Add FileCheck to branch.rs

Author: Shunpoco

tests/mir-opt/copy-prop/branch.rs

@@ -1,4 +1,3 @@
-// skip-filecheck
 // EMIT_MIR_FOR_EACH_PANIC_STRATEGY
 //! Tests that we bail out when there are multiple assignments to the same local.
 //@ test-mir-pass: CopyProp
@@ -12,6 +11,14 @@ fn cond() -> bool {
 
 // EMIT_MIR branch.foo.CopyProp.diff
 fn foo() -> i32 {
+    // CHECK-LABEL: fn foo(
+    // CHECK: debug x => [[x:_.*]];
+    // CHECK: debug y => [[y:_.*]];
+    // CHECK: bb3: {
+    // CHECK: [[y]] = copy [[x]];
+    // CHECK: bb5: {
+    // CHECK: [[y]] = copy [[x]];
+    // CHECK: _0 = copy [[y]];
     let x = val();
 
     let y = if cond() {