Switch to WeakVHs in the value mapper, and aggressively prune dead basic
blocks in the function cloner. This removes the last case of trivially
dead code that I've been seeing in the wild getting inlined, analyzed,
re-inlined, optimized, only to be deleted. Nukes a FIXME from the
cleanup tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153572 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed