Support for precise scheduling of the instruction selection DAG,

disabled in this checkin. Sorry for the large diffs due to
refactoring. New functionality is all guarded by EnableSchedCycles.

Scheduling the isel DAG is inherently imprecise, but we give it a best
effort:
- Added MayReduceRegPressure to allow stalled nodes in the queue only
  if there is a regpressure need.
- Added BUHasStall to allow checking for either dependence stalls due to
  latency or resource stalls due to pipeline hazards.
- Added BUCompareLatency to encapsulate and standardize the heuristics
  for minimizing stall cycles (vs. reducing register pressure).
- Modified the bottom-up heuristic (now in BUCompareLatency) to
  prioritize nodes by their depth rather than height. As long as it
  doesn't stall, height is irrelevant. Depth represents the critical
  path to the DAG root.
- Added hybrid_ls_rr_sort::isReady to filter stalled nodes before
  adding them to the available queue.

Related Cleanup: most of the register reduction routines do not need
to be templates.

llvm-svn: 123468

0 files changed, 0 insertions, 0 deletions