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Re: GCC optimizes integer overflow: bug or feature?
From: |
Andrew Pinski |
Subject: |
Re: GCC optimizes integer overflow: bug or feature? |
Date: |
Tue, 19 Dec 2006 21:28:16 -0500 (EST) |
>
> Paul Brook wrote:
> >> 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.
>
> Now that's a bit TOO strong a statement, critical optimizations like
> register allocation and instruction scheduling will generally not change
> the behavior of the program (though the basic decision to put something
> in a register will, and *surely* no one suggests avoiding this critical
> optimization).
Actually they will with multi threaded program, since you can have a case
where it works and now it is broken because one thread has speed up so much it
writes to a variable which had a copy on another thread's stack. So the
argument
about it being too strong is wrong because timming matters now a days.
Instruction
scheduling can cause the same issue as it forces a write too early for another
thread
to act on.
Thanks,
Andrew Pinski
- Re: GCC optimizes integer overflow: bug or feature?, (continued)
- 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, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/19
- Re: GCC optimizes integer overflow: bug or feature?,
Andrew Pinski <=
- 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
- Re: GCC optimizes integer overflow: bug or feature?, Matthew Woehlke, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Seongbae Park, 2006/12/20