Apply fast path to old solver too

2 files changed, 10 insertions, 2 deletions

diff --git a/compiler/rustc_trait_selection/src/traits/fulfill.rs b/compiler/rustc_trait_selection/src/traits/fulfill.rs
index 951dfb879ae..d018f0c7207 100644
--- a/compiler/rustc_trait_selection/src/traits/fulfill.rs
+++ b/compiler/rustc_trait_selection/src/traits/fulfill.rs
@@ -12,7 +12,7 @@ use rustc_middle::bug;
 use rustc_middle::ty::abstract_const::NotConstEvaluatable;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::{self, Binder, Const, GenericArgsRef, TypeVisitableExt, TypingMode};
-use thin_vec::ThinVec;
+use thin_vec::{ThinVec, thin_vec};
 use tracing::{debug, debug_span, instrument};
 
 use super::effects::{self, HostEffectObligation};
@@ -336,7 +336,7 @@ 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![]);
+            return ProcessResult::Changed(thin_vec![]);
         }
 
         if obligation.predicate.has_aliases() {
@@ -541,6 +541,10 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 }
 
                 ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(term)) => {
+                    if term.is_trivially_wf(self.selcx.tcx()) {
+                        return ProcessResult::Changed(thin_vec![]);
+                    }
+
                     match wf::obligations(
                         self.selcx.infcx,
                         obligation.param_env,
diff --git a/compiler/rustc_trait_selection/src/traits/select/mod.rs b/compiler/rustc_trait_selection/src/traits/select/mod.rs
index 9c0ccb26e53..e2d19244e6d 100644
--- a/compiler/rustc_trait_selection/src/traits/select/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/select/mod.rs
@@ -660,6 +660,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
 
                 ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(term)) => {
+                    if term.is_trivially_wf(self.tcx()) {
+                        return Ok(EvaluatedToOk);
+                    }
+
                     // So, there is a bit going on here. First, `WellFormed` predicates
                     // are coinductive, like trait predicates with auto traits.
                     // This means that we need to detect if we have recursively