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coverage: Defer part of counter-creation until codegen

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This commit is contained in:
Zalathar 2025-01-22 13:55:08 +11:00
parent ee7dc06cf1
commit 20d051ec87
19 changed files with 205 additions and 305 deletions
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69
compiler/rustc_mir_transform/src/coverage/counters.rs
View file

@ -2,7 +2,6 @@ use std::cmp::Ordering;
use either::Either;
use itertools::Itertools;
use rustc_data_structures::captures::Captures;
use rustc_data_structures::fx::{FxHashMap, FxIndexMap};
use rustc_data_structures::graph::DirectedGraph;
use rustc_index::IndexVec;
@ -11,31 +10,35 @@ use rustc_middle::mir::coverage::{CounterId, CovTerm, Expression, ExpressionId,
use crate::coverage::counters::balanced_flow::BalancedFlowGraph;
use crate::coverage::counters::node_flow::{
CounterTerm, NodeCounters, make_node_counters, node_flow_data_for_balanced_graph,
CounterTerm, NodeCounters, NodeFlowData, node_flow_data_for_balanced_graph,
};
use crate::coverage::graph::{BasicCoverageBlock, CoverageGraph};
mod balanced_flow;
mod node_flow;
pub(crate) mod node_flow;
mod union_find;
/// Ensures that each BCB node needing a counter has one, by creating physical
/// counters or counter expressions for nodes as required.
pub(super) fn make_bcb_counters(
graph: &CoverageGraph,
bcb_needs_counter: &DenseBitSet<BasicCoverageBlock>,
) -> CoverageCounters {
/// Struct containing the results of [`prepare_bcb_counters_data`].
pub(crate) struct BcbCountersData {
pub(crate) node_flow_data: NodeFlowData<BasicCoverageBlock>,
pub(crate) priority_list: Vec<BasicCoverageBlock>,
}
/// Analyzes the coverage graph to create intermediate data structures that
/// will later be used (during codegen) to create physical counters or counter
/// expressions for each BCB node that needs one.
pub(crate) fn prepare_bcb_counters_data(graph: &CoverageGraph) -> BcbCountersData {
// Create the derived graphs that are necessary for subsequent steps.
let balanced_graph = BalancedFlowGraph::for_graph(graph, |n| !graph[n].is_out_summable);
let node_flow_data = node_flow_data_for_balanced_graph(&balanced_graph);
// Use those graphs to determine which nodes get physical counters, and how
// to compute the execution counts of other nodes from those counters.
// Also create a "priority list" of coverage graph nodes, to help determine
// which ones get physical counters or counter expressions. This needs to
// be done now, because the later parts of the counter-creation process
// won't have access to the original coverage graph.
let priority_list = make_node_flow_priority_list(graph, balanced_graph);
let node_counters = make_node_counters(&node_flow_data, &priority_list);
// Convert the counters into a form suitable for embedding into MIR.
transcribe_counters(&node_counters, bcb_needs_counter)
BcbCountersData { node_flow_data, priority_list }
}
/// Arranges the nodes in `balanced_graph` into a list, such that earlier nodes
@ -74,7 +77,7 @@ fn make_node_flow_priority_list(
}
// Converts node counters into a form suitable for embedding into MIR.
fn transcribe_counters(
pub(crate) fn transcribe_counters(
old: &NodeCounters<BasicCoverageBlock>,
bcb_needs_counter: &DenseBitSet<BasicCoverageBlock>,
) -> CoverageCounters {
@ -129,7 +132,7 @@ fn transcribe_counters(
pub(super) struct CoverageCounters {
/// List of places where a counter-increment statement should be injected
/// into MIR, each with its corresponding counter ID.
phys_counter_for_node: FxIndexMap<BasicCoverageBlock, CounterId>,
pub(crate) phys_counter_for_node: FxIndexMap<BasicCoverageBlock, CounterId>,
next_counter_id: CounterId,
/// Coverage counters/expressions that are associated with individual BCBs.
@ -137,7 +140,7 @@ pub(super) struct CoverageCounters {
/// Table of expression data, associating each expression ID with its
/// corresponding operator (+ or -) and its LHS/RHS operands.
expressions: IndexVec<ExpressionId, Expression>,
pub(crate) expressions: IndexVec<ExpressionId, Expression>,
/// Remember expressions that have already been created (or simplified),
/// so that we don't create unnecessary duplicates.
expressions_memo: FxHashMap<Expression, CovTerm>,
@ -188,12 +191,6 @@ impl CoverageCounters {
self.make_expression(lhs, Op::Subtract, rhs_sum)
}
pub(super) fn num_counters(&self) -> usize {
let num_counters = self.phys_counter_for_node.len();
assert_eq!(num_counters, self.next_counter_id.as_usize());
num_counters
}
fn set_node_counter(&mut self, bcb: BasicCoverageBlock, counter: CovTerm) -> CovTerm {
let existing = self.node_counters[bcb].replace(counter);
assert!(
@ -202,30 +199,4 @@ impl CoverageCounters {
);
counter
}
/// Returns an iterator over all the nodes in the coverage graph that
/// should have a counter-increment statement injected into MIR, along with
/// each site's corresponding counter ID.
pub(super) fn counter_increment_sites(
&self,
) -> impl Iterator<Item = (CounterId, BasicCoverageBlock)> + Captures<'_> {
self.phys_counter_for_node.iter().map(|(&site, &id)| (id, site))
}
/// Returns an iterator over the subset of BCB nodes that have been associated
/// with a counter *expression*, along with the ID of that expression.
pub(super) fn bcb_nodes_with_coverage_expressions(
&self,
) -> impl Iterator<Item = (BasicCoverageBlock, ExpressionId)> + Captures<'_> {
self.node_counters.iter_enumerated().filter_map(|(bcb, &counter)| match counter {
// Yield the BCB along with its associated expression ID.
Some(CovTerm::Expression(id)) => Some((bcb, id)),
// This BCB is associated with a counter or nothing, so skip it.
Some(CovTerm::Counter { .. } | CovTerm::Zero) | None => None,
})
}
pub(super) fn into_expressions(self) -> IndexVec<ExpressionId, Expression> {
self.expressions
}
}

25
compiler/rustc_mir_transform/src/coverage/counters/node_flow.rs
View file

@ -9,6 +9,7 @@
use rustc_data_structures::graph;
use rustc_index::bit_set::DenseBitSet;
use rustc_index::{Idx, IndexSlice, IndexVec};
pub(crate) use rustc_middle::mir::coverage::NodeFlowData;
use rustc_middle::mir::coverage::Op;
use crate::coverage::counters::union_find::UnionFind;
@ -16,30 +17,6 @@ use crate::coverage::counters::union_find::UnionFind;
#[cfg(test)]
mod tests;
/// Data representing a view of some underlying graph, in which each node's
/// successors have been merged into a single "supernode".
///
/// The resulting supernodes have no obvious meaning on their own.
/// However, merging successor nodes means that a node's out-edges can all
/// be combined into a single out-edge, whose flow is the same as the flow
/// (execution count) of its corresponding node in the original graph.
///
/// With all node flows now in the original graph now represented as edge flows
/// in the merged graph, it becomes possible to analyze the original node flows
/// using techniques for analyzing edge flows.
#[derive(Debug)]
pub(crate) struct NodeFlowData<Node: Idx> {
/// Maps each node to the supernode that contains it, indicated by some
/// arbitrary "root" node that is part of that supernode.
supernodes: IndexVec<Node, Node>,
/// For each node, stores the single supernode that all of its successors
/// have been merged into.
///
/// (Note that each node in a supernode can potentially have a _different_
/// successor supernode from its peers.)
succ_supernodes: IndexVec<Node, Node>,
}
/// Creates a "merged" view of an underlying graph.
///
/// The given graph is assumed to have [“balanced flow”](balanced-flow),

61
compiler/rustc_mir_transform/src/coverage/mappings.rs
View file

@ -1,9 +1,7 @@
use std::collections::BTreeSet;
use rustc_data_structures::fx::FxIndexMap;
use rustc_data_structures::graph::DirectedGraph;
use rustc_index::IndexVec;
use rustc_index::bit_set::DenseBitSet;
use rustc_middle::mir::coverage::{
BlockMarkerId, BranchSpan, ConditionId, ConditionInfo, CoverageInfoHi, CoverageKind,
};
@ -63,10 +61,6 @@ const MCDC_MAX_BITMAP_SIZE: usize = i32::MAX as usize;
#[derive(Default)]
pub(super) struct ExtractedMappings {
/// Store our own copy of [`CoverageGraph::num_nodes`], so that we don't
/// need access to the whole graph when allocating per-BCB data. This is
/// only public so that other code can still use exhaustive destructuring.
pub(super) num_bcbs: usize,
pub(super) code_mappings: Vec<CodeMapping>,
pub(super) branch_pairs: Vec<BranchPair>,
pub(super) mcdc_bitmap_bits: usize,
@ -118,7 +112,6 @@ pub(super) fn extract_all_mapping_info_from_mir<'tcx>(
);
ExtractedMappings {
num_bcbs: graph.num_nodes(),
code_mappings,
branch_pairs,
mcdc_bitmap_bits,
@ -127,60 +120,6 @@ pub(super) fn extract_all_mapping_info_from_mir<'tcx>(
}
}
impl ExtractedMappings {
pub(super) fn all_bcbs_with_counter_mappings(&self) -> DenseBitSet<BasicCoverageBlock> {
// Fully destructure self to make sure we don't miss any fields that have mappings.
let Self {
num_bcbs,
code_mappings,
branch_pairs,
mcdc_bitmap_bits: _,
mcdc_degraded_branches,
mcdc_mappings,
} = self;
// Identify which BCBs have one or more mappings.
let mut bcbs_with_counter_mappings = DenseBitSet::new_empty(*num_bcbs);
let mut insert = |bcb| {
bcbs_with_counter_mappings.insert(bcb);
};
for &CodeMapping { span: _, bcb } in code_mappings {
insert(bcb);
}
for &BranchPair { true_bcb, false_bcb, .. } in branch_pairs {
insert(true_bcb);
insert(false_bcb);
}
for &MCDCBranch { true_bcb, false_bcb, .. } in mcdc_degraded_branches
.iter()
.chain(mcdc_mappings.iter().map(|(_, branches)| branches.into_iter()).flatten())
{
insert(true_bcb);
insert(false_bcb);
}
// MC/DC decisions refer to BCBs, but don't require those BCBs to have counters.
if bcbs_with_counter_mappings.is_empty() {
debug_assert!(
mcdc_mappings.is_empty(),
"A function with no counter mappings shouldn't have any decisions: {mcdc_mappings:?}",
);
}
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) -> DenseBitSet<BasicCoverageBlock> {
let mut bcbs = DenseBitSet::new_empty(self.num_bcbs);
for &CodeMapping { span: _, bcb } in &self.code_mappings {
bcbs.insert(bcb);
}
bcbs
}
}
fn resolve_block_markers(
coverage_info_hi: &CoverageInfoHi,
mir_body: &mir::Body<'_>,

70
compiler/rustc_mir_transform/src/coverage/mod.rs
View file

@ -21,7 +21,7 @@ use rustc_span::Span;
use rustc_span::def_id::LocalDefId;
use tracing::{debug, debug_span, trace};
use crate::coverage::counters::CoverageCounters;
use crate::coverage::counters::BcbCountersData;
use crate::coverage::graph::CoverageGraph;
use crate::coverage::mappings::ExtractedMappings;
@ -82,29 +82,21 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
let extracted_mappings =
mappings::extract_all_mapping_info_from_mir(tcx, mir_body, &hir_info, &graph);
////////////////////////////////////////////////////
// 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 bcbs_with_counter_mappings = extracted_mappings.all_bcbs_with_counter_mappings();
if bcbs_with_counter_mappings.is_empty() {
// No relevant spans were found in MIR, so skip instrumenting this function.
return;
}
let coverage_counters = counters::make_bcb_counters(&graph, &bcbs_with_counter_mappings);
let mappings = create_mappings(&extracted_mappings);
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;
}
let term_for_bcb = coverage_counters.node_counters.clone();
inject_coverage_statements(mir_body, &graph, &extracted_mappings, &coverage_counters);
// Use the coverage graph to prepare intermediate data that will eventually
// be used to assign physical counters and counter expressions to points in
// the control-flow graph
let BcbCountersData { node_flow_data, priority_list } =
counters::prepare_bcb_counters_data(&graph);
// Inject coverage statements into MIR.
inject_coverage_statements(mir_body, &graph);
inject_mcdc_statements(mir_body, &graph, &extracted_mappings);
let mcdc_num_condition_bitmaps = extracted_mappings
@ -118,11 +110,10 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
function_source_hash: hir_info.function_source_hash,
body_span: hir_info.body_span,
num_counters: coverage_counters.num_counters(),
expressions: coverage_counters.into_expressions(),
node_flow_data,
priority_list,
mappings,
term_for_bcb,
mcdc_bitmap_bits: extracted_mappings.mcdc_bitmap_bits,
mcdc_num_condition_bitmaps,
@ -137,7 +128,6 @@ fn instrument_function_for_coverage<'tcx>(tcx: TyCtxt<'tcx>, mir_body: &mut mir:
fn create_mappings(extracted_mappings: &ExtractedMappings) -> Vec<Mapping> {
// Fully destructure the mappings struct to make sure we don't miss any kinds.
let ExtractedMappings {
num_bcbs: _,
code_mappings,
branch_pairs,
mcdc_bitmap_bits: _,
@ -215,41 +205,11 @@ fn create_mappings(extracted_mappings: &ExtractedMappings) -> Vec<Mapping> {
mappings
}
/// 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>,
graph: &CoverageGraph,
extracted_mappings: &ExtractedMappings,
coverage_counters: &CoverageCounters,
) {
// Inject counter-increment statements into MIR.
for (id, bcb) in coverage_counters.counter_increment_sites() {
let target_bb = graph[bcb].leader_bb();
inject_statement(mir_body, CoverageKind::CounterIncrement { id }, target_bb);
}
// For each counter expression that is directly associated with at least one
// span, we inject an "expression-used" statement, so that coverage codegen
// 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, _)| eligible_bcbs.contains(bcb))
{
inject_statement(
mir_body,
CoverageKind::ExpressionUsed { id: expression_id },
graph[bcb].leader_bb(),
);
/// Inject any necessary coverage statements into MIR, so that they influence codegen.
fn inject_coverage_statements<'tcx>(mir_body: &mut mir::Body<'tcx>, graph: &CoverageGraph) {
for (bcb, data) in graph.iter_enumerated() {
let target_bb = data.leader_bb();
inject_statement(mir_body, CoverageKind::VirtualCounter { bcb }, target_bb);
}
}

