add optimization codegen tests

src/test/codegen/match-optimizes-away.rs

@@ -0,0 +1,44 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// no-system-llvm
+// compile-flags: -O
+#![crate_type="lib"]
+
+pub enum Three { First, Second, Third }
+use Three::*;
+
+pub enum Four { First, Second, Third, Fourth }
+use Four::*;
+
+#[no_mangle]
+pub fn three_valued(x: Three) -> Three {
+    // CHECK-LABEL: @three_valued
+    // CHECK-NEXT: {{^.*:$}}
+    // CHECK-NEXT: ret i8 %0
+    match x {
+        First => First,
+        Second => Second,
+        Third => Third,
+    }
+}
+
+#[no_mangle]
+pub fn four_valued(x: Four) -> Four {
+    // CHECK-LABEL: @four_valued
+    // CHECK-NEXT: {{^.*:$}}
+    // CHECK-NEXT: ret i8 %0
+    match x {
+        First => First,
+        Second => Second,
+        Third => Third,
+        Fourth => Fourth,
+    }
+}