[ACTIVITY] Weekly status

[Richard Sandiford]

== This week ==

* Submitted a fix for the performance regression caused by my
  arm_comparison_operator patch.  Applied upstream after approval
  from Ramana (thanks).  Will backport to Linaro towards the end
  of next week if there are no reported problems.

* Went back to looking at -fsched-pressure.  To recap, a colleague
  ran SPEC for s390 comparing:

    (a) normal -O3 based flags
    (b) (a) + -fsched-pressure without my patch
    (c) (a) + -fsched-pressure with my patch

  (c) got the best geomean result, but there were some individual
  tests for which (b) was significantly worse than (a), and for
  which (c) only partly closed the gap.

  Found one problem.  It looks like -fsched-pressure only really
  operates on the issue rate and instruction latencies; it doesn't
  seem to use the DFA.  This seems to be unintentional, and fixing
  it showed some nice results.

  Also, the -fsched-pressure patch that I wrote at Connect set the
  starting pressure based on the set of registers that are both live
  on entry to the block _and_ used within the enclosing loop,
  This still seems to be a bit too conservative, in that it makes
  the scheduler go out of its way to preserve loop invariants,
  even if there are too many of them.  Experimented with changing
  "used" to "defined".  This too seemed to be a win.

* Got access to some PowerPC GNU/Linux machines that are suitable
  for running SPEC.  Set up my account there and got SPEC building.
  The idea is to use this to get more cross-target evidence for the
  -fsched-pressure submission(s).

* Discussion about the SMS register-scheduling patches after great
  feedback from Ayal.  While drafting a still-unsent reply justifying
  the main part of the patch, I found I was also explaining why another
  part of the patch (specifically the prologue/epilogue part) was wrong.
  Thought about that a bit today.

* Submitted fix for LP 641126.

== Next week ==

* More SMS register scheduling.

* More -fsched-pressure.

* Hopefully remerge the arm_comparison_operator patch with this week's fix.

Richard