112
compiler/rustc_mir_transform/src/coverage/query.rs
View file

@ -1,9 +1,10 @@
use rustc_data_structures::captures::Captures;
use rustc_index::IndexSlice;
use rustc_index::bit_set::DenseBitSet;
use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
use rustc_middle::mir::coverage::{
CounterId, CovTerm, CoverageIdsInfo, CoverageKind, Expression, ExpressionId,
FunctionCoverageInfo, MappingKind, Op,
BasicCoverageBlock, CounterId, CovTerm, CoverageIdsInfo, CoverageKind, Expression,
ExpressionId, MappingKind, Op,
};
use rustc_middle::mir::{Body, Statement, StatementKind};
use rustc_middle::ty::{self, TyCtxt};
@ -12,6 +13,9 @@ use rustc_span::def_id::LocalDefId;
use rustc_span::sym;
use tracing::trace;
use crate::coverage::counters::node_flow::make_node_counters;
use crate::coverage::counters::{CoverageCounters, transcribe_counters};
/// Registers query/hook implementations related to coverage.
pub(crate) fn provide(providers: &mut Providers) {
providers.hooks.is_eligible_for_coverage = is_eligible_for_coverage;
@ -89,41 +93,85 @@ fn coverage_ids_info<'tcx>(
let mir_body = tcx.instance_mir(instance_def);
let fn_cov_info = mir_body.function_coverage_info.as_deref()?;
let mut counters_seen = DenseBitSet::new_empty(fn_cov_info.num_counters);
let mut expressions_seen = DenseBitSet::new_filled(fn_cov_info.expressions.len());
// For each expression ID that is directly used by one or more mappings,
// mark it as not-yet-seen. This indicates that we expect to see a
// corresponding `ExpressionUsed` statement during MIR traversal.
for mapping in fn_cov_info.mappings.iter() {
// Currently we only worry about ordinary code mappings.
// For branch and MC/DC mappings, expressions might not correspond
// to any particular point in the control-flow graph.
// (Keep this in sync with the injection of `ExpressionUsed`
// statements in the `InstrumentCoverage` MIR pass.)
if let MappingKind::Code { bcb } = mapping.kind
&& let Some(CovTerm::Expression(id)) = fn_cov_info.term_for_bcb[bcb]
{
expressions_seen.remove(id);
}
}
// Scan through the final MIR to see which BCBs survived MIR opts.
// Any BCB not in this set was optimized away.
let mut bcbs_seen = DenseBitSet::new_empty(fn_cov_info.priority_list.len());
for kind in all_coverage_in_mir_body(mir_body) {
match *kind {
CoverageKind::CounterIncrement { id } => {
counters_seen.insert(id);
}
CoverageKind::ExpressionUsed { id } => {
expressions_seen.insert(id);
CoverageKind::VirtualCounter { bcb } => {
bcbs_seen.insert(bcb);
}
_ => {}
}
}
let zero_expressions =
identify_zero_expressions(fn_cov_info, &counters_seen, &expressions_seen);
// Determine the set of BCBs that are referred to by mappings, and therefore
// need a counter. Any node not in this set will only get a counter if it
// is part of the counter expression for a node that is in the set.
let mut bcb_needs_counter =
DenseBitSet::<BasicCoverageBlock>::new_empty(fn_cov_info.priority_list.len());
for mapping in &fn_cov_info.mappings {
match mapping.kind {
MappingKind::Code { bcb } => {
bcb_needs_counter.insert(bcb);
}
MappingKind::Branch { true_bcb, false_bcb } => {
bcb_needs_counter.insert(true_bcb);
bcb_needs_counter.insert(false_bcb);
}
MappingKind::MCDCBranch { true_bcb, false_bcb, mcdc_params: _ } => {
bcb_needs_counter.insert(true_bcb);
bcb_needs_counter.insert(false_bcb);
}
MappingKind::MCDCDecision(_) => {}
}
}
Some(CoverageIdsInfo { counters_seen, zero_expressions })
