re-use sized fast path

There's an existing fast path for the `type_op_prove_predicate`
predicate, checking for trivially `Sized` types, which can be re-used
when evaluating obligations within queries. This should improve
performance, particularly in anticipation of new sizedness traits being
added which can take advantage of this.

12 files changed, 70 insertions, 31 deletions

diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index 27ee363f1c1..e1708879946 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1872,14 +1872,14 @@ impl<'tcx> Ty<'tcx> {
 
     /// Fast path helper for testing if a type is `Sized`.
     ///
-    /// Returning true means the type is known to be sized. Returning
-    /// `false` means nothing -- could be sized, might not be.
+    /// Returning true means the type is known to implement `Sized`. Returning `false` means
+    /// nothing -- could be sized, might not be.
     ///
-    /// Note that we could never rely on the fact that a type such as `[_]` is
-    /// trivially `!Sized` because we could be in a type environment with a
-    /// bound such as `[_]: Copy`. A function with such a bound obviously never
-    /// can be called, but that doesn't mean it shouldn't typecheck. This is why
-    /// this method doesn't return `Option<bool>`.
+    /// Note that we could never rely on the fact that a type such as `[_]` is trivially `!Sized`
+    /// because we could be in a type environment with a bound such as `[_]: Copy`. A function with
+    /// such a bound obviously never can be called, but that doesn't mean it shouldn't typecheck.
+    /// This is why this method doesn't return `Option<bool>`.
+    #[instrument(skip(tcx), level = "debug")]
     pub fn is_trivially_sized(self, tcx: TyCtxt<'tcx>) -> bool {
         match self.kind() {
             ty::Infer(ty::IntVar(_) | ty::FloatVar(_))
diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index e98a240a53f..1b76d48e431 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -24,10 +24,10 @@ 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};
 
 pub(crate) type PendingPredicateObligations<'tcx> = ThinVec<PendingPredicateObligation<'tcx>>;
 
@@ -335,6 +335,10 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
         let infcx = self.selcx.infcx;
 
+        if sizedness_fast_path(infcx.tcx, obligation.predicate) {
+            return ProcessResult::Changed(thin_vec::thin_vec![]);
+        }
+
         if obligation.predicate.has_aliases() {
             let mut obligations = PredicateObligations::new();
             let predicate = normalize_with_depth_to(
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index de337710b5e..f2713b98f0a 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -65,8 +65,8 @@ pub use self::specialize::{
 pub use self::structural_normalize::StructurallyNormalizeExt;
 pub use self::util::{
     BoundVarReplacer, PlaceholderReplacer, elaborate, expand_trait_aliases, impl_item_is_final,
-    supertrait_def_ids, supertraits, transitive_bounds_that_define_assoc_item, upcast_choices,
-    with_replaced_escaping_bound_vars,
+    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;
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
index 4f9e2e79d62..87fc532adaf 100644
--- 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
@@ -1,4 +1,3 @@
-use rustc_hir::LangItem;
 use rustc_infer::traits::Obligation;
 use rustc_middle::traits::ObligationCause;
 use rustc_middle::traits::query::NoSolution;
@@ -7,7 +6,7 @@ use rustc_middle::ty::{self, ParamEnvAnd, TyCtxt};
 use rustc_span::Span;
 
 use crate::infer::canonical::{CanonicalQueryInput, CanonicalQueryResponse};
-use crate::traits::ObligationCtxt;
+use crate::traits::{ObligationCtxt, sizedness_fast_path};
 
 impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
     type QueryResponse = ();
@@ -16,15 +15,7 @@ impl<'tcx> super::QueryTypeOp<'tcx> for ProvePredicate<'tcx> {
         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::Clause(ty::ClauseKind::Trait(trait_ref)) =
-            key.value.predicate.kind().skip_binder()
-            && tcx.is_lang_item(trait_ref.def_id(), LangItem::Sized)
-            && trait_ref.self_ty().is_trivially_sized(tcx)
-        {
+        if sizedness_fast_path(tcx, key.value.predicate) {
             return Some(());
         }
 
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 56ff46e89e7..4d88a23250a 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -49,7 +49,9 @@ 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};
+use crate::traits::{
+    EvaluateConstErr, ProjectionCacheKey, Unimplemented, effects, sizedness_fast_path,
+};
 
 mod _match;
 mod candidate_assembly;
@@ -603,6 +605,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             None => self.check_recursion_limit(&obligation, &obligation)?,
         }
 
+        if sizedness_fast_path(self.tcx(), obligation.predicate) {
+            return Ok(EvaluatedToOk);
+        }
+
         ensure_sufficient_stack(|| {
             let bound_predicate = obligation.predicate.kind();
             match bound_predicate.skip_binder() {
diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs
index 9f20cd7eacb..035fd38c48a 100644
--- a/compiler/rustc_trait_selection/src/traits/util.rs
+++ b/compiler/rustc_trait_selection/src/traits/util.rs
@@ -1,6 +1,7 @@
 use std::collections::{BTreeMap, VecDeque};
 
