[dev.ssa] cmd/compile: treat control ops as live at end of block

Failure to treat control ops as live can lead
to them being eliminated when they live in
other blocks.

Change-Id: I604a1977a3d3884b1f4516bea4e15885ce38272d
Reviewed-on: https://go-review.googlesource.com/13138
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/ssa/regalloc_test.go

@@ -0,0 +1,32 @@
+// Copyright 2015 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 ssa
+
+import "testing"
+
+func TestLiveControlOps(t *testing.T) {
+	c := testConfig(t)
+	f := Fun(c, "entry",
+		Bloc("entry",
+			Valu("mem", OpArg, TypeMem, 0, ".mem"),
+			Valu("x", OpAMD64MOVBconst, TypeInt8, 0, 1),
+			Valu("y", OpAMD64MOVBconst, TypeInt8, 0, 2),
+			Valu("a", OpAMD64TESTB, TypeBool, 0, nil, "x", "y"),
+			Valu("b", OpAMD64TESTB, TypeBool, 0, nil, "y", "x"),
+			If("a", "if", "exit"),
+		),
+		Bloc("if",
+			If("b", "plain", "exit"),
+		),
+		Bloc("plain",
+			Goto("exit"),
+		),
+		Bloc("exit",
+			Exit("mem"),
+		),
+	)
+	regalloc(f.f)
+	checkFunc(f.f)
+}