cmd/compile: don't put Noalg types in typelinks

They could get picked up by reflect code, yielding the wrong type.

Fixes #22605

Change-Id: Ie11fb361ca7f3255e662037b3407565c8f0a2c4c
Reviewed-on: https://go-review.googlesource.com/76315
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

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

@@ -960,10 +960,17 @@ func dcommontype(lsym *obj.LSym, ot int, t *types.Type) int {
 	return ot
 }
 
+// typeHasNoAlg returns whether t does not have any associated hash/eq
+// algorithms because t, or some component of t, is marked Noalg.
+func typeHasNoAlg(t *types.Type) bool {
+	a, bad := algtype1(t)
+	return a == ANOEQ && bad.Noalg()
+}
+
 func typesymname(t *types.Type) string {
 	name := t.ShortString()
 	// Use a separate symbol name for Noalg types for #17752.
-	if a, bad := algtype1(t); a == ANOEQ && bad.Noalg() {
+	if typeHasNoAlg(t) {
 		name = "noalg." + name
 	}
 	return name
@@ -1394,6 +1401,10 @@ func dtypesym(t *types.Type) *obj.LSym {
 			keep = true
 		}
 	}
+	// Do not put Noalg types in typelinks.  See issue #22605.
+	if typeHasNoAlg(t) {
+		keep = false
+	}
 	lsym.Set(obj.AttrMakeTypelink, keep)
 
 	return lsym

test/fixedbugs/issue22605.go

+// run
+
+// Copyright 2017 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.
+
+// We were picking up a special noalg type from typelinks.
+
+package main
+
+import "reflect"
+
+func f(m map[string]int) int {
+	return m["a"]
+}
+
+func g(m map[[8]string]int) int {
+	t := reflect.ArrayOf(8, reflect.TypeOf(""))
+	a := reflect.New(t).Elem()
+	return m[a.Interface().([8]string)]
+}
+
+func main() {
+	m := map[[8]string]int{}
+	g(m)
+}