Rafael Auler 4ecd3856e9 [BOLT] Fix shrink-wrapping bugs ...

Summary:
Make shrink-wrapping more stable. Changes:

* Correctly detect landing pads at the dominance frontier, bailing
  on such cases because we are not prepared to split LPs that are target
  of a critical edge.
* Disable FOP's store removal by default - this is experimental and
  shouldn t go to prod because removing a store that we failed to detect
  it's actually necessary is disastrous. This pass currently doesn't
  have a great impact on the number of stores reduced, so it is not a
  problem. Most stores reduced are due shrink wrapping anyway.
* Fix stack access identification - correctly estimate memory length of
  weird instructions, bail if we don't know.
* Make rules for shrink-wrapping more strict: cancel shrink wrapping on
  a number of cases when we are not 100% sure that we are dealing with a
  regular callee-saved register.
* Add basic block folding to SW. Sometimes when splitting critical edges
  we create a lot of redundant BBs with the same instructions, same
  successor but different predecessor. Fold all identical BBs created by
  splitting critical edges.
* Change defaults: now the threshold used to determine when to perform
  SW is more conservative, to be sure we are moving a spill to a colder
  area. This effort, along with BB folding, helps us to avoid hurting
  icache performance by indiscriminately increasing code size.

(cherry picked from FBD5315086)

2017-06-22 16:34:01 -07:00

bolt

[BOLT] Fix shrink-wrapping bugs

2017-06-22 16:34:01 -07:00

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