[llvm] [X86] Support EGPR (R16-R31) for APX (PR #70958)

[Shengchen Kan via llvm-commits]

KanRobert wrote:

For both O3 and O0 build we have 2M more instruction counts, b/c O0 baseline has fewer instructions, regression for O0 is more.
The remaining regression comes from iterating on new registers and register classes scattered here and there. I tried to fix it but it didn't help much.

In my humble opinion, the remaining compile time regression is not big and may not become a blocking issue. Could we move forward on this?

https://github.com/llvm/llvm-project/pull/70958