perf: Store view downcaster in function ingredients directly

components/salsa-macro-rules/src/setup_tracked_fn.rs

@@ -142,12 +142,13 @@ macro_rules! setup_tracked_fn {
             impl $Configuration {
                 fn fn_ingredient(db: &dyn $Db) -> &$zalsa::function::IngredientImpl<$Configuration> {
                     $FN_CACHE.get_or_create(db.as_dyn_database(), || {
-                        <dyn $Db as $Db>::zalsa_db(db);
+                        <dyn $Db as $Db>::zalsa_register_downcaster(db);
                         db.zalsa().add_or_lookup_jar_by_type::<$Configuration>()
                     })
                 }
 
                 pub fn fn_ingredient_mut(db: &mut dyn $Db) -> &mut $zalsa::function::IngredientImpl<Self> {
+                    <dyn $Db as $Db>::zalsa_register_downcaster(db);
                     let zalsa_mut = db.zalsa_mut();
                     let index = zalsa_mut.add_or_lookup_jar_by_type::<$Configuration>();
                     let (ingredient, _) = zalsa_mut.lookup_ingredient_mut(index);
@@ -159,6 +160,7 @@ macro_rules! setup_tracked_fn {
                         db: &dyn $Db,
                     ) -> &$zalsa::interned::IngredientImpl<$Configuration> {
                         $INTERN_CACHE.get_or_create(db.as_dyn_database(), || {
+                            <dyn $Db as $Db>::zalsa_register_downcaster(db);
                             db.zalsa().add_or_lookup_jar_by_type::<$Configuration>().successor(0)
                         })
                     }
@@ -249,7 +251,8 @@ macro_rules! setup_tracked_fn {
                     let fn_ingredient = <$zalsa::function::IngredientImpl<$Configuration>>::new(
                         first_index,
                         memo_ingredient_indices,
-                        $lru
+                        $lru,
+                        zalsa.views().downcaster_for::<dyn $Db>()
                     );
                     $zalsa::macro_if! {
                         if $needs_interner {

components/salsa-macros/src/db.rs

@@ -89,10 +89,12 @@ impl DbMacro {
                 use salsa::plumbing as #zalsa;
 
                 unsafe impl #zalsa::HasStorage for #db {
+                    #[inline(always)]
                     fn storage(&self) -> &#zalsa::Storage<Self> {
                         &self.#storage
                     }
 
+                    #[inline(always)]
                     fn storage_mut(&mut self) -> &mut #zalsa::Storage<Self> {
                         &mut self.#storage
                     }
@@ -102,16 +104,26 @@ impl DbMacro {
     }
 
     fn add_salsa_view_method(&self, input: &mut syn::ItemTrait) -> syn::Result<()> {
+        let trait_name = &input.ident;
         input.items.push(parse_quote! {
             #[doc(hidden)]
-            fn zalsa_db(&self);
+            fn zalsa_register_downcaster(&self);
+        });
+
+        let comment = format!(" Downcast a [`dyn Database`] to a [`dyn {trait_name}`]");
+        input.items.push(parse_quote! {
+            #[doc = #comment]
+            ///
+            /// # Safety
+            ///
+            /// The input database must be of type `Self`.
+            #[doc(hidden)]
+            unsafe fn downcast(db: &dyn salsa::plumbing::Database) -> &dyn #trait_name where Self: Sized;
         });
         Ok(())
     }
 
     fn add_salsa_view_method_impl(&self, input: &mut syn::ItemImpl) -> syn::Result<()> {
-        let zalsa = self.hygiene.ident("zalsa");
-
         let Some((_, TraitPath, _)) = &input.trait_ else {
             return Err(syn::Error::new_spanned(
                 &input.self_ty,
@@ -121,9 +133,18 @@ impl DbMacro {
 
         input.items.push(parse_quote! {
             #[doc(hidden)]
-            fn zalsa_db(&self) {
-                use salsa::plumbing as #zalsa;
-                #zalsa::views(self).add::<Self, dyn #TraitPath>(|t| t);
+            #[inline(always)]
+            fn zalsa_register_downcaster(&self)  {
+                salsa::plumbing::views(self).add(<Self as #TraitPath>::downcast);
+            }
+        });
+        input.items.push(parse_quote! {
+            #[doc(hidden)]
+            #[inline(always)]
+            unsafe fn downcast(db: &dyn salsa::plumbing::Database) -> &dyn #TraitPath where Self: Sized {
+                debug_assert_eq!(db.type_id(), ::core::any::TypeId::of::<Self>());
+                // SAFETY: Same as the safety of the `downcast` method.
+                unsafe { &*salsa::plumbing::transmute_data_ptr::<dyn salsa::plumbing::Database, Self>(db) }
             }
         });
         Ok(())

components/salsa-macros/src/lib.rs

@@ -2,8 +2,6 @@
 
 #![recursion_limit = "256"]
 
-extern crate proc_macro;
-extern crate proc_macro2;
 #[macro_use]
 extern crate quote;
 

src/accumulator.rs

@@ -100,7 +100,7 @@ impl<A: Accumulator> Ingredient for IngredientImpl<A> {
         self.index
     }
 
-    fn maybe_changed_after(
+    unsafe fn maybe_changed_after(
         &self,
         _db: &dyn Database,
         _input: Id,

src/database.rs

@@ -121,6 +121,7 @@ impl dyn Database {
     /// If the view has not been added to the database (see [`crate::views::Views`]).
     #[track_caller]
     pub fn as_view<DbView: ?Sized + Database>(&self) -> &DbView {
-        self.zalsa().views().try_view_as(self).unwrap()
+        let views = self.zalsa().views();
+        views.downcaster_for().downcast(self)
     }
 }

src/function.rs

@@ -8,6 +8,7 @@ use crate::{
     plumbing::MemoIngredientMap,
     salsa_struct::SalsaStructInDb,
     table::Table,
+    views::DatabaseDownCaster,
     zalsa::{IngredientIndex, MemoIngredientIndex, Zalsa},
     zalsa_local::QueryOrigin,
     Cycle, Database, Id, Revision,
@@ -105,6 +106,14 @@ pub struct IngredientImpl<C: Configuration> {
     /// Used to find memos to throw out when we have too many memoized values.
     lru: lru::Lru,
 
