Rollup merge of #96090 - JakobDegen:mir-tests, r=nagisa

Implement MIR opt unit tests

This implements rust-lang/compiler-team#502 .

There's not much to say here, this implementation does everything as proposed. I also added the flag to a bunch of existing tests (mostly those to which I could add it without causing huge diffs due to changes in line numbers). Summarizing the changes to test outputs:
 - Every time an `MirPatch` is created, it adds a cleanup block to the body if it did not exist already. If this block is unused (as is usually the case), it usually gets removed soon after by some pass calling `SimplifyCFG` for unrelated reasons (in many cases this cycle happens quite a few times for a single body). We now run `SimplifyCFG` less often, so those blocks end up in some of our outputs. I looked at changing `MirPatch` to not do this, but that seemed too complicated for this PR. I may still do that in a follow-up.
 - The `InstCombine` test had set `-C opt-level=0` in its flags and so there were no storage markers. I don't really see a good motivation for doing this, so bringing it back in line with what everything else does seems correct.
 - One of the `EarlyOtherwiseBranch` tests had `UnreachableProp` running on it. Preventing that kind of thing is the goal of this feature, so this seems fine.

For the remaining tests for which this feature might be useful, we can gradually migrate them as opportunities present themselves.

In terms of documentation, I plan on submitting a PR to the rustc dev guide in the near future documenting this and other recent changes to MIR. If there's any other places to update, do let me know

r? `@nagisa`

src/test/mir-opt/combine_clone_of_primitives.rs

@@ -1,4 +1,4 @@
-// compile-flags: -C opt-level=0 -Z inline_mir=no
+// unit-test: InstCombine
 // ignore-wasm32 compiled with panic=abort by default
 
 // EMIT_MIR combine_clone_of_primitives.{impl#0}-clone.InstCombine.diff

src/test/mir-opt/combine_clone_of_primitives.{impl#0}-clone.InstCombine.diff

@@ -23,9 +23,15 @@
       }
   
       bb0: {
+          StorageLive(_2);                 // scope 0 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
           _2 = &((*_1).0: T);              // scope 0 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
+          StorageLive(_3);                 // scope 0 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
           _3 = &((*_1).1: u64);            // scope 0 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
+          StorageLive(_4);                 // scope 0 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
           _4 = &((*_1).2: [f32; 3]);       // scope 0 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
+          StorageLive(_5);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
+          StorageLive(_6);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
+          StorageLive(_7);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
 -         _7 = &(*_2);                     // scope 1 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
 -         _6 = &(*_7);                     // scope 1 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
 +         _7 = _2;                         // scope 1 at $DIR/combine_clone_of_primitives.rs:8:5: 8:9
@@ -37,6 +43,10 @@
       }
   
       bb1: {
+          StorageDead(_6);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:8:8: 8:9
+          StorageLive(_8);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
+          StorageLive(_9);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
+          StorageLive(_10);                // scope 1 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
 -         _10 = &(*_3);                    // scope 1 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
 -         _9 = &(*_10);                    // scope 1 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
 -         _8 = <u64 as Clone>::clone(move _9) -> [return: bb2, unwind: bb4]; // scope 1 at $DIR/combine_clone_of_primitives.rs:9:5: 9:11
@@ -50,6 +60,10 @@
       }
   
       bb2: {
+          StorageDead(_9);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:9:10: 9:11
+          StorageLive(_11);                // scope 1 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
+          StorageLive(_12);                // scope 1 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
+          StorageLive(_13);                // scope 1 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
 -         _13 = &(*_4);                    // scope 1 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
 -         _12 = &(*_13);                   // scope 1 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
 -         _11 = <[f32; 3] as Clone>::clone(move _12) -> [return: bb3, unwind: bb4]; // scope 1 at $DIR/combine_clone_of_primitives.rs:10:5: 10:16
@@ -63,10 +77,20 @@
       }
   
