[PATCH] Use DomTree in MachineSink to sink over diamonds.

[Patrik Hägglund H]

This is a patch provided by Jonas Paulsson.

@Manman Ren: Can you check the change in test/CodeGen/X86/ragreedy-hoist-spill.ll?


According to a previous FIXME comment we now not only look at MBB
successors, but also handle code sinking past them:

  x = computation
  if () {} else {}
  use x

The instruction could be sunk over the whole diamond for the
if/then/else (or loop, etc), allowing it to be sunk into other blocks
after that.

Modified test added in r204522, due to one spill less present.

Minor fixes in comments.
---
lib/CodeGen/MachineSink.cpp              | 34 ++++++++++++++++++--------------
test/CodeGen/X86/ragreedy-hoist-spill.ll |  1 -
2 files changed, 19 insertions(+), 16 deletions(-)


/Patrik Hägglund
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