a18c5f3b75
Coverage codegen can now allocate arrays based on the number of counters/expressions originally used by the instrumentor. The existing query that inspects coverage statements is still used for determining the number of counters passed to `llvm.instrprof.increment`. If some high-numbered counters were removed by MIR optimizations, the instrumented binary can potentially use less memory and disk space at runtime.
290 lines
13 KiB
Rust
290 lines
13 KiB
Rust
use crate::coverageinfo::ffi::{Counter, CounterExpression, ExprKind};
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use rustc_data_structures::fx::FxIndexSet;
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use rustc_index::IndexVec;
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use rustc_middle::mir::coverage::{
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CodeRegion, CounterId, ExpressionId, FunctionCoverageInfo, Op, Operand,
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};
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use rustc_middle::ty::Instance;
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#[derive(Clone, Debug, PartialEq)]
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pub struct Expression {
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lhs: Operand,
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op: Op,
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rhs: Operand,
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code_regions: Vec<CodeRegion>,
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}
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/// Collects all of the coverage regions associated with (a) injected counters, (b) counter
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/// expressions (additions or subtraction), and (c) unreachable regions (always counted as zero),
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/// for a given Function. This struct also stores the `function_source_hash`,
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/// computed during instrumentation, and forwarded with counters.
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///
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/// Note, it may be important to understand LLVM's definitions of `unreachable` regions versus "gap
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/// regions" (or "gap areas"). A gap region is a code region within a counted region (either counter
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/// or expression), but the line or lines in the gap region are not executable (such as lines with
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/// only whitespace or comments). According to LLVM Code Coverage Mapping documentation, "A count
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/// for a gap area is only used as the line execution count if there are no other regions on a
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/// line."
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#[derive(Debug)]
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pub struct FunctionCoverage<'tcx> {
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/// Coverage info that was attached to this function by the instrumentor.
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function_coverage_info: &'tcx FunctionCoverageInfo,
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is_used: bool,
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counters: IndexVec<CounterId, Option<Vec<CodeRegion>>>,
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expressions: IndexVec<ExpressionId, Option<Expression>>,
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unreachable_regions: Vec<CodeRegion>,
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}
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impl<'tcx> FunctionCoverage<'tcx> {
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/// Creates a new set of coverage data for a used (called) function.
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pub fn new(
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instance: Instance<'tcx>,
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function_coverage_info: &'tcx FunctionCoverageInfo,
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) -> Self {
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Self::create(instance, function_coverage_info, true)
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}
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/// Creates a new set of coverage data for an unused (never called) function.
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pub fn unused(
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instance: Instance<'tcx>,
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function_coverage_info: &'tcx FunctionCoverageInfo,
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) -> Self {
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Self::create(instance, function_coverage_info, false)
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}
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fn create(
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instance: Instance<'tcx>,
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function_coverage_info: &'tcx FunctionCoverageInfo,
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is_used: bool,
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) -> Self {
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let num_counters = function_coverage_info.num_counters;
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let num_expressions = function_coverage_info.num_expressions;
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debug!(
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"FunctionCoverage::create(instance={instance:?}) has \
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num_counters={num_counters}, num_expressions={num_expressions}, is_used={is_used}"
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);
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Self {
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function_coverage_info,
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is_used,
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counters: IndexVec::from_elem_n(None, num_counters),
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expressions: IndexVec::from_elem_n(None, num_expressions),
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unreachable_regions: Vec::new(),
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}
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}
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/// Returns true for a used (called) function, and false for an unused function.
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pub fn is_used(&self) -> bool {
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self.is_used
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}
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/// Adds code regions to be counted by an injected counter intrinsic.
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#[instrument(level = "debug", skip(self))]
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pub(crate) fn add_counter(&mut self, id: CounterId, code_regions: &[CodeRegion]) {
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if code_regions.is_empty() {
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return;
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}
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let slot = &mut self.counters[id];
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match slot {
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None => *slot = Some(code_regions.to_owned()),
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// If this counter ID slot has already been filled, it should
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// contain identical information.
