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coverage: Skip spans that can't be un-expanded back to the function body #118525

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merged 1 commit into from
Dec 3, 2023
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coverage: Skip spans that can't be un-expanded back to the function body #118525

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12 changes: 7 additions & 5 deletions compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -63,14 +63,14 @@ fn bcb_to_initial_coverage_spans<'a, 'tcx>(

let statement_spans = data.statements.iter().filter_map(move |statement| {
let expn_span = filtered_statement_span(statement)?;
let span = function_source_span(expn_span, body_span);
let span = unexpand_into_body_span(expn_span, body_span)?;

Some(CoverageSpan::new(span, expn_span, bcb, is_closure(statement)))
});

let terminator_span = Some(data.terminator()).into_iter().filter_map(move |terminator| {
let expn_span = filtered_terminator_span(terminator)?;
let span = function_source_span(expn_span, body_span);
let span = unexpand_into_body_span(expn_span, body_span)?;

Some(CoverageSpan::new(span, expn_span, bcb, false))
});
Expand Down Expand Up @@ -180,14 +180,16 @@ fn filtered_terminator_span(terminator: &Terminator<'_>) -> Option<Span> {
/// Returns an extrapolated span (pre-expansion[^1]) corresponding to a range
/// within the function's body source. This span is guaranteed to be contained
/// within, or equal to, the `body_span`. If the extrapolated span is not
/// contained within the `body_span`, the `body_span` is returned.
/// contained within the `body_span`, `None` is returned.
///
/// [^1]Expansions result from Rust syntax including macros, syntactic sugar,
/// etc.).
#[inline]
fn function_source_span(span: Span, body_span: Span) -> Span {
fn unexpand_into_body_span(span: Span, body_span: Span) -> Option<Span> {
use rustc_span::source_map::original_sp;

// FIXME(#118525): Consider switching from `original_sp` to `Span::find_ancestor_inside`,
// which is similar but gives slightly different results in some edge cases.
Comment on lines +191 to +192
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I wasn't comfortable with actually switching to Span::find_ancestor_inside as part of this PR, since I don't quite understand the subtle differences from the status quo.

So instead I'm leaving this note to indicate that it might be worth looking into.

let original_span = original_sp(span, body_span).with_ctxt(body_span.ctxt());
if body_span.contains(original_span) { original_span } else { body_span }
body_span.contains(original_span).then_some(original_span)
}
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This function looks a lot like Span::find_ancestor_inside. Should it be reused? Or is there a subtle difference?

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I was mostly just modifying the existing code, and didn't know about Span::find_ancestor_inside as a potential option.

I tried switching over, and the results are mostly the same, with a few small differences in some corner cases.

At a glance the changes seem like they might be improvements, but I'm not confident in that conclusion. What I might do is stick with the status quo (original_sp) for now, but leave a FIXME to remind me to investigate switching over as a separate PR.

12 changes: 6 additions & 6 deletions tests/coverage/async.cov-map
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Original file line number Diff line number Diff line change
Expand Up @@ -74,28 +74,28 @@ Number of file 0 mappings: 6
= ((c0 + c1) - c1)

Function name: async::executor::block_on::VTABLE::{closure#0}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 72, 11, 00, 33]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 72, 11, 00, 31]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 114, 17) to (start + 0, 51)
- Code(Counter(0)) at (prev + 114, 17) to (start + 0, 49)

Function name: async::executor::block_on::VTABLE::{closure#1}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 73, 11, 00, 33]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 73, 11, 00, 31]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 115, 17) to (start + 0, 51)
- Code(Counter(0)) at (prev + 115, 17) to (start + 0, 49)

Function name: async::executor::block_on::VTABLE::{closure#2}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 74, 11, 00, 33]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 74, 11, 00, 31]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 116, 17) to (start + 0, 51)
- Code(Counter(0)) at (prev + 116, 17) to (start + 0, 49)

