From 871eb6233ed4b5c3a3c5fe96e88e4dacc046e45f Mon Sep 17 00:00:00 2001 From: Gary Guo Date: Wed, 1 Sep 2021 00:49:14 +0100 Subject: [PATCH] Stop allocating vtable entries for non-object-safe methods --- .../rustc_trait_selection/src/traits/mod.rs | 8 ++++---- .../rustc_trait_selection/src/traits/util.rs | 13 +++++++++---- .../ui/traits/vtable/vtable-non-object-safe.rs | 18 ++++++++++++++++++ .../vtable/vtable-non-object-safe.stderr | 16 ++++++++++++++++ src/test/ui/traits/vtable/vtable-vacant.rs | 7 +++++-- src/test/ui/traits/vtable/vtable-vacant.stderr | 4 ++-- 6 files changed, 54 insertions(+), 12 deletions(-) create mode 100644 src/test/ui/traits/vtable/vtable-non-object-safe.rs create mode 100644 src/test/ui/traits/vtable/vtable-non-object-safe.stderr diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs index 17a4184c3c9..f5a02ee7ad2 100644 --- a/compiler/rustc_trait_selection/src/traits/mod.rs +++ b/compiler/rustc_trait_selection/src/traits/mod.rs @@ -647,14 +647,14 @@ fn vtable_entries<'tcx>( .filter(|item| item.kind == ty::AssocKind::Fn); // Now list each method's DefId and InternalSubsts (for within its trait). // If the method can never be called from this object, produce `Vacant`. - let own_entries = trait_methods.map(move |trait_method| { + let own_entries = trait_methods.filter_map(move |trait_method| { debug!("vtable_entries: trait_method={:?}", trait_method); let def_id = trait_method.def_id; // Some methods cannot be called on an object; skip those. if !is_vtable_safe_method(tcx, trait_ref.def_id(), &trait_method) { debug!("vtable_entries: not vtable safe"); - return VtblEntry::Vacant; + return None; } // The method may have some early-bound lifetimes; add regions for those. @@ -681,7 +681,7 @@ fn vtable_entries<'tcx>( let predicates = tcx.predicates_of(def_id).instantiate_own(tcx, substs); if impossible_predicates(tcx, predicates.predicates) { debug!("vtable_entries: predicates do not hold"); - return VtblEntry::Vacant; + return Some(VtblEntry::Vacant); } let instance = ty::Instance::resolve_for_vtable( @@ -691,7 +691,7 @@ fn vtable_entries<'tcx>( substs, ) .expect("resolution failed during building vtable representation"); - VtblEntry::Method(instance) + Some(VtblEntry::Method(instance)) }); entries.extend(own_entries); diff --git a/compiler/rustc_trait_selection/src/traits/util.rs b/compiler/rustc_trait_selection/src/traits/util.rs index fd94f9f7998..3b98fe48c8c 100644 --- a/compiler/rustc_trait_selection/src/traits/util.rs +++ b/compiler/rustc_trait_selection/src/traits/util.rs @@ -289,7 +289,9 @@ pub fn count_own_vtable_entries(tcx: TyCtxt<'tcx>, trait_ref: ty::PolyTraitRef<' // Count number of methods and add them to the total offset. // Skip over associated types and constants. for trait_item in tcx.associated_items(trait_ref.def_id()).in_definition_order() { - if trait_item.kind == ty::AssocKind::Fn { + let is_vtable_safe_method = trait_item.kind == ty::AssocKind::Fn + && super::is_vtable_safe_method(tcx, trait_ref.def_id(), trait_item); + if is_vtable_safe_method { entries += 1; } } @@ -308,13 +310,16 @@ pub fn get_vtable_index_of_object_method( // add them to the total offset. // Skip over associated types and constants, as those aren't