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Unrolled build for rust-lang#120292
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Rollup merge of rust-lang#120292 - Zalathar:dismantle, r=oli-obk

coverage: Dismantle `Instrumentor` and flatten span refinement

This is a combination of two refactorings that are unrelated, but would otherwise have a merge conflict.

No functional changes, other than a small tweak to debug logging as part of rearranging some functions.

Ignoring whitespace is highly recommended, since most of the modified lines have just been reindented.

---

The first change is to dismantle `Instrumentor` into ordinary functions.

This is one of those cases where encapsulating several values into a struct ultimately hurts more than it helps. With everything stored as local variables in one main function, and passed explicitly into helper functions, it's easier to see what is used where, and make changes as necessary.

---

The second change is to flatten the functions for extracting/refining coverage spans.

Consolidating this code into flatter functions reduces the amount of pointer-chasing required to read and modify it.
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@rust-timer
rust-timer committed Jan 25, 2024
2 parents d93fecc + 572d7e9 commit 30b22dc
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Showing 3 changed files with 178 additions and 212 deletions.
265 changes: 126 additions & 139 deletions compiler/rustc_mir_transform/src/coverage/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -59,167 +59,154 @@ impl<'tcx> MirPass<'tcx> for InstrumentCoverage {
_ => {}
}

trace!("InstrumentCoverage starting for {def_id:?}");
Instrumentor::new(tcx, mir_body).inject_counters();
trace!("InstrumentCoverage done for {def_id:?}");
instrument_function_for_coverage(tcx, mir_body);
}
}

struct Instrumentor<'a, 'tcx> {
tcx: TyCtxt<'tcx>,
mir_body: &'a mut mir::Body<'tcx>,
hir_info: ExtractedHirInfo,
basic_coverage_blocks: CoverageGraph,
}

impl<'a, 'tcx> Instrumentor<'a, 'tcx> {
fn new(tcx: TyCtxt<'tcx>, mir_body: &'a mut mir::Body<'tcx>) -> Self {
let hir_info = extract_hir_info(tcx, mir_body.source.def_id().expect_local());
fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir::Body<'tcx>) {
let def_id = mir_body.source.def_id();
let _span = debug_span!("instrument_function_for_coverage", ?def_id).entered();

debug!(?hir_info, "instrumenting {:?}", mir_body.source.def_id());
let hir_info = extract_hir_info(tcx, def_id.expect_local());
let basic_coverage_blocks = CoverageGraph::from_mir(mir_body);

let basic_coverage_blocks = CoverageGraph::from_mir(mir_body);
////////////////////////////////////////////////////
// Compute coverage spans from the `CoverageGraph`.
let Some(coverage_spans) =
spans::generate_coverage_spans(mir_body, &hir_info, &basic_coverage_blocks)
else {
// No relevant spans were found in MIR, so skip instrumenting this function.
return;
};

Self { tcx, mir_body, hir_info, basic_coverage_blocks }
////////////////////////////////////////////////////
// Create an optimized mix of `Counter`s and `Expression`s for the `CoverageGraph`. Ensure
// every coverage span has a `Counter` or `Expression` assigned to its `BasicCoverageBlock`
// and all `Expression` dependencies (operands) are also generated, for any other
// `BasicCoverageBlock`s not already associated with a coverage span.
let bcb_has_coverage_spans = |bcb| coverage_spans.bcb_has_coverage_spans(bcb);
let coverage_counters =
CoverageCounters::make_bcb_counters(&basic_coverage_blocks, bcb_has_coverage_spans);

let mappings = create_mappings(tcx, &hir_info, &coverage_spans, &coverage_counters);
if mappings.is_empty() {
// No spans could be converted into valid mappings, so skip this function.
debug!("no spans could be converted into valid mappings; skipping");
return;
}

fn inject_counters(&'a mut self) {
////////////////////////////////////////////////////
// Compute coverage spans from the `CoverageGraph`.
let Some(coverage_spans) = CoverageSpans::generate_coverage_spans(
self.mir_body,
&self.hir_info,
&self.basic_coverage_blocks,
) else {
// No relevant spans were found in MIR, so skip instrumenting this function.
return;
};