let node_counters = make_node_counters(&fn_cov_info.node_flow_data, &fn_cov_info.priority_list);
let coverage_counters = transcribe_counters(&node_counters, &bcb_needs_counter);
let mut counters_seen = DenseBitSet::new_empty(coverage_counters.node_counters.len());
let mut expressions_seen = DenseBitSet::new_filled(coverage_counters.expressions.len());
// For each expression ID that is directly used by one or more mappings,
// mark it as not-yet-seen. This indicates that we expect to see a
// corresponding `VirtualCounter` statement during MIR traversal.
for mapping in fn_cov_info.mappings.iter() {
// Currently we only worry about ordinary code mappings.
// For branch and MC/DC mappings, expressions might not correspond
// to any particular point in the control-flow graph.
if let MappingKind::Code { bcb } = mapping.kind
&& let Some(CovTerm::Expression(id)) = coverage_counters.node_counters[bcb]
{
expressions_seen.remove(id);
}
}
for bcb in bcbs_seen.iter() {
if let Some(&id) = coverage_counters.phys_counter_for_node.get(&bcb) {
counters_seen.insert(id);
}
if let Some(CovTerm::Expression(id)) = coverage_counters.node_counters[bcb] {
expressions_seen.insert(id);
}
}
let zero_expressions = identify_zero_expressions(
&coverage_counters.expressions,
&counters_seen,
&expressions_seen,
);
let CoverageCounters { phys_counter_for_node, node_counters, expressions, .. } =
coverage_counters;
Some(CoverageIdsInfo {
counters_seen,
zero_expressions,
phys_counter_for_node,
term_for_bcb: node_counters,
expressions,
})
}
fn all_coverage_in_mir_body<'a, 'tcx>(
@ -150,7 +198,7 @@ fn is_inlined(body: &Body<'_>, statement: &Statement<'_>) -> bool {
/// already being performed by the Rust-side expression renumbering, so that
/// the resulting coverage mappings don't get worse.
fn identify_zero_expressions(
fn_cov_info: &FunctionCoverageInfo,
expressions: &IndexSlice<ExpressionId, Expression>,
counters_seen: &DenseBitSet<CounterId>,
expressions_seen: &DenseBitSet<ExpressionId>,
) -> DenseBitSet<ExpressionId> {
@ -158,13 +206,13 @@ fn identify_zero_expressions(
// have zero as both of their operands, and will therefore always have
// a value of zero. Other expressions that refer to these as operands
// can have those operands replaced with `CovTerm::Zero`.
let mut zero_expressions = DenseBitSet::new_empty(fn_cov_info.expressions.len());
let mut zero_expressions = DenseBitSet::new_empty(expressions.len());
// Simplify a copy of each expression based on lower-numbered expressions,
// and then update the set of always-zero expressions if necessary.
// (By construction, expressions can only refer to other expressions
// that have lower IDs, so one pass is sufficient.)
for (id, expression) in fn_cov_info.expressions.iter_enumerated() {
for (id, expression) in expressions.iter_enumerated() {
if !expressions_seen.contains(id) {
// If an expression was not seen, it must have been optimized away,
// so any operand that refers to it can be replaced with zero.

3
compiler/rustc_mir_transform/src/coverage/spans/from_mir.rs
View file

@ -137,8 +137,7 @@ fn filtered_statement_span(statement: &Statement<'_>) -> Option<Span> {
// These coverage statements should not exist prior to coverage instrumentation.
StatementKind::Coverage(
CoverageKind::CounterIncrement { .. }
| CoverageKind::ExpressionUsed { .. }
CoverageKind::VirtualCounter { .. }
| CoverageKind::CondBitmapUpdate { .. }
| CoverageKind::TestVectorBitmapUpdate { .. },
) => bug!(