[clang] [X86] Emit Warnings for frontend options to enable knl/knm. (PR #75580)

[Simon Pilgrim via cfe-commits]

RKSimon wrote:

> @RKSimon @phoebewang Thanks comments! knm has AVX512_VPOPCNTDQ, I guess we also require it work without avx512vl? And we are going to keep -march/mtune/mcpu support for knl/knm, but removing some specific ISA's intrinsic and lowering supports? Did I get your point wrong?

That's correct - we keep -march/mtune/mcpu support for knl/knm but reduce its feature set to avx512f/avx512cd and we don't provide any support for xeon-phi specific features (avx512pf etc.) apart from the minimal binutils/assembly handling necessary.

If we keep support for VPOPCNTDQ on knm then yes we will need to allow non-VLX handling, but I don't know much about general availability of knm workstations (knl cpus/machines do turn up on ebay etc. quite frequently).



https://github.com/llvm/llvm-project/pull/75580