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coverage: Enlarge empty spans during MIR instrumentation, not codegen

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This allows us to assume that coverage spans will only be discarded during
codegen in very unusual situations.
This commit is contained in:
Zalathar 2025-05-04 14:09:52 +10:00
parent da1e442ebd
commit 339556eb02
8 changed files with 57 additions and 46 deletions
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28
compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/spans.rs
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@ -39,7 +39,10 @@ impl Coords {
/// or other expansions), and if it does happen then skipping a span or function is
/// better than an ICE or `llvm-cov` failure that the user might have no way to avoid.
pub(crate) fn make_coords(source_map: &SourceMap, file: &SourceFile, span: Span) -> Option<Coords> {
let span = ensure_non_empty_span(source_map, span)?;
if span.is_empty() {
debug_assert!(false, "can't make coords from empty span: {span:?}");
return None;
}
let lo = span.lo();
let hi = span.hi();
@ -70,29 +73,6 @@ pub(crate) fn make_coords(source_map: &SourceMap, file: &SourceFile, span: Span)
})
}
fn ensure_non_empty_span(source_map: &SourceMap, span: Span) -> Option<Span> {
if !span.is_empty() {
return Some(span);
}
// The span is empty, so try to enlarge it to cover an adjacent '{' or '}'.
source_map
.span_to_source(span, |src, start, end| try {
// Adjusting span endpoints by `BytePos(1)` is normally a bug,
// but in this case we have specifically checked that the character
// we're skipping over is one of two specific ASCII characters, so
// adjusting by exactly 1 byte is correct.
if src.as_bytes().get(end).copied() == Some(b'{') {
Some(span.with_hi(span.hi() + BytePos(1)))
} else if start > 0 && src.as_bytes()[start - 1] == b'}' {
Some(span.with_lo(span.lo() - BytePos(1)))
} else {
None
}
})
.ok()?
}
/// If `llvm-cov` sees a source region that is improperly ordered (end < start),
/// it will immediately exit with a fatal error. To prevent that from happening,
/// discard regions that are improperly ordered, or might be interpreted in a

38
compiler/rustc_mir_transform/src/coverage/spans.rs
View File

@ -1,7 +1,8 @@
use rustc_data_structures::fx::FxHashSet;
use rustc_middle::mir;
use rustc_middle::ty::TyCtxt;
use rustc_span::{DesugaringKind, ExpnKind, MacroKind, Span};
use rustc_span::source_map::SourceMap;
use rustc_span::{BytePos, DesugaringKind, ExpnKind, MacroKind, Span};
use tracing::instrument;
use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
@ -83,8 +84,18 @@ pub(super) fn extract_refined_covspans<'tcx>(
// Discard any span that overlaps with a hole.
discard_spans_overlapping_holes(&mut covspans, &holes);
// Perform more refinement steps after holes have been dealt with.
// Discard spans that overlap in unwanted ways.
let mut covspans = remove_unwanted_overlapping_spans(covspans);
// For all empty spans, either enlarge them to be non-empty, or discard them.
let source_map = tcx.sess.source_map();
covspans.retain_mut(|covspan| {
let Some(span) = ensure_non_empty_span(source_map, covspan.span) else { return false };
covspan.span = span;
true
});
// Merge covspans that can be merged.
covspans.dedup_by(|b, a| a.merge_if_eligible(b));
code_mappings.extend(covspans.into_iter().map(|Covspan { span, bcb }| {
@ -230,3 +241,26 @@ fn compare_spans(a: Span, b: Span) -> std::cmp::Ordering {
// - Both have the same start and span A extends further right
.then_with(|| Ord::cmp(&a.hi(), &b.hi()).reverse())
}
fn ensure_non_empty_span(source_map: &SourceMap, span: Span) -> Option<Span> {
if !span.is_empty() {
return Some(span);
}
// The span is empty, so try to enlarge it to cover an adjacent '{' or '}'.
source_map
.span_to_source(span, |src, start, end| try {
// Adjusting span endpoints by `BytePos(1)` is normally a bug,
// but in this case we have specifically checked that the character
// we're skipping over is one of two specific ASCII characters, so
// adjusting by exactly 1 byte is correct.
if src.as_bytes().get(end).copied() == Some(b'{') {
Some(span.with_hi(span.hi() + BytePos(1)))
} else if start > 0 && src.as_bytes()[start - 1] == b'}' {
Some(span.with_lo(span.lo() - BytePos(1)))
} else {
None
}
})
.ok()?
}

