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Use a Vec instead of a HashMap for existing drops. #147678

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Use a Vec instead of a HashMap for existing drops. #147678

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33 changes: 18 additions & 15 deletions compiler/rustc_mir_build/src/builder/scope.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,6 @@ that contains only loops and breakable blocks. It tracks where a `break`,
use std::mem;

use interpret::ErrorHandled;
use rustc_data_structures::fx::FxHashMap;
use rustc_hir::HirId;
use rustc_index::{IndexSlice, IndexVec};
use rustc_middle::middle::region;
Expand Down Expand Up @@ -232,8 +231,6 @@ const ROOT_NODE: DropIdx = DropIdx::ZERO;
struct DropTree {
/// Nodes in the drop tree, containing drop data and a link to the next node.
drop_nodes: IndexVec<DropIdx, DropNode>,
/// Map for finding the index of an existing node, given its contents.
existing_drops_map: FxHashMap<DropNodeKey, DropIdx>,
/// Edges into the `DropTree` that need to be added once it's lowered.
entry_points: Vec<(DropIdx, BasicBlock)>,
}
Expand All @@ -245,13 +242,14 @@ struct DropNode {
data: DropData,
/// Index of the "next" drop to perform (in drop order, not declaration order).
next: DropIdx,
/// Map for finding the index of an existing node, given its contents.
existing_drops_map: Vec<(Local, DropIdx)>,
}

/// Subset of [`DropNode`] used for reverse lookup in a hash table.
#[derive(Debug, PartialEq, Eq, Hash)]
struct DropNodeKey {
next: DropIdx,
local: Local,
impl DropNode {
fn new(data: DropData, next: DropIdx) -> DropNode {
DropNode { data, next, existing_drops_map: Vec::new() }
}
}

impl Scope {
Expand Down Expand Up @@ -299,8 +297,8 @@ impl DropTree {
let fake_source_info = SourceInfo::outermost(DUMMY_SP);
let fake_data =
DropData { source_info: fake_source_info, local: Local::MAX, kind: DropKind::Storage };
let drop_nodes = IndexVec::from_raw(vec![DropNode { data: fake_data, next: DropIdx::MAX }]);
Self { drop_nodes, entry_points: Vec::new(), existing_drops_map: FxHashMap::default() }
let drop_nodes = IndexVec::from_raw(vec![DropNode::new(fake_data, DropIdx::MAX)]);
Self { drop_nodes, entry_points: Vec::new() }
}

/// Adds a node to the drop tree, consisting of drop data and the index of
Expand All @@ -310,11 +308,16 @@ impl DropTree {
/// that node's index is returned. Otherwise, the new node's index is returned.
fn add_drop(&mut self, data: DropData, next: DropIdx) -> DropIdx {
let drop_nodes = &mut self.drop_nodes;
*self
.existing_drops_map
.entry(DropNodeKey { next, local: data.local })
if let Some((_, existing)) =
drop_nodes[next].existing_drops_map.iter().find(|(local, _)| *local == data.local)
{
*existing
} else {
// Create a new node, and also add its index to the map.
.or_insert_with(|| drop_nodes.push(DropNode { data, next }))
let new = drop_nodes.push(DropNode::new(data, next));
drop_nodes[next].existing_drops_map.push((data.local, new));
new
}
}

/// Registers `from` as an entry point to this drop tree, at `to`.
Expand Down Expand Up @@ -2012,7 +2015,7 @@ impl<'a, 'tcx: 'a> Builder<'a, 'tcx> {
}
// Link the exit drop tree to dropline drop tree (coroutine drop path) for async drops
if is_coroutine
&& drops.drop_nodes.iter().any(|DropNode { data, next: _ }| {
&& drops.drop_nodes.iter().any(|DropNode { data, .. }| {
data.kind == DropKind::Value && self.is_async_drop(data.local)
})
{
Expand Down
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