Auto merge of #91840 - JakobDegen:fix_early_otherwise, r=oli-obk

Fix the unsoundness in the `early_otherwise_branch` mir opt pass

Closes #78496 .

This change is a significant rewrite of much of the pass. Exactly what it does is documented in the source file (with ascii art!), and all the changes that are made to the MIR that are not trivially sound are carefully documented. That being said, this is my first time touching MIR, so there are probably some invariants I did not know about that I broke.

This version of the optimization is also somewhat more flexible than the original; for example, we do not care how or where the value on which the parent is switching is computed. There is no requirement that any types be the same. This could be made even more flexible in the future by allowing a wider range of statements in the bodies of `BBC, BBD` (as long as they are all the same of course). This should be a good first step though.

Probably needs a perf run.

r? `@oli-obk` who reviewed things the last time this was touched

Author: bors

compiler/rustc_mir_transform/src/early_otherwise_branch.rs

@@ -12,8 +12,8 @@
       let mut _7: isize;                   // in scope 0 at $DIR/early_otherwise_branch.rs:5:10: 5:17
       let _8: u32;                         // in scope 0 at $DIR/early_otherwise_branch.rs:5:15: 5:16
       let _9: u32;                         // in scope 0 at $DIR/early_otherwise_branch.rs:5:24: 5:25
-+     let mut _10: isize;                  // in scope 0 at $DIR/early_otherwise_branch.rs:5:19: 5:26
-+     let mut _11: bool;                   // in scope 0 at $DIR/early_otherwise_branch.rs:5:19: 5:26
++     let mut _10: isize;                  // in scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
++     let mut _11: bool;                   // in scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
       scope 1 {
           debug a => _8;                   // in scope 1 at $DIR/early_otherwise_branch.rs:5:15: 5:16
           debug b => _9;                   // in scope 1 at $DIR/early_otherwise_branch.rs:5:24: 5:25
@@ -34,7 +34,7 @@
 +         StorageLive(_10);                // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
 +         _10 = discriminant((_3.1: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
 +         StorageLive(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
-+         _11 = Ne(_10, _7);               // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
++         _11 = Ne(_7, move _10);          // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
 +         StorageDead(_10);                // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
 +         switchInt(move _11) -> [false: bb4, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:4:5: 4:17
       }
@@ -70,8 +70,8 @@
 +     }
 + 
 +     bb4: {
-+         StorageDead(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:5:19: 5:26
-+         switchInt(_7) -> [1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:5:19: 5:26
++         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.opt1.EarlyOtherwiseBranch.diff

@@ -13,8 +13,8 @@
       let mut _8: isize;                   // in scope 0 at $DIR/early_otherwise_branch.rs:13:10: 13:17
       let _9: u32;                         // in scope 0 at $DIR/early_otherwise_branch.rs:13:15: 13:16
       let _10: u32;                        // in scope 0 at $DIR/early_otherwise_branch.rs:13:24: 13:25
-+     let mut _11: isize;                  // in scope 0 at $DIR/early_otherwise_branch.rs:14:16: 14:20
-+     let mut _12: bool;                   // in scope 0 at $DIR/early_otherwise_branch.rs:14:16: 14:20
++     let mut _11: isize;                  // in scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
++     let mut _12: bool;                   // in scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
       scope 1 {
           debug a => _9;                   // in scope 1 at $DIR/early_otherwise_branch.rs:13:15: 13:16
           debug b => _10;                  // in scope 1 at $DIR/early_otherwise_branch.rs:13:24: 13:25
@@ -35,7 +35,7 @@
 +         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
-+         _12 = Ne(_11, _8);               // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
++         _12 = Ne(_8, move _11);          // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
 +         StorageDead(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
 +         switchInt(move _12) -> [false: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:12:5: 12:17
       }
@@ -84,8 +84,8 @@
 +     }
 + 
 +     bb5: {
-+         StorageDead(_12);                // scope 0 at $DIR/early_otherwise_branch.rs:14:16: 14:20
-+         switchInt(_8) -> [0_isize: bb3, 1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:14:16: 14:20
++         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.opt2.EarlyOtherwiseBranch.diff