21
tests/coverage/async_closure.cov-map
View File

@ -37,32 +37,29 @@ Number of file 0 mappings: 8
Highest counter ID seen: c0
Function name: async_closure::main::{closure#0}
Raw bytes (14): 0x[01, 01, 00, 02, 01, 0b, 22, 00, 23, 01, 00, 23, 00, 24]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 0b, 22, 00, 24]
Number of files: 1
- file 0 => $DIR/async_closure.rs
Number of expressions: 0
Number of file 0 mappings: 2
- Code(Counter(0)) at (prev + 11, 34) to (start + 0, 35)
- Code(Counter(0)) at (prev + 0, 35) to (start + 0, 36)
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 11, 34) to (start + 0, 36)
Highest counter ID seen: c0
Function name: async_closure::main::{closure#0}
Raw bytes (14): 0x[01, 01, 00, 02, 01, 0b, 22, 00, 23, 01, 00, 23, 00, 24]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 0b, 22, 00, 24]
Number of files: 1
- file 0 => $DIR/async_closure.rs
Number of expressions: 0
Number of file 0 mappings: 2
- Code(Counter(0)) at (prev + 11, 34) to (start + 0, 35)
- Code(Counter(0)) at (prev + 0, 35) to (start + 0, 36)
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 11, 34) to (start + 0, 36)
Highest counter ID seen: c0
Function name: async_closure::main::{closure#0}::{closure#0}::<i16>
Raw bytes (14): 0x[01, 01, 00, 02, 01, 0b, 22, 00, 23, 01, 00, 23, 00, 24]
Raw bytes (9): 0x[01, 01, 00, 01, 01, 0b, 22, 00, 24]
Number of files: 1
- file 0 => $DIR/async_closure.rs
Number of expressions: 0
Number of file 0 mappings: 2
- Code(Counter(0)) at (prev + 11, 34) to (start + 0, 35)
- Code(Counter(0)) at (prev + 0, 35) to (start + 0, 36)
Number of file 0 mappings: 1
- Code(Counter(0)) at (prev + 11, 34) to (start + 0, 36)
Highest counter ID seen: c0

2
tests/mir-opt/coverage/branch_match_arms.main.InstrumentCoverage.diff
View File

@ -40,7 +40,7 @@
+ coverage Code { bcb: bcb5 } => $DIR/branch_match_arms.rs:19:17: 19:18 (#0);
+ coverage Code { bcb: bcb5 } => $DIR/branch_match_arms.rs:19:23: 19:30 (#0);
+ coverage Code { bcb: bcb5 } => $DIR/branch_match_arms.rs:19:31: 19:32 (#0);
+ coverage Code { bcb: bcb2 } => $DIR/branch_match_arms.rs:21:2: 21:2 (#0);
+ coverage Code { bcb: bcb2 } => $DIR/branch_match_arms.rs:21:1: 21:2 (#0);
+
bb0: {
+ Coverage::VirtualCounter(bcb0);

2
tests/mir-opt/coverage/instrument_coverage.bar.InstrumentCoverage.diff
View File

@ -6,7 +6,7 @@
+ coverage Code { bcb: bcb0 } => $DIR/instrument_coverage.rs:27:1: 27:17 (#0);
+ coverage Code { bcb: bcb0 } => $DIR/instrument_coverage.rs:28:5: 28:9 (#0);
+ coverage Code { bcb: bcb0 } => $DIR/instrument_coverage.rs:29:2: 29:2 (#0);
+ coverage Code { bcb: bcb0 } => $DIR/instrument_coverage.rs:29:1: 29:2 (#0);
+
bb0: {
+ Coverage::VirtualCounter(bcb0);

