Always merge simplifiable or-patterns

Author: Nadrieril

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

@@ -1276,8 +1276,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 // At least one of the candidates has been split into subcandidates.
                 // We need to change the candidate list to include those.
                 let mut new_candidates = Vec::new();
-
-                for candidate in candidates {
+                for candidate in candidates.iter_mut() {
                     candidate.visit_leaves(|leaf_candidate| new_candidates.push(leaf_candidate));
                 }
                 self.match_simplified_candidates(
@@ -1287,6 +1286,10 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     otherwise_block,
                     &mut *new_candidates,
                 );
+
+                for candidate in candidates {
+                    self.merge_trivial_subcandidates(candidate);
+                }
             } else {
                 self.match_simplified_candidates(
                     span,

tests/mir-opt/issues/issue_75439.foo.MatchBranchSimplification.diff

@@ -26,18 +26,20 @@
           _3 = _1;
           _2 = move _3 as [u32; 4] (Transmute);
           StorageDead(_3);
-          switchInt(_2[0 of 4]) -> [0: bb1, otherwise: bb6];
+          switchInt(_2[0 of 4]) -> [0: bb1, otherwise: bb4];
       }
 
       bb1: {
-          switchInt(_2[1 of 4]) -> [0: bb2, otherwise: bb6];
+          switchInt(_2[1 of 4]) -> [0: bb2, otherwise: bb4];
       }
 
       bb2: {
-          switchInt(_2[2 of 4]) -> [0: bb4, 4294901760: bb5, otherwise: bb6];
+          switchInt(_2[2 of 4]) -> [0: bb3, 4294901760: bb3, otherwise: bb4];
       }
 
       bb3: {
+          StorageLive(_4);
+          _4 = _2[3 of 4];
           StorageLive(_5);
           StorageLive(_6);
           _6 = _4;
@@ -46,27 +48,15 @@
           _0 = Option::<[u8; 4]>::Some(move _5);
           StorageDead(_5);
           StorageDead(_4);
-          goto -> bb7;
+          goto -> bb5;
       }
 
       bb4: {
-          StorageLive(_4);
-          _4 = _2[3 of 4];
-          goto -> bb3;
-      }
-  
-      bb5: {
-          StorageLive(_4);
-          _4 = _2[3 of 4];
-          goto -> bb3;
-      }
-  
-      bb6: {
           _0 = Option::<[u8; 4]>::None;
-          goto -> bb7;
+          goto -> bb5;
       }
 
-      bb7: {
+      bb5: {
           StorageDead(_2);
           return;
       }