Intel Removes Knights Mill & Knights Landing Xeon Phi Support In LLVM 19

Similar to the GCC compiler dropping support for the Xeon Phi Knights Mill and Knights Landing accelerators a few days ago, Intel has also gone ahead and seen to the removal of Xeon Phi support for the LLVM/Clang 19 compiler.

Since earlier this year in LLVM/Clang 18 the Xeon Phi Knights Mill and Knights Landing support was treated as deprecated. Now for the LLVM 19 release due out around September, the support is removed entirely. This aligns with GCC 14 having deprecated Xeon Phi support too and now in GCC 15 Git having the code removed.

Back when deprecating the support, in the merge request the Intel argument for removing the support amounted to:

- INTEL has officially announced these products’ EOL on about Aug. 2017

- Even for now, clang/llvm’s supports on these products are incomplete. For example, knm targets has AVX5124FMAPS instructions, while its intrinsic and assembly support is missing. And it is weird that avx5124fmaps is still listed at llvm/include/llvm/TargetParser/X86TargetParser.def.

- It sometimes leads to bad performance by wrong usage of options.

- We can claim this change on release notes to notify users intentionally support these targets to use older releases.

- Previously ICC and ICX has removed the support and emitted errors

- We would also like to remove the support in GCC to reduce maintainence effort

So as of this commit overnight the Knights Mill and Knights Landing ISA support has been removed.