reflect: uncomment allocation test

We no longer force Value content to escape and the compiler's
escape analysis can handle it now.

Change-Id: I0628f3241e6ef37dce710c2394725e280790479a
Reviewed-on: https://go-review.googlesource.com/c/go/+/542975
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: David Chase <[email protected]>

Author: cherrymui

src/reflect/all_test.go

@@ -3503,16 +3503,24 @@ func TestAllocations(t *testing.T) {
 		var i any
 		var v Value
 
-		// We can uncomment this when compiler escape analysis
-		// is good enough to see that the integer assigned to i
-		// does not escape and therefore need not be allocated.
-		//
-		// i = 42 + j
-		// v = ValueOf(i)
-		// if int(v.Int()) != 42+j {
-		// 	panic("wrong int")
-		// }
-
+		i = 42 + j
+		v = ValueOf(i)
+		if int(v.Int()) != 42+j {
+			panic("wrong int")
+		}
+	})
+	noAlloc(t, 100, func(j int) {
+		var i any
+		var v Value
+		i = [3]int{j, j, j}
+		v = ValueOf(i)
+		if v.Len() != 3 {
+			panic("wrong length")
+		}
+	})
+	noAlloc(t, 100, func(j int) {
+		var i any
+		var v Value
 		i = func(j int) int { return j }
 		v = ValueOf(i)
 		if v.Interface().(func(int) int)(j) != j {