Get all variants to eliminate the default branching if we cannot get the layout of type

compiler/rustc_mir_transform/src/uninhabited_enum_branching.rs

@@ -95,6 +95,12 @@ fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
 
             let mut allowed_variants = if let Ok(layout) = layout {
                 variant_discriminants(&layout, discriminant_ty, tcx)
+            } else if let Some(variant_range) = discriminant_ty.variant_range(tcx) {
+                variant_range
+                    .map(|variant| {
+                        discriminant_ty.discriminant_for_variant(tcx, variant).unwrap().val
+                    })
+                    .collect()
             } else {
                 continue;
             };

tests/mir-opt/issues/issue_59352.num_to_digit.PreCodegen.after.panic-abort.mir

@@ -33,13 +33,13 @@ fn num_to_digit(_1: char) -> u32 {
         _3 = &_2;
         StorageLive(_4);
         _4 = discriminant(_2);
-        StorageDead(_3);
+        switchInt(move _4) -> [1: bb2, 0: bb6, otherwise: bb8];
-        StorageDead(_2);
-        switchInt(move _4) -> [1: bb2, otherwise: bb7];
     }
 
     bb2: {
         StorageDead(_4);
+        StorageDead(_3);
+        StorageDead(_2);
         StorageLive(_5);
         _5 = char::methods::<impl char>::to_digit(move _1, const 8_u32) -> [return: bb3, unwind unreachable];
     }
@@ -47,7 +47,7 @@ fn num_to_digit(_1: char) -> u32 {
     bb3: {
         StorageLive(_6);
         _6 = discriminant(_5);
-        switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb6];
+        switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb8];
     }
 
     bb4: {
@@ -58,20 +58,22 @@ fn num_to_digit(_1: char) -> u32 {
         _0 = move ((_5 as Some).0: u32);
         StorageDead(_6);
         StorageDead(_5);
-        goto -> bb8;
+        goto -> bb7;
     }
 
     bb6: {
-        unreachable;
+        StorageDead(_4);
+        StorageDead(_3);
+        StorageDead(_2);
+        _0 = const 0_u32;
+        goto -> bb7;
     }
 
     bb7: {
-        StorageDead(_4);
+        return;
-        _0 = const 0_u32;
-        goto -> bb8;
     }
 
     bb8: {
-        return;
+        unreachable;
     }
 }

tests/mir-opt/issues/issue_59352.num_to_digit.PreCodegen.after.panic-unwind.mir

@@ -33,13 +33,13 @@ fn num_to_digit(_1: char) -> u32 {
         _3 = &_2;
         StorageLive(_4);
         _4 = discriminant(_2);
-        StorageDead(_3);
+        switchInt(move _4) -> [1: bb2, 0: bb6, otherwise: bb8];
-        StorageDead(_2);
-        switchInt(move _4) -> [1: bb2, otherwise: bb7];
     }
 
     bb2: {
         StorageDead(_4);
+        StorageDead(_3);
+        StorageDead(_2);
         StorageLive(_5);
         _5 = char::methods::<impl char>::to_digit(move _1, const 8_u32) -> [return: bb3, unwind continue];
     }
@@ -47,7 +47,7 @@ fn num_to_digit(_1: char) -> u32 {
     bb3: {
         StorageLive(_6);
         _6 = discriminant(_5);
-        switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb6];
+        switchInt(move _6) -> [0: bb4, 1: bb5, otherwise: bb8];
     }
 
     bb4: {
@@ -58,20 +58,22 @@ fn num_to_digit(_1: char) -> u32 {
         _0 = move ((_5 as Some).0: u32);
         StorageDead(_6);
         StorageDead(_5);
-        goto -> bb8;
+        goto -> bb7;
     }
 
     bb6: {
-        unreachable;
+        StorageDead(_4);
+        StorageDead(_3);
+        StorageDead(_2);
+        _0 = const 0_u32;
+        goto -> bb7;
     }
 
     bb7: {
-        StorageDead(_4);
+        return;
-        _0 = const 0_u32;
-        goto -> bb8;
     }
 
     bb8: {
-        return;
+        unreachable;
     }
 }

tests/mir-opt/simplify_locals_fixedpoint.foo.SimplifyLocals-final.panic-abort.diff

@@ -28,7 +28,7 @@
   
       bb1: {
           _4 = discriminant((_1.1: std::option::Option<T>));
-          switchInt(move _4) -> [0: bb2, otherwise: bb3];
+          switchInt(move _4) -> [0: bb2, 1: bb3, otherwise: bb5];
       }
   
       bb2: {

tests/mir-opt/simplify_locals_fixedpoint.foo.SimplifyLocals-final.panic-unwind.diff

@@ -28,7 +28,7 @@
   
       bb1: {
           _4 = discriminant((_1.1: std::option::Option<T>));
-          switchInt(move _4) -> [0: bb2, otherwise: bb3];
+          switchInt(move _4) -> [0: bb2, 1: bb3, otherwise: bb5];
       }
   
       bb2: {

tests/mir-opt/uninhabited_enum_branching.otherwise_t4_uninhabited_default_2.UninhabitedEnumBranching.panic-abort.diff

