rustc_codegen_llvm/coverageinfo/map_data.rs
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use rustc_data_structures::captures::Captures;
use rustc_data_structures::fx::FxIndexSet;
use rustc_index::bit_set::BitSet;
use rustc_middle::mir::coverage::{
CounterId, CovTerm, Expression, ExpressionId, FunctionCoverageInfo, Mapping, MappingKind, Op,
SourceRegion,
};
use rustc_middle::ty::Instance;
use rustc_span::Symbol;
use tracing::{debug, instrument};
use crate::coverageinfo::ffi::{Counter, CounterExpression, ExprKind};
/// Holds all of the coverage mapping data associated with a function instance,
/// collected during traversal of `Coverage` statements in the function's MIR.
#[derive(Debug)]
pub(crate) struct FunctionCoverageCollector<'tcx> {
/// Coverage info that was attached to this function by the instrumentor.
function_coverage_info: &'tcx FunctionCoverageInfo,
is_used: bool,
/// Tracks which counters have been seen, so that we can identify mappings
/// to counters that were optimized out, and set them to zero.
counters_seen: BitSet<CounterId>,
/// Contains all expression IDs that have been seen in an `ExpressionUsed`
/// coverage statement, plus all expression IDs that aren't directly used
/// by any mappings (and therefore do not have expression-used statements).
/// After MIR traversal is finished, we can conclude that any IDs missing
/// from this set must have had their statements deleted by MIR opts.
expressions_seen: BitSet<ExpressionId>,
}
impl<'tcx> FunctionCoverageCollector<'tcx> {
/// Creates a new set of coverage data for a used (called) function.
pub(crate) fn new(
instance: Instance<'tcx>,
function_coverage_info: &'tcx FunctionCoverageInfo,
) -> Self {
Self::create(instance, function_coverage_info, true)
}
/// Creates a new set of coverage data for an unused (never called) function.
pub(crate) fn unused(
instance: Instance<'tcx>,
function_coverage_info: &'tcx FunctionCoverageInfo,
) -> Self {
Self::create(instance, function_coverage_info, false)
}
fn create(
instance: Instance<'tcx>,
function_coverage_info: &'tcx FunctionCoverageInfo,
is_used: bool,
) -> Self {
let num_counters = function_coverage_info.num_counters;
let num_expressions = function_coverage_info.expressions.len();
debug!(
"FunctionCoverage::create(instance={instance:?}) has \
num_counters={num_counters}, num_expressions={num_expressions}, is_used={is_used}"
);
// Create a filled set of expression IDs, so that expressions not
// directly used by mappings will be treated as "seen".
// (If they end up being unused, LLVM will delete them for us.)
let mut expressions_seen = BitSet::new_filled(num_expressions);
// 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 function_coverage_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(term) = mapping.kind
&& let CovTerm::Expression(id) = term
{
expressions_seen.remove(id);
}
}
Self {
function_coverage_info,
is_used,
counters_seen: BitSet::new_empty(num_counters),
expressions_seen,
}
}
/// Marks a counter ID as having been seen in a counter-increment statement.
#[instrument(level = "debug", skip(self))]
pub(crate) fn mark_counter_id_seen(&mut self, id: CounterId) {
self.counters_seen.insert(id);
}
/// Marks an expression ID as having been seen in an expression-used statement.
#[instrument(level = "debug", skip(self))]
pub(crate) fn mark_expression_id_seen(&mut self, id: ExpressionId) {
self.expressions_seen.insert(id);
}
/// Identify expressions that will always have a value of zero, and note
/// their IDs in [`ZeroExpressions`]. Mappings that refer to a zero expression
/// can instead become mappings to a constant zero value.
///
/// This method mainly exists to preserve the simplifications that were
/// already being performed by the Rust-side expression renumbering, so that
/// the resulting coverage mappings don't get worse.
fn identify_zero_expressions(&self) -> ZeroExpressions {
// The set of expressions that either were optimized out entirely, or
// 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 = ZeroExpressions::default();
// 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 self.function_coverage_info.expressions.iter_enumerated() {
if !self.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.
zero_expressions.insert(id);
continue;
}
// We don't need to simplify the actual expression data in the
// expressions list; we can just simplify a temporary copy and then
// use that to update the set of always-zero expressions.
let Expression { mut lhs, op, mut rhs } = *expression;
// If an expression has an operand that is also an expression, the
// operand's ID must be strictly lower. This is what lets us find
// all zero expressions in one pass.
let assert_operand_expression_is_lower = |operand_id: ExpressionId| {
assert!(
operand_id < id,
"Operand {operand_id:?} should be less than {id:?} in {expression:?}",
)
};
// If an operand refers to a counter or expression that is always
// zero, then that operand can be replaced with `CovTerm::Zero`.
let maybe_set_operand_to_zero = |operand: &mut CovTerm| {
if let CovTerm::Expression(id) = *operand {
assert_operand_expression_is_lower(id);
}
if is_zero_term(&self.counters_seen, &zero_expressions, *operand) {
*operand = CovTerm::Zero;
}
};
maybe_set_operand_to_zero(&mut lhs);
maybe_set_operand_to_zero(&mut rhs);
// Coverage counter values cannot be negative, so if an expression
// involves subtraction from zero, assume that its RHS must also be zero.
