[clang] [clang][FMV] Direct-call FMV callees from FMV callers (PR #80093)

[Erich Keane via cfe-commits]

erichkeane wrote:

> I'm not sure llvm needs to know the priorities. I haven't had time to work on this, but my plan was to have something that attempts to step through the resolver instruction by instruction with known bits for the value loaded from `__aarch64_cpu_features.features` according to the caller's target features. If the return value is known, then we can fold away the resolver for that call site. If we encounter a loop, a call, or some other pattern we don't understand, then bail & leave that call site alone.

That seems sensible to me.  It would be nice to be able to recognize this /get this optimization for 'hand rolled' resolvers as well.

https://github.com/llvm/llvm-project/pull/80093