cmd/compile: fix maplit init panics for dynamic entry

golang.org/cl/174498 removes dynamic map entry handling in maplit, by
filtering the static entry only. It panics if it see a dynamic entry.
It relies on order to remove all dynamic entries.

But after recursively call order on the statics, some static entries
become dynamic, e.g OCONVIFACE node:

	type i interface {
		j()
	}
	type s struct{}

	func (s) j() {}

	type foo map[string]i

	var f = foo{
		"1": s{},
	}

To fix it, we recursively call order on each static entry, if it changed
to dynamic, put entry to dynamic then.

Fixes #31777

Change-Id: I1004190ac8f2d1eaa4beb6beab989db74099b025
Reviewed-on: https://go-review.googlesource.com/c/go/+/174777
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -1262,18 +1262,24 @@ func (o *Order) expr(n, lhs *Node) *Node {
 			if r.Op != OKEY {
 				Fatalf("OMAPLIT entry not OKEY: %v\n", r)
 			}
-			if isStaticCompositeLiteral(r.Left) && isStaticCompositeLiteral(r.Right) {
-				statics = append(statics, r)
-			} else {
+
+			if !isStaticCompositeLiteral(r.Left) || !isStaticCompositeLiteral(r.Right) {
+				dynamics = append(dynamics, r)
+				continue
+			}
+
+			// Recursively ordering some static entries can change them to dynamic;
+			// e.g., OCONVIFACE nodes. See #31777.
+			r = o.expr(r, nil)
+			if !isStaticCompositeLiteral(r.Left) || !isStaticCompositeLiteral(r.Right) {
 				dynamics = append(dynamics, r)
+				continue
 			}
+
+			statics = append(statics, r)
 		}
 		n.List.Set(statics)
 
-		// Note: we don't need to recursively call order on the statics.
-		// But do it anyway, just in case that's not true in the future.
-		o.exprList(n.List)
-
 		if len(dynamics) == 0 {
 			break
 		}

test/fixedbugs/issue31777.go

+// compile
+
+// Copyright 2019 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.
+
+// Compile with static map literal.
+
+package p
+
+type i interface {
+	j()
+}
+
+type s struct{}
+
+func (s) j() {}
+
+type foo map[string]i
+
+var f = foo{
+	"1": s{},
+	"2": s{},
+}