Re: Strange prolog function issue

Huh, I had heard frame pointer omission wasn't a huge optimization. We 
turned it off to get reliable stacks off of our release builds. A quick 
google doesn't mention much other than how to turn it off or that it 
affects ebp. Does anyone have any numbers on performance, or in what 
circumstances it makes a large difference?

By the way, in VS8.0 "Optimize for Speed" and "Optimize for Size" both 
force enable frame pointer omission. From the docs:
"The /Ox (Full Optimization) 
<http://msdn2.microsoft.com/en-us/library/59a3b321.aspx> (Full 
Optimization) and /O1, /O2 (Minimize Size, Maximize Speed) 
<http://msdn2.microsoft.com/en-us/library/8f8h5cxt.aspx> (Fast Code) 
options imply */Oy*. Specifying */Oy–* after the */Ox*, */O1*, or */O2* 
option disables */Oy*, whether it is explicit or implied."

-Dan

Kevin Wasserman wrote:
> Make sure properties->optimization "omit frame pointers" is set to "No" for 
> your release build, otherwise the compiler will feel free to do what it 
> wants with ebp.
>
> My understanding was that if you ever use _alloca() in a function, though, 
> the compiler would be forced to use ebp as a frame pointer regardless 
> because of the exception handling cleanup issue. This was a strong reason 
> not to use _alloca because the "omit frame pointers" optimization can be a 
> quite significant performance gain.  All this may have changed with 7.1, 
> however.
>
> -Kevin Wasserman
>
>   
>> Date: Tue, 25 Jul 2006 23:12:40 +0000 (GMT)
>> From: Emmanuel Astier <[email protected]>
>> Subject: [GD-Windows] Re :  Strange prolog function issue
>> To: Game Development for MS Windows
>> 	<[email protected]>
>> Message-ID: <[email protected]>
>> Content-Type: text/plain; charset=utf-8
>>
>> Hi,
>>
>> It only happens in release build. And as you said, I suspect a compiler 
>> bug.
>>
>> Actually, I don't understand when the compiler decide to switch to a 
>> different prolog for the function, where ebp doesn't have the same meaning.
>> It is all fine as the function code knows the different ebp meaning, and 
>> has no trouble accessing local vars, but the exception handler seems not to 
>> be aware of the change in the ebp meaning.
>>
>> Thanks for your help,
>> we send a mail to microsoft, we will wait for their anwser...
>>
>> Emmanuel
>>
>> Ps : Kent, replying to your mails only replies to you, not to the list...
>>     
>
>
>
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