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Date: Sun, 22 Oct 2006 14:24:25 -0400
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Subject: Re: GNAT compiler switches and optimization
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Date: 2006-10-22T14:24:25-04:00
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Georg Bauhaus wrote:

> 
> I think that's a pity when seen from a "just Ada" perspective. There
> is one more thing (allocators) you have to think about if you
> want speed for local array variables when using GNAT.
> 
> 
> Windows x86, GNAT GPL 2006, and OA 8.2 U15. The first, middle and last 
> element of the array are referenced. Pragma volatile
> has been tried, too.

It sounds like you are running some different code and I'd be hestitant 
to make any assertions about runtime for certain constructs without 
seeing it since

1) We just spent 3 days talking about the code that started this thread 
and there have been all sorts of assertions about things being 
faster/slower,etc.

2) You mention something about just accessing first, middle and last of 
your arrays so it really sounds like you really are just timing 
allocations and and not actually really hitting the array indexing 
(though hard to say without seeing the code).

Don't take either of those as any sort of severe criticism but I am just 
trying to make sure that any discussions of performance are tied to 
clear,open and repeatable measurements so we all know what each other 
are talkig about.

The problem is that too often, performance critisim is done via vague 
references rather than hard facts and thus they get dismissed 
(sometimes) by some compiler writers.

The bug submitted on this issue (whether or not it ever gets fixed) 
certainly has generated real and useful discussions amoung the 
developers with few of the typical 'silly user' responses that we 
sometimes see.