cmd/compile: added cheapexpr call to simplify operand of CONVIFACE

New special case for booleans and byte-sized integer types
converted to interfaces needs to ensure that the operand is
not too complex, if it were to appear in a parameter list
for example.

Added test, also increased the recursive node dump depth to
a level that was actually useful for an actual bug.

Fixes #19275.

Change-Id: If36ac3115edf439e886703f32d149ee0a46eb2a5
Reviewed-on: https://go-review.googlesource.com/37470
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>

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

@@ -1486,7 +1486,7 @@ func (n *Node) nodedump(s fmt.State, flag FmtFlag) {
 
 	if recur {
 		indent(s)
-		if dumpdepth > 10 {
+		if dumpdepth > 40 {
 			fmt.Fprint(s, "...")
 			return
 		}

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

@@ -886,6 +886,7 @@ opswitch:
 			value = zerobase
 		case n.Left.Type.IsBoolean() || (n.Left.Type.Size() == 1 && n.Left.Type.IsInteger()):
 			// n.Left is a bool/byte. Use staticbytes[n.Left].
+			n.Left = cheapexpr(n.Left, init)
 			value = nod(OINDEX, staticbytes, byteindex(n.Left))
 			value.Bounded = true
 		case n.Left.Class == PEXTERN && n.Left.Name != nil && n.Left.Name.Readonly:

test/fixedbugs/issue19275.go

@@ -0,0 +1,72 @@
+// 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.
+
+package main
+
+import (
+	"fmt"
+)
+
+type PI struct {
+	Enabled bool
+}
+
+type SI struct {
+	M map[string]*PI
+}
+
+//go:noinline
+func (s *SI) test(name string) (*int, error) {
+	n := new(int)
+	*n = 99
+	if err := addUpdate(n, s.M[name].Enabled, "enabled"); err != nil { // this was miscompiled
+		return nil, fmt.Errorf(" error adding update for enable flag %t : %s",
+			s.M[name].Enabled, err)
+	}
+	return n, nil
+}
+
+//go:noinline
+func addUpdate(n *int, in interface{}, s ...string) error {
+	if *n != 99 {
+		println("FAIL, *n should be 99, not", *n)
+	}
+	return nil
+}
+
+func main1() {
+	s := &SI{make(map[string]*PI)}
+	s.M["dog"] = &PI{}
+	s.test("dog")
+}
+
+//go:noinline
+func g(b *byte, i interface{}) error {
+	if *b != 17 {
+		println("FAIL, *b should be 17, not", *b)
+	}
+	return nil
+}
+
+//go:noinline
+func f(x *byte, m map[string]*bool) {
+	if err := g(x, *m["hello"]); err != nil { // this was miscompiled
+		return
+	}
+}
+
+func main2() {
+	m := make(map[string]*bool)
+	x := false
+	m["hello"] = &x
+	b := byte(17)
+	f(&b, m)
+}
+
+func main() {
+	main2()
+	main1()
+}