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coverage: Extract module mapgen::unused for handling unused functions
1 parent c211076 commit 75135aa

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2 files changed

+132
-125
lines changed

2 files changed

+132
-125
lines changed

‎compiler/rustc_codegen_llvm/src/coverageinfo/mapgen.rs

+4-125
Original file line numberDiff line numberDiff line change
@@ -5,15 +5,11 @@ use rustc_abi::Align;
55
use rustc_codegen_ssa::traits::{
66
BaseTypeCodegenMethods, ConstCodegenMethods, StaticCodegenMethods,
77
};
8-
use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
9-
use rustc_hir::def_id::{DefId, LocalDefId};
8+
use rustc_data_structures::fx::FxIndexMap;
109
use rustc_index::IndexVec;
11-
use rustc_middle::mir;
12-
use rustc_middle::mir::mono::MonoItemPartitions;
13-
use rustc_middle::ty::{self, TyCtxt};
10+
use rustc_middle::ty::TyCtxt;
1411
use rustc_session::RemapFileNameExt;
1512
use rustc_session::config::RemapPathScopeComponents;
16-
use rustc_span::def_id::DefIdSet;
1713
use rustc_span::{SourceFile, StableSourceFileId};
1814
use tracing::debug;
1915

@@ -24,6 +20,7 @@ use crate::llvm;
2420

2521
mod covfun;
2622
mod spans;
23+
mod unused;
2724

2825
/// Generates and exports the coverage map, which is embedded in special
2926
/// linker sections in the final binary.
@@ -76,7 +73,7 @@ pub(crate) fn finalize(cx: &CodegenCx<'_, '_>) {
7673
// In a single designated CGU, also prepare covfun records for functions
7774
// in this crate that were instrumented for coverage, but are unused.
7875
if cx.codegen_unit.is_code_coverage_dead_code_cgu() {
79-
let mut unused_instances = gather_unused_function_instances(cx);
76+
let mut unused_instances = unused::gather_unused_function_instances(cx);
8077
// Sort the unused instances by symbol name, for the same reason as the used ones.
8178
unused_instances.sort_by_cached_key(|&instance| tcx.symbol_name(instance).name);
8279
covfun_records.extend(unused_instances.into_iter().filter_map(|instance| {
@@ -249,121 +246,3 @@ fn generate_covmap_record<'ll>(cx: &CodegenCx<'ll, '_>, version: u32, filenames_
249246