       bb3: {
+          StorageDead(_12);                // scope 1 at $DIR/combine_clone_of_primitives.rs:10:15: 10:16
           Deinit(_0);                      // scope 1 at $DIR/combine_clone_of_primitives.rs:6:10: 6:15
           (_0.0: T) = move _5;             // scope 1 at $DIR/combine_clone_of_primitives.rs:6:10: 6:15
           (_0.1: u64) = move _8;           // scope 1 at $DIR/combine_clone_of_primitives.rs:6:10: 6:15
           (_0.2: [f32; 3]) = move _11;     // scope 1 at $DIR/combine_clone_of_primitives.rs:6:10: 6:15
+          StorageDead(_13);                // scope 1 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_11);                // scope 1 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_10);                // scope 1 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_8);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_7);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_5);                 // scope 1 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_4);                 // scope 0 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_3);                 // scope 0 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
+          StorageDead(_2);                 // scope 0 at $DIR/combine_clone_of_primitives.rs:6:14: 6:15
           return;                          // scope 0 at $DIR/combine_clone_of_primitives.rs:6:15: 6:15
       }
   

src/test/mir-opt/early_otherwise_branch.opt1.EarlyOtherwiseBranch.diff

@@ -68,8 +68,10 @@
 +     bb3: {
           StorageDead(_3);                 // scope 0 at $DIR/early_otherwise_branch.rs:8:1: 8:2
           return;                          // scope 0 at $DIR/early_otherwise_branch.rs:8:2: 8:2
-+     }
-+ 
+      }
+  
+-     bb5 (cleanup): {
+-         resume;                          // scope 0 at $DIR/early_otherwise_branch.rs:3:1: 8:2
 +     bb4: {
 +         StorageDead(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
 +         switchInt(_7) -> [1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17

src/test/mir-opt/early_otherwise_branch.opt2.EarlyOtherwiseBranch.diff

@@ -32,7 +32,7 @@
           StorageDead(_5);                 // scope 0 at $DIR/early_otherwise_branch.rs:12:16: 12:17
           StorageDead(_4);                 // scope 0 at $DIR/early_otherwise_branch.rs:12:16: 12:17
           _8 = discriminant((_3.0: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch.rs:12:11: 12:17
--         switchInt(move _8) -> [0_isize: bb1, 1_isize: bb3, otherwise: bb7]; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
+-         switchInt(move _8) -> [0_isize: bb1, 1_isize: bb3, otherwise: bb2]; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
 +         StorageLive(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
 +         _11 = discriminant((_3.1: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
 +         StorageLive(_12);                // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
@@ -84,8 +84,8 @@
           return;                          // scope 0 at $DIR/early_otherwise_branch.rs:17:2: 17:2
       }
   
--     bb7: {
--         unreachable;                     // scope 0 at $DIR/early_otherwise_branch.rs:15:14: 15:15
+-     bb7 (cleanup): {
+-         resume;                          // scope 0 at $DIR/early_otherwise_branch.rs:11:1: 17:2
 +     bb5: {
 +         StorageDead(_12);                // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
 +         switchInt(_8) -> [0_isize: bb3, 1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17

src/test/mir-opt/early_otherwise_branch.opt3.EarlyOtherwiseBranch.diff

@@ -68,8 +68,10 @@
 +     bb3: {
           StorageDead(_3);                 // scope 0 at $DIR/early_otherwise_branch.rs:26:1: 26:2
           return;                          // scope 0 at $DIR/early_otherwise_branch.rs:26:2: 26:2
-+     }
-+ 
+      }
+  
+-     bb5 (cleanup): {
+-         resume;                          // scope 0 at $DIR/early_otherwise_branch.rs:21:1: 26:2
 +     bb4: {
 +         StorageDead(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
 +         switchInt(_7) -> [1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17

src/test/mir-opt/early_otherwise_branch.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z mir-opt-level=4 -Z unsound-mir-opts
+// unit-test: EarlyOtherwiseBranch
 // EMIT_MIR early_otherwise_branch.opt1.EarlyOtherwiseBranch.diff
 fn opt1(x: Option<u32>, y: Option<u32>) -> u32 {
     match (x, y) {

src/test/mir-opt/early_otherwise_branch_3_element_tuple.opt1.EarlyOtherwiseBranch.diff

