1 files changed, 23 insertions, 17 deletions
diff --git a/compiler/rustc_infer/src/traits/mod.rs b/compiler/rustc_infer/src/traits/mod.rs
index 626dd9359..a5b2ccce8 100644
--- a/compiler/rustc_infer/src/traits/mod.rs
+++ b/compiler/rustc_infer/src/traits/mod.rs
@@ -9,6 +9,7 @@ mod structural_impls;
 pub mod util;
 
 use std::cmp;
+use std::hash::{Hash, Hasher};
 
 use hir::def_id::LocalDefId;
 use rustc_hir as hir;
@@ -36,7 +37,7 @@ pub use rustc_middle::traits::*;
 /// either identifying an `impl` (e.g., `impl Eq for i32`) that
 /// satisfies the obligation, or else finding a bound that is in
 /// scope. The eventual result is usually a `Selection` (defined below).
-#[derive(Clone, PartialEq, Eq, Hash)]
+#[derive(Clone)]
 pub struct Obligation<'tcx, T> {
     /// The reason we have to prove this thing.
     pub cause: ObligationCause<'tcx>,
@@ -55,6 +56,27 @@ pub struct Obligation<'tcx, T> {
     pub recursion_depth: usize,
 }
 
+impl<'tcx, T: PartialEq> PartialEq<Obligation<'tcx, T>> for Obligation<'tcx, T> {
+    #[inline]
+    fn eq(&self, other: &Obligation<'tcx, T>) -> bool {
+        // Ignore `cause` and `recursion_depth`. This is a small performance
+        // win for a few crates, and a huge performance win for the crate in
+        // https://github.com/rust-lang/rustc-perf/pull/1680, which greatly
+        // stresses the trait system.
+        self.param_env == other.param_env && self.predicate == other.predicate
+    }
+}
+
+impl<T: Eq> Eq for Obligation<'_, T> {}
+
+impl<T: Hash> Hash for Obligation<'_, T> {
+    fn hash<H: Hasher>(&self, state: &mut H) -> () {
+        // See the comment on `Obligation::eq`.
+        self.param_env.hash(state);
+        self.predicate.hash(state);
+    }
+}
+
 impl<'tcx, P> From<Obligation<'tcx, P>> for solve::Goal<'tcx, P> {
     fn from(value: Obligation<'tcx, P>) -> Self {
         solve::Goal { param_env: value.param_env, predicate: value.predicate }
@@ -77,25 +99,9 @@ impl<'tcx> PredicateObligation<'tcx> {
             recursion_depth: self.recursion_depth,
         })
     }
-
-    pub fn without_const(mut self, tcx: TyCtxt<'tcx>) -> PredicateObligation<'tcx> {
-        self.param_env = self.param_env.without_const();
-        if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred)) = self.predicate.kind().skip_binder() && trait_pred.is_const_if_const() {
-            self.predicate = tcx.mk_predicate(self.predicate.kind().map_bound(|_| ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred.without_const()))));
-        }
-        self
-    }
 }
 
 impl<'tcx> PolyTraitObligation<'tcx> {
-    /// Returns `true` if the trait predicate is considered `const` in its ParamEnv.
-    pub fn is_const(&self) -> bool {
-        matches!(
-            (self.predicate.skip_binder().constness, self.param_env.constness()),
-            (ty::BoundConstness::ConstIfConst, hir::Constness::Const)
-        )
-    }
-
     pub fn derived_cause(
         &self,
         variant: impl FnOnce(DerivedObligationCause<'tcx>) -> ObligationCauseCode<'tcx>,