cmd/compile: don't skip PPARAMOUT in esccall after varargs

Fixes bug I introduced in CL 21202.

Fixes #15013.

Change-Id: I2344d7e22b8273425a0a56f4a77588b5c6e4d8c6
Reviewed-on: https://go-review.googlesource.com/21270
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -1478,17 +1478,16 @@ func esccall(e *EscState, n *Node, up *Node) {
 		lls := ll.Slice()
 		sawRcvr := false
 		var src *Node
-	DclLoop:
 		for _, n2 := range fn.Name.Defn.Func.Dcl {
 			switch n2.Class {
 			case PPARAM:
 				if n.Op != OCALLFUNC && !sawRcvr {
 					escassignNilWhy(e, n2, n.Left.Left, "call receiver")
 					sawRcvr = true
-					continue DclLoop
+					continue
 				}
 				if len(lls) == 0 {
-					continue DclLoop
+					continue
 				}
 				src = lls[0]
 				if n2.Isddd && !n.Isddd {
@@ -1502,15 +1501,6 @@ func esccall(e *EscState, n *Node, up *Node) {
 				}
 				escassignNilWhy(e, n2, src, "arg to recursive call")
 				if src != lls[0] {
-					break DclLoop
-				}
-				lls = lls[1:]
-
-			case PPARAMOUT:
-				nE.Escretval.Append(n2)
-			}
-		}
-
 					// "..." arguments are untracked
 					for _, n2 := range lls {
 						if Debug['m'] > 3 {
@@ -1518,6 +1508,17 @@ func esccall(e *EscState, n *Node, up *Node) {
 						}
 						escassignSinkNilWhy(e, src, n2, "... arg to recursive call")
 					}
+					// No more PPARAM processing, but keep
+					// going for PPARAMOUT.
+					lls = nil
+					continue
+				}
+				lls = lls[1:]
+
+			case PPARAMOUT:
+				nE.Escretval.Append(n2)
+			}
+		}
 
 		return
 	}

test/fixedbugs/issue15013.go

+// compile
+
+// Copyright 2016 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// CL 21202 introduced a compiler crash in the handling of a varargs
+// function in the same recursive group as a function that calls it.
+// Nothing in the standard library caught the problem, so adding a test.
+
+package p
+
+func F1(p *int, a ...*int) (int, *int) {
+	if p == nil {
+		return F2(), a[0]
+	}
+	return 0, a[0]
+}
+
+func F2() int {
+	var i0, i1 int
+	a, _ := F1(&i0, &i1)
+	return a
+}