@@ -16,15 +16,11 @@
           StorageLive(_2);
           _2 = Test4::C;
           _3 = discriminant(_2);
--         switchInt(move _3) -> [0: bb1, 1: bb5, 2: bb6, otherwise: bb2];
+-         switchInt(move _3) -> [0: bb2, 1: bb5, 2: bb6, otherwise: bb1];
-+         switchInt(move _3) -> [0: bb1, 1: bb5, 2: bb6, 3: bb2, otherwise: bb8];
++         switchInt(move _3) -> [0: bb2, 1: bb5, 2: bb6, 3: bb1, otherwise: bb8];
       }
   
       bb1: {
-          switchInt(((_2 as A).0: i32)) -> [1: bb3, 2: bb4, otherwise: bb2];
-      }
-  
-      bb2: {
           StorageLive(_7);
           _7 = const "A(other)D";
           _1 = &(*_7);
@@ -32,6 +28,10 @@
           goto -> bb7;
       }
   
+      bb2: {
+          switchInt(((_2 as A).0: i32)) -> [1: bb3, 2: bb4, otherwise: bb1];
+      }
+  
       bb3: {
           _1 = const "A(1)";
           goto -> bb7;

tests/mir-opt/uninhabited_enum_branching.otherwise_t5_uninhabited_default.UninhabitedEnumBranching.panic-abort.diff

@@ -5,7 +5,7 @@
       let mut _0: ();
       let _1: &str;
       let mut _2: Test5<T>;
-      let mut _3: isize;
+      let mut _3: i8;
       let _4: &str;
       let _5: &str;
       let _6: &str;
@@ -15,7 +15,8 @@
           StorageLive(_2);
           _2 = Test5::<T>::C;
           _3 = discriminant(_2);
-          switchInt(move _3) -> [0: bb2, 1: bb3, 2: bb4, otherwise: bb1];
+-         switchInt(move _3) -> [255: bb2, 0: bb3, 5: bb4, otherwise: bb1];
++         switchInt(move _3) -> [255: bb2, 0: bb3, 5: bb4, 3: bb1, otherwise: bb7];
       }
   
       bb1: {
@@ -56,6 +57,10 @@
           StorageDead(_1);
           _0 = const ();
           return;
++     }
++ 
++     bb7: {
++         unreachable;
       }
   }
   

tests/mir-opt/uninhabited_enum_branching.otherwise_t5_uninhabited_default.UninhabitedEnumBranching.panic-unwind.diff

@@ -5,7 +5,7 @@
       let mut _0: ();
       let _1: &str;
       let mut _2: Test5<T>;
-      let mut _3: isize;
+      let mut _3: i8;
       let _4: &str;
       let _5: &str;
       let _6: &str;
@@ -15,7 +15,8 @@
           StorageLive(_2);
           _2 = Test5::<T>::C;
           _3 = discriminant(_2);
-          switchInt(move _3) -> [0: bb2, 1: bb3, 2: bb4, otherwise: bb1];
+-         switchInt(move _3) -> [255: bb2, 0: bb3, 5: bb4, otherwise: bb1];
++         switchInt(move _3) -> [255: bb2, 0: bb3, 5: bb4, 3: bb1, otherwise: bb8];
       }
   
       bb1: {
@@ -60,6 +61,10 @@
   
       bb7 (cleanup): {
           resume;
++     }
++ 
++     bb8: {
++         unreachable;
       }
   }
   

tests/mir-opt/uninhabited_enum_branching.rs

@@ -32,11 +32,12 @@ enum Test4 {
     D,
 }
 
+#[repr(i8)]
 enum Test5<T> {
-    A(T),
+    A(T) = -1,
-    B(T),
+    B(T) = 0,
-    C,
+    C = 5,
-    D,
+    D = 3,
 }
 
 struct Plop {
@@ -165,10 +166,9 @@ fn otherwise_t4() {
 fn otherwise_t5_uninhabited_default<T>() {
     // CHECK-LABEL: fn otherwise_t5_uninhabited_default(
     // CHECK: [[discr:_.*]] = discriminant(
-    // CHECK: switchInt(move [[discr]]) -> [0: bb2, 1: bb3, 2: bb4, otherwise: bb1];
+    // CHECK: switchInt(move [[discr]]) -> [255: bb2, 0: bb3, 5: bb4, 3: bb1, otherwise: [[unreachable:bb.*]]];
-    // CHECK: bb1: {
+    // CHECK: [[unreachable]]: {
-    // CHECK-NOT: unreachable;
+    // CHECK-NEXT: unreachable;
-    // CHECK: }
     match Test5::<T>::C {
         Test5::A(_) => "A(T)",
         Test5::B(_) => "B(T)",