cmd/compile: SSA, don't let write barrier clobber return values
When we do *p = f(), we might need to copy the return value from
f to p with a write barrier. The write barrier itself is a call,
so we need to copy the return value of f to a temporary location
before we call the write barrier function. Otherwise, the call
itself (specifically, marshalling the args to typedmemmove) will
clobber the value we're trying to write.
Fixes #15854
Change-Id: I5703da87634d91a9884e3ec098d7b3af713462e7
Reviewed-on: https://go-review.googlesource.com/23522 Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>