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internal: Use ManuallyDrop in RootDatabase to improve build times #10069

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merged 1 commit into from
Aug 28, 2021
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internal: Use ManuallyDrop in RootDatabase to improve build times #10069

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20 changes: 16 additions & 4 deletions crates/ide_db/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -19,7 +19,7 @@ pub mod path_transform;
pub mod search;
pub mod rename;

use std::{fmt, sync::Arc};
use std::{fmt, mem::ManuallyDrop, sync::Arc};

use base_db::{
salsa::{self, Durability},
Expand All @@ -44,7 +44,19 @@ pub use base_db;
hir::db::HirDatabaseStorage
)]
pub struct RootDatabase {
storage: salsa::Storage<RootDatabase>,
// We use `ManuallyDrop` here because every codegen unit that contains a
// `&RootDatabase -> &dyn OtherDatabase` cast will instantiate its drop glue in the vtable,
// which duplicates `Weak::drop` and `Arc::drop` tens of thousands of times, which makes
// compile times of all `ide_*` and downstream crates suffer greatly.
storage: ManuallyDrop<salsa::Storage<RootDatabase>>,
}

impl Drop for RootDatabase {
fn drop(&mut self) {
unsafe {
ManuallyDrop::drop(&mut self.storage);
}
}
}

impl fmt::Debug for RootDatabase {
Expand Down Expand Up @@ -93,7 +105,7 @@ impl Default for RootDatabase {

impl RootDatabase {
pub fn new(lru_capacity: Option<usize>) -> RootDatabase {
let mut db = RootDatabase { storage: salsa::Storage::default() };
let mut db = RootDatabase { storage: ManuallyDrop::new(salsa::Storage::default()) };
db.set_crate_graph_with_durability(Default::default(), Durability::HIGH);
db.set_local_roots_with_durability(Default::default(), Durability::HIGH);
db.set_library_roots_with_durability(Default::default(), Durability::HIGH);
Expand All @@ -112,7 +124,7 @@ impl RootDatabase {

impl salsa::ParallelDatabase for RootDatabase {
fn snapshot(&self) -> salsa::Snapshot<RootDatabase> {
salsa::Snapshot::new(RootDatabase { storage: self.storage.snapshot() })
salsa::Snapshot::new(RootDatabase { storage: ManuallyDrop::new(self.storage.snapshot()) })
}
}

Expand Down