[WIP] Re-enable the early otherwise branch optimization

tests/codegen/enum/enum-early-otherwise-branch.rs

@@ -0,0 +1,25 @@
+//@ compile-flags: -O
+
+#![crate_type = "lib"]
+
+pub enum Enum {
+    A(u32),
+    B(u32),
+    C(u32),
+}
+
+#[no_mangle]
+pub fn foo(lhs: &Enum, rhs: &Enum) -> bool {
+    // CHECK-LABEL: define{{.*}}i1 @foo(
+    // CHECK-NOT: switch
+    // CHECK-NOT: br
+    // CHECK: [[SELECT:%.*]] = select
+    // CHECK-NEXT: ret i1 [[SELECT]]
+    // CHECK-NEXT: }
+    match (lhs, rhs) {
+        (Enum::A(lhs), Enum::A(rhs)) => lhs == rhs,
+        (Enum::B(lhs), Enum::B(rhs)) => lhs == rhs,
+        (Enum::C(lhs), Enum::C(rhs)) => lhs == rhs,
+        _ => false,
+    }
+}

tests/mir-opt/early_otherwise_branch.opt1.EarlyOtherwiseBranch.diff

@@ -12,8 +12,6 @@
       let mut _7: isize;
       let _8: u32;
       let _9: u32;
-+     let mut _10: isize;
-+     let mut _11: bool;
       scope 1 {
           debug a => _8;
           debug b => _9;
@@ -29,48 +27,33 @@
           StorageDead(_5);
           StorageDead(_4);
           _7 = discriminant((_3.0: std::option::Option<u32>));
--         switchInt(move _7) -> [1: bb2, otherwise: bb1];
-+         StorageLive(_10);
-+         _10 = discriminant((_3.1: std::option::Option<u32>));
-+         StorageLive(_11);
-+         _11 = Ne(_7, move _10);
-+         StorageDead(_10);
-+         switchInt(move _11) -> [0: bb4, otherwise: bb1];
+          switchInt(move _7) -> [1: bb2, otherwise: bb1];
       }
 
       bb1: {
-+         StorageDead(_11);
           _0 = const 1_u32;
--         goto -> bb4;
-+         goto -> bb3;
+          goto -> bb4;
       }
 
       bb2: {
--         _6 = discriminant((_3.1: std::option::Option<u32>));
--         switchInt(move _6) -> [1: bb3, otherwise: bb1];
--     }
-- 
--     bb3: {
+          _6 = discriminant((_3.1: std::option::Option<u32>));
+          switchInt(move _6) -> [1: bb3, otherwise: bb1];
+      }
+  
+      bb3: {
           StorageLive(_8);
           _8 = (((_3.0: std::option::Option<u32>) as Some).0: u32);
           StorageLive(_9);
           _9 = (((_3.1: std::option::Option<u32>) as Some).0: u32);
           _0 = const 0_u32;
           StorageDead(_9);
           StorageDead(_8);
--         goto -> bb4;
-+         goto -> bb3;
+          goto -> bb4;
       }
 
--     bb4: {
-+     bb3: {
+      bb4: {
           StorageDead(_3);
           return;
-+     }
-+ 
-+     bb4: {
-+         StorageDead(_11);
-+         switchInt(_7) -> [1: bb2, otherwise: bb1];
       }
   }
 

tests/mir-opt/early_otherwise_branch.opt10.EarlyOtherwiseBranch.diff

@@ -0,0 +1,90 @@
+- // MIR for `opt10` before EarlyOtherwiseBranch
++ // MIR for `opt10` after EarlyOtherwiseBranch
+
+  fn opt10(_1: E8, _2: E16) -> u32 {
+      debug x => _1;
+      debug y => _2;
+      let mut _0: u32;
+      let mut _3: (E8, E16);
+      let mut _4: E8;
+      let mut _5: E16;
+      let mut _6: u16;
+      let mut _7: u16;
+      let mut _8: u16;
+      let mut _9: u8;
++     let mut _10: u16;
+
+      bb0: {
+          StorageLive(_3);
+          StorageLive(_4);
+          _4 = move _1;
+          StorageLive(_5);
+          _5 = move _2;
+          _3 = (move _4, move _5);
+          StorageDead(_5);
+          StorageDead(_4);
+          _9 = discriminant((_3.0: E8));
+-         switchInt(move _9) -> [0: bb2, 1: bb3, 2: bb4, otherwise: bb9];
++         StorageLive(_10);
++         _10 = discriminant((_3.1: E16));
++         switchInt(move _10) -> [0: bb7, otherwise: bb1];
+      }
+
+      bb1: {
++         StorageDead(_10);
+          _0 = const 0_u32;
+-         goto -> bb8;
++         goto -> bb5;
+      }
+
+      bb2: {
+-         _6 = discriminant((_3.1: E16));
+-         switchInt(move _6) -> [0: bb5, otherwise: bb1];
++         _0 = const 1_u32;
++         goto -> bb5;
+      }
+
+      bb3: {
+-         _7 = discriminant((_3.1: E16));
+-         switchInt(move _7) -> [0: bb6, otherwise: bb1];
++         _0 = const 2_u32;
++         goto -> bb5;
+      }
+
+      bb4: {
+-         _8 = discriminant((_3.1: E16));
+-         switchInt(move _8) -> [0: bb7, otherwise: bb1];
++         _0 = const 3_u32;
++         goto -> bb5;
+      }
+
+      bb5: {
+-         _0 = const 1_u32;
+-         goto -> bb8;
++         StorageDead(_3);
++         return;
+      }
+
+      bb6: {
+-         _0 = const 2_u32;
+-         goto -> bb8;
++         unreachable;
+      }
+
+      bb7: {
+-         _0 = const 3_u32;
+-         goto -> bb8;
+-     }
+- 
+-     bb8: {
+-         StorageDead(_3);
+-         return;
+-     }
+- 
+-     bb9: {
+-         unreachable;
++         StorageDead(_10);
++         switchInt(_9) -> [0: bb2, 1: bb3, 2: bb4, otherwise: bb6];
+      }
+  }
+