+    /// A downcaster from `dyn Database` to `C::DbView`.
+    ///
+    /// # Safety
+    ///
+    /// The supplied database must be be the same as the database used to construct the [`Views`]
+    /// instances that this downcaster was derived from.
+    view_caster: DatabaseDownCaster<C::DbView>,
+
     /// When `fetch` and friends executes, they return a reference to the
     /// value stored in the memo that is extended to live as long as the `&self`
     /// reference we start with. This means that whenever we remove something
@@ -135,12 +144,14 @@ where
         index: IngredientIndex,
         memo_ingredient_indices: <C::SalsaStruct<'static> as SalsaStructInDb>::MemoIngredientMap,
         lru: usize,
+        view_caster: DatabaseDownCaster<C::DbView>,
     ) -> Self {
         Self {
             index,
             memo_ingredient_indices,
             lru: lru::Lru::new(lru),
             deleted_entries: Default::default(),
+            view_caster,
         }
     }
 
@@ -213,13 +224,14 @@ where
         self.index
     }
 
-    fn maybe_changed_after(
+    unsafe fn maybe_changed_after(
         &self,
         db: &dyn Database,
         input: Id,
         revision: Revision,
     ) -> MaybeChangedAfter {
-        let db = db.as_view::<C::DbView>();
+        // SAFETY: The `db` belongs to the ingredient as per caller invariant
+        let db = unsafe { self.view_caster.downcast_unchecked(db) };
         self.maybe_changed_after(db, input, revision)
     }
 
@@ -279,7 +291,7 @@ where
         db: &'db dyn Database,
         key_index: Id,
     ) -> (Option<&'db AccumulatedMap>, InputAccumulatedValues) {
-        let db = db.as_view::<C::DbView>();
+        let db = self.view_caster.downcast(db);
         self.accumulated_map(db, key_index)
     }
 }

src/ingredient.rs

@@ -51,7 +51,11 @@ pub trait Ingredient: Any + std::fmt::Debug + Send + Sync {
     fn debug_name(&self) -> &'static str;
 
     /// Has the value for `input` in this ingredient changed after `revision`?
-    fn maybe_changed_after<'db>(
+    ///
+    /// # Safety
+    ///
+    /// The passed in database needs to be the same one that the ingredient was created with.
+    unsafe fn maybe_changed_after<'db>(
         &'db self,
         db: &'db dyn Database,
         input: Id,

src/input.rs

@@ -215,7 +215,7 @@ impl<C: Configuration> Ingredient for IngredientImpl<C> {
         self.ingredient_index
     }
 
-    fn maybe_changed_after(
+    unsafe fn maybe_changed_after(
         &self,
         _db: &dyn Database,
         _input: Id,

src/input/input_field.rs

@@ -49,7 +49,7 @@ where
         CycleRecoveryStrategy::Panic
     }
 
-    fn maybe_changed_after(
+    unsafe fn maybe_changed_after(
         &self,
         db: &dyn Database,
         input: Id,

src/interned.rs

@@ -282,7 +282,7 @@ where
         self.ingredient_index
     }
 
-    fn maybe_changed_after(
+    unsafe fn maybe_changed_after(
         &self,
         _db: &dyn Database,
         _input: Id,

src/key.rs

@@ -100,10 +100,12 @@ impl InputDependencyIndex {
         last_verified_at: crate::Revision,
     ) -> MaybeChangedAfter {
         match self.key_index {
-            Some(key_index) => db
-                .zalsa()
-                .lookup_ingredient(self.ingredient_index)
-                .maybe_changed_after(db, key_index, last_verified_at),
+            // SAFETY: The `db` belongs to the ingredient
+            Some(key_index) => unsafe {
+                db.zalsa()
+                    .lookup_ingredient(self.ingredient_index)
+                    .maybe_changed_after(db, key_index, last_verified_at)
+            },
             // Data in tables themselves remain valid until the table as a whole is reset.
             None => MaybeChangedAfter::No(InputAccumulatedValues::Empty),
         }

src/lib.rs

@@ -1,5 +1,7 @@
 #![forbid(unsafe_op_in_unsafe_fn)]
 
+extern crate self as salsa;
+
 mod accumulator;
 mod active_query;
 mod array;
@@ -107,6 +109,7 @@ pub mod plumbing {
     pub use crate::update::helper::Dispatch as UpdateDispatch;
     pub use crate::update::helper::Fallback as UpdateFallback;
     pub use crate::update::Update;
+    pub use crate::zalsa::transmute_data_ptr;
     pub use crate::zalsa::views;
     pub use crate::zalsa::IngredientCache;
     pub use crate::zalsa::IngredientIndex;

src/tracked_struct.rs

@@ -735,7 +735,7 @@ where
         self.ingredient_index
     }
 
-    fn maybe_changed_after(
+    unsafe fn maybe_changed_after(
         &self,
         db: &dyn Database,
         input: Id,

src/tracked_struct/tracked_field.rs

@@ -55,7 +55,7 @@ where
         crate::cycle::CycleRecoveryStrategy::Panic
     }
 
-    fn maybe_changed_after<'db>(
+    unsafe fn maybe_changed_after<'db>(
         &'db self,
         db: &'db dyn Database,
         input: Id,