FileCheck return_place.

Author: cjgillot

tests/mir-opt/const_prop/return_place.rs

@@ -1,11 +1,12 @@
-// skip-filecheck
 // unit-test: ConstProp
 // EMIT_MIR_FOR_EACH_PANIC_STRATEGY
 // compile-flags: -C overflow-checks=on
 
 // EMIT_MIR return_place.add.ConstProp.diff
 // EMIT_MIR return_place.add.PreCodegen.before.mir
 fn add() -> u32 {
+    // CHECK-LABEL: fn add(
+    // CHECK: _0 = const 4_u32;
     2 + 2
 }