[clang] [llvm] [Loads] Check context instruction for context-sensitive derefability (PR #109277)

[Eli Friedman via cfe-commits]

efriedma-quic wrote:

Please update the documentation for isSafeToSpeculativelyExecute() to specify the semantics in the case where the operands of the instruction don't dominate CtxI.

https://github.com/llvm/llvm-project/pull/109277