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Some(ref previous_regions) => assert_eq!(
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previous_regions, code_regions,
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"add_counter: code regions for id changed"
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),
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}
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}
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/// Adds information about a coverage expression, along with zero or more
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/// code regions mapped to that expression.
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///
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/// Both counters and "counter expressions" (or simply, "expressions") can be operands in other
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/// expressions. These are tracked as separate variants of `Operand`, so there is no ambiguity
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/// between operands that are counter IDs and operands that are expression IDs.
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#[instrument(level = "debug", skip(self))]
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pub(crate) fn add_counter_expression(
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&mut self,
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expression_id: ExpressionId,
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lhs: Operand,
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op: Op,
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rhs: Operand,
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code_regions: &[CodeRegion],
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) {
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debug_assert!(
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expression_id.as_usize() < self.expressions.len(),
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"expression_id {} is out of range for expressions.len() = {}
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for {:?}",
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expression_id.as_usize(),
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self.expressions.len(),
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self,
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);
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let expression = Expression { lhs, op, rhs, code_regions: code_regions.to_owned() };
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let slot = &mut self.expressions[expression_id];
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match slot {
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None => *slot = Some(expression),
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// If this expression ID slot has already been filled, it should
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// contain identical information.
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Some(ref previous_expression) => assert_eq!(
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previous_expression, &expression,
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"add_counter_expression: expression for id changed"
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),
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}
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}
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/// Adds regions that will be marked as "unreachable", with a constant "zero counter".
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#[instrument(level = "debug", skip(self))]
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pub(crate) fn add_unreachable_regions(&mut self, code_regions: &[CodeRegion]) {
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assert!(!code_regions.is_empty(), "unreachable regions always have code regions");
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self.unreachable_regions.extend_from_slice(code_regions);
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}
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/// Perform some simplifications to make the final coverage mappings
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/// slightly smaller.
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///
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/// This method mainly exists to preserve the simplifications that were
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/// already being performed by the Rust-side expression renumbering, so that
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/// the resulting coverage mappings don't get worse.
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pub(crate) fn simplify_expressions(&mut self) {
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// The set of expressions that either were optimized out entirely, or
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// have zero as both of their operands, and will therefore always have
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// a value of zero. Other expressions that refer to these as operands
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// can have those operands replaced with `Operand::Zero`.
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let mut zero_expressions = FxIndexSet::default();
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// For each expression, perform simplifications based on lower-numbered
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// expressions, and then update the set of always-zero expressions if
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// necessary.
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// (By construction, expressions can only refer to other expressions
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// that have lower IDs, so one simplification pass is sufficient.)
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for (id, maybe_expression) in self.expressions.iter_enumerated_mut() {
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let Some(expression) = maybe_expression else {
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// If an expression is missing, it must have been optimized away,
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// so any operand that refers to it can be replaced with zero.
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zero_expressions.insert(id);
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continue;
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};
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// If an operand refers to an expression that is always zero, then
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// that operand can be replaced with `Operand::Zero`.
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let maybe_set_operand_to_zero = |operand: &mut Operand| match &*operand {
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Operand::Expression(id) if zero_expressions.contains(id) => {
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*operand = Operand::Zero;
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}
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_ => (),
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};
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maybe_set_operand_to_zero(&mut expression.lhs);
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maybe_set_operand_to_zero(&mut expression.rhs);
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// Coverage counter values cannot be negative, so if an expression
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// involves subtraction from zero, assume that its RHS must also be zero.
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// (Do this after simplifications that could set the LHS to zero.)
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if let Expression { lhs: Operand::Zero, op: Op::Subtract, .. } = expression {
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expression.rhs = Operand::Zero;
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}
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// After the above simplifications, if both operands are zero, then
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// we know that this expression is always zero too.
