[Instructions -0.40% vs main; paired PGO estimate] Return successful type-operation fast paths before setup

compiler/rustc_infer/src/infer/outlives/mod.rs

@@ -32,6 +32,16 @@ pub fn explicit_outlives_bounds<'tcx>(
 }
 
 impl<'tcx> InferCtxt<'tcx> {
+    pub fn has_pending_region_state(&self) -> bool {
+        let inner = self.inner.borrow();
+        !inner.region_obligations.is_empty()
+            || !inner.region_assumptions.is_empty()
+            || inner
+                .region_constraint_storage
+                .as_ref()
+                .is_none_or(|storage| !storage.data.is_empty())
+    }
+
     /// Process the region constraints and return any errors that
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use

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

@@ -134,6 +134,19 @@ where
         root_def_id: LocalDefId,
         span: Span,
     ) -> Result<TypeOpOutput<'tcx, Self>, ErrorGuaranteed> {
+        if !infcx.next_trait_solver()
+            && !infcx.disable_trait_solver_fast_paths()
+            && !infcx.in_snapshot()
+            && let Some(output) = Q::try_fast_path(infcx.tcx, &self)
+            && !infcx.has_pending_region_state()
+        {
+            return Ok(TypeOpOutput {
+                output: infcx.deeply_resolve_ignoring_regions(output),
+                constraints: None,
+                error_info: None,
+            });
+        }
+
         let mut error_info = None;
         let mut region_constraints = QueryRegionConstraints::default();