////////////////////////////////////////////////////
// Create an optimized mix of `Counter`s and `Expression`s for the `CoverageGraph`. Ensure
// every coverage span has a `Counter` or `Expression` assigned to its `BasicCoverageBlock`
// and all `Expression` dependencies (operands) are also generated, for any other
// `BasicCoverageBlock`s not already associated with a coverage span.
let bcb_has_coverage_spans = |bcb| coverage_spans.bcb_has_coverage_spans(bcb);
let coverage_counters = CoverageCounters::make_bcb_counters(
&self.basic_coverage_blocks,
bcb_has_coverage_spans,
);
inject_coverage_statements(
mir_body,
&basic_coverage_blocks,
bcb_has_coverage_spans,
&coverage_counters,
);

let mappings = self.create_mappings(&coverage_spans, &coverage_counters);
if mappings.is_empty() {
// No spans could be converted into valid mappings, so skip this function.
debug!("no spans could be converted into valid mappings; skipping");
return;
}
mir_body.function_coverage_info = Some(Box::new(FunctionCoverageInfo {
function_source_hash: hir_info.function_source_hash,
num_counters: coverage_counters.num_counters(),
expressions: coverage_counters.into_expressions(),
mappings,
}));
}

self.inject_coverage_statements(bcb_has_coverage_spans, &coverage_counters);
/// For each coverage span extracted from MIR, create a corresponding
/// mapping.
///
/// Precondition: All BCBs corresponding to those spans have been given
/// coverage counters.
fn create_mappings<'tcx>(
tcx: TyCtxt<'tcx>,
hir_info: &ExtractedHirInfo,
coverage_spans: &CoverageSpans,
coverage_counters: &CoverageCounters,
) -> Vec<Mapping> {
let source_map = tcx.sess.source_map();
let body_span = hir_info.body_span;

let source_file = source_map.lookup_source_file(body_span.lo());
use rustc_session::RemapFileNameExt;
let file_name = Symbol::intern(&source_file.name.for_codegen(tcx.sess).to_string_lossy());

let term_for_bcb = |bcb| {
coverage_counters
.bcb_counter(bcb)
.expect("all BCBs with spans were given counters")
.as_term()
};

self.mir_body.function_coverage_info = Some(Box::new(FunctionCoverageInfo {
function_source_hash: self.hir_info.function_source_hash,
num_counters: coverage_counters.num_counters(),
expressions: coverage_counters.into_expressions(),
mappings,
}));
}
coverage_spans
.all_bcb_mappings()
.filter_map(|&BcbMapping { kind: bcb_mapping_kind, span }| {
let kind = match bcb_mapping_kind {
BcbMappingKind::Code(bcb) => MappingKind::Code(term_for_bcb(bcb)),
};
let code_region = make_code_region(source_map, file_name, span, body_span)?;
Some(Mapping { kind, code_region })
})
.collect::<Vec<_>>()
}

/// For each coverage span extracted from MIR, create a corresponding
/// mapping.
///
/// Precondition: All BCBs corresponding to those spans have been given
/// coverage counters.
fn create_mappings(
&self,
coverage_spans: &CoverageSpans,
coverage_counters: &CoverageCounters,
) -> Vec<Mapping> {
let source_map = self.tcx.sess.source_map();
let body_span = self.hir_info.body_span;

let source_file = source_map.lookup_source_file(body_span.lo());
use rustc_session::RemapFileNameExt;
let file_name =
Symbol::intern(&source_file.name.for_codegen(self.tcx.sess).to_string_lossy());

let term_for_bcb = |bcb| {
coverage_counters
.bcb_counter(bcb)
.expect("all BCBs with spans were given counters")
.as_term()
/// For each BCB node or BCB edge that has an associated coverage counter,
/// inject any necessary coverage statements into MIR.
fn inject_coverage_statements<'tcx>(
mir_body: &mut mir::Body<'tcx>,
basic_coverage_blocks: &CoverageGraph,
bcb_has_coverage_spans: impl Fn(BasicCoverageBlock) -> bool,
coverage_counters: &CoverageCounters,
) {
// Process the counters associated with BCB nodes.
for (bcb, counter_kind) in coverage_counters.bcb_node_counters() {
let do_inject = match counter_kind {
// Counter-increment statements always need to be injected.
BcbCounter::Counter { .. } => true,
// The only purpose of expression-used statements is to detect
// when a mapping is unreachable, so we only inject them for
// expressions with one or more mappings.
BcbCounter::Expression { .. } => bcb_has_coverage_spans(bcb),
};

coverage_spans
.all_bcb_mappings()
.filter_map(|&BcbMapping { kind: bcb_mapping_kind, span }| {
let kind = match bcb_mapping_kind {
BcbMappingKind::Code(bcb) => MappingKind::Code(term_for_bcb(bcb)),
};
let code_region = make_code_region(source_map, file_name, span, body_span)?;
Some(Mapping { kind, code_region })
})
.collect::<Vec<_>>()
if do_inject {
inject_statement(
mir_body,
make_mir_coverage_kind(counter_kind),
basic_coverage_blocks[bcb].leader_bb(),
);
}
}