@@ -0,0 +1,77 @@
+- // MIR for `opt3` before EarlyOtherwiseBranch
++ // MIR for `opt3` after EarlyOtherwiseBranch
+  
+  fn opt3(_1: Option<u32>, _2: Option<bool>) -> u32 {
+      debug x => _1;                       // in scope 0 at $DIR/early_otherwise_branch.rs:21:9: 21:10
+      debug y => _2;                       // in scope 0 at $DIR/early_otherwise_branch.rs:21:25: 21:26
+      let mut _0: u32;                     // return place in scope 0 at $DIR/early_otherwise_branch.rs:21:45: 21:48
+      let mut _3: (std::option::Option<u32>, std::option::Option<bool>); // in scope 0 at $DIR/early_otherwise_branch.rs:22:11: 22:17
+      let mut _4: std::option::Option<u32>; // in scope 0 at $DIR/early_otherwise_branch.rs:22:12: 22:13
+      let mut _5: std::option::Option<bool>; // in scope 0 at $DIR/early_otherwise_branch.rs:22:15: 22:16
+      let mut _6: isize;                   // in scope 0 at $DIR/early_otherwise_branch.rs:23:19: 23:26
+      let mut _7: isize;                   // in scope 0 at $DIR/early_otherwise_branch.rs:23:10: 23:17
+      let _8: u32;                         // in scope 0 at $DIR/early_otherwise_branch.rs:23:15: 23:16
+      let _9: bool;                        // in scope 0 at $DIR/early_otherwise_branch.rs:23:24: 23:25
++     let mut _10: isize;                  // in scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
++     let mut _11: bool;                   // in scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
+      scope 1 {
+          debug a => _8;                   // in scope 1 at $DIR/early_otherwise_branch.rs:23:15: 23:16
+          debug b => _9;                   // in scope 1 at $DIR/early_otherwise_branch.rs:23:24: 23:25
+      }
+  
+      bb0: {
+          StorageLive(_3);                 // scope 0 at $DIR/early_otherwise_branch.rs:22:11: 22:17
+          StorageLive(_4);                 // scope 0 at $DIR/early_otherwise_branch.rs:22:12: 22:13
+          _4 = _1;                         // scope 0 at $DIR/early_otherwise_branch.rs:22:12: 22:13
+          StorageLive(_5);                 // scope 0 at $DIR/early_otherwise_branch.rs:22:15: 22:16
+          _5 = _2;                         // scope 0 at $DIR/early_otherwise_branch.rs:22:15: 22:16
+          (_3.0: std::option::Option<u32>) = move _4; // scope 0 at $DIR/early_otherwise_branch.rs:22:11: 22:17
+          (_3.1: std::option::Option<bool>) = move _5; // scope 0 at $DIR/early_otherwise_branch.rs:22:11: 22:17
+          StorageDead(_5);                 // scope 0 at $DIR/early_otherwise_branch.rs:22:16: 22:17
+          StorageDead(_4);                 // scope 0 at $DIR/early_otherwise_branch.rs:22:16: 22:17
+          _7 = discriminant((_3.0: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch.rs:22:11: 22:17
+-         switchInt(move _7) -> [1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
++         StorageLive(_10);                // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
++         _10 = discriminant((_3.1: std::option::Option<bool>)); // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
++         StorageLive(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
++         _11 = Ne(_7, move _10);          // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
++         StorageDead(_10);                // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
++         switchInt(move _11) -> [false: bb4, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
+      }
+  
+      bb1: {
++         StorageDead(_11);                // scope 0 at $DIR/early_otherwise_branch.rs:24:14: 24:15
+          _0 = const 1_u32;                // scope 0 at $DIR/early_otherwise_branch.rs:24:14: 24:15
+-         goto -> bb4;                     // scope 0 at $DIR/early_otherwise_branch.rs:24:14: 24:15
++         goto -> bb3;                     // scope 0 at $DIR/early_otherwise_branch.rs:24:14: 24:15
+      }
+  
+      bb2: {
+-         _6 = discriminant((_3.1: std::option::Option<bool>)); // scope 0 at $DIR/early_otherwise_branch.rs:22:11: 22:17
+-         switchInt(move _6) -> [1_isize: bb3, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch.rs:22:5: 22:17
+-     }
+- 
+-     bb3: {
+          StorageLive(_8);                 // scope 0 at $DIR/early_otherwise_branch.rs:23:15: 23:16
+          _8 = (((_3.0: std::option::Option<u32>) as Some).0: u32); // scope 0 at $DIR/early_otherwise_branch.rs:23:15: 23:16
+          StorageLive(_9);                 // scope 0 at $DIR/early_otherwise_branch.rs:23:24: 23:25
+          _9 = (((_3.1: std::option::Option<bool>) as Some).0: bool); // scope 0 at $DIR/early_otherwise_branch.rs:23:24: 23:25
+          _0 = const 0_u32;                // scope 1 at $DIR/early_otherwise_branch.rs:23:31: 23:32
+          StorageDead(_9);                 // scope 0 at $DIR/early_otherwise_branch.rs:23:31: 23:32
+          StorageDead(_8);                 // scope 0 at $DIR/early_otherwise_branch.rs:23:31: 23:32
+-         goto -> bb4;                     // scope 0 at $DIR/early_otherwise_branch.rs:23:31: 23:32
++         goto -> bb3;                     // scope 0 at $DIR/early_otherwise_branch.rs:23:31: 23:32
+      }
+  
+-     bb4: {
++     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
++     }
++ 
++     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.opt3.EarlyOtherwiseBranch.diff

