[all-commits] [llvm/llvm-project] 3db8a3: [InstCombine] avoid crash from deleting an instruc...

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  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: 3db8a3ef86e7b3331ab466a78c10a62be9e69829
      https://github.com/llvm/llvm-project/commit/3db8a3ef86e7b3331ab466a78c10a62be9e69829
  Author: Sanjay Patel <spatel at rotateright.com>
  Date:   2019-11-11 (Mon, 11 Nov 2019)

  Changed paths:
    M llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    M llvm/test/Transforms/InstCombine/builtin-object-size-ptr.ll

  Log Message:
  -----------
  [InstCombine] avoid crash from deleting an instruction that still has uses (PR43723) (3rd try)

Re-try because earlier attempts were reverted due to use-after-free.
Hopefully, diagnosed correctly this time - we replace/remove the
invariant.start first rather than the invariant.end to avoid angering
worklist-based iteration.

We gather a set of white-listed instructions in isAllocSiteRemovable() and then
replace/erase them. But we don't know in general if the instructions in the set
have uses amongst themselves, so order of deletion makes a difference.

There's already a special-case for the llvm.objectsize intrinsic, so add another
for llvm.invariant.start.

Should fix:
https://bugs.llvm.org/show_bug.cgi?id=43723

Differential Revision: https://reviews.llvm.org/D69977