cmd/compile: don't write back unchanged slice results
Don't write back parts of a slicing operation if they
are unchanged from the source of the slice. For example:
x.s = x.s[0:5] // don't write back pointer or cap
x.s = x.s[:5] // don't write back pointer or cap
x.s = x.s[:5:7] // don't write back pointer
There is more to be done here, for example:
x.s = x.s[:len(x.s):7] // don't write back ptr or len
This CL can't handle that one yet.
Fixes #14855
Change-Id: Id1e1a4fa7f3076dc1a76924a7f1cd791b81909bb
Reviewed-on: https://go-review.googlesource.com/20954
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Keith Randall <khr@golang.org>
diff --git a/test/writebarrier.go b/test/writebarrier.go
index 7510728..44e42f0 100644
--- a/test/writebarrier.go
+++ b/test/writebarrier.go
@@ -176,8 +176,9 @@
func f18(p *T18, x *[]int) {
p.a = p.a[:5] // no barrier
- p.a = p.a[3:5] // no barrier
- p.a = p.a[1:2:3] // no barrier
- p.s = p.s[8:9] // no barrier
- *x = (*x)[3:5] // no barrier
+ *x = (*x)[0:5] // no barrier
+ p.a = p.a[3:5] // ERROR "write barrier"
+ p.a = p.a[1:2:3] // ERROR "write barrier"
+ p.s = p.s[8:9] // ERROR "write barrier"
+ *x = (*x)[3:5] // ERROR "write barrier"
}
