Improve caching during trait evaluation

compiler/rustc_infer/src/infer/canonical/canonicalizer.rs

@@ -102,20 +102,11 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
         )
     }
 
-    /// A hacky variant of `canonicalize_query` that does not
-    /// canonicalize `'static`. Unfortunately, the existing leak
-    /// check treats `'static` differently in some cases (see also
-    /// #33684), so if we are performing an operation that may need to
-    /// prove "leak-check" related things, we leave `'static`
-    /// alone.
-    ///
-    /// `'static` is also special cased when winnowing candidates when
-    /// selecting implementation candidates, so we also have to leave `'static`
-    /// alone for queries that do selection.
-    //
-    // FIXME(#48536): once the above issues are resolved, we can remove this
-    // and just use `canonicalize_query`.
-    pub fn canonicalize_hr_query_hack<V>(
+    /// A variant of `canonicalize_query` that does not
+    /// canonicalize `'static`. This is useful when
+    /// the query implementation can perform more efficient
+    /// handling of `'static` regions (e.g. trait evaluation).
+    pub fn canonicalize_query_keep_static<V>(
         &self,
         value: V,
         query_state: &mut OriginalQueryValues<'tcx>,

compiler/rustc_infer/src/infer/freshen.rs

@@ -47,16 +47,18 @@ pub struct TypeFreshener<'a, 'tcx> {
     const_freshen_count: u32,
     ty_freshen_map: FxHashMap<ty::InferTy, Ty<'tcx>>,
     const_freshen_map: FxHashMap<ty::InferConst<'tcx>, &'tcx ty::Const<'tcx>>,
+    keep_static: bool,
 }
 
 impl<'a, 'tcx> TypeFreshener<'a, 'tcx> {
-    pub fn new(infcx: &'a InferCtxt<'a, 'tcx>) -> TypeFreshener<'a, 'tcx> {
+    pub fn new(infcx: &'a InferCtxt<'a, 'tcx>, keep_static: bool) -> TypeFreshener<'a, 'tcx> {
         TypeFreshener {
             infcx,
             ty_freshen_count: 0,
             const_freshen_count: 0,
             ty_freshen_map: Default::default(),
             const_freshen_map: Default::default(),
+            keep_static,
         }
     }
 
@@ -124,8 +126,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
                 r
             }
 
-            ty::ReStatic
-            | ty::ReEarlyBound(..)
+            ty::ReEarlyBound(..)
             | ty::ReFree(_)
             | ty::ReVar(_)
             | ty::RePlaceholder(..)
@@ -134,6 +135,13 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
                 // replace all free regions with 'erased
                 self.tcx().lifetimes.re_erased
             }
+            ty::ReStatic => {
+                if self.keep_static {
+                    r
+                } else {
+                    self.tcx().lifetimes.re_erased
+                }
+            }
         }
     }
 

compiler/rustc_infer/src/infer/mod.rs

@@ -646,7 +646,12 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 
     pub fn freshener<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
-        freshen::TypeFreshener::new(self)
+        freshen::TypeFreshener::new(self, false)
+    }
+
+    /// Like `freshener`, but does not replace `'static` regions.
+    pub fn freshener_keep_static<'b>(&'b self) -> TypeFreshener<'b, 'tcx> {
+        freshen::TypeFreshener::new(self, true)
     }
 
     pub fn type_is_unconstrained_numeric(&'a self, ty: Ty<'_>) -> UnconstrainedNumeric {

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -365,6 +365,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                     let project_obligation = obligation.with(binder.rebind(data));
 
                     self.process_projection_obligation(
+                        obligation,
                         project_obligation,
                         &mut pending_obligation.stalled_on,
                     )
@@ -419,6 +420,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
                     let project_obligation = obligation.with(Binder::dummy(*data));
 
                     self.process_projection_obligation(
+                        obligation,
                         project_obligation,
                         &mut pending_obligation.stalled_on,
                     )
@@ -666,10 +668,22 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
 
     fn process_projection_obligation(
         &mut self,
+        obligation: &PredicateObligation<'tcx>,
         project_obligation: PolyProjectionObligation<'tcx>,
         stalled_on: &mut Vec<TyOrConstInferVar<'tcx>>,
     ) -> ProcessResult<PendingPredicateObligation<'tcx>, FulfillmentErrorCode<'tcx>> {
         let tcx = self.selcx.tcx();
+
+        if obligation.predicate.is_global() {
+            // no type variables present, can use evaluation for better caching.
+            // FIXME: consider caching errors too.
+            if self.selcx.infcx().predicate_must_hold_considering_regions(obligation) {
+                return ProcessResult::Changed(vec![]);
+            } else {
+                tracing::debug!("Does NOT hold: {:?}", obligation);
+            }
+        }
+
         match project::poly_project_and_unify_type(self.selcx, &project_obligation) {
             Ok(Ok(Some(os))) => ProcessResult::Changed(mk_pending(os)),
             Ok(Ok(None)) => {

