incr.comp.: Remove outdated comment about TraitSelect dep-node.

Author: michaelwoerister

src/librustc/dep_graph/dep_node.rs

@@ -539,31 +539,6 @@ define_dep_nodes!( <'tcx>
 
     [input] AllLocalTraitImpls,
 
-    // Trait selection cache is a little funny. Given a trait
-    // reference like `Foo: SomeTrait<Bar>`, there could be
-    // arbitrarily many def-ids to map on in there (e.g., `Foo`,
-    // `SomeTrait`, `Bar`). We could have a vector of them, but it
-    // requires heap-allocation, and trait sel in general can be a
-    // surprisingly hot path. So instead we pick two def-ids: the
-    // trait def-id, and the first def-id in the input types. If there
-    // is no def-id in the input types, then we use the trait def-id
-    // again. So for example:
-    //
-    // - `i32: Clone` -> `TraitSelect { trait_def_id: Clone, self_def_id: Clone }`
-    // - `u32: Clone` -> `TraitSelect { trait_def_id: Clone, self_def_id: Clone }`
-    // - `Clone: Clone` -> `TraitSelect { trait_def_id: Clone, self_def_id: Clone }`
-    // - `Vec<i32>: Clone` -> `TraitSelect { trait_def_id: Clone, self_def_id: Vec }`
-    // - `String: Clone` -> `TraitSelect { trait_def_id: Clone, self_def_id: String }`
-    // - `Foo: Trait<Bar>` -> `TraitSelect { trait_def_id: Trait, self_def_id: Foo }`
-    // - `Foo: Trait<i32>` -> `TraitSelect { trait_def_id: Trait, self_def_id: Foo }`
-    // - `(Foo, Bar): Trait` -> `TraitSelect { trait_def_id: Trait, self_def_id: Foo }`
-    // - `i32: Trait<Foo>` -> `TraitSelect { trait_def_id: Trait, self_def_id: Foo }`
-    //
-    // You can see that we map many trait refs to the same
-    // trait-select node.  This is not a problem, it just means
-    // imprecision in our dep-graph tracking.  The important thing is
-    // that for any given trait-ref, we always map to the **same**
-    // trait-select node.
     [anon] TraitSelect,
 
     [] ParamEnv(DefId),