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coverage: Restrict ExpressionUsed simplification to Code mappings

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In the future, branch and MC/DC mappings might have expressions that don't
correspond to any single point in the control-flow graph. That makes it
trickier to keep track of which expressions should expect an `ExpressionUsed`
node.

We therefore sidestep that complexity by only performing `ExpressionUsed`
simplification for expressions associated directly with ordinary `Code`
mappings.
This commit is contained in:
Zalathar 2024-07-15 20:32:14 +10:00
parent 741ed01646
commit d4f1f92426
4 changed files with 27 additions and 19 deletions
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9
compiler/rustc_mir_transform/src/coverage/mappings.rs
View file

@ -159,6 +159,15 @@ impl ExtractedMappings {
bcbs_with_counter_mappings
}
/// Returns the set of BCBs that have one or more `Code` mappings.
pub(super) fn bcbs_with_ordinary_code_mappings(&self) -> BitSet<BasicCoverageBlock> {
let mut bcbs = BitSet::new_empty(self.num_bcbs);
for &CodeMapping { span: _, bcb } in &self.code_mappings {
bcbs.insert(bcb);
}
bcbs
}
}
fn resolve_block_markers(

13
compiler/rustc_mir_transform/src/coverage/mod.rs
View file

@ -25,7 +25,7 @@ use rustc_span::source_map::SourceMap;
use rustc_span::{BytePos, Pos, RelativeBytePos, Span, Symbol};
use crate::coverage::counters::{CounterIncrementSite, CoverageCounters};
use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
use crate::coverage::graph::CoverageGraph;
use crate::coverage::mappings::ExtractedMappings;
use crate::MirPass;
@ -108,7 +108,7 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
inject_coverage_statements(
mir_body,
&basic_coverage_blocks,
bcb_has_counter_mappings,
&extracted_mappings,
&coverage_counters,
);
@ -219,7 +219,7 @@ fn create_mappings<'tcx>(
fn inject_coverage_statements<'tcx>(
mir_body: &mut mir::Body<'tcx>,
basic_coverage_blocks: &CoverageGraph,
bcb_has_coverage_spans: impl Fn(BasicCoverageBlock) -> bool,
extracted_mappings: &ExtractedMappings,
coverage_counters: &CoverageCounters,
) {
// Inject counter-increment statements into MIR.
@ -252,11 +252,16 @@ fn inject_coverage_statements<'tcx>(
// can check whether the injected statement survived MIR optimization.
// (BCB edges can't have spans, so we only need to process BCB nodes here.)
//
// We only do this for ordinary `Code` mappings, because branch and MC/DC
// mappings might have expressions that don't correspond to any single
// point in the control-flow graph.
//
// See the code in `rustc_codegen_llvm::coverageinfo::map_data` that deals
// with "expressions seen" and "zero terms".
let eligible_bcbs = extracted_mappings.bcbs_with_ordinary_code_mappings();
for (bcb, expression_id) in coverage_counters
.bcb_nodes_with_coverage_expressions()
.filter(|&(bcb, _)| bcb_has_coverage_spans(bcb))
.filter(|&(bcb, _)| eligible_bcbs.contains(bcb))
{
inject_statement(
mir_body,