compiler/rustc_trait_selection/src/traits/query/evaluate_obligation.rs

@@ -64,8 +64,10 @@ impl<'cx, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'cx, 'tcx> {
         obligation: &PredicateObligation<'tcx>,
     ) -> Result<EvaluationResult, OverflowError> {
         let mut _orig_values = OriginalQueryValues::default();
-        let c_pred = self
-            .canonicalize_query(obligation.param_env.and(obligation.predicate), &mut _orig_values);
+        let c_pred = self.canonicalize_query_keep_static(
+            obligation.param_env.and(obligation.predicate),
+            &mut _orig_values,
+        );
         // Run canonical query. If overflow occurs, rerun from scratch but this time
         // in standard trait query mode so that overflow is handled appropriately
         // within `SelectionContext`.

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -180,7 +180,7 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 // so we cannot canonicalize it.
                 let c_data = self
                     .infcx
-                    .canonicalize_hr_query_hack(self.param_env.and(data), &mut orig_values);
+                    .canonicalize_query_keep_static(self.param_env.and(data), &mut orig_values);
                 debug!("QueryNormalizer: c_data = {:#?}", c_data);
                 debug!("QueryNormalizer: orig_values = {:#?}", orig_values);
                 match tcx.normalize_projection_ty(c_data) {
@@ -249,7 +249,7 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for QueryNormalizer<'cx, 'tcx> {
                 // so we cannot canonicalize it.
                 let c_data = self
                     .infcx
-                    .canonicalize_hr_query_hack(self.param_env.and(data), &mut orig_values);
+                    .canonicalize_query_keep_static(self.param_env.and(data), &mut orig_values);
                 debug!("QueryNormalizer: c_data = {:#?}", c_data);
                 debug!("QueryNormalizer: orig_values = {:#?}", orig_values);
                 let normalized_ty = match tcx.normalize_projection_ty(c_data) {

compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs

@@ -77,12 +77,13 @@ pub trait QueryTypeOp<'tcx>: fmt::Debug + Sized + TypeFoldable<'tcx> + 'tcx {
         }
 
         // FIXME(#33684) -- We need to use
-        // `canonicalize_hr_query_hack` here because of things
+        // `canonicalize_query_keep_static` here because of things
         // like the subtype query, which go awry around
         // `'static` otherwise.
         let mut canonical_var_values = OriginalQueryValues::default();
         let old_param_env = query_key.param_env;
-        let canonical_self = infcx.canonicalize_hr_query_hack(query_key, &mut canonical_var_values);
+        let canonical_self =
+            infcx.canonicalize_query_keep_static(query_key, &mut canonical_var_values);
         let canonical_result = Self::perform_query(infcx.tcx, canonical_self)?;
 
         let InferOk { value, obligations } = infcx

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -216,7 +216,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     pub fn new(infcx: &'cx InferCtxt<'cx, 'tcx>) -> SelectionContext<'cx, 'tcx> {
         SelectionContext {
             infcx,
-            freshener: infcx.freshener(),
+            freshener: infcx.freshener_keep_static(),
             intercrate: false,
             intercrate_ambiguity_causes: None,
             allow_negative_impls: false,
@@ -227,7 +227,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     pub fn intercrate(infcx: &'cx InferCtxt<'cx, 'tcx>) -> SelectionContext<'cx, 'tcx> {
         SelectionContext {
             infcx,
-            freshener: infcx.freshener(),
+            freshener: infcx.freshener_keep_static(),
             intercrate: true,
             intercrate_ambiguity_causes: None,
             allow_negative_impls: false,
@@ -242,7 +242,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!(?allow_negative_impls, "with_negative");
         SelectionContext {
             infcx,
-            freshener: infcx.freshener(),
+            freshener: infcx.freshener_keep_static(),
             intercrate: false,
             intercrate_ambiguity_causes: None,
             allow_negative_impls,
@@ -257,7 +257,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!(?query_mode, "with_query_mode");
         SelectionContext {
             infcx,
-            freshener: infcx.freshener(),
+            freshener: infcx.freshener_keep_static(),
             intercrate: false,
             intercrate_ambiguity_causes: None,
             allow_negative_impls: false,