@@ -16,7 +16,17 @@ fn opt2(x: Option<u32>, y: Option<u32>) -> u32 {
     }
 }
 
+// optimize despite different types
+// EMIT_MIR early_otherwise_branch.opt3.EarlyOtherwiseBranch.diff
+fn opt3(x: Option<u32>, y: Option<bool>) -> u32 {
+    match (x, y) {
+        (Some(a), Some(b)) => 0,
+        _ => 1,
+    }
+}
+
 fn main() {
     opt1(None, Some(0));
     opt2(None, Some(0));
+    opt3(None, Some(false));
 }

src/test/mir-opt/early_otherwise_branch.rs

@@ -16,10 +16,10 @@
       let _11: u32;                        // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:15: 6:16
       let _12: u32;                        // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:24: 6:25
       let _13: u32;                        // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:33: 6:34
-+     let mut _14: isize;                  // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:19: 6:26
-+     let mut _15: bool;                   // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:19: 6:26
-+     let mut _16: isize;                  // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:28: 6:35
-+     let mut _17: bool;                   // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:28: 6:35
++     let mut _14: isize;                  // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
++     let mut _15: bool;                   // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
++     let mut _16: isize;                  // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
++     let mut _17: bool;                   // in scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
       scope 1 {
           debug a => _11;                  // in scope 1 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:15: 6:16
           debug b => _12;                  // in scope 1 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:24: 6:25
@@ -45,7 +45,7 @@
 +         StorageLive(_14);                // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
 +         _14 = discriminant((_4.1: std::option::Option<u32>)); // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
 +         StorageLive(_15);                // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
-+         _15 = Ne(_14, _10);              // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
++         _15 = Ne(_10, move _14);         // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
 +         StorageDead(_14);                // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
 +         switchInt(move _15) -> [false: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:5:5: 5:20
       }
@@ -92,8 +92,8 @@
 +     }
 + 
 +     bb5: {
-+         StorageDead(_15);                // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:19: 6:26
-+         switchInt(_10) -> [1_isize: bb2, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_3_element_tuple.rs:6:19: 6:26
++         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.opt1.EarlyOtherwiseBranch.diff

