[llvm] [LangRef] Document accessing memory outside of object is UB. (PR #128429)

[Eli Friedman via llvm-commits]

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@@ -11108,12 +11110,9 @@ operation (that is, the alignment of the memory address). It is the
 responsibility of the code emitter to ensure that the alignment information is
 correct. Overestimating the alignment results in undefined behavior.
 Underestimating the alignment may produce less efficient code. An alignment of
-1 is always safe. The maximum possible alignment is ``1 << 32``. An alignment
-value higher than the size of the loaded type implies memory up to the
-alignment value bytes can be safely loaded without trapping in the default
-address space. Access of the high bytes can interfere with debugging tools, so
-should not be accessed if the function has the ``sanitize_thread`` or
-``sanitize_address`` attributes.
+1 is always safe. The maximum possible alignment is ``1 << 32``. Access of the
+high bytes can interfere with debugging tools, so should not be accessed if the
+function has the ``sanitize_thread`` or ``sanitize_address`` attributes.
----------------
efriedma-quic wrote:

"store" has similar language.

The language about sanitize_thread/sanitize_address isn't relevant if you're removing the allowance to load bytes past the end.

This was added in 7020f255b1807704e0dfc5a42f3016b0b940327b ; CC @arsenm .

https://github.com/llvm/llvm-project/pull/128429