[perf] HIR analysis: Preallocate when lowering bounds

Author: fmease

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -37,7 +37,7 @@ fn associated_type_bounds<'tcx>(
         );
 
         let icx = ItemCtxt::new(tcx, assoc_item_def_id);
-        let mut bounds = Vec::new();
+        let mut bounds = Vec::with_capacity(hir_bounds.len());
         icx.lowerer().lower_bounds(item_ty, hir_bounds, &mut bounds, ty::List::empty(), filter);
         // Associated types are implicitly sized unless a `?Sized` bound is found
         match filter {
@@ -326,7 +326,7 @@ fn opaque_type_bounds<'tcx>(
 ) -> &'tcx [(ty::Clause<'tcx>, Span)] {
     ty::print::with_reduced_queries!({
         let icx = ItemCtxt::new(tcx, opaque_def_id);
-        let mut bounds = Vec::new();
+        let mut bounds = Vec::with_capacity(hir_bounds.len());
         icx.lowerer().lower_bounds(item_ty, hir_bounds, &mut bounds, ty::List::empty(), filter);
         // Opaque types are implicitly sized unless a `?Sized` bound is found
         match filter {

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -177,7 +177,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     // on a trait we must also consider the bounds that follow the trait's name,
     // like `trait Foo: A + B + C`.
     if let Some(self_bounds) = is_trait {
-        let mut bounds = Vec::new();
+        let mut bounds = Vec::with_capacity(self_bounds.len());
         icx.lowerer().lower_bounds(
             tcx.types.self_param,
             self_bounds,
@@ -263,7 +263,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     }
                 }
 
-                let mut bounds = Vec::new();
+                let mut bounds = Vec::with_capacity(bound_pred.bounds.len());
                 icx.lowerer().lower_bounds(
                     ty,
                     bound_pred.bounds,
@@ -626,7 +626,7 @@ pub(super) fn implied_predicates_with_filter<'tcx>(
     let icx = ItemCtxt::new(tcx, trait_def_id);
 
     let self_param_ty = tcx.types.self_param;
-    let mut bounds = Vec::new();
+    let mut bounds = Vec::with_capacity(superbounds.len());
     icx.lowerer().lower_bounds(self_param_ty, superbounds, &mut bounds, ty::List::empty(), filter);
 
     let where_bounds_that_match =

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2399,7 +2399,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 // Impl trait in bindings lower as an infer var with additional
                 // set of type bounds.
                 let self_ty = self.ty_infer(None, hir_ty.span);
-                let mut bounds = Vec::new();
+                let mut bounds = Vec::with_capacity(hir_bounds.len());
                 self.lower_bounds(
                     self_ty,
                     hir_bounds.iter(),