wip: perf: re-add optimisation

Author: davidtwco

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -24,10 +24,11 @@ use super::{
 };
 use crate::error_reporting::InferCtxtErrorExt;
 use crate::infer::{InferCtxt, TyOrConstInferVar};
+use crate::traits::EvaluateConstErr;
 use crate::traits::normalize::normalize_with_depth_to;
 use crate::traits::project::{PolyProjectionObligation, ProjectionCacheKeyExt as _};
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
-use crate::traits::{EvaluateConstErr, sizedness_fast_path};
+use crate::traits::util::extended_sizedness_fast_path;
 
 pub(crate) type PendingPredicateObligations<'tcx> = ThinVec<PendingPredicateObligation<'tcx>>;
 
@@ -335,7 +336,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
         let infcx = self.selcx.infcx;
 
-        if sizedness_fast_path(infcx.tcx, obligation.predicate) {
+        if extended_sizedness_fast_path(infcx, obligation) {
             return ProcessResult::Changed(thin_vec::thin_vec![]);
         }
 

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -64,9 +64,10 @@ pub use self::specialize::{
 };
 pub use self::structural_normalize::StructurallyNormalizeExt;
 pub use self::util::{
-    BoundVarReplacer, PlaceholderReplacer, elaborate, expand_trait_aliases, impl_item_is_final,
-    sizedness_fast_path, supertrait_def_ids, supertraits, transitive_bounds_that_define_assoc_item,
-    upcast_choices, with_replaced_escaping_bound_vars,
+    BoundVarReplacer, PlaceholderReplacer, elaborate, expand_trait_aliases,
+    extended_sizedness_fast_path, impl_item_is_final, sizedness_fast_path, supertrait_def_ids,
+    supertraits, transitive_bounds_that_define_assoc_item, upcast_choices,
+    with_replaced_escaping_bound_vars,
 };
 use crate::error_reporting::InferCtxtErrorExt;
 use crate::infer::outlives::env::OutlivesEnvironment;

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

@@ -15,6 +15,7 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
         tcx: TyCtxt<'tcx>,
         key: &ParamEnvAnd<'tcx, Self>,
     ) -> Option<Self::QueryResponse> {
+        // Using `extended_sizedness_fast_path` with a fresh `InferCtxt` causes an ICE.
         if sizedness_fast_path(tcx, key.value.predicate) {
             return Some(());
         }

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

@@ -48,9 +48,8 @@ use crate::infer::{InferCtxt, InferOk, TypeFreshener};
 use crate::solve::InferCtxtSelectExt as _;
 use crate::traits::normalize::{normalize_with_depth, normalize_with_depth_to};
 use crate::traits::project::{ProjectAndUnifyResult, ProjectionCacheKeyExt};
-use crate::traits::{
-    EvaluateConstErr, ProjectionCacheKey, Unimplemented, effects, sizedness_fast_path,
-};
+use crate::traits::util::extended_sizedness_fast_path;
+use crate::traits::{EvaluateConstErr, ProjectionCacheKey, Unimplemented, effects};
 
 mod _match;
 mod candidate_assembly;
@@ -604,7 +603,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             None => self.check_recursion_limit(&obligation, &obligation)?,
         }
 
-        if sizedness_fast_path(self.tcx(), obligation.predicate) {
+        if extended_sizedness_fast_path(self.infcx, &obligation) {
             return Ok(EvaluatedToOk);
         }
 

compiler/rustc_trait_selection/src/traits/util.rs

@@ -4,8 +4,8 @@ use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_hir::LangItem;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::InferCtxt;
-use rustc_infer::traits::PolyTraitObligation;
 pub use rustc_infer::traits::util::*;
+use rustc_infer::traits::{PolyTraitObligation, PredicateObligation};
 use rustc_middle::bug;
 use rustc_middle::ty::{
     self, PolyTraitPredicate, SizedTraitKind, Ty, TyCtxt, TypeFoldable, TypeFolder,
@@ -508,10 +508,35 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for PlaceholderReplacer<'_, 'tcx> {
     }
 }
 
+/// In addition to checks in `sizedness_fast_path`, exists early if for `MetaSized` obligation with
+/// a matching `Sized` obligation in the `ParamEnv`.
+pub fn extended_sizedness_fast_path<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    obligation: &PredicateObligation<'tcx>,
+) -> bool {
+    if sizedness_fast_path(infcx.tcx, obligation.predicate) {
+        return true;
+    }
+
+    if let Some(trait_clause) = obligation.predicate.as_trait_clause() {
+        if unelaborated_sizedness_candidate_from_obligation(
+            infcx,
+            &obligation.with(infcx.tcx, trait_clause),
+        )
+        .is_some()
+        {
+            debug!("fast path -- metasized paramenv");
+            return true;
+        }
+    }
+
+    false
+}
+
+/// Proving `Sized`/`MetaSized`/`PointeeSized`, very often on "obviously sized" types like
+/// `&T`, accounts for about 60% percentage of the predicates we have to prove. In these cases,
+/// skip canonicalization and as much trait solving machinery as possible.
 pub fn sizedness_fast_path<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tcx>) -> bool {
-    // Proving `Sized`/`MetaSized`/`PointeeSized`, 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::Clause(ty::ClauseKind::Trait(trait_ref)) =
         predicate.kind().skip_binder()
     {

