runtime: only clear inline mark bits on span alloc if necessary
This change modifies initInlineMarkBits to only clear mark bits if the
span wasn't just freshly allocated from the OS, where we know the bits
are already zeroed. This probably doesn't make a huge difference most of
the time, but it's an easy optimization and helps rule it out as a
source of slowdown.
For #73581.
Change-Id: I78cd4d8968bb0bf6536c0a38ef9397475c39f0ad
Reviewed-on: https://go-review.googlesource.com/c/go/+/687937
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Michael Pratt <mpratt@google.com>