[clang] [llvm] [AArch64] set AppleA14 architecture version to v8.4-a (PR #92600)

[Ahmed Bougacha via llvm-commits]

ahmedbougacha wrote:

> > Correct, apple-m1 does not have BTI, but BTI is required for v8.5. My mistake.
> 
> Not sure if you are involved in writing the optimization guide itself at Apple, but the way the chip is described as having 8.5 minus BTI is a bit confusing since that would technically make the chip not v8.5 @jroelofs

Sure, it makes the chip "v8.5 (excluding FEAT_BTI)", which is what's written in the guide ;)   The guide is intended as a human-readable guide for high-performance software writers, not as much as the almost-only-machine-readable specifications we're used to reading.  The alternative would have been "v8.4a + all these features from v8.5" which is worse.

https://github.com/llvm/llvm-project/pull/92600