cmd/compile: handle loops better during stack allocation of slices

Don't use the move2heap optimization if the move2heap is inside
a loop deeper than the declaration of the slice. We really only want
to do the move2heap operation once.

Change-Id: I4a68d01609c2c9d4e0abe4580839e70059393a81
Reviewed-on: https://go-review.googlesource.com/c/go/+/722440
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

1 files changed, 32 insertions, 0 deletions

diff --git a/test/codegen/append.go b/test/codegen/append.go
index 0e58a48c45..e90fa87ed2 100644
--- a/test/codegen/append.go
+++ b/test/codegen/append.go
@@ -185,6 +185,38 @@ func Append17(n int) []int {
 	return r
 }
 
+func Append18(n int, p *[]int) {
+	var r []int
+	for i := range n {
+		// amd64:-`.*moveSliceNoCapNoScan`
+		*p = r
+		// amd64:`.*growslice`
+		r = append(r, i)
+	}
+}
+
+func Append19(n int, p [][]int) {
+	for j := range p {
+		var r []int
+		for i := range n {
+			// amd64:`.*growslice`
+			r = append(r, i)
+		}
+		// amd64:`.*moveSliceNoCapNoScan`
+		p[j] = r
+	}
+}
+
+func Append20(n int, p [][]int) {
+	for j := range p {
+		var r []int
+		// amd64:`.*growslice`
+		r = append(r, 0)
+		// amd64:-`.*moveSliceNoCapNoScan`
+		p[j] = r
+	}
+}
+
 //go:noinline
 func useSlice(s []int) {
 }