cmd/compile: ignore contentEscapes for marking nodes as escaping

Redo of CL 28575 with fixed test.
We're in a pre-KeepAlive world for a bit yet, the old tests
were in a client which was in a post-KeepAlive world.

Change-Id: I114fd630339d761ab3306d1d99718d3cb973678d
Reviewed-on: https://go-review.googlesource.com/28582
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -1572,7 +1572,7 @@ func esccall(e *EscState, n *Node, up *Node) {
 		}
 
 		if haspointers(t.Type) {
-			if escassignfromtag(e, note, nE.Escretval, src) == EscNone && up.Op != ODEFER && up.Op != OPROC {
+			if escassignfromtag(e, note, nE.Escretval, src)&EscMask == EscNone && up.Op != ODEFER && up.Op != OPROC {
 				a := src
 				for a.Op == OCONVNOP {
 					a = a.Left

test/live.go

@@ -643,3 +643,14 @@ func good40() {
 	printnl() // ERROR "live at call to printnl: autotmp_[0-9]+ ret$"
 	_ = t
 }
+
+func ddd1(x, y *int) { // ERROR "live at entry to ddd1: x y$"
+	ddd2(x, y) // ERROR "live at call to ddd2: x y autotmp_[0-9]+$"
+	printnl()  // ERROR "live at call to printnl: x y$"
+	// Note: no autotmp live at printnl.  See issue 16996.
+}
+func ddd2(a ...*int) { // ERROR "live at entry to ddd2: a$"
+	sink = a[0]
+}
+
+var sink *int

test/live_ssa.go

@@ -646,3 +646,12 @@ func good40() {
 	printnl() // ERROR "live at call to printnl: autotmp_[0-9]+ ret$"
 	_ = t
 }
+
+func ddd1(x, y *int) { // ERROR "live at entry to ddd1: x y$"
+	ddd2(x, y) // ERROR "live at call to ddd2: x y autotmp_[0-9]+$"
+	printnl()  // ERROR "live at call to printnl: x y$"
+	// Note: no autotmp live at printnl.  See issue 16996.
+}
+func ddd2(a ...*int) { // ERROR "live at entry to ddd2: a$"
+	sink = a[0]
+}