// (Do this after simplifications that could set the LHS to zero.)
if lhs == CovTerm::Zero && op == Op::Subtract {
rhs = CovTerm::Zero;
}
// After the above simplifications, if both operands are zero, then
// we know that this expression is always zero too.
if lhs == CovTerm::Zero && rhs == CovTerm::Zero {
zero_expressions.insert(id);
}
}
zero_expressions
}
pub(crate) fn into_finished(self) -> FunctionCoverage<'tcx> {
let zero_expressions = self.identify_zero_expressions();
let FunctionCoverageCollector { function_coverage_info, is_used, counters_seen, .. } = self;
FunctionCoverage { function_coverage_info, is_used, counters_seen, zero_expressions }
}
}
pub(crate) struct FunctionCoverage<'tcx> {
function_coverage_info: &'tcx FunctionCoverageInfo,
is_used: bool,
counters_seen: BitSet<CounterId>,
zero_expressions: ZeroExpressions,
}
impl<'tcx> FunctionCoverage<'tcx> {
/// Returns true for a used (called) function, and false for an unused function.
pub(crate) fn is_used(&self) -> bool {
self.is_used
}
/// Return the source hash, generated from the HIR node structure, and used to indicate whether
/// or not the source code structure changed between different compilations.
pub(crate) fn source_hash(&self) -> u64 {
if self.is_used { self.function_coverage_info.function_source_hash } else { 0 }
}
/// Returns an iterator over all filenames used by this function's mappings.
pub(crate) fn all_file_names(&self) -> impl Iterator<Item = Symbol> + Captures<'_> {
self.function_coverage_info.mappings.iter().map(|mapping| mapping.source_region.file_name)
}
/// Convert this function's coverage expression data into a form that can be
/// passed through FFI to LLVM.
pub(crate) fn counter_expressions(
&self,
) -> impl Iterator<Item = CounterExpression> + ExactSizeIterator + Captures<'_> {
// We know that LLVM will optimize out any unused expressions before
// producing the final coverage map, so there's no need to do the same
// thing on the Rust side unless we're confident we can do much better.
// (See `CounterExpressionsMinimizer` in `CoverageMappingWriter.cpp`.)
self.function_coverage_info.expressions.iter().map(move |&Expression { lhs, op, rhs }| {
CounterExpression {
lhs: self.counter_for_term(lhs),
kind: match op {
Op::Add => ExprKind::Add,
Op::Subtract => ExprKind::Subtract,
},
rhs: self.counter_for_term(rhs),
}
})
}
/// Converts this function's coverage mappings into an intermediate form
/// that will be used by `mapgen` when preparing for FFI.
pub(crate) fn counter_regions(
&self,
) -> impl Iterator<Item = (MappingKind, &SourceRegion)> + ExactSizeIterator {
self.function_coverage_info.mappings.iter().map(move |mapping| {
let Mapping { kind, source_region } = mapping;
let kind =
kind.map_terms(|term| if self.is_zero_term(term) { CovTerm::Zero } else { term });
(kind, source_region)
})
}
fn counter_for_term(&self, term: CovTerm) -> Counter {
if self.is_zero_term(term) { Counter::ZERO } else { Counter::from_term(term) }
}
fn is_zero_term(&self, term: CovTerm) -> bool {
is_zero_term(&self.counters_seen, &self.zero_expressions, term)
}
}
/// Set of expression IDs that are known to always evaluate to zero.
/// Any mapping or expression operand that refers to these expressions can have
/// that reference replaced with a constant zero value.
#[derive(Default)]
struct ZeroExpressions(FxIndexSet<ExpressionId>);
impl ZeroExpressions {
fn insert(&mut self, id: ExpressionId) {
self.0.insert(id);
}
fn contains(&self, id: ExpressionId) -> bool {
self.0.contains(&id)
}
}
/// Returns `true` if the given term is known to have a value of zero, taking
/// into account knowledge of which counters are unused and which expressions
/// are always zero.
fn is_zero_term(
counters_seen: &BitSet<CounterId>,
zero_expressions: &ZeroExpressions,
term: CovTerm,
) -> bool {
match term {
CovTerm::Zero => true,
CovTerm::Counter(id) => !counters_seen.contains(id),
CovTerm::Expression(id) => zero_expressions.contains(id),
}
}