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Move vtable methods into its own module

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This commit is contained in:
Michael Goulet 2022-12-08 04:51:46 +00:00
parent 48270044b0
commit b36035c20f
4 changed files with 398 additions and 378 deletions
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367
compiler/rustc_trait_selection/src/traits/mod.rs
View file

@ -20,9 +20,9 @@ mod select;
mod specialize;
mod structural_match;
mod util;
mod vtable;
pub mod wf;
use crate::errors::DumpVTableEntries;
use crate::infer::outlives::env::OutlivesEnvironment;
use crate::infer::{InferCtxt, TyCtxtInferExt};
use crate::traits::error_reporting::TypeErrCtxtExt as _;
@ -30,15 +30,11 @@ use crate::traits::query::evaluate_obligation::InferCtxtExt as _;
use rustc_errors::ErrorGuaranteed;
use rustc_hir as hir;
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_middle::ty::fold::TypeFoldable;
use rustc_middle::ty::visit::TypeVisitable;
use rustc_middle::ty::{
self, DefIdTree, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeSuperVisitable, VtblEntry,
};
use rustc_middle::ty::{self, DefIdTree, ToPredicate, Ty, TyCtxt, TypeSuperVisitable};
use rustc_middle::ty::{InternalSubsts, SubstsRef};
use rustc_span::{sym, Span};
use smallvec::SmallVec;
use rustc_span::Span;
use std::fmt::Debug;
use std::ops::ControlFlow;
@ -567,368 +563,13 @@ fn is_impossible_method<'tcx>(
false
}
#[derive(Clone, Debug)]
enum VtblSegment<'tcx> {
MetadataDSA,
TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
}
/// Prepare the segments for a vtable
fn prepare_vtable_segments<'tcx, T>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
) -> Option<T> {
// The following constraints holds for the final arrangement.
// 1. The whole virtual table of the first direct super trait is included as the
// the prefix. If this trait doesn't have any super traits, then this step
// consists of the dsa metadata.
// 2. Then comes the proper pointer metadata(vptr) and all own methods for all
// other super traits except those already included as part of the first
// direct super trait virtual table.
// 3. finally, the own methods of this trait.
// This has the advantage that trait upcasting to the first direct super trait on each level
// is zero cost, and to another trait includes only replacing the pointer with one level indirection,
// while not using too much extra memory.
// For a single inheritance relationship like this,
// D --> C --> B --> A
// The resulting vtable will consists of these segments:
// DSA, A, B, C, D
// For a multiple inheritance relationship like this,
// D --> C --> A
// \-> B
// The resulting vtable will consists of these segments:
// DSA, A, B, B-vptr, C, D
// For a diamond inheritance relationship like this,
// D --> B --> A
// \-> C -/
// The resulting vtable will consists of these segments:
// DSA, A, B, C, C-vptr, D
// For a more complex inheritance relationship like this:
// O --> G --> C --> A
// \ \ \-> B
// | |-> F --> D
// | \-> E
// |-> N --> J --> H
// \ \-> I
// |-> M --> K
// \-> L
// The resulting vtable will consists of these segments:
// DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
// H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
// N, N-vptr, O
// emit dsa segment first.
if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
return Some(v);
}
let mut emit_vptr_on_new_entry = false;
let mut visited = util::PredicateSet::new(tcx);
let predicate = trait_ref.without_const().to_predicate(tcx);
let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
visited.insert(predicate);
// the main traversal loop:
// basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
// that each node is emitted after all its descendents have been emitted.
// so we convert the directed graph into a tree by skipping all previously visited nodes using a visited set.
// this is done on the fly.
// Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
// stops after it finds a node that has a next-sibling node.
// This next-sibling node will used as the starting point of next slice.
// Example:
// For a diamond inheritance relationship like this,
// D#1 --> B#0 --> A#0
// \-> C#1 -/
// Starting point 0 stack [D]
// Loop run #0: Stack after diving in is [D B A], A is "childless"
// after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
// Loop run #0: Emitting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
// Loop run #0: Stack after exiting out is [D C], C is the next starting point.
// Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
// Loop run #1: Emitting the slice [D C] (in reverse order). No one has a next-sibling node.
// Loop run #1: Stack after exiting out is []. Now the function exits.
loop {
// dive deeper into the stack, recording the path
'diving_in: loop {
if let Some((inner_most_trait_ref, _, _)) = stack.last() {
let inner_most_trait_ref = *inner_most_trait_ref;
let mut direct_super_traits_iter = tcx
.super_predicates_of(inner_most_trait_ref.def_id())
.predicates
.into_iter()
.filter_map(move |(pred, _)| {
pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
});
'diving_in_skip_visited_traits: loop {
if let Some(next_super_trait) = direct_super_traits_iter.next() {
if visited.insert(next_super_trait.to_predicate(tcx)) {
// We're throwing away potential constness of super traits here.
