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Re: GCC optimizes integer overflow: bug or feature?
From: |
Paul Brook |
Subject: |
Re: GCC optimizes integer overflow: bug or feature? |
Date: |
Tue, 19 Dec 2006 21:46:38 +0000 |
User-agent: |
KMail/1.9.5 |
> Compiler can optimize it any way it wants,
> as long as result is the same as unoptimized one.
We have an option for that. It's called -O0.
Pretty much all optimization will change the behavior of your program. The
important distinction is whether that difference is observable in valid
programs. The whole point of langage standards is that they define what
constitutes a valid program.
By your definition all writes to vairables must translate into a write to
memory (for "correct" behavior in multithreaded applications and with signal
handlers). This implies all variables are effectively volatile.
You can argue that signed overflow is an extension that it's worth supporting
by default. Other people (eg. those interested in autovectorization) will
argue that it provides useful optimization opportunities. I don't know which
of these is better, but either what it's a lot different to saying "never
change the behavior of any program.
Paul
- Re: GCC optimizes integer overflow: bug or feature?, (continued)
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Florian Weimer, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Joseph S. Myers, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Florian Weimer, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Denis Vlasenko, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Andrew Haley, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Denis Vlasenko, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?,
Paul Brook <=
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Andrew Pinski, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- RE: GCC optimizes integer overflow: bug or feature?, Dave Korn, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?, Mike Stump, 2006/12/20
- RE: GCC optimizes integer overflow: bug or feature?, Dave Korn, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Matthew Woehlke, 2006/12/20
- RE: GCC optimizes integer overflow: bug or feature?, Dave Korn, 2006/12/20
- Message not available
- Re: GCC optimizes integer overflow: bug or feature?, Andreas Schwab, 2006/12/20