@@ -90,8 +90,10 @@
 +     bb4: {
           StorageDead(_4);                 // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:9:1: 9:2
           return;                          // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:9:2: 9:2
-+     }
-+ 
+      }
+  
+-     bb6 (cleanup): {
+-         resume;                          // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:4:1: 9:2
 +     bb5: {
 +         StorageDead(_15);                // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
 +         switchInt(_10) -> [1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20

src/test/mir-opt/early_otherwise_branch_3_element_tuple.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z mir-opt-level=4 -Z unsound-mir-opts
+// unit-test: EarlyOtherwiseBranch
 
 // EMIT_MIR early_otherwise_branch_3_element_tuple.opt1.EarlyOtherwiseBranch.diff
 fn opt1(x: Option<u32>, y: Option<u32>, z: Option<u32>) -> u32 {

src/test/mir-opt/early_otherwise_branch_noopt.noopt1.EarlyOtherwiseBranch.diff

@@ -38,25 +38,29 @@
           StorageDead(_5);                 // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:16: 8:17
           StorageDead(_4);                 // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:16: 8:17
           _8 = discriminant((_3.0: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:11: 8:17
-          switchInt(move _8) -> [0_isize: bb1, otherwise: bb3]; // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:5: 8:17
+          switchInt(move _8) -> [0_isize: bb1, 1_isize: bb4, otherwise: bb3]; // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:5: 8:17
       }
   
       bb1: {
           _6 = discriminant((_3.1: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:11: 8:17
-          switchInt(move _6) -> [0_isize: bb2, otherwise: bb6]; // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:5: 8:17
+          switchInt(move _6) -> [0_isize: bb2, 1_isize: bb7, otherwise: bb3]; // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:5: 8:17
       }
   
       bb2: {
           _0 = const 3_u32;                // scope 0 at $DIR/early_otherwise_branch_noopt.rs:12:25: 12:26
-          goto -> bb7;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:12:25: 12:26
+          goto -> bb8;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:12:25: 12:26
       }
   
       bb3: {
-          _7 = discriminant((_3.1: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:11: 8:17
-          switchInt(move _7) -> [0_isize: bb5, otherwise: bb4]; // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:5: 8:17
+          unreachable;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:11: 8:17
       }
   
       bb4: {
+          _7 = discriminant((_3.1: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:11: 8:17
+          switchInt(move _7) -> [0_isize: bb6, 1_isize: bb5, otherwise: bb3]; // scope 0 at $DIR/early_otherwise_branch_noopt.rs:8:5: 8:17
+      }
+  
+      bb5: {
           StorageLive(_9);                 // scope 0 at $DIR/early_otherwise_branch_noopt.rs:9:15: 9:16
           _9 = (((_3.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_noopt.rs:9:15: 9:16
           StorageLive(_10);                // scope 0 at $DIR/early_otherwise_branch_noopt.rs:9:24: 9:25
@@ -64,28 +68,32 @@
           _0 = const 0_u32;                // scope 1 at $DIR/early_otherwise_branch_noopt.rs:9:31: 9:32
           StorageDead(_10);                // scope 0 at $DIR/early_otherwise_branch_noopt.rs:9:31: 9:32
           StorageDead(_9);                 // scope 0 at $DIR/early_otherwise_branch_noopt.rs:9:31: 9:32
-          goto -> bb7;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:9:31: 9:32
+          goto -> bb8;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:9:31: 9:32
       }
   
