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

[Nikita Popov via llvm-commits]

nikic wrote:

> On higher-level question: is this attribute useful as specified? The caller only knows that the initialized range was written to, but it can be poison, undef, or a concrete value. There's nothing it can assume about the stored value. All it knows it that the range is dereferenceable, but for that we already have an attribute. What am I missing?

This attribute is used to DSE stores *before* the call. We don't care about what the value after the call is, only about dropping stores before the call.

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