BMI1 includes four instructions (ANDN, BLSI, BLSMSK, BLSR) that are
easy to peephole optimize, and which GCC always seems to favor using
when available and applicable.
Updates #45453.
Change-Id: I0274184057058f5c579e5bc3ea9c414396d3cf46
Reviewed-on: https://go-review.googlesource.com/c/go/+/351130
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
