1 files changed, 43 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
new file mode 100644
index 000000000..081308ac7
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/prove_predicate.rs
@@ -0,0 +1,43 @@
+use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
+use crate::traits::query::Fallible;
+use rustc_middle::ty::{self, ParamEnvAnd, TyCtxt};
+
+pub use rustc_middle::traits::query::type_op::ProvePredicate;
+
+impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
+    type QueryResponse = ();
+
+    fn try_fast_path(
+        tcx: TyCtxt<'tcx>,
+        key: &ParamEnvAnd<'tcx, Self>,
+    ) -> Option<Self::QueryResponse> {
+        // Proving Sized, very often on "obviously sized" types like
+        // `&T`, accounts for about 60% percentage of the predicates
+        // we have to prove. No need to canonicalize and all that for
+        // such cases.
+        if let ty::PredicateKind::Trait(trait_ref) = key.value.predicate.kind().skip_binder() {
+            if let Some(sized_def_id) = tcx.lang_items().sized_trait() {
+                if trait_ref.def_id() == sized_def_id {
+                    if trait_ref.self_ty().is_trivially_sized(tcx) {
+                        return Some(());
+                    }
+                }
+            }
+        }
+
+        None
+    }
+
+    fn perform_query(
+        tcx: TyCtxt<'tcx>,
+        mut canonicalized: Canonicalized<'tcx, ParamEnvAnd<'tcx, Self>>,
+    ) -> Fallible<CanonicalizedQueryResponse<'tcx, ()>> {
+        match canonicalized.value.value.predicate.kind().skip_binder() {
+            ty::PredicateKind::Trait(pred) => {
+                canonicalized.value.param_env.remap_constness_with(pred.constness);
+            }
+            _ => canonicalized.value.param_env = canonicalized.value.param_env.without_const(),
+        }
+        tcx.type_op_prove_predicate(canonicalized)
+    }
+}