Auto merge of #85603 - ogoffart:fix-uninhabited-enum-branching-pass, r=wesleywiser

Fix uninhabited enum branching pass

when the discriminant is taken with some projection.

4 files changed, 305 insertions, 7 deletions

diff --git a/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs b/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs
index 465832c89fd..5c6c158d46e 100644
--- a/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs
+++ b/compiler/rustc_mir/src/transform/uninhabited_enum_branching.rs
@@ -24,6 +24,7 @@ fn get_discriminant_local(terminator: &TerminatorKind<'_>) -> Option<Local> {
 /// discriminant is read from. Otherwise, returns None.
 fn get_switched_on_type<'tcx>(
     block_data: &BasicBlockData<'tcx>,
+    tcx: TyCtxt<'tcx>,
     body: &Body<'tcx>,
 ) -> Option<Ty<'tcx>> {
     let terminator = block_data.terminator();
@@ -36,12 +37,9 @@ fn get_switched_on_type<'tcx>(
         if let Some(StatementKind::Assign(box (l, Rvalue::Discriminant(place)))) = stmt_before_term
         {
             if l.as_local() == Some(local) {
-                if let Some(r_local) = place.as_local() {
-                    let ty = body.local_decls[r_local].ty;
-
-                    if ty.is_enum() {
-                        return Some(ty);
-                    }
+                let ty = place.ty(body, tcx).ty;
+                if ty.is_enum() {
+                    return Some(ty);
                 }
             }
         }
@@ -86,7 +84,7 @@ impl<'tcx> MirPass<'tcx> for UninhabitedEnumBranching {
             trace!("processing block {:?}", bb);
 
             let discriminant_ty =
-                if let Some(ty) = get_switched_on_type(&body.basic_blocks()[bb], body) {
+                if let Some(ty) = get_switched_on_type(&body.basic_blocks()[bb], tcx, body) {
                     ty
                 } else {
                     continue;
diff --git a/src/test/mir-opt/uninhabited_enum_branching2.main.SimplifyCfg-after-uninhabited-enum-branching.after.mir b/src/test/mir-opt/uninhabited_enum_branching2.main.SimplifyCfg-after-uninhabited-enum-branching.after.mir
new file mode 100644
index 00000000000..373be9f174b
--- /dev/null
+++ b/src/test/mir-opt/uninhabited_enum_branching2.main.SimplifyCfg-after-uninhabited-enum-branching.after.mir
@@ -0,0 +1,106 @@
+// MIR for `main` after SimplifyCfg-after-uninhabited-enum-branching
+
+fn main() -> () {
+    let mut _0: ();                      // return place in scope 0 at $DIR/uninhabited_enum_branching2.rs:18:11: 18:11
+    let _1: Plop;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:19:9: 19:13
+    let mut _2: Test1;                   // in scope 0 at $DIR/uninhabited_enum_branching2.rs:19:38: 19:46
+    let _3: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+    let mut _4: &Test1;                  // in scope 0 at $DIR/uninhabited_enum_branching2.rs:21:11: 21:22
+    let mut _5: isize;                   // in scope 0 at $DIR/uninhabited_enum_branching2.rs:22:9: 22:20
+    let _6: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:23:24: 23:34
+    let _7: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+    let _8: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+    let _9: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+    let mut _10: isize;                  // in scope 0 at $DIR/uninhabited_enum_branching2.rs:29:9: 29:20
+    let _11: &str;                       // in scope 0 at $DIR/uninhabited_enum_branching2.rs:30:24: 30:34
+    let _12: &str;                       // in scope 0 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+    let _13: &str;                       // in scope 0 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+    scope 1 {
+        debug plop => _1;                // in scope 1 at $DIR/uninhabited_enum_branching2.rs:19:9: 19:13
+    }
+
+    bb0: {
+        StorageLive(_1);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:9: 19:13
+        StorageLive(_2);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:38: 19:46
+        discriminant(_2) = 2;            // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:38: 19:46
+        (_1.0: u32) = const 51_u32;      // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:16: 19:48
+        (_1.1: Test1) = move _2;         // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:16: 19:48
+        StorageDead(_2);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:47: 19:48
+        StorageLive(_3);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+        StorageLive(_4);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:11: 21:22
+        _4 = &(_1.1: Test1);             // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:11: 21:22
+        _5 = discriminant((*_4));        // scope 1 at $DIR/uninhabited_enum_branching2.rs:22:9: 22:20
+        switchInt(move _5) -> [2_isize: bb2, otherwise: bb1]; // scope 1 at $DIR/uninhabited_enum_branching2.rs:22:9: 22:20
+    }
+
+    bb1: {
