[fweimer]

One clear reason to use 128-bit instructions: naturally aligned 128-bit loads and stores are only atomic if encoded as EVEX.128 (or VEX.128 etc.).

The default auto-vectorization tuning for current Intel server CPUs using 256-bit registers, which is perhaps another counterexample.

[janwas]

The auto-vectorization (which I anyway would not rely on) default setting also sounds like a workaround for the SKX issue.

For atomic, I'm curious how you make use of that?