[MemorySSA] Fix def optimization handling
In order for more complex updates of MSSA to happen (e.g. those in
D45299), MemoryDefs need to be actual `Use`s of what they're optimized
to. This patch makes that happen.
In addition, this patch changes our optimization behavior for Defs
slightly: we'll now consider a Def optimization invalid if the
MemoryAccess it's optimized to changes. That we weren't doing this
before was a bug, but given that we were tracking these with a WeakVH
before, it was sort of difficult for that to matter.
We're already have both of these behaviors for MemoryUses. The
difference is that a MemoryUse's defining access is always its optimized
access, and defining accesses are always `Use`s (in the LLVM sense).
Nothing exploded when testing a stage3 clang+llvm locally, so...
This also includes the test-case promised in r340461.
llvm-svn: 340577
2 files changed