Intel still shares ports between vector and scalar on P-cores; a scalar multiply in the loop will definitely fight with a vector port, and the bits of pointer bumps and branch and whatnot can fill up the 1 or 2 scalar-only ports. And maybe there are some minor power savings from wasting resources on the scalar overhead. Still, clang does unroll way too much.

My understanding is that they've changed this for Lion Cove and all future P cores, moving to much more of a Zen-like setup with seperate schedulers and ports for vector and scalar ops.