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| -rw-r--r-- | llvm/docs/Atomics.rst | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/llvm/docs/Atomics.rst b/llvm/docs/Atomics.rst index 450b5b36f63..60d7090790f 100644 --- a/llvm/docs/Atomics.rst +++ b/llvm/docs/Atomics.rst @@ -87,8 +87,10 @@ The following is equivalent in non-concurrent situations: 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. |
