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perf(dep_graph): Avoid allocating a set on when the number reads are … #69778

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Merged
merged 2 commits into from
Mar 23, 2020
Merged

perf(dep_graph): Avoid allocating a set on when the number reads are … #69778

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c6f1215
perf(dep_graph): Avoid allocating a set on when the number reads are …
Mar 6, 2020
4168c25
refactor: Add an alias for the SmallVec in dep_graph
Mar 7, 2020
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19 changes: 17 additions & 2 deletions src/librustc/dep_graph/graph.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1128,11 +1128,25 @@ impl DepGraphData {
let icx = if let Some(icx) = icx { icx } else { return };
if let Some(task_deps) = icx.task_deps {
let mut task_deps = task_deps.lock();
let task_deps = &mut *task_deps;
if cfg!(debug_assertions) {
self.current.total_read_count.fetch_add(1, Relaxed);
}
if task_deps.read_set.insert(source) {

// As long as we only have a low number of reads we can avoid doing a hash
// insert and potentially allocating/reallocating the hashmap
let new_read = if task_deps.reads.len() < TASK_DEPS_READS_CAP {
task_deps.reads.iter().all(|other| *other != source)
} else {
task_deps.read_set.insert(source)
};
if new_read {
task_deps.reads.push(source);
if task_deps.reads.len() == TASK_DEPS_READS_CAP {
// Fill `read_set` with what we have so far so we can use the hashset next
// time
task_deps.read_set.extend(task_deps.reads.iter().copied());
}

#[cfg(debug_assertions)]
{
Expand All @@ -1154,10 +1168,11 @@ impl DepGraphData {
}
}

const TASK_DEPS_READS_CAP: usize = 8;
pub struct TaskDeps {
#[cfg(debug_assertions)]
node: Option<DepNode>,
reads: SmallVec<[DepNodeIndex; 8]>,
reads: SmallVec<[DepNodeIndex; TASK_DEPS_READS_CAP]>,
read_set: FxHashSet<DepNodeIndex>,
}

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