Auto merge of rust-lang#140937 - yotamofek:pr/alloc_from_iter, r=<try>

Use `Arena::alloc_from_iter` to avoid redundant vec allocations

Doesn't show up on my local perf run, but might improve performance by a bit in certain cases.
(second commit is a small drive-by cleanup)

Author: bors

compiler/rustc_middle/src/ty/trait_def.rs

@@ -203,9 +203,8 @@ pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> Trait
     // Traits defined in the current crate can't have impls in upstream
     // crates, so we don't bother querying the cstore.
     if !trait_id.is_local() {
-        for &cnum in tcx.crates(()).iter() {
-            for &(impl_def_id, simplified_self_ty) in
-                tcx.implementations_of_trait((cnum, trait_id)).iter()
+        for &cnum in tcx.crates(()) {
+            for &(impl_def_id, simplified_self_ty) in tcx.implementations_of_trait((cnum, trait_id))
             {
                 if let Some(simplified_self_ty) = simplified_self_ty {
                     impls
@@ -239,37 +238,33 @@ pub(super) fn trait_impls_of_provider(tcx: TyCtxt<'_>, trait_id: DefId) -> Trait
 
 /// Query provider for `incoherent_impls`.
 pub(super) fn incoherent_impls_provider(tcx: TyCtxt<'_>, simp: SimplifiedType) -> &[DefId] {
-    let mut impls = Vec::new();
-    for cnum in iter::once(LOCAL_CRATE).chain(tcx.crates(()).iter().copied()) {
-        for &impl_def_id in tcx.crate_incoherent_impls((cnum, simp)) {
-            impls.push(impl_def_id)
-        }
-    }
-    debug!(?impls);
+    let impls = iter::once(&LOCAL_CRATE)
+        .chain(tcx.crates(()))
+        .flat_map(|&cnum| tcx.crate_incoherent_impls((cnum, simp)))
+        .copied();
+
+    debug!(impls = ?impls.clone().collect::<Vec<_>>());
 
-    tcx.arena.alloc_slice(&impls)
+    tcx.arena.alloc_from_iter(impls)
 }
 
 pub(super) fn traits_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> &[DefId] {
-    let mut traits = Vec::new();
-    for id in tcx.hir_free_items() {
-        if matches!(tcx.def_kind(id.owner_id), DefKind::Trait | DefKind::TraitAlias) {
-            traits.push(id.owner_id.to_def_id())
-        }
-    }
+    let traits = tcx
+        .hir_free_items()
+        .filter(|id| matches!(tcx.def_kind(id.owner_id), DefKind::Trait | DefKind::TraitAlias))
+        .map(|id| id.owner_id.to_def_id());
 
-    tcx.arena.alloc_slice(&traits)
+    tcx.arena.alloc_from_iter(traits)
 }
 
 pub(super) fn trait_impls_in_crate_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> &[DefId] {
-    let mut trait_impls = Vec::new();
-    for id in tcx.hir_free_items() {
-        if matches!(tcx.def_kind(id.owner_id), DefKind::Impl { .. })
-            && tcx.impl_trait_ref(id.owner_id).is_some()
-        {
-            trait_impls.push(id.owner_id.to_def_id())
-        }
-    }
-
-    tcx.arena.alloc_slice(&trait_impls)
+    let trait_impls = tcx
+        .hir_free_items()
+        .filter(|id| {
+            matches!(tcx.def_kind(id.owner_id), DefKind::Impl { .. })
+                && tcx.impl_trait_ref(id.owner_id).is_some()
+        })
+        .map(|id| id.owner_id.to_def_id());
+
+    tcx.arena.alloc_from_iter(trait_impls)
 }

compiler/rustc_ty_utils/src/implied_bounds.rs

@@ -34,13 +34,10 @@ fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx [(Ty<'
         DefKind::AssocFn => {
             let sig = tcx.fn_sig(def_id).instantiate_identity();
             let liberated_sig = tcx.liberate_late_bound_regions(def_id.to_def_id(), sig);
-            let mut assumed_wf_types: Vec<_> =
-                tcx.assumed_wf_types(tcx.local_parent(def_id)).into();
-            assumed_wf_types.extend(itertools::zip_eq(
-                liberated_sig.inputs_and_output,
-                fn_sig_spans(tcx, def_id),
-            ));
-            tcx.arena.alloc_slice(&assumed_wf_types)
+            tcx.arena.alloc_from_iter(iter::chain(
+                tcx.assumed_wf_types(tcx.local_parent(def_id)).iter().copied(),
+                itertools::zip_eq(liberated_sig.inputs_and_output, fn_sig_spans(tcx, def_id)),
+            ))
         }
         DefKind::Impl { .. } => {
             // Trait arguments and the self type for trait impls or only the self type for

compiler/rustc_ty_utils/src/lib.rs

@@ -13,6 +13,7 @@
 #![feature(associated_type_defaults)]
 #![feature(box_patterns)]
 #![feature(if_let_guard)]
+#![feature(iter_chain)]
 #![feature(iterator_try_collect)]
 #![feature(never_type)]
 #![feature(rustdoc_internals)]