+        StorageLive(_8);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+        _8 = const "D";                  // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+                                         // ty::Const
+                                         // + ty: &str
+                                         // + val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                         // mir::Constant
+                                         // + span: $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+                                         // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+        _3 = &(*_8);                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+        StorageDead(_8);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:23: 25:24
+        goto -> bb3;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+    }
+
+    bb2: {
+        StorageLive(_7);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+        _7 = const "C";                  // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+                                         // ty::Const
+                                         // + ty: &str
+                                         // + val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                         // mir::Constant
+                                         // + span: $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+                                         // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+        _3 = &(*_7);                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+        StorageDead(_7);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:23: 24:24
+        goto -> bb3;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+    }
+
+    bb3: {
+        StorageDead(_4);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:26:6: 26:7
+        StorageDead(_3);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:26:6: 26:7
+        StorageLive(_9);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+        _10 = discriminant((_1.1: Test1)); // scope 1 at $DIR/uninhabited_enum_branching2.rs:29:9: 29:20
+        switchInt(move _10) -> [2_isize: bb5, otherwise: bb4]; // scope 1 at $DIR/uninhabited_enum_branching2.rs:29:9: 29:20
+    }
+
+    bb4: {
+        StorageLive(_13);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+        _13 = const "D";                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+                                         // ty::Const
+                                         // + ty: &str
+                                         // + val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                         // mir::Constant
+                                         // + span: $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+                                         // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+        _9 = &(*_13);                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+        StorageDead(_13);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:23: 32:24
+        goto -> bb6;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+    }
+
+    bb5: {
+        StorageLive(_12);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+        _12 = const "C";                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+                                         // ty::Const
+                                         // + ty: &str
+                                         // + val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                         // mir::Constant
+                                         // + span: $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+                                         // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+        _9 = &(*_12);                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+        StorageDead(_12);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:23: 31:24
+        goto -> bb6;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+    }
+
+    bb6: {
+        StorageDead(_9);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:33:6: 33:7
+        _0 = const ();                   // scope 0 at $DIR/uninhabited_enum_branching2.rs:18:11: 34:2
+        StorageDead(_1);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:34:1: 34:2
+        return;                          // scope 0 at $DIR/uninhabited_enum_branching2.rs:34:2: 34:2
+    }
+}
diff --git a/src/test/mir-opt/uninhabited_enum_branching2.main.UninhabitedEnumBranching.diff b/src/test/mir-opt/uninhabited_enum_branching2.main.UninhabitedEnumBranching.diff
new file mode 100644
index 00000000000..f9488bae4c8
--- /dev/null
+++ b/src/test/mir-opt/uninhabited_enum_branching2.main.UninhabitedEnumBranching.diff
@@ -0,0 +1,160 @@
+- // MIR for `main` before UninhabitedEnumBranching
++ // MIR for `main` after UninhabitedEnumBranching
+  
+  fn main() -> () {
+      let mut _0: ();                      // return place in scope 0 at $DIR/uninhabited_enum_branching2.rs:18:11: 18:11