Function name: async::executor::block_on::VTABLE::{closure#3}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 75, 11, 00, 13]
Expand Down
12 changes: 6 additions & 6 deletions tests/coverage/async2.cov-map
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -78,28 +78,28 @@ Number of file 0 mappings: 6
= ((c0 + c1) - c1)

Function name: async2::executor::block_on::VTABLE::{closure#0}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 2b, 11, 00, 33]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 2b, 11, 00, 31]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 43, 17) to (start + 0, 51)
- Code(Counter(0)) at (prev + 43, 17) to (start + 0, 49)

Function name: async2::executor::block_on::VTABLE::{closure#1}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 2c, 11, 00, 33]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 2c, 11, 00, 31]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 44, 17) to (start + 0, 51)
- Code(Counter(0)) at (prev + 44, 17) to (start + 0, 49)

Function name: async2::executor::block_on::VTABLE::{closure#2}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 2d, 11, 00, 33]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 2d, 11, 00, 31]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 45, 17) to (start + 0, 51)
- Code(Counter(0)) at (prev + 45, 17) to (start + 0, 49)

Function name: async2::executor::block_on::VTABLE::{closure#3}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 2e, 11, 00, 13]
Expand Down
4 changes: 2 additions & 2 deletions tests/coverage/inline.cov-map
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Original file line number Diff line number Diff line change
Expand Up @@ -15,12 +15,12 @@ Number of file 0 mappings: 5
= ((c0 + c1) - c1)

Function name: inline::error
Raw bytes (9): 0x[01, 01, 00, 01, 01, 31, 01, 02, 02]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 31, 01, 01, 14]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 49, 1) to (start + 2, 2)
- Code(Counter(0)) at (prev + 49, 1) to (start + 1, 20)

Function name: inline::length::<char>
Raw bytes (9): 0x[01, 01, 00, 01, 01, 1e, 01, 02, 02]
Expand Down
2 changes: 1 addition & 1 deletion tests/coverage/inline.coverage
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Original file line number Diff line number Diff line change
Expand Up @@ -50,5 +50,5 @@
LL| |#[inline(always)]
LL| 0|fn error() {
LL| 0| panic!("error");
LL| 0|}
LL| |}

12 changes: 6 additions & 6 deletions tests/coverage/unreachable.cov-map
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Original file line number Diff line number Diff line change
@@ -1,24 +1,24 @@
Function name: unreachable::UNREACHABLE_CLOSURE::{closure#0}
Raw bytes (9): 0x[01, 01, 00, 01, 01, 0f, 27, 00, 49]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 0f, 27, 00, 47]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 15, 39) to (start + 0, 73)
- Code(Counter(0)) at (prev + 15, 39) to (start + 0, 71)

Function name: unreachable::unreachable_function
Raw bytes (9): 0x[01, 01, 00, 01, 01, 11, 01, 02, 02]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 11, 01, 01, 25]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 17, 1) to (start + 2, 2)
- Code(Counter(0)) at (prev + 17, 1) to (start + 1, 37)

Function name: unreachable::unreachable_intrinsic
Raw bytes (9): 0x[01, 01, 00, 01, 01, 16, 01, 02, 02]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 16, 01, 01, 2c]
Number of files: 1
- file 0 => global file 1
Number of expressions: 0
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 22, 1) to (start + 2, 2)
- Code(Counter(0)) at (prev + 22, 1) to (start + 1, 44)

4 changes: 2 additions & 2 deletions tests/coverage/unreachable.coverage
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Original file line number Diff line number Diff line change
Expand Up @@ -16,12 +16,12 @@
LL| |
LL| 0|fn unreachable_function() {
LL| 0| unsafe { unreachable_unchecked() }
LL| 0|}
LL| |}
LL| |
LL| |// Use an intrinsic to more reliably trigger unreachable-propagation.
LL| 0|fn unreachable_intrinsic() {
LL| 0| unsafe { std::intrinsics::unreachable() }
LL| 0|}
LL| |}
LL| |
LL| |#[coverage(off)]
LL| |fn main() {
Expand Down
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