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LangRef: storing poison in memory is UB #141339

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LangRef: storing poison in memory is UB #141339

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6 changes: 6 additions & 0 deletions llvm/docs/LangRef.rst
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Expand Up @@ -11433,6 +11433,12 @@ If ``<value>`` is of aggregate type, padding is filled with
:ref:`undef <undefvalues>`.
If ``<pointer>`` is not a well-defined value, the behavior is undefined.

If ``<value>`` is poison, then behavior currently is effectively undefined due
to the fact that many LLVM passes assume they can do load widening, and having
poison in memory would "infect" the entire widened load. This can hopefully be
alleviated in the future, but until then, frontends should refrain from
generating code that stores poison values in memory.

Example:
""""""""

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