Don't try to save an extra block

This is preparation for the next commit.

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

@@ -2021,19 +2021,7 @@ 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
@@ -2061,6 +2049,14 @@ 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;
  }
 }