Re: g77 performance on ALPHA

[Jeffrey A Law <law@cygnus.com>]

  In message <199909011920.PAA06128@jwlab.FEITH.COM>you write:
  > > Linus Torvalds <torvalds@transmeta.com> wrote:
  > > >
  > > >It looks like the Compaq compiler knows the stores cannot alias the
  > > >loads, while g77 thinks (or tells the instruction scheduler) that the
  > > >stores could alias and thus they never get moved down. 
  > > 
  > > Naah, I didn't notice that the gcc output actually has all the
  > > compare-and-branch instructions still in the unrolled body of the loop,
  > > and those will obviously be serialization points regardless of any
  > > aliases: the reason the loads haven't migrated up and the stores down
  > > like they should is all those control dependencies. 
  > 
  > Not sure if this is relevant, however attached is a patch I'm playing with
  > which eliminates redundant conditional jumps resulting from loop unrolling.
  > I'm not aware of any problems with it, though it's still a work in progress
  > I would be interested in hearing if it helps.
This looks like something "thread_jumps" is supposed to be handling.

jeff