/// For each BCB node or BCB edge that has an associated coverage counter,
/// inject any necessary coverage statements into MIR.
fn inject_coverage_statements(
&mut self,
bcb_has_coverage_spans: impl Fn(BasicCoverageBlock) -> bool,
coverage_counters: &CoverageCounters,
) {
// Process the counters associated with BCB nodes.
for (bcb, counter_kind) in coverage_counters.bcb_node_counters() {
let do_inject = match counter_kind {
// Counter-increment statements always need to be injected.
BcbCounter::Counter { .. } => true,
// The only purpose of expression-used statements is to detect
// when a mapping is unreachable, so we only inject them for
// expressions with one or more mappings.
BcbCounter::Expression { .. } => bcb_has_coverage_spans(bcb),
};
if do_inject {
inject_statement(
self.mir_body,
self.make_mir_coverage_kind(counter_kind),
self.basic_coverage_blocks[bcb].leader_bb(),
);
}
// Process the counters associated with BCB edges.
for (from_bcb, to_bcb, counter_kind) in coverage_counters.bcb_edge_counters() {
let do_inject = match counter_kind {
// Counter-increment statements always need to be injected.
BcbCounter::Counter { .. } => true,
// BCB-edge expressions never have mappings, so they never need
// a corresponding statement.
BcbCounter::Expression { .. } => false,
};
if !do_inject {
continue;
}

// Process the counters associated with BCB edges.
for (from_bcb, to_bcb, counter_kind) in coverage_counters.bcb_edge_counters() {
let do_inject = match counter_kind {
// Counter-increment statements always need to be injected.
BcbCounter::Counter { .. } => true,
// BCB-edge expressions never have mappings, so they never need
// a corresponding statement.
BcbCounter::Expression { .. } => false,
};
if !do_inject {
continue;
}

// We need to inject a coverage statement into a new BB between the
// last BB of `from_bcb` and the first BB of `to_bcb`.
let from_bb = self.basic_coverage_blocks[from_bcb].last_bb();
let to_bb = self.basic_coverage_blocks[to_bcb].leader_bb();
// We need to inject a coverage statement into a new BB between the
// last BB of `from_bcb` and the first BB of `to_bcb`.
let from_bb = basic_coverage_blocks[from_bcb].last_bb();
let to_bb = basic_coverage_blocks[to_bcb].leader_bb();

let new_bb = inject_edge_counter_basic_block(self.mir_body, from_bb, to_bb);
debug!(
"Edge {from_bcb:?} (last {from_bb:?}) -> {to_bcb:?} (leader {to_bb:?}) \
let new_bb = inject_edge_counter_basic_block(mir_body, from_bb, to_bb);
debug!(
"Edge {from_bcb:?} (last {from_bb:?}) -> {to_bcb:?} (leader {to_bb:?}) \
requires a new MIR BasicBlock {new_bb:?} for edge counter {counter_kind:?}",
);
);

// Inject a counter into the newly-created BB.
inject_statement(self.mir_body, self.make_mir_coverage_kind(counter_kind), new_bb);
}
// Inject a counter into the newly-created BB.
inject_statement(mir_body, make_mir_coverage_kind(counter_kind), new_bb);
}
}

fn make_mir_coverage_kind(&self, counter_kind: &BcbCounter) -> CoverageKind {
match *counter_kind {
BcbCounter::Counter { id } => CoverageKind::CounterIncrement { id },
BcbCounter::Expression { id } => CoverageKind::ExpressionUsed { id },
}
fn make_mir_coverage_kind(counter_kind: &BcbCounter) -> CoverageKind {
match *counter_kind {
BcbCounter::Counter { id } => CoverageKind::CounterIncrement { id },
BcbCounter::Expression { id } => CoverageKind::ExpressionUsed { id },
}
}

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