Re: Feedback-driven optimization

[Robert Myers <rmyers1400@attbi.com>]

Jan Hubicka wrote:

>>On Sun, Feb 23, 2003 at 02:04:38AM -0500, Robert Myers wrote:
>>    
>>
>>>One problem: my instincts tell me I should be working with RTL, not 
>>>binary, but gcc doesn't permit routine dump of RTL.
>>>      
>>>
>>Nope.  You'll have to make your modifications within gcc itself.
>>    
>>
>
>Also there is already support for profile feedback in number of
>optimizers.  I am not sure how much more can be done in IA-64 specific
>way - probably ifcvt can be made to use it better (there are papers
>about profile based hyperblock formation, perhaps it is worthwhile to
>implement this) and scheduler - there is already code for trace
>schedling but it is not done on IA-64 compilation path as it does
>scheduling.  The modification would be trivial.  I would be greatly
>interested in results of these.
>
>  
>
Thanks for all of your comments.  Trimaran, as suggested by Robert 
Dewar, looks like the right place to start.

As much as I'd like to be able to contribute something useful to gcc, 
I'm a long way from being ready even to try to do that.

What I'd like to know, from anybody who is willing to venture a guess, 
is how much of the point will I miss by working in the idealized 
environment of Trimaran.

What I want to know is how much of the disappointing performance of VLIW 
is fundamental: the information just isn't there, and how much is 
pragmatic: the information might be there but no one can imagine putting 
the effort in that would be necessary to exploit it.

RM