georg Bauhaus
2005-07-15 13:33 ` Georg Bauhaus
2005-07-15 14:31 ` Dave Korn
2005-07-16 12:04 ` Georg Bauhaus
2005-07-16 14:26 ` Paul Schlie
2005-07-15 15:03 ` Paul Schlie
2005-07-16 12:12 ` Georg Bauhaus
2005-07-14 20:35 ` Paul Koning
2005-07-14 21:58 ` Paul Schlie
2005-07-15 7:04 ` Avi Kivity
-- strict thread matches above, loose matches on Subject: below --
2005-07-14 1:10 Paul Schlie
2005-07-14 1:59 ` Robert Dewar
2005-07-14 5:28 ` Paul Schlie
2005-07-14 17:57 ` Matthew Woodcraft
2005-07-14 18:36 ` Paul Koning
2005-07-11 14:58 Nicholas Nethercote
2005-07-11 15:07 ` Dave Korn
2005-07-11 16:07 ` Nicholas Nethercote
2005-07-11 17:04 ` Dave Korn
2005-07-11 15:15 ` Nathan Sidwell
2005-07-11 15:23 ` Dave Korn
2005-07-12 23:13 ` Michael Meissner
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