cmd/compile: propagate len([]T{}) to make builtin to allow stack allocation

Updates #75620

Change-Id: I6a6a6964af4512e30eb4806e1dc7b0fd0835744f
Reviewed-on: https://go-review.googlesource.com/c/go/+/707255
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/test/escape_make_non_const.go b/test/escape_make_non_const.go
index 7a9b28d5e3..11854ac4f4 100644
--- a/test/escape_make_non_const.go
+++ b/test/escape_make_non_const.go
@@ -106,3 +106,18 @@ type m struct {
 func newM(l int) m { // ERROR "can inline"
 	return m{make(map[string]int, l)} // ERROR "make.*escapes to heap"
 }
+
+//go:noinline
+func testLenOfSliceLit() {
+	ints := []int{0, 1, 2, 3, 4, 5} // ERROR "\[\]int\{\.\.\.\} does not escape"'
+	_ = make([]int, len(ints))      // ERROR "make\(\[\]int, 6\) does not escape"
+	_ = allocLenOf(ints)            // ERROR "inlining call", "make\(\[\]int, 6\) does not escape"
+
+	_ = make([]int, 2, len(ints))  // ERROR "make\(\[\]int, 2, 6\) does not escape"
+	_ = make([]int, len(ints), 2)  // ERROR "make\(\[\]int, len\(ints\), 2\) does not escape"
+	_ = make([]int, 10, len(ints)) // ERROR "make\(\[\]int, 10, 6\) does not escape"
+}
+
+func allocLenOf(s []int) []int { // ERROR "can inline" "s does not escape"
+	return make([]int, len(s)) // ERROR "escapes to heap"
+}