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coverage: Simplify adding BCB successors to the traversal worklists

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This commit is contained in:
Zalathar 2023-10-12 13:31:35 +11:00
parent 59f4f1c89d
commit d99ab97b02
1 changed files with 37 additions and 36 deletions
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73
compiler/rustc_mir_transform/src/coverage/graph.rs
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@ -450,7 +450,7 @@ impl<'a> TraverseCoverageGraphWithLoops<'a> {
worklist: VecDeque::new(), worklist: VecDeque::new(),
}); });
} }
self.extend_worklist(bcb); self.add_successors_to_worklists(bcb);
return Some(bcb); return Some(bcb);
} else { } else {
// Strip contexts with empty worklists from the top of the stack // Strip contexts with empty worklists from the top of the stack
@ -461,10 +461,10 @@ impl<'a> TraverseCoverageGraphWithLoops<'a> {
None None
} }
pub fn extend_worklist(&mut self, bcb: BasicCoverageBlock) { pub fn add_successors_to_worklists(&mut self, bcb: BasicCoverageBlock) {
let Self { basic_coverage_blocks, .. } = *self; let successors = &self.basic_coverage_blocks.successors[bcb];
let successors = &basic_coverage_blocks.successors[bcb];
debug!("{:?} has {} successors:", bcb, successors.len()); debug!("{:?} has {} successors:", bcb, successors.len());
for &successor in successors { for &successor in successors {
if successor == bcb { if successor == bcb {
debug!( debug!(
@ -473,43 +473,44 @@ impl<'a> TraverseCoverageGraphWithLoops<'a> {
bcb bcb
); );
// Don't re-add this successor to the worklist. We are already processing it. // Don't re-add this successor to the worklist. We are already processing it.
// FIXME: This claims to skip just the self-successor, but it actually skips
// all other successors as well. Does that matter?
break; break;
} }
for context in self.context_stack.iter_mut().rev() {
// Add successors of the current BCB to the appropriate context. Successors that
// stay within a loop are added to the BCBs context worklist. Successors that
// exit the loop (they are not dominated by the loop header) must be reachable
// from other BCBs outside the loop, and they will be added to a different
// worklist.
//
// Branching blocks (with more than one successor) must be processed before
// blocks with only one successor, to prevent unnecessarily complicating
// `Expression`s by creating a Counter in a `BasicCoverageBlock` that the
// branching block would have given an `Expression` (or vice versa).
let (some_successor_to_add, _) =
if let Some(loop_header) = context.loop_header {
if basic_coverage_blocks.dominates(loop_header, successor) {
(Some(successor), Some(loop_header))
} else {
(None, None)
}
} else {
(Some(successor), None)
};
// FIXME: The code below had debug messages claiming to add items to a // Add successors of the current BCB to the appropriate context. Successors that
// particular end of the worklist, but was confused about which end was // stay within a loop are added to the BCBs context worklist. Successors that
// which. The existing behaviour has been preserved for now, but it's // exit the loop (they are not dominated by the loop header) must be reachable
// unclear what the intended behaviour was. // from other BCBs outside the loop, and they will be added to a different
// worklist.
//
// Branching blocks (with more than one successor) must be processed before
// blocks with only one successor, to prevent unnecessarily complicating
// `Expression`s by creating a Counter in a `BasicCoverageBlock` that the
// branching block would have given an `Expression` (or vice versa).
if let Some(successor_to_add) = some_successor_to_add { let context = self
if basic_coverage_blocks.successors[successor_to_add].len() > 1 { .context_stack
context.worklist.push_back(successor_to_add); .iter_mut()
} else { .rev()
context.worklist.push_front(successor_to_add); .find(|context| match context.loop_header {
Some(loop_header) => {
self.basic_coverage_blocks.dominates(loop_header, successor)
} }
break; None => true,
} })
.unwrap_or_else(|| bug!("should always fall back to the root non-loop context"));
debug!("adding to worklist for {:?}", context.loop_header);
// FIXME: The code below had debug messages claiming to add items to a
// particular end of the worklist, but was confused about which end was
// which. The existing behaviour has been preserved for now, but it's
// unclear what the intended behaviour was.
if self.basic_coverage_blocks.successors[successor].len() > 1 {
context.worklist.push_back(successor);
} else {
context.worklist.push_front(successor);
} }
} }
} }