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Improve merge_trivial_subcandidates

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Zalathar 2024-07-18 20:58:52 +10:00
parent 3b7e4bc77a
commit e091c356fa
1 changed files with 15 additions and 5 deletions
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20
compiler/rustc_mir_build/src/build/matches/mod.rs
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@ -1744,8 +1744,12 @@ fn finalize_or_candidate(
/// Try to merge all of the subcandidates of the given candidate into one. This avoids /// Try to merge all of the subcandidates of the given candidate into one. This avoids
/// exponentially large CFGs in cases like `(1 | 2, 3 | 4, ...)`. The candidate should have been /// exponentially large CFGs in cases like `(1 | 2, 3 | 4, ...)`. The candidate should have been
/// expanded with `create_or_subcandidates`. /// expanded with `create_or_subcandidates`.
///
/// Note that this takes place _after_ the subcandidates have participated
/// in match tree lowering.
fn merge_trivial_subcandidates(&mut self, candidate: &mut Candidate<'_, 'tcx>) { fn merge_trivial_subcandidates(&mut self, candidate: &mut Candidate<'_, 'tcx>) {
if candidate.subcandidates.is_empty() || candidate.has_guard { assert!(!candidate.subcandidates.is_empty());
if candidate.has_guard {
// FIXME(or_patterns; matthewjasper) Don't give up if we have a guard. // FIXME(or_patterns; matthewjasper) Don't give up if we have a guard.
return; return;
} }
@ -1759,7 +1763,8 @@ fn merge_trivial_subcandidates(&mut self, candidate: &mut Candidate<'_, 'tcx>) {
} }
let mut last_otherwise = None; let mut last_otherwise = None;
let any_matches = self.cfg.start_new_block(); let shared_pre_binding_block = self.cfg.start_new_block();
// This candidate is about to become a leaf, so unset `or_span`.
let or_span = candidate.or_span.take().unwrap(); let or_span = candidate.or_span.take().unwrap();
let source_info = self.source_info(or_span); let source_info = self.source_info(or_span);
@ -1767,12 +1772,17 @@ fn merge_trivial_subcandidates(&mut self, candidate: &mut Candidate<'_, 'tcx>) {
candidate.false_edge_start_block = candidate.subcandidates[0].false_edge_start_block; candidate.false_edge_start_block = candidate.subcandidates[0].false_edge_start_block;
} }
// Remove the (known-trivial) subcandidates from the candidate tree,
// so that they aren't visible after match tree lowering, and wire them
// all to join up at a single shared pre-binding block.
// (Note that the subcandidates have already had their part of the match
// tree lowered by this point, which is why we can add a goto to them.)
for subcandidate in mem::take(&mut candidate.subcandidates) { for subcandidate in mem::take(&mut candidate.subcandidates) {
let or_block = subcandidate.pre_binding_block.unwrap(); let subcandidate_block = subcandidate.pre_binding_block.unwrap();
self.cfg.goto(or_block, source_info, any_matches); self.cfg.goto(subcandidate_block, source_info, shared_pre_binding_block);
last_otherwise = subcandidate.otherwise_block; last_otherwise = subcandidate.otherwise_block;
} }
candidate.pre_binding_block = Some(any_matches); candidate.pre_binding_block = Some(shared_pre_binding_block);
assert!(last_otherwise.is_some()); assert!(last_otherwise.is_some());
candidate.otherwise_block = last_otherwise; candidate.otherwise_block = last_otherwise;
} }