cmd/compile: separate out unsafe mark for end-of-block instructions
Even if a block is empty, we need to keep track of whether the
end-of-block instructions are preemptible.
This CL allows us to not mark the load+compare in instruction
sequences like
CMPL $0, runtime·writeBarrier(SB)
JEQ ...
Before, we had to mark the CMPL as uninterruptible because there
was no way to mark just the JEQ. Now there is, so there is no need
to mark the CMPL itself.
Change-Id: I4c27c0dc211c03b14637d420899cd2c2cccf3493
Reviewed-on: https://go-review.googlesource.com/c/go/+/518539 Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>