-      bb5: {
+      bb6: {
           StorageLive(_11);                // scope 0 at $DIR/early_otherwise_branch_noopt.rs:10:15: 10:16
           _11 = (((_3.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_noopt.rs:10:15: 10:16
           _0 = const 1_u32;                // scope 2 at $DIR/early_otherwise_branch_noopt.rs:10:28: 10:29
           StorageDead(_11);                // scope 0 at $DIR/early_otherwise_branch_noopt.rs:10:28: 10:29
-          goto -> bb7;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:10:28: 10:29
+          goto -> bb8;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:10:28: 10:29
       }
   
-      bb6: {
+      bb7: {
           StorageLive(_12);                // scope 0 at $DIR/early_otherwise_branch_noopt.rs:11:21: 11:22
           _12 = (((_3.1: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch_noopt.rs:11:21: 11:22
           _0 = const 2_u32;                // scope 3 at $DIR/early_otherwise_branch_noopt.rs:11:28: 11:29
           StorageDead(_12);                // scope 0 at $DIR/early_otherwise_branch_noopt.rs:11:28: 11:29
-          goto -> bb7;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:11:28: 11:29
+          goto -> bb8;                     // scope 0 at $DIR/early_otherwise_branch_noopt.rs:11:28: 11:29
       }
   
-      bb7: {
+      bb8: {
           StorageDead(_3);                 // scope 0 at $DIR/early_otherwise_branch_noopt.rs:14:1: 14:2
           return;                          // scope 0 at $DIR/early_otherwise_branch_noopt.rs:14:2: 14:2
       }
+  
+      bb9 (cleanup): {
+          resume;                          // scope 0 at $DIR/early_otherwise_branch_noopt.rs:7:1: 14:2
+      }
   }
   

src/test/mir-opt/early_otherwise_branch_noopt.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z mir-opt-level=4 -Zunsound-mir-opts
+// unit-test: EarlyOtherwiseBranch
 
 // must not optimize as it does not follow the pattern of
 // left and right hand side being the same variant

src/test/mir-opt/early_otherwise_branch_soundness.no_deref_ptr.EarlyOtherwiseBranch.diff

@@ -19,7 +19,7 @@
   
       bb1: {
           _0 = const 0_i32;                // scope 0 at $DIR/early_otherwise_branch_soundness.rs:25:14: 25:15
-          return;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:25:14: 25:15
+          goto -> bb5;                     // scope 0 at $DIR/early_otherwise_branch_soundness.rs:25:14: 25:15
       }
   
       bb2: {
@@ -29,7 +29,7 @@
   
       bb3: {
           _0 = const 0_i32;                // scope 0 at $DIR/early_otherwise_branch_soundness.rs:23:18: 23:19
-          return;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:23:18: 23:19
+          goto -> bb5;                     // scope 0 at $DIR/early_otherwise_branch_soundness.rs:23:18: 23:19
       }
   
       bb4: {
@@ -37,7 +37,15 @@
           _5 = (((*_2) as Some).0: i32);   // scope 0 at $DIR/early_otherwise_branch_soundness.rs:22:18: 22:19
           _0 = _5;                         // scope 1 at $DIR/early_otherwise_branch_soundness.rs:22:24: 22:25
           StorageDead(_5);                 // scope 0 at $DIR/early_otherwise_branch_soundness.rs:22:24: 22:25
-          return;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:22:24: 22:25
+          goto -> bb5;                     // scope 0 at $DIR/early_otherwise_branch_soundness.rs:22:24: 22:25
+      }
+  
+      bb5: {
+          return;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:27:2: 27:2
+      }
+  
+      bb6 (cleanup): {
+          resume;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:18:1: 27:2
       }
   }
   

src/test/mir-opt/early_otherwise_branch_soundness.no_downcast.EarlyOtherwiseBranch.diff

