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coverage: Detect functions that have lost all their coverage statements

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If a function was instrumented for coverage, but all of its coverage statements
have been removed by later MIR transforms, it should be treated as "unused"
even if the compiler generates an unreachable stub for it.
This commit is contained in:
Zalathar 2024-03-22 13:23:04 +11:00
parent e3f66b2493
commit 54116c8cae
1 changed files with 18 additions and 4 deletions
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22
compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs
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@ -353,10 +353,11 @@ fn add_unused_functions(cx: &CodegenCx<'_, '_>) {
// To be eligible for "unused function" mappings, a definition must: // To be eligible for "unused function" mappings, a definition must:
// - Be function-like // - Be function-like
// - Not participate directly in codegen // - Not participate directly in codegen (or have lost all its coverage statements)
// - Not have any coverage statements inlined into codegenned functions // - Not have any coverage statements inlined into codegenned functions
tcx.def_kind(def_id).is_fn_like() tcx.def_kind(def_id).is_fn_like()
&& !usage.all_mono_items.contains(&def_id) && (!usage.all_mono_items.contains(&def_id)
|| usage.missing_own_coverage.contains(&def_id))
&& !usage.used_via_inlining.contains(&def_id) && !usage.used_via_inlining.contains(&def_id)
}; };
@ -379,6 +380,7 @@ fn add_unused_functions(cx: &CodegenCx<'_, '_>) {
struct UsageSets<'tcx> { struct UsageSets<'tcx> {
all_mono_items: &'tcx DefIdSet, all_mono_items: &'tcx DefIdSet,
used_via_inlining: FxHashSet<DefId>, used_via_inlining: FxHashSet<DefId>,
missing_own_coverage: FxHashSet<DefId>,
} }
/// Prepare sets of definitions that are relevant to deciding whether something /// Prepare sets of definitions that are relevant to deciding whether something
@ -406,8 +408,13 @@ fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
// Functions whose coverage statments were found inlined into other functions. // Functions whose coverage statments were found inlined into other functions.
let mut used_via_inlining = FxHashSet::default(); let mut used_via_inlining = FxHashSet::default();
// Functions that were instrumented, but had all of their coverage statements
// removed by later MIR transforms (e.g. UnreachablePropagation).
let mut missing_own_coverage = FxHashSet::default();
for (def_id, body) in def_and_mir_for_all_mono_fns {
let mut saw_own_coverage = false;
for (_def_id, body) in def_and_mir_for_all_mono_fns {
// Inspect every coverage statement in the function's MIR. // Inspect every coverage statement in the function's MIR.
for stmt in body for stmt in body
.basic_blocks .basic_blocks
@ -418,11 +425,18 @@ fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) { if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) {
// This coverage statement was inlined from another function. // This coverage statement was inlined from another function.
used_via_inlining.insert(inlined.def_id()); used_via_inlining.insert(inlined.def_id());
} else {
// Non-inlined coverage statements belong to the enclosing function.
saw_own_coverage = true;
} }
} }
if !saw_own_coverage && body.function_coverage_info.is_some() {
missing_own_coverage.insert(def_id);
}
} }
UsageSets { all_mono_items, used_via_inlining } UsageSets { all_mono_items, used_via_inlining, missing_own_coverage }
} }
fn add_unused_function_coverage<'tcx>( fn add_unused_function_coverage<'tcx>(