cmd/compile: duplicate nil check to two branches of write barrier
Currently, for a write of a pointer (e.g. *p = x where x is a
pointer), we generate an explicit nil check of p, despite that the
store instruction may have the same faulting behavior as the nil
check. This is because the write needs a write barrier, which
creates a control flow, which prevents the nil check being removed
as it is in a differnt block as the actual store.
This CL duplicates the nil check to two branches, so it is likely
that they will be followed by the actual store and the write
barrier load, which may have the same faulting behavior, so they
can be removed.
Change-Id: Ied9480de5dd6a8fcbd5affc5f6e029944943cc07
Reviewed-on: https://go-review.googlesource.com/c/go/+/705156 Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Keith Randall <khr@google.com>