src/librustc/traits/query/type_op/prove_predicate.rs

   1 use crate::infer::canonical::{Canonicalized, CanonicalizedQueryResponse};
   2 use crate::traits::query::Fallible;
   3 use crate::ty::{ParamEnvAnd, Predicate, TyCtxt};
   4
   5 #[derive(Copy, Clone, Debug, Hash, PartialEq, Eq, HashStable, TypeFoldable, Lift)]
   6 pub struct ProvePredicate<'tcx> {
   7     pub predicate: Predicate<'tcx>,
   8 }
   9
  10 impl<'tcx> ProvePredicate<'tcx> {
  11     pub fn new(predicate: Predicate<'tcx>) -> Self {
  12         ProvePredicate { predicate }
  13     }
  14 }
  15
  16 impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
  17     type QueryResponse = ();
  18
  19     fn try_fast_path(
  20         tcx: TyCtxt<'tcx>,
  21         key: &ParamEnvAnd<'tcx, Self>,
  22     ) -> Option<Self::QueryResponse> {
  23         // Proving Sized, very often on "obviously sized" types like
  24         // `&T`, accounts for about 60% percentage of the predicates
  25         // we have to prove. No need to canonicalize and all that for
  26         // such cases.
  27         if let Predicate::Trait(trait_ref, _) = key.value.predicate {
  28             if let Some(sized_def_id) = tcx.lang_items().sized_trait() {
  29                 if trait_ref.def_id() == sized_def_id {
  30                     if trait_ref.skip_binder().self_ty().is_trivially_sized(tcx) {
  31                         return Some(());
  32                     }
  33                 }
  34             }
  35         }
  36
  37         None
  38     }
  39
  40     fn perform_query(
  41         tcx: TyCtxt<'tcx>,
  42         canonicalized: Canonicalized<'tcx, ParamEnvAnd<'tcx, Self>>,
  43     ) -> Fallible<CanonicalizedQueryResponse<'tcx, ()>> {
  44         tcx.type_op_prove_predicate(canonicalized)
  45     }
  46 }