[PATCH] D146233: [LICM] Don't promote store to global even in single-thread mode

[Nikita Popov via Phabricator via llvm-commits]

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Even if there are no thread-safety concerns, we should not promote (not guaranteed-to-execute) stores to globals: While the global may be writable, we may not have provenance to perform the write. The `@promote_global_noalias` test case illustrates a miscompile in the presence of a `noalias` pointer to the global.

Worth noting that the load-only promotion may also not be well-defined depending on precise semantics (we don't specify whether load violating noalias is poison or UB -- though I believe the general inclination is to make it poison, and only stores UB), but that's a more general issue.

This is inspired by https://github.com/llvm/llvm-project/issues/60860, which is a related issue with TBAA metadata.


https://reviews.llvm.org/D146233

Files:
  llvm/lib/Transforms/Scalar/LICM.cpp
  llvm/test/Transforms/LICM/promote-single-thread.ll

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