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Rollup merge of #118695 - Zalathar:push-refined, r=davidtwco
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coverage: Merge refined spans in a separate final pass

Pulling this merge step out of `push_refined_span` and into a separate pass lets us push directly to `refined_spans` instead of calling a helper method.

Because the compiler can now see partial borrows of `refined_spans`, we can remove some extra code that was jumping through hoops to satisfy the borrow checker.

---

``@rustbot`` label +A-code-coverage
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@matthiaskrgr
matthiaskrgr authored Dec 8, 2023
2 parents 646d627 + 9a43215 commit f7c892e
Showing 1 changed file with 37 additions and 50 deletions.
87 changes: 37 additions & 50 deletions compiler/rustc_mir_transform/src/coverage/spans.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -89,10 +89,10 @@ impl CoverageSpan {
}
}

pub fn merge_from(&mut self, mut other: CoverageSpan) {
debug_assert!(self.is_mergeable(&other));
pub fn merge_from(&mut self, other: &Self) {
debug_assert!(self.is_mergeable(other));
self.span = self.span.to(other.span);
self.merged_spans.append(&mut other.merged_spans);
self.merged_spans.extend_from_slice(&other.merged_spans);
}

pub fn cutoff_statements_at(&mut self, cutoff_pos: BytePos) {
Expand Down Expand Up @@ -267,15 +267,15 @@ impl<'a> CoverageSpansGenerator<'a> {
if curr.is_mergeable(prev) {
debug!(" same bcb (and neither is a closure), merge with prev={prev:?}");
let prev = self.take_prev();
self.curr_mut().merge_from(prev);
self.curr_mut().merge_from(&prev);
self.maybe_push_macro_name_span();
// Note that curr.span may now differ from curr_original_span
} else if prev.span.hi() <= curr.span.lo() {
debug!(
" different bcbs and disjoint spans, so keep curr for next iter, and add prev={prev:?}",
);
let prev = self.take_prev();
self.push_refined_span(prev);
self.refined_spans.push(prev);
self.maybe_push_macro_name_span();
} else if prev.is_closure {
// drop any equal or overlapping span (`curr`) and keep `prev` to test again in the
Expand Down Expand Up @@ -322,11 +322,10 @@ impl<'a> CoverageSpansGenerator<'a> {
let prev = self.take_prev();
debug!(" AT END, adding last prev={prev:?}");

// Take `pending_dups` so that we can drain it while calling self methods.
// It is never used as a field after this point.
for dup in std::mem::take(&mut self.pending_dups) {
// Drain any remaining dups into the output.
for dup in self.pending_dups.drain(..) {
debug!(" ...adding at least one pending dup={:?}", dup);
self.push_refined_span(dup);
self.refined_spans.push(dup);
}

// Async functions wrap a closure that implements the body to be executed. The enclosing
Expand All @@ -343,28 +342,27 @@ impl<'a> CoverageSpansGenerator<'a> {
};

if !body_ends_with_closure {
self.push_refined_span(prev);
self.refined_spans.push(prev);
}

// Do one last merge pass, to simplify the output.
self.refined_spans.dedup_by(|b, a| {
if a.is_mergeable(b) {
debug!(?a, ?b, "merging list-adjacent refined spans");
a.merge_from(b);
true
} else {
false
}
});

// Remove `CoverageSpan`s derived from closures, originally added to ensure the coverage
// regions for the current function leave room for the closure's own coverage regions
// (injected separately, from the closure's own MIR).
self.refined_spans.retain(|covspan| !covspan.is_closure);
self.refined_spans
}

fn push_refined_span(&mut self, covspan: CoverageSpan) {
if let Some(last) = self.refined_spans.last_mut()
&& last.is_mergeable(&covspan)
{
// Instead of pushing the new span, merge it with the last refined span.
debug!(?last, ?covspan, "merging new refined span with last refined span");
last.merge_from(covspan);
} else {
self.refined_spans.push(covspan);
}
}