compiler/rustc_traits/src/codegen.rs

@@ -6,11 +6,11 @@
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::bug;
 use rustc_middle::traits::CodegenObligationError;
-use rustc_middle::ty::{self, PseudoCanonicalInput, TyCtxt, TypeVisitableExt, Upcast};
+use rustc_middle::ty::{self, PseudoCanonicalInput, TyCtxt, TypeVisitableExt};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::traits::{
     ImplSource, Obligation, ObligationCause, ObligationCtxt, ScrubbedTraitError, SelectionContext,
-    Unimplemented, sizedness_fast_path,
+    Unimplemented, extended_sizedness_fast_path,
 };
 use tracing::debug;
 
@@ -34,15 +34,22 @@ pub(crate) fn codegen_select_candidate<'tcx>(
     let (infcx, param_env) = tcx.infer_ctxt().ignoring_regions().build_with_typing_env(typing_env);
     let mut selcx = SelectionContext::new(&infcx);
 
-    if sizedness_fast_path(tcx, trait_ref.upcast(tcx)) {
+    let obligation_cause = ObligationCause::dummy();
+    let obligation = Obligation::new(tcx, obligation_cause, param_env, trait_ref);
+
+    if extended_sizedness_fast_path(&infcx, &obligation) {
         return Ok(&*tcx.arena.alloc(ImplSource::Builtin(
             ty::solve::BuiltinImplSource::Trivial,
             Default::default(),
         )));
     }
 
-    let obligation_cause = ObligationCause::dummy();
-    let obligation = Obligation::new(tcx, obligation_cause, param_env, trait_ref);
+    // Calling `sizedness_fast_path` upcasts to `PolyObligation`, rather than `TraitObligation`
+    let obligation = if let Some(clause) = obligation.predicate.as_trait_clause() {
+        obligation.with(tcx, clause.skip_binder())
+    } else {
+        bug!("trait ref upcast to non-trait clause");
+    };
 
     let selection = match selcx.select(&obligation) {
         Ok(Some(selection)) => selection,

compiler/rustc_traits/src/evaluate_obligation.rs

@@ -5,7 +5,7 @@ use rustc_span::DUMMY_SP;
 use rustc_trait_selection::traits::query::CanonicalPredicateGoal;
 use rustc_trait_selection::traits::{
     EvaluationResult, Obligation, ObligationCause, OverflowError, SelectionContext, TraitQueryMode,
-    sizedness_fast_path,
+    extended_sizedness_fast_path,
 };
 use tracing::debug;
 
@@ -24,12 +24,12 @@ fn evaluate_obligation<'tcx>(
     debug!("evaluate_obligation: goal={:#?}", goal);
     let ParamEnvAnd { param_env, value: predicate } = goal;
 
-    if sizedness_fast_path(tcx, predicate) {
-        return Ok(EvaluationResult::EvaluatedToOk);
-    }
-
     let mut selcx = SelectionContext::with_query_mode(infcx, TraitQueryMode::Canonical);
     let obligation = Obligation::new(tcx, ObligationCause::dummy(), param_env, predicate);
 
+    if extended_sizedness_fast_path(infcx, &obligation) {
+        return Ok(EvaluationResult::EvaluatedToOk);
+    }
+
     selcx.evaluate_root_obligation(&obligation)
 }

tests/ui/sized-hierarchy/generic-const-exprs.stderr

@@ -2,30 +2,30 @@ error: internal compiler error: Encountered anon const with inference variable a
    |
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = error: internal compiler error: Encountered anon const with inference variable args but no error reported
    |
-   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:596:27 - disabled backtrace
+   = note: delayed at compiler/rustc_trait_selection/src/traits/mod.rs:597:27 - disabled backtrace
    = query stack during panic:
 end of query stack

tests/ui/where-clauses/ignore-err-clauses.rs

@@ -1,7 +1,6 @@
 use std::ops::Add;
 
 fn dbl<T>(x: T) -> <T as Add>::Output
-//~^ ERROR type annotations needed
 where
     T: Copy + Add,
     UUU: Copy,

tests/ui/where-clauses/ignore-err-clauses.stderr

@@ -1,16 +1,9 @@
 error[E0412]: cannot find type `UUU` in this scope
-  --> $DIR/ignore-err-clauses.rs:7:5
+  --> $DIR/ignore-err-clauses.rs:6:5
    |
 LL |     UUU: Copy,
    |     ^^^ not found in this scope
 
-error[E0282]: type annotations needed
-  --> $DIR/ignore-err-clauses.rs:3:14
-   |
-LL | fn dbl<T>(x: T) -> <T as Add>::Output
-   |              ^ cannot infer type for type parameter `T`
-
-error: aborting due to 2 previous errors
+error: aborting due to 1 previous error
 
-Some errors have detailed explanations: E0282, E0412.
-For more information about an error, try `rustc --explain E0282`.
+For more information about this error, try `rustc --explain E0412`.