cmd/gc: do not reuse bool temporaries for composite equality.

Reusing it when multiple comparisons occurred in the same
function call led to bad overwriting.

Fixes #5162.

R=golang-dev, daniel.morsing
CC=golang-dev
https://golang.org/cl/8174047

src/cmd/gc/walk.c

@@ -2856,11 +2856,19 @@ walkcompare(Node **np, NodeList **init)
 	typecheck(&call, Etop);
 	walkstmt(&call);
 	*init = list(*init, call);
-	
-	if(n->op == OEQ)
-		r = tempbool;
-	else
-		r = nod(ONOT, tempbool, N);
+
+	// tempbool cannot be used directly as multiple comparison
+	// expressions may exist in the same statement. Create another
+	// temporary to hold the value (its address is not taken so it can
+	// be optimized away).
+	r = temp(types[TBOOL]);
+	a = nod(OAS, r, tempbool);
+	typecheck(&a, Etop);
+	walkstmt(&a);
+	*init = list(*init, a);
+
+	if(n->op != OEQ)
+		r = nod(ONOT, r, N);
 	typecheck(&r, Erv);
 	walkexpr(&r, init);
 	*np = r;

test/fixedbugs/issue5162.go

+// runoutput
+
+// Copyright 2013 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.
+
+// issue 5162: bad array equality when multiple comparisons
+// happen in the same expression.
+
+package main
+
+import (
+	"fmt"
+	"strings"
+)
+
+const template = `
+func CheckEqNNN_TTT() {
+	onesA := [NNN]ttt{ONES}
+	onesB := [NNN]ttt{ONES}
+	twos := [NNN]ttt{TWOS}
+	if onesA != onesB {
+		println("onesA != onesB in CheckEqNNN_TTT")
+	}
+	if onesA == twos {
+		println("onesA == twos in CheckEqNNN_TTT")
+	}
+	if onesB == twos {
+		println("onesB == twos in CheckEqNNN_TTT")
+	}
+	if s := fmt.Sprint(onesA == onesB, onesA != twos, onesB != twos); s != "true true true" {
+		println("fail in CheckEqNNN_TTT:", s)
+	}
+}
+
+func CheckEqNNN_TTTExtraVar() {
+	onesA := [NNN]ttt{ONES}
+	onesB := [NNN]ttt{ONES}
+	twos := [NNN]ttt{TWOS}
+	onesX := onesA
+	if onesA != onesB {
+		println("onesA != onesB in CheckEqNNN_TTTExtraVar")
+	}
+	if onesA == twos {
+		println("onesA == twos in CheckEqNNN_TTTExtraVar")
+	}
+	if onesB == twos {
+		println("onesB == twos in CheckEqNNN_TTTExtraVar")
+	}
+	if s := fmt.Sprint(onesA == onesB, onesA != twos, onesB != twos); s != "true true true" {
+		println("fail in CheckEqNNN_TTTExtraVar:", s)
+	}
+	if s := fmt.Sprint(onesB == onesX); s != "true" {
+		println("extra var fail in CheckEqNNN_TTTExtraVar")
+	}
+}
+`
+
+func main() {
+	fmt.Print("// run\n\n")
+	fmt.Print("// THIS FILE IS AUTO-GENERATED\n\n")
+	fmt.Print("package main\n\n")
+	fmt.Println(`import "fmt"`)
+
+	types := []string{
+		"int", "int8", "int16", "int32", "int64",
+		"uint", "uint8", "uint16", "uint32", "uint64",
+		"float32", "float64"}
+	tocall := make([]string, 0, 32*len(types))
+	for i := 1; i <= 32; i++ {
+		for _, typ := range types {
+			src := template
+			src = strings.Replace(src, "NNN", fmt.Sprint(i), -1)
+			src = strings.Replace(src, "TTT", strings.Title(typ), -1)
+			src = strings.Replace(src, "ttt", typ, -1)
+			src = strings.Replace(src, "ONES", "1"+strings.Repeat(", 1", i-1), -1)
+			src = strings.Replace(src, "TWOS", "2"+strings.Repeat(", 2", i-1), -1)
+			fmt.Print(src)
+			tocall = append(tocall, fmt.Sprintf("CheckEq%d_%s", i, strings.Title(typ)))
+		}
+	}
+	fmt.Println("func main() {")
+	for _, fun := range tocall {
+		fmt.Printf("\t%s()\n", fun)
+		fmt.Printf("\t%sExtraVar()\n", fun)
+	}
+	fmt.Println("}")
+}