Q: Profile-directed optimizations

[N8TM@aol.com]

In a message dated 9/2/98 7:42:16 AM Pacific Daylight Time, law@cygnus.com
writes:

>   > 1) it is difficult to do,
>    > 2) it wouldn't buy much performance, or
>    > 3) just that no one has gotten around to it?  
>  #1, #3.
>  
>  Some folks might also claim #2.  I'm not convinced either way on whether
>  or not profile directed feedback helps real code.

I imagine #1 is particularly true if it's never been done for a multiple
architecture compiler, and that would contribute to #2.  I've tried profile-
directed optimization on both real codes and Livermore Kernels, and what was
gained in one section was lost in another.