osx-arm64 optimal code generation

[sdmaclea]

The Apple Silicon dev kit reports the following hardware features.

$ sysctl-a | grep hw.optional
hw.optional.floatingpoint: 1                                                   
hw.optional.watchpoint: 4           
hw.optional.breakpoint: 6                                                      
hw.optional.neon: 1                
hw.optional.neon_hpfp: 1              
hw.optional.neon_fp16: 1                                                       
hw.optional.armv8_1_atomics: 1  
hw.optional.armv8_crc32: 1                                                     
hw.optional.armv8_2_fhm: 0                                                     
hw.optional.amx_version: 0           
hw.optional.ucnormal_mem: 0                                                    
hw.optional.arm64: 1                                                           

I believe there is at least draft support for armv8_1_atomics, but given these are performance critical we should try to make sure we have used them in any perf critical code.

I believe we have enabled armv8_crc32 intrinsics

@tannergooding was looking for half precision floating point for AI work. Given that it is supported here it might be good to at least add the intrinsics. Maybe consider higher level support too.

category:cq
theme:vector-codegen
skill-level:expert
cost:large
impact:large

[BruceForstall]

@echesakovMSFT Arm64 intrinsics and Apple silicon

[echesakov]

@sdmaclea Does it support ARMv8.3-CompNum ? I was planning to work on these too.

[sdmaclea]

The above list was unabridged. It is not on the list on the Apple Silicon prototype. We will have to see what is on the commercial hardware.