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coverage: Streamline several names of things in counter creation
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@Zalathar
Zalathar committed Oct 19, 2024
1 parent 341881f commit a66fe69
Showing 1 changed file with 69 additions and 85 deletions.
154 changes: 69 additions & 85 deletions compiler/rustc_mir_transform/src/coverage/counters.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,6 @@ use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::graph::DirectedGraph;
use rustc_index::IndexVec;
use rustc_index::bit_set::BitSet;
use rustc_middle::bug;
use rustc_middle::mir::coverage::{CounterId, CovTerm, Expression, ExpressionId, Op};
use tracing::{debug, debug_span, instrument};

Expand Down Expand Up @@ -58,13 +57,13 @@ pub(super) struct CoverageCounters {
counter_increment_sites: IndexVec<CounterId, CounterIncrementSite>,

/// Coverage counters/expressions that are associated with individual BCBs.
bcb_counters: IndexVec<BasicCoverageBlock, Option<BcbCounter>>,
node_counters: IndexVec<BasicCoverageBlock, Option<BcbCounter>>,
/// Coverage counters/expressions that are associated with the control-flow
/// edge between two BCBs.
///
/// We currently don't iterate over this map, but if we do in the future,
/// switch it back to `FxIndexMap` to avoid query stability hazards.
bcb_edge_counters: FxHashMap<(BasicCoverageBlock, BasicCoverageBlock), BcbCounter>,
edge_counters: FxHashMap<(BasicCoverageBlock, BasicCoverageBlock), BcbCounter>,

/// Table of expression data, associating each expression ID with its
/// corresponding operator (+ or -) and its LHS/RHS operands.
Expand All @@ -78,20 +77,20 @@ impl CoverageCounters {
/// Ensures that each BCB node needing a counter has one, by creating physical
/// counters or counter expressions for nodes and edges as required.
pub(super) fn make_bcb_counters(
basic_coverage_blocks: &CoverageGraph,
graph: &CoverageGraph,
bcb_needs_counter: &BitSet<BasicCoverageBlock>,
) -> Self {
let mut counters = MakeBcbCounters::new(basic_coverage_blocks, bcb_needs_counter);
counters.make_bcb_counters();
let mut builder = CountersBuilder::new(graph, bcb_needs_counter);
builder.make_bcb_counters();

counters.coverage_counters
builder.counters
}

fn with_num_bcbs(num_bcbs: usize) -> Self {
Self {
counter_increment_sites: IndexVec::new(),
bcb_counters: IndexVec::from_elem_n(None, num_bcbs),
bcb_edge_counters: FxHashMap::default(),
node_counters: IndexVec::from_elem_n(None, num_bcbs),
edge_counters: FxHashMap::default(),
expressions: IndexVec::new(),
expressions_memo: FxHashMap::default(),
}
Expand Down Expand Up @@ -189,35 +188,31 @@ impl CoverageCounters {
self.counter_increment_sites.len()
}

fn set_bcb_counter(&mut self, bcb: BasicCoverageBlock, counter_kind: BcbCounter) -> BcbCounter {
if let Some(replaced) = self.bcb_counters[bcb].replace(counter_kind) {
bug!(
"attempt to set a BasicCoverageBlock coverage counter more than once; \
{bcb:?} already had counter {replaced:?}",
);
} else {
counter_kind
}
fn set_node_counter(&mut self, bcb: BasicCoverageBlock, counter: BcbCounter) -> BcbCounter {
let existing = self.node_counters[bcb].replace(counter);
assert!(
existing.is_none(),
"node {bcb:?} already has a counter: {existing:?} => {counter:?}"
);
counter
}

fn set_bcb_edge_counter(
fn set_edge_counter(
&mut self,
from_bcb: BasicCoverageBlock,
to_bcb: BasicCoverageBlock,
counter_kind: BcbCounter,
counter: BcbCounter,
) -> BcbCounter {
if let Some(replaced) = self.bcb_edge_counters.insert((from_bcb, to_bcb), counter_kind) {
bug!(
"attempt to set an edge counter more than once; from_bcb: \
{from_bcb:?} already had counter {replaced:?}",
);
} else {
counter_kind
}
let existing = self.edge_counters.insert((from_bcb, to_bcb), counter);
assert!(
existing.is_none(),
"edge ({from_bcb:?} -> {to_bcb:?}) already has a counter: {existing:?} => {counter:?}"
);
counter
}

pub(super) fn term_for_bcb(&self, bcb: BasicCoverageBlock) -> Option<CovTerm> {
self.bcb_counters[bcb].map(|counter| counter.as_term())
self.node_counters[bcb].map(|counter| counter.as_term())
}

