Remove deprecated SIMD support
The following platforms and SIMD layers were deprecated in !938 (merged) (which was in release 2021) after discussion at #3818 (closed) and should be removed:
-
ARM Neon (ie. impl_arm_neon, not impl_arm_neon_asimd) -
Power 7 (ie. impl_ibm_vmx) -
x86 MIC (ie. KNC support in impl_86_mic; note this does not affect support on KNL) -
Sparc64 HPC ACE (ie. impl_sparc64_hpc_ace; the architecture of the former K computer) -
Decide future of tree reduction used for MIC -
Remove tree reduction used for MIC
Related cmake detection and code paths should also go away. They're not tested in CI, so nothing changes there.
There's a fancy tree reduction for MIC that could go away, which might be desirable because it is implemented using stuff from thread-MPI, whereas these days one would implement it with something like the std::atomc_flag<ptrdiff_t>
or (C++20) std::latch
.