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

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

@@ -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.opt2.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.opt3.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.rs

@@ -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_3_element_tuple.opt1.EarlyOtherwiseBranch.diff

@@ -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_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
@@ -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.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
  }
  }