/// Returns an iterator over all the nodes/edges in the coverage graph that
Expand All @@ -234,7 +229,7 @@ impl CoverageCounters {
pub(super) fn bcb_nodes_with_coverage_expressions(
&self,
) -> impl Iterator<Item = (BasicCoverageBlock, ExpressionId)> + Captures<'_> {
self.bcb_counters.iter_enumerated().filter_map(|(bcb, &counter_kind)| match counter_kind {
self.node_counters.iter_enumerated().filter_map(|(bcb, &counter)| match counter {
// Yield the BCB along with its associated expression ID.
Some(BcbCounter::Expression { id }) => Some((bcb, id)),
// This BCB is associated with a counter or nothing, so skip it.
Expand All @@ -261,22 +256,20 @@ impl CoverageCounters {
}
}

/// Helper struct that allows counter creation to inspect the BCB graph.
struct MakeBcbCounters<'a> {
coverage_counters: CoverageCounters,
basic_coverage_blocks: &'a CoverageGraph,
/// Helper struct that allows counter creation to inspect the BCB graph, and
/// the set of nodes that need counters.
struct CountersBuilder<'a> {
counters: CoverageCounters,
graph: &'a CoverageGraph,
bcb_needs_counter: &'a BitSet<BasicCoverageBlock>,
}

impl<'a> MakeBcbCounters<'a> {
fn new(
basic_coverage_blocks: &'a CoverageGraph,
bcb_needs_counter: &'a BitSet<BasicCoverageBlock>,
) -> Self {
assert_eq!(basic_coverage_blocks.num_nodes(), bcb_needs_counter.domain_size());
impl<'a> CountersBuilder<'a> {
fn new(graph: &'a CoverageGraph, bcb_needs_counter: &'a BitSet<BasicCoverageBlock>) -> Self {
assert_eq!(graph.num_nodes(), bcb_needs_counter.domain_size());
Self {
coverage_counters: CoverageCounters::with_num_bcbs(basic_coverage_blocks.num_nodes()),
basic_coverage_blocks,
counters: CoverageCounters::with_num_bcbs(graph.num_nodes()),
graph,
bcb_needs_counter,
}
}
Expand All @@ -291,7 +284,7 @@ impl<'a> MakeBcbCounters<'a> {
// nodes within the loop are visited before visiting any nodes outside
// the loop. It also keeps track of which loop(s) the traversal is
// currently inside.
let mut traversal = TraverseCoverageGraphWithLoops::new(self.basic_coverage_blocks);
let mut traversal = TraverseCoverageGraphWithLoops::new(self.graph);
while let Some(bcb) = traversal.next() {
let _span = debug_span!("traversal", ?bcb).entered();
if self.bcb_needs_counter.contains(bcb) {
Expand All @@ -318,26 +311,26 @@ impl<'a> MakeBcbCounters<'a> {
// We might also use that counter to compute one of the out-edge counters.
let node_counter = self.get_or_make_node_counter(from_bcb);

let successors = self.basic_coverage_blocks.successors[from_bcb].as_slice();
let successors = self.graph.successors[from_bcb].as_slice();

// If this node's out-edges won't sum to the node's counter,
// then there's no reason to create edge counters here.
if !self.basic_coverage_blocks[from_bcb].is_out_summable {
if !self.graph[from_bcb].is_out_summable {
return;
}

