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RE: GCC optimizes integer overflow: bug or feature?
From: |
Dave Korn |
Subject: |
RE: GCC optimizes integer overflow: bug or feature? |
Date: |
Wed, 20 Dec 2006 02:53:24 -0000 |
On 20 December 2006 02:40, Mike Stump wrote:
> On Dec 19, 2006, at 6:33 PM, Dave Korn wrote:
>> On 20 December 2006 02:28, Andrew Pinski wrote:
>>
>>>> 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.
>>
>> Why isn't that just a buggy program with wilful disregard for the use of
>> correct synchronisation techniques?
>
> It is that, as well as a program that features a result that is
> different from unoptimized code.
Well, I for one wish to complain. All the empty for loops that I use for
precision timing have been getting faster and faster over the past few years.
It used to take several minutes for i to count from one to a hundred million.
Now it seems to take no time at all!
cheers,
DaveK
--
Can't think of a witty .sigline today....
- Re: GCC optimizes integer overflow: bug or feature?, (continued)
- 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, 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 <=
- 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
- RE: GCC optimizes integer overflow: bug or feature?, Dave Korn, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Gabriel Dos Reis, 2006/12/20
- Message not available
- Re: GCC optimizes integer overflow: bug or feature?, Ian Lance Taylor, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Zdenek Dvorak, 2006/12/20
- Re: GCC optimizes integer overflow: bug or feature?, Robert Dewar, 2006/12/20