+      let _1: Plop;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:19:9: 19:13
+      let mut _2: Test1;                   // in scope 0 at $DIR/uninhabited_enum_branching2.rs:19:38: 19:46
+      let _3: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+      let mut _4: &Test1;                  // in scope 0 at $DIR/uninhabited_enum_branching2.rs:21:11: 21:22
+      let mut _5: isize;                   // in scope 0 at $DIR/uninhabited_enum_branching2.rs:22:9: 22:20
+      let _6: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:23:24: 23:34
+      let _7: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+      let _8: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+      let _9: &str;                        // in scope 0 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+      let mut _10: isize;                  // in scope 0 at $DIR/uninhabited_enum_branching2.rs:29:9: 29:20
+      let _11: &str;                       // in scope 0 at $DIR/uninhabited_enum_branching2.rs:30:24: 30:34
+      let _12: &str;                       // in scope 0 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+      let _13: &str;                       // in scope 0 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+      scope 1 {
+          debug plop => _1;                // in scope 1 at $DIR/uninhabited_enum_branching2.rs:19:9: 19:13
+      }
+  
+      bb0: {
+          StorageLive(_1);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:9: 19:13
+          StorageLive(_2);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:38: 19:46
+          discriminant(_2) = 2;            // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:38: 19:46
+          (_1.0: u32) = const 51_u32;      // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:16: 19:48
+          (_1.1: Test1) = move _2;         // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:16: 19:48
+          StorageDead(_2);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:19:47: 19:48
+          StorageLive(_3);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+          StorageLive(_4);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:11: 21:22
+          _4 = &(_1.1: Test1);             // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:11: 21:22
+          _5 = discriminant((*_4));        // scope 1 at $DIR/uninhabited_enum_branching2.rs:22:9: 22:20
+-         switchInt(move _5) -> [0_isize: bb2, 1_isize: bb3, 2_isize: bb4, otherwise: bb1]; // scope 1 at $DIR/uninhabited_enum_branching2.rs:22:9: 22:20
++         switchInt(move _5) -> [2_isize: bb4, otherwise: bb1]; // scope 1 at $DIR/uninhabited_enum_branching2.rs:22:9: 22:20
+      }
+  
+      bb1: {
+          StorageLive(_8);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+          _8 = const "D";                  // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+          _3 = &(*_8);                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:21: 25:24
+          StorageDead(_8);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:25:23: 25:24
+          goto -> bb5;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+      }
+  
+      bb2: {
+          _3 = const "A(Empty)";           // scope 1 at $DIR/uninhabited_enum_branching2.rs:22:24: 22:34
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [65, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:22:24: 22:34
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [65, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 }) }
+          goto -> bb5;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+      }
+  
+      bb3: {
+          StorageLive(_6);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:23:24: 23:34
+          _6 = const "B(Empty)";           // scope 1 at $DIR/uninhabited_enum_branching2.rs:23:24: 23:34
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [66, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:23:24: 23:34
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [66, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 }) }
+          _3 = &(*_6);                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:23:24: 23:34
+          StorageDead(_6);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:23:33: 23:34
+          goto -> bb5;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+      }
+  
+      bb4: {
+          StorageLive(_7);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+          _7 = const "C";                  // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+          _3 = &(*_7);                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:21: 24:24
+          StorageDead(_7);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:24:23: 24:24
+          goto -> bb5;                     // scope 1 at $DIR/uninhabited_enum_branching2.rs:21:5: 26:6
+      }
+  
+      bb5: {
+          StorageDead(_4);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:26:6: 26:7
+          StorageDead(_3);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:26:6: 26:7
