Re: Patch to Avoid Bad Prefetching

[Zdenek Dvorak <rakdver at kam dot mff dot cuni dot cz>]

Hi,

> However, using the command-line option you propose likely won't do the
> job for this anyway, as different loops behave differently.  A better
> solution for such optimization would be per-loop hints, e.g.
> #pragma loop count used by the intel compiler.
> 
> [Ghassan] Totally agree that such user hints will give more precise
> information and hence better performance, but the point is: what's the
> best that we can do when that precise information is not available?
> Should we just give up? My answer is "No". 

right; so why don't you implement #pragma loop count?  It should take
just a few hours to do, and would be hugely more useful, as other
passes can take advantage of it too.

> Also, at the point where the customer pays you to spend hours or days on
> fidling with the compiler options, it likely won't hurt you to spend a
> few minutes on modifying the makefiles (and getting the necessary
> testcases)
> to enable profile feedback, either,
> 
> [Ghassan] Yes, but what about the compile time cost? Many users are not
> willing to pay that cost every time they compile.

You only need to enable the profile feedback for the final compilation
(or before performance testing etc.)

Zdenek