Look up impls by self type

This speeds up inference in analysis-stats by ~30% (even more with the recursive
solver).

crates/ra_hir_ty/src/traits.rs

@@ -7,7 +7,7 @@ use ra_db::{impl_intern_key, salsa, CrateId};
 use ra_prof::profile;
 use rustc_hash::FxHashSet;
 
-use crate::{db::HirDatabase, DebruijnIndex};
+use crate::{db::HirDatabase, method_resolution::TyFingerprint, DebruijnIndex};
 
 use super::{Canonical, GenericPredicate, HirDisplay, ProjectionTy, TraitRef, Ty, TypeWalk};
 
@@ -40,7 +40,12 @@ pub(crate) fn impls_for_trait_query(
     db: &dyn HirDatabase,
     krate: CrateId,
     trait_: TraitId,
+    self_ty_fp: Option<TyFingerprint>,
 ) -> Arc<[ImplId]> {
+    // FIXME: We could be a lot smarter here - because of the orphan rules and
+    // the fact that the trait and the self type need to be in the dependency
+    // tree of a crate somewhere for an impl to exist, we could skip looking in
+    // a lot of crates completely
     let mut impls = FxHashSet::default();
     // We call the query recursively here. On the one hand, this means we can
     // reuse results from queries for different crates; on the other hand, this
@@ -48,10 +53,13 @@ pub(crate) fn impls_for_trait_query(
     // ones the user is editing), so this may actually be a waste of memory. I'm
     // doing it like this mainly for simplicity for now.
     for dep in &db.crate_graph()[krate].dependencies {
-        impls.extend(db.impls_for_trait(dep.crate_id, trait_).iter());
+        impls.extend(db.impls_for_trait(dep.crate_id, trait_, self_ty_fp).iter());
     }
     let crate_impl_defs = db.impls_in_crate(krate);
-    impls.extend(crate_impl_defs.lookup_impl_defs_for_trait(trait_));
+    match self_ty_fp {
+        Some(fp) => impls.extend(crate_impl_defs.lookup_impl_defs_for_trait_and_ty(trait_, fp)),
+        None => impls.extend(crate_impl_defs.lookup_impl_defs_for_trait(trait_)),
+    }
     impls.into_iter().collect()
 }