From 95b968ea6adbb25586a4514d941f692608f64343 Mon Sep 17 00:00:00 2001
From: Nadrieril <nadrieril+git@gmail.com>
Date: Wed, 21 Feb 2024 00:48:15 +0100
Subject: [PATCH] Move a bit of the logic to `match_simplified_candidates`

---
 .../rustc_mir_build/src/build/matches/mod.rs  | 82 ++++++++++---------
 1 file changed, 42 insertions(+), 40 deletions(-)

diff --git a/compiler/rustc_mir_build/src/build/matches/mod.rs b/compiler/rustc_mir_build/src/build/matches/mod.rs
index d25d6f833137..cf2ffc2a9843 100644
--- a/compiler/rustc_mir_build/src/build/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/build/matches/mod.rs
@@ -1260,9 +1260,34 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     fake_borrows,
                 )
             }
+            [first, remaining @ ..]
+                if matches!(first.match_pairs[0].pattern.kind, PatKind::Or { .. }) =>
+            {
+                // The first candidate has an or-pattern.
+                let remainder_start = self.cfg.start_new_block();
+                // Test the or-pattern.
+                self.test_or_candidate(
+                    span,
+                    scrutinee_span,
+                    first,
+                    start_block,
+                    remainder_start,
+                    fake_borrows,
+                );
+                // Test the remaining candidates.
+                self.match_candidates(
+                    span,
+                    scrutinee_span,
+                    remainder_start,
+                    otherwise_block,
+                    remaining,
+                    fake_borrows,
+                );
+            }
             candidates => {
-                // The first candidate has some unsatisfied match pairs; we proceed to do more tests.
-                self.test_candidates_with_or(
+                // The first candidate has some unsatisfied match pairs that aren't or-patterns; we
+                // proceed to do more tests.
+                self.test_candidates(
                     span,
                     scrutinee_span,
                     candidates,
@@ -1350,8 +1375,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         otherwise_block
     }
 
-    /// Tests a candidate where there are only or-patterns left to test, or
-    /// forwards to [Builder::test_candidates].
+    /// Tests a candidate whose first match-pair is an or-pattern.
     ///
     /// Given a pattern `(P | Q, R | S)` we (in principle) generate a CFG like
     /// so:
@@ -1403,40 +1427,28 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
     ///      |
     ///     ...
     /// ```
-    fn test_candidates_with_or(
+    fn test_or_candidate(
         &mut self,
         span: Span,
         scrutinee_span: Span,
-        candidates: &mut [&mut Candidate<'_, 'tcx>],
+        candidate: &mut Candidate<'_, 'tcx>,
         start_block: BasicBlock,
         otherwise_block: BasicBlock,
         fake_borrows: &mut Option<FxIndexSet<Place<'tcx>>>,
     ) {
-        let (first_candidate, remaining_candidates) = candidates.split_first_mut().unwrap();
-        assert!(first_candidate.subcandidates.is_empty());
-        if !matches!(first_candidate.match_pairs[0].pattern.kind, PatKind::Or { .. }) {
-            self.test_candidates(
-                span,
-                scrutinee_span,
-                candidates,
-                start_block,
-                otherwise_block,
-                fake_borrows,
-            );
-            return;
-        }
-
-        let match_pairs = mem::take(&mut first_candidate.match_pairs);
+        assert!(candidate.subcandidates.is_empty());
+        let match_pairs = mem::take(&mut candidate.match_pairs);
         let (first_match_pair, remaining_match_pairs) = match_pairs.split_first().unwrap();
-        let PatKind::Or { ref pats } = &first_match_pair.pattern.kind else { unreachable!() };
+        let PatKind::Or { ref pats } = &first_match_pair.pattern.kind else {
+            bug!("Only call `test_or_candidate` if the first match pair is an or-pattern")
+        };
 
-        let remainder_start = self.cfg.start_new_block();
         let or_span = first_match_pair.pattern.span;
         // Test the alternatives of this or-pattern.
         self.test_or_pattern(
-            first_candidate,
+            candidate,
             start_block,
-            remainder_start,
+            otherwise_block,
             pats,
             or_span,
             &first_match_pair.place,
@@ -1448,34 +1460,24 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
             // We could add them to the or-candidates before the call to `test_or_pattern` but this
             // would make it impossible to detect simplifiable or-patterns. That would guarantee
             // exponentially large CFGs for cases like `(1 | 2, 3 | 4, ...)`.
-            first_candidate.visit_leaves(|leaf_candidate| {
+            candidate.visit_leaves(|leaf_candidate| {
                 assert!(leaf_candidate.match_pairs.is_empty());
                 leaf_candidate.match_pairs.extend(remaining_match_pairs.iter().cloned());
                 let or_start = leaf_candidate.pre_binding_block.unwrap();
                 // In a case like `(a | b, c | d)`, if `a` succeeds and `c | d` fails, we know `(b,
                 // c | d)` will fail too. If there is no guard, we skip testing of `b` by branching
-                // directly to `remainder_start`. If there is a guard, we have to try `(b, c | d)`.
-                let or_otherwise = leaf_candidate.otherwise_block.unwrap_or(remainder_start);
-                self.test_candidates_with_or(
+                // directly to `otherwise_block`. If there is a guard, we have to try `(b, c | d)`.
+                let or_otherwise = leaf_candidate.otherwise_block.unwrap_or(otherwise_block);
+                self.match_simplified_candidates(
                     span,
                     scrutinee_span,
-                    &mut [leaf_candidate],
                     or_start,
                     or_otherwise,
+                    &mut [leaf_candidate],
                     fake_borrows,
                 );
             });
         }
-
-        // Test the remaining candidates.
-        self.match_candidates(
-            span,
-            scrutinee_span,
-            remainder_start,
-            otherwise_block,
-            remaining_candidates,
-            fake_borrows,
-        );
     }
 
     #[instrument(