250247
cx.add_used_global(covmap_global);
251248
}
252-
253-
/// Each CGU will normally only emit coverage metadata for the functions that it actually generates.
254-
/// But since we don't want unused functions to disappear from coverage reports, we also scan for
255-
/// functions that were instrumented but are not participating in codegen.
256-
///
257-
/// These unused functions don't need to be codegenned, but we do need to add them to the function
258-
/// coverage map (in a single designated CGU) so that we still emit coverage mappings for them.
259-
/// We also end up adding their symbol names to a special global array that LLVM will include in
260-
/// its embedded coverage data.
261-
fn gather_unused_function_instances<'tcx>(cx: &CodegenCx<'_, 'tcx>) -> Vec<ty::Instance<'tcx>> {
262-
assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
263-
264-
let tcx = cx.tcx;
265-
let usage = prepare_usage_sets(tcx);
266-
267-
let is_unused_fn = |def_id: LocalDefId| -> bool {
268-
// Usage sets expect `DefId`, so convert from `LocalDefId`.
269-
let d: DefId = LocalDefId::to_def_id(def_id);
270-
// To be potentially eligible for "unused function" mappings, a definition must:
271-
// - Be eligible for coverage instrumentation
272-
// - Not participate directly in codegen (or have lost all its coverage statements)
273-
// - Not have any coverage statements inlined into codegenned functions
274-
tcx.is_eligible_for_coverage(def_id)
275-
&& (!usage.all_mono_items.contains(&d) || usage.missing_own_coverage.contains(&d))
276-
&& !usage.used_via_inlining.contains(&d)
277-
};
278-
279-
// FIXME(#79651): Consider trying to filter out dummy instantiations of
280-
// unused generic functions from library crates, because they can produce
281-
// "unused instantiation" in coverage reports even when they are actually
282-
// used by some downstream crate in the same binary.
283-
284-
tcx.mir_keys(())
285-
.iter()
286-
.copied()
287-
.filter(|&def_id| is_unused_fn(def_id))
288-
.map(|def_id| make_dummy_instance(tcx, def_id))
289-
.collect::<Vec<_>>()
290-
}
291-
292-
struct UsageSets<'tcx> {
293-
all_mono_items: &'tcx DefIdSet,
294-
used_via_inlining: FxHashSet<DefId>,
295-
missing_own_coverage: FxHashSet<DefId>,
296-
}
297-
298-
/// Prepare sets of definitions that are relevant to deciding whether something
299-
/// is an "unused function" for coverage purposes.
300-
fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
301-
let MonoItemPartitions { all_mono_items, codegen_units, .. } =
302-
tcx.collect_and_partition_mono_items(());
303-
304-
// Obtain a MIR body for each function participating in codegen, via an
305-
// arbitrary instance.
306-
let mut def_ids_seen = FxHashSet::default();
307-
let def_and_mir_for_all_mono_fns = codegen_units
308-
.iter()
309-
.flat_map(|cgu| cgu.items().keys())
310-
.filter_map(|item| match item {
311-
mir::mono::MonoItem::Fn(instance) => Some(instance),
312-
mir::mono::MonoItem::Static(_) | mir::mono::MonoItem::GlobalAsm(_) => None,
313-
})
314-
// We only need one arbitrary instance per definition.
315-
.filter(move |instance| def_ids_seen.insert(instance.def_id()))
316-
.map(|instance| {
317-
// We don't care about the instance, just its underlying MIR.
318-
let body = tcx.instance_mir(instance.def);
319-
(instance.def_id(), body)
320-
});
321-
322-
// Functions whose coverage statements were found inlined into other functions.
323-
let mut used_via_inlining = FxHashSet::default();
324-
// Functions that were instrumented, but had all of their coverage statements
325-
// removed by later MIR transforms (e.g. UnreachablePropagation).
326-
let mut missing_own_coverage = FxHashSet::default();
327-
328-
for (def_id, body) in def_and_mir_for_all_mono_fns {
329-
let mut saw_own_coverage = false;
330-
331-
// Inspect every coverage statement in the function's MIR.
332-
for stmt in body
333-
.basic_blocks
334-
.iter()
335-
.flat_map(|block| &block.statements)
336-
.filter(|stmt| matches!(stmt.kind, mir::StatementKind::Coverage(_)))
337-
{
338-
if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) {
339-
// This coverage statement was inlined from another function.
340-
used_via_inlining.insert(inlined.def_id());
341-
} else {
342-
// Non-inlined coverage statements belong to the enclosing function.
343-
saw_own_coverage = true;
344-
}
345-
}
346-
347-
if !saw_own_coverage && body.function_coverage_info.is_some() {
348-
missing_own_coverage.insert(def_id);
349-
}
350-
}
351-
352-
UsageSets { all_mono_items, used_via_inlining, missing_own_coverage }
353-
}
354-
355-
fn make_dummy_instance<'tcx>(tcx: TyCtxt<'tcx>, local_def_id: LocalDefId) -> ty::Instance<'tcx> {
356-
let def_id = local_def_id.to_def_id();
357-
358-
// Make a dummy instance that fills in all generics with placeholders.
359-
ty::Instance::new(
360-
def_id,
361-
ty::GenericArgs::for_item(tcx, def_id, |param, _| {
362-
if let ty::GenericParamDefKind::Lifetime = param.kind {
363-
tcx.lifetimes.re_erased.into()
364-
} else {
365-
tcx.mk_param_from_def(param)
366-
}
367-
}),
368-
)
369-
}