@@ -36,8 +36,8 @@
       let mut _31: f32;                    // in scope 0 at $DIR/early_otherwise_branch_68867.rs:25:50: 25:55
       let mut _32: !;                      // in scope 0 at $DIR/early_otherwise_branch_68867.rs:26:14: 26:28
       let mut _33: ();                     // in scope 0 at $DIR/early_otherwise_branch_68867.rs:26:25: 26:27
-+     let mut _34: isize;                  // in scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
-+     let mut _35: bool;                   // in scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
++     let mut _34: isize;                  // in scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
++     let mut _35: bool;                   // in scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
       scope 1 {
 -         debug one => _12;                // in scope 1 at $DIR/early_otherwise_branch_68867.rs:22:14: 22:17
 -         debug other => _13;              // in scope 1 at $DIR/early_otherwise_branch_68867.rs:22:24: 22:29
@@ -85,7 +85,7 @@
 +         StorageLive(_34);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         _34 = discriminant((*(_4.1: &ViewportPercentageLength))); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         StorageLive(_35);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
-+         _35 = Ne(_34, _11);              // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
++         _35 = Ne(_11, move _34);         // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         StorageDead(_34);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         switchInt(move _35) -> [false: bb7, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
       }
@@ -293,8 +293,8 @@
 -         StorageDead(_3);                 // scope 0 at $DIR/early_otherwise_branch_68867.rs:27:6: 27:7
 -         StorageDead(_4);                 // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:1: 28:2
 -         return;                          // scope 0 at $DIR/early_otherwise_branch_68867.rs:28:2: 28:2
-+         StorageDead(_35);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
-+         switchInt(_11) -> [0_isize: bb2, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
++         StorageDead(_35);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
++         switchInt(_11) -> [0_isize: bb2, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
       }
   }
 

src/test/mir-opt/early_otherwise_branch_68867.try_sum.EarlyOtherwiseBranch.before-SimplifyConstCondition-final.after.diff

@@ -36,8 +36,8 @@
       let mut _31: f32;                    // in scope 0 at $DIR/early_otherwise_branch_68867.rs:25:50: 25:55
       let mut _32: !;                      // in scope 0 at $DIR/early_otherwise_branch_68867.rs:26:14: 26:28
       let mut _33: ();                     // in scope 0 at $DIR/early_otherwise_branch_68867.rs:26:25: 26:27
-+     let mut _34: isize;                  // in scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
-+     let mut _35: bool;                   // in scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
++     let mut _34: isize;                  // in scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
++     let mut _35: bool;                   // in scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
       scope 1 {
           debug one => _12;                // in scope 1 at $DIR/early_otherwise_branch_68867.rs:22:14: 22:17
           debug other => _13;              // in scope 1 at $DIR/early_otherwise_branch_68867.rs:22:24: 22:29
@@ -71,7 +71,7 @@
 +         StorageLive(_34);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         _34 = discriminant((*(_4.1: &ViewportPercentageLength))); // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         StorageLive(_35);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
-+         _35 = Ne(_34, _11);              // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
++         _35 = Ne(_11, move _34);         // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         StorageDead(_34);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
 +         switchInt(move _35) -> [false: bb7, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
       }
@@ -209,8 +209,8 @@
 +     }
 + 
 +     bb7: {
-+         StorageDead(_35);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
-+         switchInt(_11) -> [0_isize: bb2, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:22:21: 22:30
++         StorageDead(_35);                // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
++         switchInt(_11) -> [0_isize: bb2, 1_isize: bb3, 2_isize: bb4, 3_isize: bb5, otherwise: bb1]; // scope 0 at $DIR/early_otherwise_branch_68867.rs:21:8: 21:24
       }
   }