[release-branch.go1.12] cmd/compile: copy volatile values before emitting write barrier call
It is possible that a "volatile" value (one that can be clobbered
by preparing args of a call) to be used in multiple write barrier
calls. We used to copy the volatile value right before each call.
But this doesn't work if the value is used the second time, after
the first call where it is already clobbered. Copy it before
emitting any call.
Updates #30977.
Fixes #30996.
Change-Id: Iedcc91ad848d5ded547bf37a8359c125d32e994c
Reviewed-on: https://go-review.googlesource.com/c/go/+/168677
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
(cherry picked from commit
f23c601bf9f66ef4a0d9d2dcd003b95e78fb28f8)
Reviewed-on: https://go-review.googlesource.com/c/go/+/168817
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>