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
+use rustc_hir::LangItem;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::InferCtxt;
 pub use rustc_infer::traits::util::*;
@@ -504,3 +505,21 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for PlaceholderReplacer<'_, 'tcx> {
         }
     }
 }
+
+pub fn sizedness_fast_path<'tcx>(tcx: TyCtxt<'tcx>, predicate: ty::Predicate<'tcx>) -> bool {
+    // 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::Clause(ty::ClauseKind::Trait(trait_ref)) =
+        predicate.kind().skip_binder()
+    {
+        if tcx.is_lang_item(trait_ref.def_id(), LangItem::Sized)
+            && trait_ref.self_ty().is_trivially_sized(tcx)
+        {
+            debug!("fast path -- trivial sizedness");
+            return true;
+        }
+    }
+
+    false
+}
diff --git a/compiler/rustc_traits/src/codegen.rs b/compiler/rustc_traits/src/codegen.rs
index 4a889abfc28..88f02d16c7d 100644
--- a/compiler/rustc_traits/src/codegen.rs
+++ b/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};
+use rustc_middle::ty::{self, PseudoCanonicalInput, TyCtxt, TypeVisitableExt, Upcast};
 use rustc_trait_selection::error_reporting::InferCtxtErrorExt;
 use rustc_trait_selection::traits::{
     ImplSource, Obligation, ObligationCause, ObligationCtxt, ScrubbedTraitError, SelectionContext,
-    Unimplemented,
+    Unimplemented, sizedness_fast_path,
 };
 use tracing::debug;
 
@@ -34,6 +34,13 @@ 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)) {
+        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);
 
diff --git a/compiler/rustc_traits/src/evaluate_obligation.rs b/compiler/rustc_traits/src/evaluate_obligation.rs
index c9ad096c6e9..7771db855d7 100644
--- a/compiler/rustc_traits/src/evaluate_obligation.rs
+++ b/compiler/rustc_traits/src/evaluate_obligation.rs
@@ -5,6 +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,
 };
 use tracing::debug;
 
@@ -23,6 +24,10 @@ 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);
 
diff --git a/tests/ui/closures/issue-78720.rs b/tests/ui/closures/issue-78720.rs
index 81af030fe55..a615cdf2690 100644
--- a/tests/ui/closures/issue-78720.rs
+++ b/tests/ui/closures/issue-78720.rs
@@ -1,5 +1,6 @@
 fn server() -> impl {
     //~^ ERROR at least one trait must be specified
+    //~^^ ERROR type annotations needed
     ().map2(|| "")
 }
 
diff --git a/tests/ui/closures/issue-78720.stderr b/tests/ui/closures/issue-78720.stderr
index 90672cd83d7..3e95fab441a 100644
--- a/tests/ui/closures/issue-78720.stderr
+++ b/tests/ui/closures/issue-78720.stderr
@@ -5,7 +5,7 @@ LL | fn server() -> impl {
    |                ^^^^
 
 error[E0412]: cannot find type `F` in this scope
-  --> $DIR/issue-78720.rs:13:12
+  --> $DIR/issue-78720.rs:14:12
    |
 LL |     _func: F,
    |            ^
@@ -22,8 +22,14 @@ help: you might be missing a type parameter
 LL | struct Map2<Segment2, F> {
    |                     +++
 
+error[E0282]: type annotations needed
+  --> $DIR/issue-78720.rs:1:16
+   |
+LL | fn server() -> impl {
+   |                ^^^^ cannot infer type
+
 error[E0308]: mismatched types
-  --> $DIR/issue-78720.rs:7:39
+  --> $DIR/issue-78720.rs:8:39
    |
 LL |     fn map2<F>(self, f: F) -> Map2<F> {}
    |                                       ^^ expected `Map2<F>`, found `()`
@@ -32,7 +38,7 @@ LL |     fn map2<F>(self, f: F) -> Map2<F> {}
            found unit type `()`
 
 error[E0277]: the size for values of type `Self` cannot be known at compilation time
-  --> $DIR/issue-78720.rs:7:16
+  --> $DIR/issue-78720.rs:8:16
    |
 LL |     fn map2<F>(self, f: F) -> Map2<F> {}
    |                ^^^^ doesn't have a size known at compile-time
@@ -47,7 +53,7 @@ help: function arguments must have a statically known size, borrowed types alway
 LL |     fn map2<F>(&self, f: F) -> Map2<F> {}
    |                +
 
-error: aborting due to 4 previous errors
+error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0277, E0308, E0412.
+Some errors have detailed explanations: E0277, E0282, E0308, E0412.
 For more information about an error, try `rustc --explain E0277`.
diff --git a/tests/ui/codegen/overflow-during-mono.rs b/tests/ui/codegen/overflow-during-mono.rs
index 83a8b6b3ef6..a9045840173 100644
--- a/tests/ui/codegen/overflow-during-mono.rs
+++ b/tests/ui/codegen/overflow-during-mono.rs
@@ -1,4 +1,4 @@
-//~ ERROR overflow evaluating the requirement `{closure@$DIR/overflow-during-mono.rs:13:41: 13:44}: Sized`
+//~ ERROR overflow evaluating the requirement `for<'a> {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}: FnMut(&'a _)`
 //@ build-fail
 
 #![recursion_limit = "32"]
diff --git a/tests/ui/codegen/overflow-during-mono.stderr b/tests/ui/codegen/overflow-during-mono.stderr
index f7a3e2df3db..74d98fde285 100644
--- a/tests/ui/codegen/overflow-during-mono.stderr
+++ b/tests/ui/codegen/overflow-during-mono.stderr
@@ -1,4 +1,4 @@
-error[E0275]: overflow evaluating the requirement `{closure@$DIR/overflow-during-mono.rs:13:41: 13:44}: Sized`
+error[E0275]: overflow evaluating the requirement `for<'a> {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}: FnMut(&'a _)`
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "64"]` attribute to your crate (`overflow_during_mono`)
    = note: required for `Filter<std::array::IntoIter<i32, 11>, {closure@$DIR/overflow-during-mono.rs:13:41: 13:44}>` to implement `Iterator`