@@ -19,12 +19,20 @@
   
       bb2: {
           _0 = const 1_u32;                // scope 0 at $DIR/early_otherwise_branch_soundness.rs:13:38: 13:39
-          return;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:13:5: 13:52
+          goto -> bb4;                     // scope 0 at $DIR/early_otherwise_branch_soundness.rs:13:5: 13:52
       }
   
       bb3: {
           _0 = const 2_u32;                // scope 0 at $DIR/early_otherwise_branch_soundness.rs:13:49: 13:50
-          return;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:13:5: 13:52
+          goto -> bb4;                     // scope 0 at $DIR/early_otherwise_branch_soundness.rs:13:5: 13:52
+      }
+  
+      bb4: {
+          return;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:14:2: 14:2
+      }
+  
+      bb5 (cleanup): {
+          resume;                          // scope 0 at $DIR/early_otherwise_branch_soundness.rs:12:1: 14:2
       }
   }
   

src/test/mir-opt/early_otherwise_branch_soundness.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z mir-opt-level=4 -Zunsound-mir-opts
+// unit-test: EarlyOtherwiseBranch
 
 // Tests various cases that the `early_otherwise_branch` opt should *not* optimize
 

src/test/mir-opt/if-condition-int.rs

@@ -1,4 +1,4 @@
-// compile-flags: -O
+// unit-test: SimplifyComparisonIntegral
 // EMIT_MIR if_condition_int.opt_u32.SimplifyComparisonIntegral.diff
 // EMIT_MIR if_condition_int.opt_negative.SimplifyComparisonIntegral.diff
 // EMIT_MIR if_condition_int.opt_char.SimplifyComparisonIntegral.diff

src/test/mir-opt/if_condition_int.dont_opt_bool.SimplifyComparisonIntegral.diff

@@ -26,5 +26,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:17:25: 17:26
           return;                          // scope 0 at $DIR/if-condition-int.rs:18:2: 18:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:16:1: 18:2
+      }
   }
   

src/test/mir-opt/if_condition_int.dont_opt_floats.SimplifyComparisonIntegral.diff

@@ -30,5 +30,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:53:34: 53:35
           return;                          // scope 0 at $DIR/if-condition-int.rs:54:2: 54:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:52:1: 54:2
+      }
   }
   

src/test/mir-opt/if_condition_int.dont_remove_comparison.SimplifyComparisonIntegral.diff

@@ -54,5 +54,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:49:1: 49:2
           return;                          // scope 0 at $DIR/if-condition-int.rs:49:2: 49:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:43:1: 49:2
+      }
   }
   

src/test/mir-opt/if_condition_int.opt_char.SimplifyComparisonIntegral.diff

@@ -35,5 +35,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:21:32: 21:33
           return;                          // scope 0 at $DIR/if-condition-int.rs:22:2: 22:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:20:1: 22:2
+      }
   }
   

src/test/mir-opt/if_condition_int.opt_i8.SimplifyComparisonIntegral.diff

@@ -35,5 +35,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:25:31: 25:32
           return;                          // scope 0 at $DIR/if-condition-int.rs:26:2: 26:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:24:1: 26:2
+      }
   }
   

src/test/mir-opt/if_condition_int.opt_multiple_ifs.SimplifyComparisonIntegral.diff

@@ -61,5 +61,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:39:5: 39:6
           return;                          // scope 0 at $DIR/if-condition-int.rs:40:2: 40:2
       }
+  
+      bb7 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:32:1: 40:2
+      }
   }
   

src/test/mir-opt/if_condition_int.opt_negative.SimplifyComparisonIntegral.diff

@@ -35,5 +35,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:29:32: 29:33
           return;                          // scope 0 at $DIR/if-condition-int.rs:30:2: 30:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:28:1: 30:2
+      }
   }
   

src/test/mir-opt/if_condition_int.opt_u32.SimplifyComparisonIntegral.diff

@@ -35,5 +35,9 @@
           StorageDead(_2);                 // scope 0 at $DIR/if-condition-int.rs:12:31: 12:32
           return;                          // scope 0 at $DIR/if-condition-int.rs:13:2: 13:2
       }
+  
+      bb4 (cleanup): {
+          resume;                          // scope 0 at $DIR/if-condition-int.rs:11:1: 13:2
+      }
   }
   

src/test/mir-opt/lower_slice_len.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Z mir-opt-level=3
+// unit-test: LowerSliceLenCalls
 
