[all-commits] [llvm/llvm-project] aa1cf3: [IR] Fix PoisoningVH relocation of a poisoned hand...

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: aa1cf3205e63c1944238b41408fb3425fc585c61
      https://github.com/llvm/llvm-project/commit/aa1cf3205e63c1944238b41408fb3425fc585c61
  Author: Fangrui Song <i at maskray.me>
  Date:   2026-05-30 (Sat, 30 May 2026)

  Changed paths:
    M llvm/include/llvm/IR/ValueHandle.h
    M llvm/unittests/IR/ValueHandleTest.cpp

  Log Message:
  -----------
  [IR] Fix PoisoningVH relocation of a poisoned handle (#200540)

In LLVM_ENABLE_ABI_BREAKING_CHECKS builds, when poisoned (`deleted()` or
`allUsesReplacedWith()`), a PoisoningVH is removed from its use list but
keeps its raw value pointer for identity, so its PrevPtr/Next are left
stale.

PoisoningVH has no move constructor, so relocating a value that embeds
one
falls back to the copy constructor, where `setRawValPtr` relinks with
the stale pointers and corrupts the use list.

This is a latent bug for any relocation of a PoisoningVH handle
but becomes load-bearing for #199615 , which relocating erase exercises
it via ScalarEvolution's BackedgeTakenInfo (its ExitNotTakenInfo holds a
PoisoningVH<BasicBlock>).

Fix by special casing the `Poisoned` case.
Aided By Claude Opus 4.8



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