[PATCH] D30849: Use a WeakVH for UnknownInstructions in AliasSetTracker

[Sanjoy Das via Phabricator via llvm-commits]

sanjoy created this revision.
Herald added a subscriber: mcrosier.

This change solves the same problem as https://reviews.llvm.org/D30726, except that this only
throws out the bathwater.

AST was not correctly tracking and deleting UnknownInstructions via
handles.  The existing code only tracks "pointers" in its
`ASTCallbackVH`, so an UnknownInstruction (that isn't also def'ing a
pointer used by another memory instruction) never gets a
`ASTCallbackVH`.

There are two other ways to solve this problem:

- Use the `PointerRec` scheme for both known and unknown instructions.
- Use a `CallbackVH` that erases the offending Instruction from the UnknownInstruction list.

Both of the above changes seemed to be significantly (and unnecessarily
IMO) more complex than this.


https://reviews.llvm.org/D30849

Files:
  include/llvm/Analysis/AliasSetTracker.h
  lib/Analysis/AliasSetTracker.cpp
  test/Transforms/LICM/pr32129.ll

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