[clang] [llvm] [RISCV] Preliminary P-ext intrinsics support (PR #174068)

[Craig Topper via cfe-commits]

topperc wrote:

> The implementation follows the Packed Addition and Subtraction specification:
> https://github.com/topperc/p-ext-intrinsics/blob/main/source/index.md#packed-addition-and-subtraction

This spec is one of two proposals I’m aware of for intrinsics. The mailing list has not made any decision about which will move forward.

https://github.com/llvm/llvm-project/pull/174068