cmd/compile: prevent double-walk of switch for OPRINT/OPRINTN

When a println arg contains a call to an inlineable function
that itself contains a switch, that switch statement will be
walked twice, once by the walkexprlist formerly in the
OPRINT/OPRINTN case, then by walkexprlistcheap in walkprint.

Remove the first walkexprlist, it is not necessary.
walkexprlist =
		s[i] = walkexpr(s[i], init)
walkexprlistcheap = {
		s[i] = cheapexpr(n, init)
		s[i] = walkexpr(s[i], init)
}

Seems like this might be possible in other places, i.e.,
calls to inlineable switch-containing functions.

See also #25776.
Fixes #29220.

Change-Id: I3781e86aad6688711597b8bee9bc7ebd3af93601
Reviewed-on: https://go-review.googlesource.com/c/154497
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -563,7 +563,6 @@ opswitch:
 		n = walkinrange(n, init)
 
 	case OPRINT, OPRINTN:
-		walkexprlist(n.List.Slice(), init)
 		n = walkprint(n, init)
 
 	case OPANIC:

test/fixedbugs/issue29220.go

+// compile
+
+// Copyright 2018 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
+
+func ascii(r rune) rune {
+	switch {
+	case 97 <= r && r <= 122:
+		return r - 32
+	case 65 <= r && r <= 90:
+		return r + 32
+	default:
+		return r
+	}
+}
+
+func main() {
+	nomeObjeto := "ABE1FK21"
+	println(string(nomeObjeto[1:4]))
+	println(ascii(rune(nomeObjeto[4])) >= 48 && ascii(rune(nomeObjeto[4])) <= 57)
+	println(string(nomeObjeto[5]))
+	println(string(nomeObjeto[6:10]))
+}