4
tests/mir-opt/coverage/instrument_coverage.main.InstrumentCoverage.diff
View File

@ -10,8 +10,8 @@
+ coverage Code { bcb: bcb0 } => $DIR/instrument_coverage.rs:13:1: 13:10 (#0);
+ coverage Code { bcb: bcb1 } => $DIR/instrument_coverage.rs:15:12: 15:15 (#0);
+ coverage Code { bcb: bcb2 } => $DIR/instrument_coverage.rs:16:13: 16:18 (#0);
+ coverage Code { bcb: bcb3 } => $DIR/instrument_coverage.rs:17:10: 17:10 (#0);
+ coverage Code { bcb: bcb2 } => $DIR/instrument_coverage.rs:19:2: 19:2 (#0);
+ coverage Code { bcb: bcb3 } => $DIR/instrument_coverage.rs:17:9: 17:10 (#0);
+ coverage Code { bcb: bcb2 } => $DIR/instrument_coverage.rs:19:1: 19:2 (#0);
+
bb0: {
+ Coverage::VirtualCounter(bcb0);

4
tests/mir-opt/coverage/instrument_coverage_cleanup.main.CleanupPostBorrowck.diff
View File

@ -10,8 +10,8 @@
coverage Code { bcb: bcb0 } => $DIR/instrument_coverage_cleanup.rs:13:1: 13:10 (#0);
coverage Code { bcb: bcb0 } => $DIR/instrument_coverage_cleanup.rs:14:8: 14:36 (#0);
coverage Code { bcb: bcb3 } => $DIR/instrument_coverage_cleanup.rs:14:37: 14:39 (#0);
coverage Code { bcb: bcb1 } => $DIR/instrument_coverage_cleanup.rs:14:39: 14:39 (#0);
coverage Code { bcb: bcb2 } => $DIR/instrument_coverage_cleanup.rs:15:2: 15:2 (#0);
coverage Code { bcb: bcb1 } => $DIR/instrument_coverage_cleanup.rs:14:38: 14:39 (#0);
coverage Code { bcb: bcb2 } => $DIR/instrument_coverage_cleanup.rs:15:1: 15:2 (#0);
coverage Branch { true_bcb: bcb3, false_bcb: bcb1 } => $DIR/instrument_coverage_cleanup.rs:14:8: 14:36 (#0);
bb0: {

4
tests/mir-opt/coverage/instrument_coverage_cleanup.main.InstrumentCoverage.diff
View File

@ -10,8 +10,8 @@
+ coverage Code { bcb: bcb0 } => $DIR/instrument_coverage_cleanup.rs:13:1: 13:10 (#0);
+ coverage Code { bcb: bcb0 } => $DIR/instrument_coverage_cleanup.rs:14:8: 14:36 (#0);
+ coverage Code { bcb: bcb3 } => $DIR/instrument_coverage_cleanup.rs:14:37: 14:39 (#0);
+ coverage Code { bcb: bcb1 } => $DIR/instrument_coverage_cleanup.rs:14:39: 14:39 (#0);
+ coverage Code { bcb: bcb2 } => $DIR/instrument_coverage_cleanup.rs:15:2: 15:2 (#0);
+ coverage Code { bcb: bcb1 } => $DIR/instrument_coverage_cleanup.rs:14:38: 14:39 (#0);
+ coverage Code { bcb: bcb2 } => $DIR/instrument_coverage_cleanup.rs:15:1: 15:2 (#0);
+ coverage Branch { true_bcb: bcb3, false_bcb: bcb1 } => $DIR/instrument_coverage_cleanup.rs:14:8: 14:36 (#0);
+
bb0: {