[llvm] [LangRef] Update initializes definition (PR #134370)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> how does undef vs poison work here?

Whether the poison value is allowed in memory is still an open problem: https://discourse.llvm.org/t/rfc-add-nopoison-attribute-metadata/79833.

If we return poison when loading from an "uninitialized" byte, elimination of `store with undef value` in InstCombine should be treated as miscompilation.




https://github.com/llvm/llvm-project/pull/134370