stored in the vtable. let mut entries = object.vtable_base; - for trait_item in tcx.associated_items(object.upcast_trait_ref.def_id()).in_definition_order() { + let trait_def_id = object.upcast_trait_ref.def_id(); + for trait_item in tcx.associated_items(trait_def_id).in_definition_order() { + let is_vtable_safe_method = trait_item.kind == ty::AssocKind::Fn + && super::is_vtable_safe_method(tcx, trait_def_id, trait_item); if trait_item.def_id == method_def_id { // The item with the ID we were given really ought to be a method. - assert_eq!(trait_item.kind, ty::AssocKind::Fn); + assert!(is_vtable_safe_method); return entries; } - if trait_item.kind == ty::AssocKind::Fn { + if is_vtable_safe_method { entries += 1; } } diff --git a/src/test/ui/traits/vtable/vtable-non-object-safe.rs b/src/test/ui/traits/vtable/vtable-non-object-safe.rs new file mode 100644 index 00000000000..45b6a8a98a7 --- /dev/null +++ b/src/test/ui/traits/vtable/vtable-non-object-safe.rs @@ -0,0 +1,18 @@ +// build-fail +#![feature(rustc_attrs)] + +// Ensure that non-object-safe methods in Iterator does not generate +// vtable entries. + +#[rustc_dump_vtable] +trait A: Iterator {} +//~^ error Vtable + +impl A for T where T: Iterator {} + +fn foo(_a: &mut dyn A) { +} + +fn main() { + foo(&mut vec![0, 1, 2, 3].into_iter()); +} diff --git a/src/test/ui/traits/vtable/vtable-non-object-safe.stderr b/src/test/ui/traits/vtable/vtable-non-object-safe.stderr new file mode 100644 index 00000000000..f3175b805d1 --- /dev/null +++ b/src/test/ui/traits/vtable/vtable-non-object-safe.stderr @@ -0,0 +1,16 @@ +error: Vtable entries for ` as A>`: [ + MetadataDropInPlace, + MetadataSize, + MetadataAlign, + Method( as Iterator>::next), + Method( as Iterator>::size_hint), + Method( as Iterator>::advance_by), + Method( as Iterator>::nth), +] + --> $DIR/vtable-non-object-safe.rs:8:1 + | +LL | trait A: Iterator {} + | ^^^^^^^^^^^^^^^^^^^^ + +error: aborting due to previous error + diff --git a/src/test/ui/traits/vtable/vtable-vacant.rs b/src/test/ui/traits/vtable/vtable-vacant.rs index ebea94171f2..429ce523799 100644 --- a/src/test/ui/traits/vtable/vtable-vacant.rs +++ b/src/test/ui/traits/vtable/vtable-vacant.rs @@ -1,22 +1,25 @@ // build-fail #![feature(rustc_attrs)] +#![feature(negative_impls)] +#![allow(where_clauses_object_safety)] // B --> A #[rustc_dump_vtable] trait A { fn foo_a1(&self) {} - fn foo_a2(&self) where Self: Sized {} + fn foo_a2(&self) where Self: Send {} } #[rustc_dump_vtable] trait B: A { //~^ error Vtable fn foo_b1(&self) {} - fn foo_b2() where Self: Sized {} + fn foo_b2(&self) where Self: Send {} } struct S; +impl !Send for S {} impl A for S {} impl B for S {} diff --git a/src/test/ui/traits/vtable/vtable-vacant.stderr b/src/test/ui/traits/vtable/vtable-vacant.stderr index 768cca52689..f5cd36264fc 100644 --- a/src/test/ui/traits/vtable/vtable-vacant.stderr +++ b/src/test/ui/traits/vtable/vtable-vacant.stderr @@ -7,12 +7,12 @@ error: Vtable entries for ``: [ Method(::foo_b1), Vacant, ] - --> $DIR/vtable-vacant.rs:13:1 + --> $DIR/vtable-vacant.rs:15:1 | LL | / trait B: A { LL | | LL | | fn foo_b1(&self) {} -LL | | fn foo_b2() where Self: Sized {} +LL | | fn foo_b2(&self) where Self: Send {} LL | | } | |_^