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Make the reasoning more explicit.

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This commit is contained in:
Camille GILLOT 2021-06-01 21:46:30 +02:00
parent 3a6d5c2beb
commit b51f24f021
1 changed files with 9 additions and 5 deletions
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14
compiler/rustc_query_system/src/dep_graph/graph.rs
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@ -44,7 +44,7 @@ rustc_index::newtype_index! {
impl DepNodeIndex {
pub const INVALID: DepNodeIndex = DepNodeIndex::MAX;
pub const DUMMY_ANON: DepNodeIndex = DepNodeIndex::from_u32(0);
pub const SINGLETON_DEPENDENCYLESS_ANON_NODE: DepNodeIndex = DepNodeIndex::from_u32(0);
}
impl std::convert::From<DepNodeIndex> for QueryInvocationId {
@ -121,14 +121,14 @@ impl<K: DepKind> DepGraph<K> {
let current =
CurrentDepGraph::new(prev_graph_node_count, encoder, record_graph, record_stats);
// Instantiate an *always green* node for dependency-less anonymous queries.
// Instantiate a dependy-less node only once for anonymous queries.
let _green_node_index = current.intern_new_node(
profiler,
DepNode { kind: DepKind::NULL, hash: current.anon_id_seed.into() },
smallvec![],
Fingerprint::ZERO,
);
debug_assert_eq!(_green_node_index, DepNodeIndex::DUMMY_ANON);
debug_assert_eq!(_green_node_index, DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE);
DepGraph {
data: Some(Lrc::new(DepGraphData {
@ -300,8 +300,12 @@ impl<K: DepKind> DepGraph<K> {
let dep_node_index = match task_deps.len() {
0 => {
// Dependency-less anonymous nodes can safely be replaced by a dummy node.
DepNodeIndex::DUMMY_ANON
// Because the dep-node id of anon nodes is computed from the sets of its
// dependencies we already know what the ID of this dependency-less node is
// going to be (i.e. equal to the precomputed
// `SINGLETON_DEPENDENCYLESS_ANON_NODE`). As a consequence we can skip creating
// a `StableHasher` and sending the node through interning.
DepNodeIndex::SINGLETON_DEPENDENCYLESS_ANON_NODE
}
1 => {
// When there is only one dependency, don't bother creating a node.