cmd/compile: avoid leak of dottype expression on double assignment form

This is a followup to issue #13805. That change avoid leaks for types that
don't have any pointers for the single assignment form of a dottype expression.
This does the same for the double assignment form.

Fixes #15796

Change-Id: I27474cade0ff1f3025cb6392f47b87b33542bc0f
Reviewed-on: https://go-review.googlesource.com/24906
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/gc/esc.go

@@ -1120,7 +1120,6 @@ func escassign(e *EscState, dst, src *Node, step *EscStep) {
 		ODOTMETH,
 		// treat recv.meth as a value with recv in it, only happens in ODEFER and OPROC
 		// iface.method already leaks iface in esccall, no need to put in extra ODOTINTER edge here
-		ODOTTYPE2,
 		OSLICE,
 		OSLICE3,
 		OSLICEARR,
@@ -1129,7 +1128,8 @@ func escassign(e *EscState, dst, src *Node, step *EscStep) {
 		// Conversions, field access, slice all preserve the input value.
 		escassign(e, dst, src.Left, e.stepAssign(step, originalDst, src, dstwhy))
 
-	case ODOTTYPE:
+	case ODOTTYPE,
+		ODOTTYPE2:
 		if src.Type != nil && !haspointers(src.Type) {
 			break
 		}

test/escape_iface.go

@@ -226,22 +226,36 @@ func dotTypeEscape() *T2 { // #11931
 	}
 }
 
-func dotTypeEscape2() { // #13805
+func dotTypeEscape2() { // #13805, #15796
 	{
 		i := 0
+		j := 0
 		var v int
+		var ok bool
 		var x interface{} = i // ERROR "i does not escape"
+		var y interface{} = j // ERROR "j does not escape"
+
 		*(&v) = x.(int) // ERROR "&v does not escape"
+		*(&v), *(&ok) = y.(int) // ERROR "&v does not escape" "&ok does not escape"
 	}
 	{
 		i := 0
+		j := 0
+		var ok bool
 		var x interface{} = i // ERROR "i does not escape"
-		sink = x.(int)        // ERROR "x.\(int\) escapes to heap"
+		var y interface{} = j // ERROR "j does not escape"
 
+		sink = x.(int)        // ERROR "x.\(int\) escapes to heap"
+		sink, *(&ok) = y.(int)     // ERROR "&ok does not escape"
 	}
 	{
 		i := 0 // ERROR "moved to heap: i"
+		j := 0 // ERROR "moved to heap: j"
+		var ok bool
 		var x interface{} = &i // ERROR "&i escapes to heap"
+		var y interface{} = &j // ERROR "&j escapes to heap"
+
 		sink = x.(*int)        // ERROR "x.\(\*int\) escapes to heap"
+		sink, *(&ok) = y.(*int)     // ERROR "&ok does not escape"
 	}
 }