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if let Expression { lhs: Operand::Zero, rhs: Operand::Zero, .. } = expression {
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zero_expressions.insert(id);
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}
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}
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}
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/// Return the source hash, generated from the HIR node structure, and used to indicate whether
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/// or not the source code structure changed between different compilations.
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pub fn source_hash(&self) -> u64 {
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if self.is_used { self.function_coverage_info.function_source_hash } else { 0 }
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}
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/// Generate an array of CounterExpressions, and an iterator over all `Counter`s and their
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/// associated `Regions` (from which the LLVM-specific `CoverageMapGenerator` will create
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/// `CounterMappingRegion`s.
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pub fn get_expressions_and_counter_regions(
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&self,
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) -> (Vec<CounterExpression>, impl Iterator<Item = (Counter, &CodeRegion)>) {
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let counter_expressions = self.counter_expressions();
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// Expression IDs are indices into `self.expressions`, and on the LLVM
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// side they will be treated as indices into `counter_expressions`, so
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// the two vectors should correspond 1:1.
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assert_eq!(self.expressions.len(), counter_expressions.len());
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let counter_regions = self.counter_regions();
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let expression_regions = self.expression_regions();
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let unreachable_regions = self.unreachable_regions();
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let counter_regions =
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counter_regions.chain(expression_regions.into_iter().chain(unreachable_regions));
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(counter_expressions, counter_regions)
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}
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fn counter_regions(&self) -> impl Iterator<Item = (Counter, &CodeRegion)> {
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self.counters
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.iter_enumerated()
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// Filter out counter IDs that we never saw during MIR traversal.
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// This can happen if a counter was optimized out by MIR transforms
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// (and replaced with `CoverageKind::Unreachable` instead).
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.filter_map(|(id, maybe_code_regions)| Some((id, maybe_code_regions.as_ref()?)))
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.flat_map(|(id, code_regions)| {
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let counter = Counter::counter_value_reference(id);
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code_regions.iter().map(move |region| (counter, region))
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})
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}
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/// Convert this function's coverage expression data into a form that can be
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/// passed through FFI to LLVM.
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fn counter_expressions(&self) -> Vec<CounterExpression> {
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// We know that LLVM will optimize out any unused expressions before
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// producing the final coverage map, so there's no need to do the same
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// thing on the Rust side unless we're confident we can do much better.
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// (See `CounterExpressionsMinimizer` in `CoverageMappingWriter.cpp`.)
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self.expressions
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.iter()
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.map(|expression| match expression {
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None => {
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// This expression ID was allocated, but we never saw the
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// actual expression, so it must have been optimized out.
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// Replace it with a dummy expression, and let LLVM take
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// care of omitting it from the expression list.
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CounterExpression::DUMMY
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}
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&Some(Expression { lhs, op, rhs, .. }) => {
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// Convert the operands and operator as normal.
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CounterExpression::new(
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Counter::from_operand(lhs),
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match op {
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Op::Add => ExprKind::Add,
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Op::Subtract => ExprKind::Subtract,
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},
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Counter::from_operand(rhs),
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)
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}
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})
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.collect::<Vec<_>>()
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}
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fn expression_regions(&self) -> Vec<(Counter, &CodeRegion)> {
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// Find all of the expression IDs that weren't optimized out AND have
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// one or more attached code regions, and return the corresponding
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// mappings as counter/region pairs.
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self.expressions
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.iter_enumerated()
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.filter_map(|(id, maybe_expression)| {
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let code_regions = &maybe_expression.as_ref()?.code_regions;
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Some((id, code_regions))
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})
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.flat_map(|(id, code_regions)| {
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let counter = Counter::expression(id);
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code_regions.iter().map(move |code_region| (counter, code_region))
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})
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.collect::<Vec<_>>()
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}
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fn unreachable_regions(&self) -> impl Iterator<Item = (Counter, &CodeRegion)> {
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self.unreachable_regions.iter().map(|region| (Counter::ZERO, region))
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}
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}
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