bjoernager/rust
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Stop allocating vtable entries for non-object-safe methods

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This commit is contained in:
Gary Guo 2021-09-01 00:49:14 +01:00
parent 03c775c955
commit 871eb6233e
6 changed files with 54 additions and 12 deletions
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8
compiler/rustc_trait_selection/src/traits/mod.rs
View file

@ -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);

13
compiler/rustc_trait_selection/src/traits/util.rs
View file

@ -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<N>(
// 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;
}
}