Don't try to save an extra block

This is preparation for the next commit.

Author: Nadrieril

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -1958,19 +1958,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         // The block that we should branch to if none of the
         // `target_candidates` match.
-        let remainder_start = if !remaining_candidates.is_empty() {
-            let remainder_start = self.cfg.start_new_block();
-            self.match_candidates(
-                span,
-                scrutinee_span,
-                remainder_start,
-                otherwise_block,
-                remaining_candidates,
-            );
-            remainder_start
-        } else {
-            otherwise_block
-        };
+        let remainder_start = self.cfg.start_new_block();
 
         // For each outcome of test, process the candidates that still apply.
         let target_blocks: FxIndexMap<_, _> = target_candidates
@@ -1998,6 +1986,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             &test,
             target_blocks,
         );
+
+        self.match_candidates(
+            span,
+            scrutinee_span,
+            remainder_start,
+            otherwise_block,
+            remaining_candidates,
+        );
     }
 }
 

tests/mir-opt/building/issue_101867.main.built.after.mir

@@ -27,13 +27,13 @@ fn main() -> () {
         StorageLive(_5);
         PlaceMention(_1);
         _6 = discriminant(_1);
-        switchInt(move _6) -> [1: bb4, otherwise: bb3];
+        switchInt(move _6) -> [1: bb5, otherwise: bb4];
     }
 
     bb1: {
         StorageLive(_3);
         StorageLive(_4);
-        _4 = begin_panic::<&str>(const "explicit panic") -> bb8;
+        _4 = begin_panic::<&str>(const "explicit panic") -> bb9;
     }
 
     bb2: {
@@ -43,31 +43,35 @@ fn main() -> () {
     }
 
     bb3: {
-        goto -> bb7;
+        goto -> bb8;
     }
 
     bb4: {
-        falseEdge -> [real: bb6, imaginary: bb3];
+        goto -> bb3;
     }
 
     bb5: {
-        goto -> bb3;
+        falseEdge -> [real: bb7, imaginary: bb3];
     }
 
     bb6: {
+        goto -> bb4;
+    }
+
+    bb7: {
         _5 = ((_1 as Some).0: u8);
         _0 = const ();
         StorageDead(_5);
         StorageDead(_1);
         return;
     }
 
-    bb7: {
+    bb8: {
         StorageDead(_5);
         goto -> bb1;
     }
 
-    bb8 (cleanup): {
+    bb9 (cleanup): {
         resume;
     }
 }

tests/mir-opt/building/issue_49232.main.built.after.mir

@@ -17,15 +17,15 @@ fn main() -> () {
     }
 
     bb1: {
-        falseUnwind -> [real: bb2, unwind: bb14];
+        falseUnwind -> [real: bb2, unwind: bb15];
     }
 
     bb2: {
         StorageLive(_2);
         StorageLive(_3);
         _3 = const true;
         PlaceMention(_3);
-        switchInt(_3) -> [0: bb4, otherwise: bb6];
+        switchInt(_3) -> [0: bb5, otherwise: bb7];
     }
 
     bb3: {
@@ -34,59 +34,63 @@ fn main() -> () {
     }
 
     bb4: {
-        falseEdge -> [real: bb8, imaginary: bb6];
+        goto -> bb3;
     }
 
     bb5: {
-        goto -> bb3;
+        falseEdge -> [real: bb9, imaginary: bb7];
     }
 
     bb6: {
-        _0 = const ();
-        goto -> bb13;
+        goto -> bb4;
     }
 
     bb7: {
-        goto -> bb3;
+        _0 = const ();
+        goto -> bb14;
     }
 
     bb8: {
-        _2 = const 4_i32;
-        goto -> bb11;
+        goto -> bb4;
     }
 
     bb9: {
-        unreachable;
+        _2 = const 4_i32;
+        goto -> bb12;
     }
 
     bb10: {
-        goto -> bb11;
+        unreachable;
     }
 
     bb11: {
+        goto -> bb12;
+    }
+
+    bb12: {
         FakeRead(ForLet(None), _2);
         StorageDead(_3);
         StorageLive(_5);
         StorageLive(_6);
         _6 = &_2;
-        _5 = std::mem::drop::<&i32>(move _6) -> [return: bb12, unwind: bb14];
+        _5 = std::mem::drop::<&i32>(move _6) -> [return: bb13, unwind: bb15];
     }
 
-    bb12: {
+    bb13: {
         StorageDead(_6);
         StorageDead(_5);
         _1 = const ();
         StorageDead(_2);
         goto -> bb1;
     }
 
-    bb13: {
+    bb14: {
         StorageDead(_3);
         StorageDead(_2);
         return;
     }
 
-    bb14 (cleanup): {
+    bb15 (cleanup): {
         resume;
     }
 }