Add FileCheck to copy_propagation_arg.rs

Author: Shunpoco

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

@@ -1,4 +1,3 @@
-// skip-filecheck
 // EMIT_MIR_FOR_EACH_PANIC_STRATEGY
 // Check that CopyProp does not propagate an assignment to a function argument
 // (doing so can break usages of the original argument value)
@@ -9,25 +8,46 @@ fn dummy(x: u8) -> u8 {
 
 // EMIT_MIR copy_propagation_arg.foo.CopyProp.diff
 fn foo(mut x: u8) {
+    // CHECK-LABEL: fn foo(
+    // CHECK: debug x => [[x:_.*]];
+    // CHECK: [[three:_.*]] = copy [[x]];
+    // CHECK: [[two:_.*]] = dummy(move [[three]])
+    // CHECK: [[x]] = move [[two]];
     // calling `dummy` to make a use of `x` that copyprop cannot eliminate
     x = dummy(x); // this will assign a local to `x`
 }
 
 // EMIT_MIR copy_propagation_arg.bar.CopyProp.diff
 fn bar(mut x: u8) {
+    // CHECK-LABEL: fn bar(
+    // CHECK: debug x => [[x:_.*]];
+    // CHECK: [[three:_.*]] = copy [[x]];
+    // CHECK: dummy(move [[three]])
+    // CHECK: [[x]] = const 5_u8;
     dummy(x);
     x = 5;
 }
 
 // EMIT_MIR copy_propagation_arg.baz.CopyProp.diff
 fn baz(mut x: i32) -> i32 {
-    // self-assignment to a function argument should be eliminated
+    // CHECK-LABEL: fn baz(
+    // CHECK: debug x => [[x:_.*]];
+    // CHECK: [[x2:_.*]] = copy [[x]];
+    // CHECK: [[x]] = move [[x2]];
+    // CHECK: _0 = copy [[x]];
+    // In the original case for DestProp, the self-assignment to a function argument is eliminated,
+    // but in CopyProp it is not eliminated.
     x = x;
     x
 }
 
 // EMIT_MIR copy_propagation_arg.arg_src.CopyProp.diff
 fn arg_src(mut x: i32) -> i32 {
+    // CHECK-LABEL: fn arg_src(
+    // CHECK: debug x => [[x:_.*]];
+    // CHECK: debug y => [[y:_.*]];
+    // CHECK: [[y]] = copy [[x]];
+    // CHECK: [[x]] = const 123_i32;
     let y = x;
     x = 123; // Don't propagate this assignment to `y`
     y