 // EMIT_MIR lower_slice_len.bound.LowerSliceLenCalls.diff
 pub fn bound(index: usize, slice: &[u8]) -> u8 {

src/test/mir-opt/nrvo-simple.rs

@@ -1,4 +1,4 @@
-// compile-flags: -Zmir-opt-level=1
+// unit-test: RenameReturnPlace
 
 // EMIT_MIR nrvo_simple.nrvo.RenameReturnPlace.diff
 fn nrvo(init: fn(&mut [u8; 1024])) -> [u8; 1024] {

src/test/mir-opt/nrvo_simple.nrvo.RenameReturnPlace.diff

@@ -39,5 +39,9 @@
 -         StorageDead(_2);                 // scope 0 at $DIR/nrvo-simple.rs:8:1: 8:2
           return;                          // scope 0 at $DIR/nrvo-simple.rs:8:2: 8:2
       }
+  
+      bb2 (cleanup): {
+          resume;                          // scope 0 at $DIR/nrvo-simple.rs:4:1: 8:2
+      }
   }
   

src/tools/compiletest/src/header.rs

@@ -157,6 +157,8 @@ pub struct TestProps {
     pub should_ice: bool,
     // If true, the stderr is expected to be different across bit-widths.
     pub stderr_per_bitwidth: bool,
+    // The MIR opt to unit test, if any
+    pub mir_unit_test: Option<String>,
 }
 
 mod directives {
@@ -189,6 +191,7 @@ mod directives {
     pub const STDERR_PER_BITWIDTH: &'static str = "stderr-per-bitwidth";
     pub const INCREMENTAL: &'static str = "incremental";
     pub const KNOWN_BUG: &'static str = "known-bug";
+    pub const MIR_UNIT_TEST: &'static str = "unit-test";
     // This isn't a real directive, just one that is probably mistyped often
     pub const INCORRECT_COMPILER_FLAGS: &'static str = "compiler-flags";
 }
@@ -232,6 +235,7 @@ impl TestProps {
             assembly_output: None,
             should_ice: false,
             stderr_per_bitwidth: false,
+            mir_unit_test: None,
         }
     }
 
@@ -392,6 +396,9 @@ impl TestProps {
                 config.set_name_directive(ln, STDERR_PER_BITWIDTH, &mut self.stderr_per_bitwidth);
                 config.set_name_directive(ln, INCREMENTAL, &mut self.incremental);
                 config.set_name_directive(ln, KNOWN_BUG, &mut self.known_bug);
+                config.set_name_value_directive(ln, MIR_UNIT_TEST, &mut self.mir_unit_test, |s| {
+                    s.trim().to_string()
+                });
             });
         }
 

src/tools/compiletest/src/runtest.rs

@@ -1856,10 +1856,14 @@ impl<'test> TestCx<'test> {
                 rustc.args(&[
                     "-Copt-level=1",
                     "-Zdump-mir=all",
-                    "-Zmir-opt-level=4",
                     "-Zvalidate-mir",
                     "-Zdump-mir-exclude-pass-number",
                 ]);
+                if let Some(pass) = &self.props.mir_unit_test {
+                    rustc.args(&["-Zmir-opt-level=0", &format!("-Zmir-enable-passes=+{}", pass)]);
+                } else {
+                    rustc.arg("-Zmir-opt-level=4");
+                }
 
                 let mir_dump_dir = self.get_mir_dump_dir();
                 let _ = fs::remove_dir_all(&mir_dump_dir);