/// If `curr` is part of a new macro expansion, carve out and push a separate
/// span that ends just after the macro name and its subsequent `!`.
fn maybe_push_macro_name_span(&mut self) {
Expand Down Expand Up @@ -397,7 +395,7 @@ impl<'a> CoverageSpansGenerator<'a> {
" and curr starts a new macro expansion, so add a new span just for \
the macro `{visible_macro}!`, new span={macro_name_cov:?}",
);
self.push_refined_span(macro_name_cov);
self.refined_spans.push(macro_name_cov);
}

fn curr(&self) -> &CoverageSpan {
Expand Down Expand Up @@ -454,19 +452,14 @@ impl<'a> CoverageSpansGenerator<'a> {
previous iteration, or prev started a new disjoint span"
);
if last_dup.span.hi() <= self.curr().span.lo() {
// Temporarily steal `pending_dups` into a local, so that we can
// drain it while calling other self methods.
let mut pending_dups = std::mem::take(&mut self.pending_dups);
for dup in pending_dups.drain(..) {
for dup in self.pending_dups.drain(..) {
debug!(" ...adding at least one pending={:?}", dup);
self.push_refined_span(dup);
self.refined_spans.push(dup);
}
// The list of dups is now empty, but we can recycle its capacity.
assert!(pending_dups.is_empty() && self.pending_dups.is_empty());
self.pending_dups = pending_dups;
} else {
self.pending_dups.clear();
}
assert!(self.pending_dups.is_empty());
}

/// Advance `prev` to `curr` (if any), and `curr` to the next `CoverageSpan` in sorted order.
Expand Down Expand Up @@ -513,22 +506,18 @@ impl<'a> CoverageSpansGenerator<'a> {
let has_pre_closure_span = prev.span.lo() < right_cutoff;
let has_post_closure_span = prev.span.hi() > right_cutoff;

// Temporarily steal `pending_dups` into a local, so that we can
// mutate and/or drain it while calling other self methods.
let mut pending_dups = std::mem::take(&mut self.pending_dups);

if has_pre_closure_span {
let mut pre_closure = self.prev().clone();
pre_closure.span = pre_closure.span.with_hi(left_cutoff);
debug!(" prev overlaps a closure. Adding span for pre_closure={:?}", pre_closure);
if !pending_dups.is_empty() {
for mut dup in pending_dups.iter().cloned() {
dup.span = dup.span.with_hi(left_cutoff);
debug!(" ...and at least one pre_closure dup={:?}", dup);
self.push_refined_span(dup);
}

for mut dup in self.pending_dups.iter().cloned() {
dup.span = dup.span.with_hi(left_cutoff);
debug!(" ...and at least one pre_closure dup={:?}", dup);
self.refined_spans.push(dup);
}
self.push_refined_span(pre_closure);

self.refined_spans.push(pre_closure);
}

if has_post_closure_span {
Expand All @@ -537,19 +526,17 @@ impl<'a> CoverageSpansGenerator<'a> {
// about how the `CoverageSpan`s are ordered.)
self.prev_mut().span = self.prev().span.with_lo(right_cutoff);
debug!(" Mutated prev.span to start after the closure. prev={:?}", self.prev());
for dup in pending_dups.iter_mut() {

for dup in &mut self.pending_dups {
debug!(" ...and at least one overlapping dup={:?}", dup);
dup.span = dup.span.with_lo(right_cutoff);
}

let closure_covspan = self.take_curr(); // Prevent this curr from becoming prev.
self.push_refined_span(closure_covspan); // since self.prev() was already updated
self.refined_spans.push(closure_covspan); // since self.prev() was already updated
} else {
pending_dups.clear();
self.pending_dups.clear();
}

// Restore the modified post-closure spans, or the empty vector's capacity.
assert!(self.pending_dups.is_empty());
self.pending_dups = pending_dups;
}

/// Called if `curr.span` equals `prev_original_span` (and potentially equal to all
Expand Down Expand Up @@ -645,7 +632,7 @@ impl<'a> CoverageSpansGenerator<'a> {
} else {
debug!(" ... adding modified prev={:?}", self.prev());
let prev = self.take_prev();
self.push_refined_span(prev);
self.refined_spans.push(prev);
}
} else {
// with `pending_dups`, `prev` cannot have any statements that don't overlap
Expand Down

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