tests/mir-opt/early_otherwise_branch.opt2.EarlyOtherwiseBranch.diff

@@ -30,13 +30,13 @@
           StorageDead(_5);
           StorageDead(_4);
           _8 = discriminant((_3.0: std::option::Option<u32>));
--         switchInt(move _8) -> [0: bb2, 1: bb3, otherwise: bb1];
+-         switchInt(move _8) -> [0: bb2, 1: bb3, otherwise: bb7];
 +         StorageLive(_11);
 +         _11 = discriminant((_3.1: std::option::Option<u32>));
 +         StorageLive(_12);
 +         _12 = Ne(_8, move _11);
 +         StorageDead(_11);
-+         switchInt(move _12) -> [0: bb5, otherwise: bb1];
++         switchInt(move _12) -> [0: bb6, otherwise: bb1];
       }
 
       bb1: {
@@ -70,7 +70,7 @@
 
 -     bb5: {
 +     bb3: {
-          _0 = const 0_u32;
+          _0 = const 2_u32;
 -         goto -> bb6;
 +         goto -> bb4;
       }
@@ -79,11 +79,16 @@
 +     bb4: {
           StorageDead(_3);
           return;
+      }
+
+-     bb7: {
++     bb5: {
+          unreachable;
 +     }
 + 
-+     bb5: {
++     bb6: {
 +         StorageDead(_12);
-+         switchInt(_8) -> [0: bb3, 1: bb2, otherwise: bb1];
++         switchInt(_8) -> [0: bb3, 1: bb2, otherwise: bb5];
       }
   }
 

tests/mir-opt/early_otherwise_branch.opt3.EarlyOtherwiseBranch.diff

@@ -10,13 +10,14 @@
       let mut _5: std::option::Option<bool>;
       let mut _6: isize;
       let mut _7: isize;
-      let _8: u32;
-      let _9: bool;
-+     let mut _10: isize;
-+     let mut _11: bool;
+      let mut _8: isize;
+      let _9: u32;
+      let _10: bool;
++     let mut _11: isize;
++     let mut _12: bool;
       scope 1 {
-          debug a => _8;
-          debug b => _9;
+          debug a => _9;
+          debug b => _10;
       }
 
       bb0: {
@@ -28,49 +29,66 @@
           _3 = (move _4, move _5);
           StorageDead(_5);
           StorageDead(_4);
-          _7 = discriminant((_3.0: std::option::Option<u32>));
--         switchInt(move _7) -> [1: bb2, otherwise: bb1];
-+         StorageLive(_10);
-+         _10 = discriminant((_3.1: std::option::Option<bool>));
+          _8 = discriminant((_3.0: std::option::Option<u32>));
+-         switchInt(move _8) -> [0: bb2, 1: bb3, otherwise: bb7];
 +         StorageLive(_11);
-+         _11 = Ne(_7, move _10);
-+         StorageDead(_10);
-+         switchInt(move _11) -> [0: bb4, otherwise: bb1];
++         _11 = discriminant((_3.1: std::option::Option<bool>));
++         StorageLive(_12);
++         _12 = Ne(_8, move _11);
++         StorageDead(_11);
++         switchInt(move _12) -> [0: bb6, otherwise: bb1];
       }
 
       bb1: {
-+         StorageDead(_11);
++         StorageDead(_12);
           _0 = const 1_u32;
--         goto -> bb4;
-+         goto -> bb3;
+-         goto -> bb6;
++         goto -> bb4;
       }
 
       bb2: {
 -         _6 = discriminant((_3.1: std::option::Option<bool>));
--         switchInt(move _6) -> [1: bb3, otherwise: bb1];
+-         switchInt(move _6) -> [0: bb5, otherwise: bb1];
 -     }
 - 
 -     bb3: {
-          StorageLive(_8);
-          _8 = (((_3.0: std::option::Option<u32>) as Some).0: u32);
+-         _7 = discriminant((_3.1: std::option::Option<bool>));
+-         switchInt(move _7) -> [1: bb4, otherwise: bb1];
+-     }
+- 
+-     bb4: {
           StorageLive(_9);
-          _9 = (((_3.1: std::option::Option<bool>) as Some).0: bool);
+          _9 = (((_3.0: std::option::Option<u32>) as Some).0: u32);
+          StorageLive(_10);
+          _10 = (((_3.1: std::option::Option<bool>) as Some).0: bool);
           _0 = const 0_u32;
+          StorageDead(_10);
           StorageDead(_9);
-          StorageDead(_8);
--         goto -> bb4;
-+         goto -> bb3;
+-         goto -> bb6;
++         goto -> bb4;
       }
 
--     bb4: {
+-     bb5: {
 +     bb3: {
+          _0 = const 2_u32;
+-         goto -> bb6;
++         goto -> bb4;
+      }
+
+-     bb6: {
++     bb4: {
           StorageDead(_3);
           return;
+      }
+
+-     bb7: {
++     bb5: {
+          unreachable;
 +     }
 + 
-+     bb4: {
-+         StorageDead(_11);
-+         switchInt(_7) -> [1: bb2, otherwise: bb1];
++     bb6: {
++         StorageDead(_12);
++         switchInt(_8) -> [0: bb3, 1: bb2, otherwise: bb5];
       }
   }