[PATCH] D65134: Clarify where the indirect UB due to write-write races comes from

[Ralf via Phabricator via llvm-commits]

RalfJung created this revision.
RalfJung added reviewers: sylvestre.ledru, majnemer, efriedma, eli.friedman.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

This is based on https://bugs.llvm.org/show_bug.cgi?id=42435#c3.


Repository:
  rL LLVM

https://reviews.llvm.org/D65134

Files:
  llvm/docs/Atomics.rst


Index: llvm/docs/Atomics.rst
===================================================================
--- llvm/docs/Atomics.rst
+++ llvm/docs/Atomics.rst
@@ -87,8 +87,10 @@
 
 However, LLVM is not allowed to transform the former to the latter: it could
 indirectly introduce undefined behavior if another thread can access ``x`` at
-the same time. (This example is particularly of interest because before the
-concurrency model was implemented, LLVM would perform this transformation.)
+the same time. That thread would read `undef` instead of the value it was
+expecting, which can lead to undefined behavior down the line. (This example is
+particularly of interest because before the concurrency model was implemented,
+LLVM would perform this transformation.)
 
 Note that speculative loads are allowed; a load which is part of a race returns
 ``undef``, but does not have undefined behavior.


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