// When choosing which out-edge should be given a counter expression, ignore edges that
// already have counters, or could use the existing counter of their target node.
let out_edge_has_counter = |to_bcb| {
if self.coverage_counters.bcb_edge_counters.contains_key(&(from_bcb, to_bcb)) {
if self.counters.edge_counters.contains_key(&(from_bcb, to_bcb)) {
return true;
}
self.basic_coverage_blocks.sole_predecessor(to_bcb) == Some(from_bcb)
&& self.coverage_counters.bcb_counters[to_bcb].is_some()
self.graph.sole_predecessor(to_bcb) == Some(from_bcb)
&& self.counters.node_counters[to_bcb].is_some()
};

// Determine the set of out-edges that could benefit from being given an expression.
let candidate_successors = self.basic_coverage_blocks.successors[from_bcb]
let candidate_successors = self.graph.successors[from_bcb]
.iter()
.copied()
.filter(|&to_bcb| !out_edge_has_counter(to_bcb))
Expand All @@ -346,7 +339,7 @@ impl<'a> MakeBcbCounters<'a> {

// If there are out-edges without counters, choose one to be given an expression
// (computed from this node and the other out-edges) instead of a physical counter.
let Some(expression_to_bcb) =
let Some(target_bcb) =
self.choose_out_edge_for_expression(traversal, &candidate_successors)
else {
return;
Expand All @@ -359,49 +352,44 @@ impl<'a> MakeBcbCounters<'a> {
.iter()
.copied()
// Skip the chosen edge, since we'll calculate its count from this sum.
.filter(|&to_bcb| to_bcb != expression_to_bcb)
.filter(|&edge_target_bcb| edge_target_bcb != target_bcb)
.map(|to_bcb| self.get_or_make_edge_counter(from_bcb, to_bcb))
.collect::<Vec<_>>();
let Some(sum_of_all_other_out_edges) =
self.coverage_counters.make_sum(&other_out_edge_counters)
let Some(sum_of_all_other_out_edges) = self.counters.make_sum(&other_out_edge_counters)
else {
return;
};

// Now create an expression for the chosen edge, by taking the counter
// for its source node and subtracting the sum of its sibling out-edges.
let expression = self.coverage_counters.make_expression(
node_counter,
Op::Subtract,
sum_of_all_other_out_edges,
);
let expression =
self.counters.make_expression(node_counter, Op::Subtract, sum_of_all_other_out_edges);

debug!("{expression_to_bcb:?} gets an expression: {expression:?}");
self.coverage_counters.set_bcb_edge_counter(from_bcb, expression_to_bcb, expression);
debug!("{target_bcb:?} gets an expression: {expression:?}");
self.counters.set_edge_counter(from_bcb, target_bcb, expression);
}

#[instrument(level = "debug", skip(self))]
fn get_or_make_node_counter(&mut self, bcb: BasicCoverageBlock) -> BcbCounter {
// If the BCB already has a counter, return it.
if let Some(counter_kind) = self.coverage_counters.bcb_counters[bcb] {
debug!("{bcb:?} already has a counter: {counter_kind:?}");
return counter_kind;
if let Some(counter) = self.counters.node_counters[bcb] {
debug!("{bcb:?} already has a counter: {counter:?}");
return counter;
}

let counter = self.make_node_counter_inner(bcb);
self.coverage_counters.set_bcb_counter(bcb, counter)
self.counters.set_node_counter(bcb, counter)
}

fn make_node_counter_inner(&mut self, bcb: BasicCoverageBlock) -> BcbCounter {
// If the node's sole in-edge already has a counter, use that.
if let Some(sole_pred) = self.basic_coverage_blocks.sole_predecessor(bcb)
&& let Some(&edge_counter) =
self.coverage_counters.bcb_edge_counters.get(&(sole_pred, bcb))
if let Some(sole_pred) = self.graph.sole_predecessor(bcb)
&& let Some(&edge_counter) = self.counters.edge_counters.get(&(sole_pred, bcb))
{
return edge_counter;
}

let predecessors = self.basic_coverage_blocks.predecessors[bcb].as_slice();
let predecessors = self.graph.predecessors[bcb].as_slice();