‎compiler/rustc_codegen_llvm/src/coverageinfo/mapgen/unused.rs

+128
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,128 @@
1+
use rustc_data_structures::fx::FxHashSet;
2+
use rustc_hir::def_id::{DefId, LocalDefId};
3+
use rustc_middle::mir;
4+
use rustc_middle::mir::mono::MonoItemPartitions;
5+
use rustc_middle::ty::{self, TyCtxt};
6+
use rustc_span::def_id::DefIdSet;
7+
8+
use crate::common::CodegenCx;
9+
10+
/// Each CGU will normally only emit coverage metadata for the functions that it actually generates.
11+
/// But since we don't want unused functions to disappear from coverage reports, we also scan for
12+
/// functions that were instrumented but are not participating in codegen.
13+
///
14+
/// These unused functions don't need to be codegenned, but we do need to add them to the function
15+
/// coverage map (in a single designated CGU) so that we still emit coverage mappings for them.
16+
/// We also end up adding their symbol names to a special global array that LLVM will include in
17+
/// its embedded coverage data.
18+
pub(crate) fn gather_unused_function_instances<'tcx>(
19+
cx: &CodegenCx<'_, 'tcx>,
20+
) -> Vec<ty::Instance<'tcx>> {
21+
assert!(cx.codegen_unit.is_code_coverage_dead_code_cgu());
22+
23+
let tcx = cx.tcx;
24+
let usage = prepare_usage_sets(tcx);
25+
26+
let is_unused_fn = |def_id: LocalDefId| -> bool {
27+
// Usage sets expect `DefId`, so convert from `LocalDefId`.
28+
let d: DefId = LocalDefId::to_def_id(def_id);
29+
// To be potentially eligible for "unused function" mappings, a definition must:
30+
// - Be eligible for coverage instrumentation
31+
// - Not participate directly in codegen (or have lost all its coverage statements)
32+
// - Not have any coverage statements inlined into codegenned functions
33+
tcx.is_eligible_for_coverage(def_id)
34+
&& (!usage.all_mono_items.contains(&d) || usage.missing_own_coverage.contains(&d))
35+
&& !usage.used_via_inlining.contains(&d)
36+
};
37+
38+
// FIXME(#79651): Consider trying to filter out dummy instantiations of
39+
// unused generic functions from library crates, because they can produce
40+
// "unused instantiation" in coverage reports even when they are actually
41+
// used by some downstream crate in the same binary.
42+
43+
tcx.mir_keys(())
44+
.iter()
45+
.copied()
46+
.filter(|&def_id| is_unused_fn(def_id))
47+
.map(|def_id| make_dummy_instance(tcx, def_id))
48+
.collect::<Vec<_>>()
49+
}
50+
51+
struct UsageSets<'tcx> {
52+
all_mono_items: &'tcx DefIdSet,
53+
used_via_inlining: FxHashSet<DefId>,
54+
missing_own_coverage: FxHashSet<DefId>,
55+
}
56+
57+
/// Prepare sets of definitions that are relevant to deciding whether something
58+
/// is an "unused function" for coverage purposes.
59+
fn prepare_usage_sets<'tcx>(tcx: TyCtxt<'tcx>) -> UsageSets<'tcx> {
60+
let MonoItemPartitions { all_mono_items, codegen_units, .. } =
61+
tcx.collect_and_partition_mono_items(());
62+
63+
// Obtain a MIR body for each function participating in codegen, via an
64+
// arbitrary instance.
65+
let mut def_ids_seen = FxHashSet::default();
66+
let def_and_mir_for_all_mono_fns = codegen_units
67+
.iter()
68+
.flat_map(|cgu| cgu.items().keys())
69+
.filter_map(|item| match item {
70+
mir::mono::MonoItem::Fn(instance) => Some(instance),
71+
mir::mono::MonoItem::Static(_) | mir::mono::MonoItem::GlobalAsm(_) => None,
72+
})
73+
// We only need one arbitrary instance per definition.
74+
.filter(move |instance| def_ids_seen.insert(instance.def_id()))
75+
.map(|instance| {
76+
// We don't care about the instance, just its underlying MIR.
77+
let body = tcx.instance_mir(instance.def);
78+
(instance.def_id(), body)
79+
});
80+
81+
// Functions whose coverage statements were found inlined into other functions.
82+
let mut used_via_inlining = FxHashSet::default();
83+
// Functions that were instrumented, but had all of their coverage statements
84+
// removed by later MIR transforms (e.g. UnreachablePropagation).
85+
let mut missing_own_coverage = FxHashSet::default();
86+
87+
for (def_id, body) in def_and_mir_for_all_mono_fns {
88+
let mut saw_own_coverage = false;
89+
90+
// Inspect every coverage statement in the function's MIR.
91+
for stmt in body
92+
.basic_blocks
93+
.iter()
94+
.flat_map(|block| &block.statements)
95+
.filter(|stmt| matches!(stmt.kind, mir::StatementKind::Coverage(_)))
96+
{
97+
if let Some(inlined) = stmt.source_info.scope.inlined_instance(&body.source_scopes) {
98+
// This coverage statement was inlined from another function.
99+
used_via_inlining.insert(inlined.def_id());
100+
} else {
101+
// Non-inlined coverage statements belong to the enclosing function.
102+
saw_own_coverage = true;
103+
}
104+
}
105+
106+
if !saw_own_coverage && body.function_coverage_info.is_some() {
107+
missing_own_coverage.insert(def_id);
108+
}
109+
}
110+
111+
UsageSets { all_mono_items, used_via_inlining, missing_own_coverage }
112+
}
113+
114+
fn make_dummy_instance<'tcx>(tcx: TyCtxt<'tcx>, local_def_id: LocalDefId) -> ty::Instance<'tcx> {
115+
let def_id = local_def_id.to_def_id();
116+
117+
// Make a dummy instance that fills in all generics with placeholders.
118+
ty::Instance::new(
119+
def_id,
120+
ty::GenericArgs::for_item(tcx, def_id, |param, _| {
121+
if let ty::GenericParamDefKind::Lifetime = param.kind {
122+
tcx.lifetimes.re_erased.into()
123+
} else {
124+
tcx.mk_param_from_def(param)
125+
}
126+
}),
127+
)
128+
}

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