﻿Pull in r221709 from upstream llvm trunk (by Frédéric Riss):

  Totally forget deallocated SDNodes in SDDbgInfo.

  What would happen before that commit is that the SDDbgValues associated with
  a deallocated SDNode would be marked Invalidated, but SDDbgInfo would keep
  a map entry keyed by the SDNode pointer pointing to this list of invalidated
  SDDbgNodes. As the memory gets reused, the list might get wrongly associated
  with another new SDNode. As the SDDbgValues are cloned when they are transfered,
  this can lead to an exponential number of SDDbgValues being produced during
  DAGCombine like in http://llvm.org/bugs/show_bug.cgi?id=20893

  Note that the previous behavior wasn't really buggy as the invalidation made
  sure that the SDDbgValues won't be used. This commit can be considered a
  memory optimization and as such is really hard to validate in a unit-test.

This should fix abnormally large memory usage and resulting OOM crashes
when compiling certain ports with debug information.

Reported by:	Dmitry Marakasov <amdmi3@amdmi3.ru>
Upstream PRs:	http://llvm.org/PR19031 http://llvm.org/PR20893
MFC after:	1 week