// Handle cases where we can't compute a node's count from its in-edges:
// - START_BCB has no in-edges, so taking the sum would panic (or be wrong).
Expand All @@ -410,7 +398,7 @@ impl<'a> MakeBcbCounters<'a> {
// leading to infinite recursion.
if predecessors.len() <= 1 || predecessors.contains(&bcb) {
debug!(?bcb, ?predecessors, "node has <=1 predecessors or is its own predecessor");
let counter = self.coverage_counters.make_phys_node_counter(bcb);
let counter = self.counters.make_phys_node_counter(bcb);
debug!(?bcb, ?counter, "node gets a physical counter");
return counter;
}
Expand All @@ -422,10 +410,8 @@ impl<'a> MakeBcbCounters<'a> {
.copied()
.map(|from_bcb| self.get_or_make_edge_counter(from_bcb, bcb))
.collect::<Vec<_>>();
let sum_of_in_edges: BcbCounter = self
.coverage_counters
.make_sum(&in_edge_counters)
.expect("there must be at least one in-edge");
let sum_of_in_edges: BcbCounter =
self.counters.make_sum(&in_edge_counters).expect("there must be at least one in-edge");

debug!("{bcb:?} gets a new counter (sum of predecessor counters): {sum_of_in_edges:?}");
sum_of_in_edges
Expand All @@ -438,15 +424,13 @@ impl<'a> MakeBcbCounters<'a> {
to_bcb: BasicCoverageBlock,
) -> BcbCounter {
// If the edge already has a counter, return it.
if let Some(&counter_kind) =
self.coverage_counters.bcb_edge_counters.get(&(from_bcb, to_bcb))
{
debug!("Edge {from_bcb:?}->{to_bcb:?} already has a counter: {counter_kind:?}");
return counter_kind;
if let Some(&counter) = self.counters.edge_counters.get(&(from_bcb, to_bcb)) {
debug!("Edge {from_bcb:?}->{to_bcb:?} already has a counter: {counter:?}");
return counter;
}

let counter = self.make_edge_counter_inner(from_bcb, to_bcb);
self.coverage_counters.set_bcb_edge_counter(from_bcb, to_bcb, counter)
self.counters.set_edge_counter(from_bcb, to_bcb, counter)
}

fn make_edge_counter_inner(
Expand All @@ -456,7 +440,7 @@ impl<'a> MakeBcbCounters<'a> {
) -> BcbCounter {
// If the target node has exactly one in-edge (i.e. this one), then just
// use the node's counter, since it will have the same value.
if let Some(sole_pred) = self.basic_coverage_blocks.sole_predecessor(to_bcb) {
if let Some(sole_pred) = self.graph.sole_predecessor(to_bcb) {
assert_eq!(sole_pred, from_bcb);
// This call must take care not to invoke `get_or_make_edge` for
// this edge, since that would result in infinite recursion!
Expand All @@ -465,13 +449,13 @@ impl<'a> MakeBcbCounters<'a> {

// If the source node has exactly one out-edge (i.e. this one) and would have
// the same execution count as that edge, then just use the node's counter.
if let Some(simple_succ) = self.basic_coverage_blocks.simple_successor(from_bcb) {
if let Some(simple_succ) = self.graph.simple_successor(from_bcb) {
assert_eq!(simple_succ, to_bcb);
return self.get_or_make_node_counter(from_bcb);
}

// Make a new counter to count this edge.
let counter = self.coverage_counters.make_phys_edge_counter(from_bcb, to_bcb);
let counter = self.counters.make_phys_edge_counter(from_bcb, to_bcb);
debug!(?from_bcb, ?to_bcb, ?counter, "edge gets a physical counter");
counter
}
Expand Down Expand Up @@ -518,9 +502,9 @@ impl<'a> MakeBcbCounters<'a> {
for &target_bcb in candidate_successors {
// An edge is a reloop edge if its target dominates any BCB that has
// an edge back to the loop header. (Otherwise it's an exit edge.)
let is_reloop_edge = reloop_bcbs.iter().any(|&reloop_bcb| {
self.basic_coverage_blocks.dominates(target_bcb, reloop_bcb)
});
let is_reloop_edge = reloop_bcbs
.iter()
.any(|&reloop_bcb| self.graph.dominates(target_bcb, reloop_bcb));
if is_reloop_edge {
// We found a good out-edge to be given an expression.
return Some(target_bcb);
Expand Down

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