+          StorageLive(_9);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+          _10 = discriminant((_1.1: Test1)); // scope 1 at $DIR/uninhabited_enum_branching2.rs:29:9: 29:20
+-         switchInt(move _10) -> [0_isize: bb7, 1_isize: bb8, 2_isize: bb9, otherwise: bb6]; // scope 1 at $DIR/uninhabited_enum_branching2.rs:29:9: 29:20
++         switchInt(move _10) -> [2_isize: bb9, otherwise: bb6]; // scope 1 at $DIR/uninhabited_enum_branching2.rs:29:9: 29:20
+      }
+  
+      bb6: {
+          StorageLive(_13);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+          _13 = const "D";                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [68], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+          _9 = &(*_13);                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:21: 32:24
+          StorageDead(_13);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:32:23: 32:24
+          goto -> bb10;                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+      }
+  
+      bb7: {
+          _9 = const "A(Empty)";           // scope 1 at $DIR/uninhabited_enum_branching2.rs:29:24: 29:34
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [65, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:29:24: 29:34
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [65, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 }) }
+          goto -> bb10;                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+      }
+  
+      bb8: {
+          StorageLive(_11);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:30:24: 30:34
+          _11 = const "B(Empty)";          // scope 1 at $DIR/uninhabited_enum_branching2.rs:30:24: 30:34
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [66, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:30:24: 30:34
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [66, 40, 69, 109, 112, 116, 121, 41], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [255], len: Size { raw: 8 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 8 }) }
+          _9 = &(*_11);                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:30:24: 30:34
+          StorageDead(_11);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:30:33: 30:34
+          goto -> bb10;                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+      }
+  
+      bb9: {
+          StorageLive(_12);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+          _12 = const "C";                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+                                           // ty::Const
+                                           // + ty: &str
+                                           // + val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 })
+                                           // mir::Constant
+                                           // + span: $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+                                           // + literal: Const { ty: &str, val: Value(Slice { data: Allocation { bytes: [67], relocations: Relocations(SortedMap { data: [] }), init_mask: InitMask { blocks: [1], len: Size { raw: 1 } }, align: Align { pow2: 0 }, mutability: Not, extra: () }, start: 0, end: 1 }) }
+          _9 = &(*_12);                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:21: 31:24
+          StorageDead(_12);                // scope 1 at $DIR/uninhabited_enum_branching2.rs:31:23: 31:24
+          goto -> bb10;                    // scope 1 at $DIR/uninhabited_enum_branching2.rs:28:5: 33:6
+      }
+  
+      bb10: {
+          StorageDead(_9);                 // scope 1 at $DIR/uninhabited_enum_branching2.rs:33:6: 33:7
+          _0 = const ();                   // scope 0 at $DIR/uninhabited_enum_branching2.rs:18:11: 34:2
+          StorageDead(_1);                 // scope 0 at $DIR/uninhabited_enum_branching2.rs:34:1: 34:2
+          return;                          // scope 0 at $DIR/uninhabited_enum_branching2.rs:34:2: 34:2
+      }
+  }
+  
diff --git a/src/test/mir-opt/uninhabited_enum_branching2.rs b/src/test/mir-opt/uninhabited_enum_branching2.rs
new file mode 100644
index 00000000000..e22e94314d9
--- /dev/null
+++ b/src/test/mir-opt/uninhabited_enum_branching2.rs
@@ -0,0 +1,34 @@
+enum Empty { }
+
+// test matching an enum with uninhabited variants
+enum Test1 {
+    A(Empty),
+    B(Empty),
+    C,
+    D,
+}
+
+struct Plop {
+    xx: u32,
+    test1: Test1,
+}
+
+// EMIT_MIR uninhabited_enum_branching2.main.UninhabitedEnumBranching.diff
+// EMIT_MIR uninhabited_enum_branching2.main.SimplifyCfg-after-uninhabited-enum-branching.after.mir
+fn main() {
+    let plop = Plop { xx: 51, test1: Test1::C };
+
+    match &plop.test1 {
+        Test1::A(_) => "A(Empty)",
+        Test1::B(_) => "B(Empty)",
+        Test1::C => "C",
+        Test1::D => "D",
+    };
+
+    match plop.test1 {
+        Test1::A(_) => "A(Empty)",
+        Test1::B(_) => "B(Empty)",
+        Test1::C => "C",
+        Test1::D => "D",
+    };
+}