You can either have performance (=write manual ASM for each platform), or portability, but not both.
What so-called "portable SIMD" libraries give you is "portable auto-vectorization". "Portable performance" is a global property of the algorithm. Relying on auto-vectorization will result in e.g. sub-optimal register spills in practice. The microbenchmarks will look great, though. ;)
Starts to get a bit philosophical on what constitutes "portable" but JIT compilers would emit an opcode based off of whatever the frontend/IR is saying to do surely?
Getting 2x or 4x performance in your inner loops using a reasonable SIMD library is infinitely better than theoretically getting 8x performance with hand-coded nonportable intrinsics, because the latter is never going to happen in most programs, so the actual point of comparison is scalar code, or autovectorized code at best.
Hot take: there is no portable SIMD.
You can either have performance (=write manual ASM for each platform), or portability, but not both.
What so-called "portable SIMD" libraries give you is "portable auto-vectorization". "Portable performance" is a global property of the algorithm. Relying on auto-vectorization will result in e.g. sub-optimal register spills in practice. The microbenchmarks will look great, though. ;)
Except in languages with a JIT compiler
Starts to get a bit philosophical on what constitutes "portable" but JIT compilers would emit an opcode based off of whatever the frontend/IR is saying to do surely?
What about numpy, numba, and torch.compile?
Those are manually optimized per arch, aren't they?
Getting 2x or 4x performance in your inner loops using a reasonable SIMD library is infinitely better than theoretically getting 8x performance with hand-coded nonportable intrinsics, because the latter is never going to happen in most programs, so the actual point of comparison is scalar code, or autovectorized code at best.
It's a continuum. Some things basically all SIMD implementations support. Want to add 2 4xf32 vectors together? That's pretty easy to do portably.
But yeah to be fair if you are at that point, you probably want to go fully non-portable anyway. Especially with AI.
Has anyone even figured out how to do vector stuff (SVE/RVV) without assembly?