// FIXME: handle ~const super traits
let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
stack.push((
next_super_trait,
emit_vptr_on_new_entry,
Some(direct_super_traits_iter),
));
break 'diving_in_skip_visited_traits;
} else {
continue 'diving_in_skip_visited_traits;
}
} else {
break 'diving_in;
}
}
}
}
// Other than the left-most path, vptr should be emitted for each trait.
emit_vptr_on_new_entry = true;
// emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
'exiting_out: loop {
if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
trait_ref: *inner_most_trait_ref,
emit_vptr: *emit_vptr,
}) {
return Some(v);
}
'exiting_out_skip_visited_traits: loop {
if let Some(siblings) = siblings_opt {
if let Some(next_inner_most_trait_ref) = siblings.next() {
if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
// We're throwing away potential constness of super traits here.
// FIXME: handle ~const super traits
let next_inner_most_trait_ref =
next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
*inner_most_trait_ref = next_inner_most_trait_ref;
*emit_vptr = emit_vptr_on_new_entry;
break 'exiting_out;
} else {
continue 'exiting_out_skip_visited_traits;
}
}
}
stack.pop();
continue 'exiting_out;
}
}
// all done
return None;
}
}
}
fn dump_vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
sp: Span,
trait_ref: ty::PolyTraitRef<'tcx>,
entries: &[VtblEntry<'tcx>],
) {
tcx.sess.emit_err(DumpVTableEntries {
span: sp,
trait_ref,
entries: format!("{:#?}", entries),
});
}
fn own_existential_vtable_entries<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId) -> &'tcx [DefId] {
let trait_methods = tcx
.associated_items(trait_def_id)
.in_definition_order()
.filter(|item| item.kind == ty::AssocKind::Fn);
// Now list each method's DefId (for within its trait).
let own_entries = trait_methods.filter_map(move |trait_method| {
debug!("own_existential_vtable_entry: 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_def_id, &trait_method) {
debug!("own_existential_vtable_entry: not vtable safe");
return None;
}
Some(def_id)
});
tcx.arena.alloc_from_iter(own_entries.into_iter())
}
/// Given a trait `trait_ref`, iterates the vtable entries
/// that come from `trait_ref`, including its supertraits.
fn vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
) -> &'tcx [VtblEntry<'tcx>] {
debug!("vtable_entries({:?})", trait_ref);
let mut entries = vec![];
let vtable_segment_callback = |segment| -> ControlFlow<()> {
match segment {
VtblSegment::MetadataDSA => {
entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES);
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
let existential_trait_ref = trait_ref
.map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
// Lookup the shape of vtable for the trait.
let own_existential_entries =
tcx.own_existential_vtable_entries(existential_trait_ref.def_id());
let own_entries = own_existential_entries.iter().copied().map(|def_id| {
debug!("vtable_entries: trait_method={:?}", def_id);
// The method may have some early-bound lifetimes; add regions for those.
let substs = trait_ref.map_bound(|trait_ref| {
InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
GenericParamDefKind::Type { .. }
| GenericParamDefKind::Const { .. } => {
trait_ref.substs[param.index as usize]
}
})
});
// The trait type may have higher-ranked lifetimes in it;
// erase them if they appear, so that we get the type
// at some particular call site.
let substs = tcx
.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
// It's possible that the method relies on where-clauses that
// do not hold for this particular set of type parameters.
// Note that this method could then never be called, so we
// do not want to try and codegen it, in that case (see #23435).
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;
}
let instance = ty::Instance::resolve_for_vtable(
tcx,
ty::ParamEnv::reveal_all(),
def_id,
substs,
)
.expect("resolution failed during building vtable representation");
VtblEntry::Method(instance)
});
entries.extend(own_entries);
if emit_vptr {
entries.push(VtblEntry::TraitVPtr(trait_ref));
}
}
}
ControlFlow::Continue(())
};
let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
let sp = tcx.def_span(trait_ref.def_id());
dump_vtable_entries(tcx, sp, trait_ref, &entries);
}
tcx.arena.alloc_from_iter(entries.into_iter())
}
/// Find slot base for trait methods within vtable entries of another trait
fn vtable_trait_first_method_offset<'tcx>(
tcx: TyCtxt<'tcx>,
key: (
ty::PolyTraitRef<'tcx>, // trait_to_be_found
ty::PolyTraitRef<'tcx>, // trait_owning_vtable
),
) -> usize {
let (trait_to_be_found, trait_owning_vtable) = key;
// #90177
let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
let vtable_segment_callback = {
let mut vtable_base = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
return ControlFlow::Break(vtable_base);
}
vtable_base += util::count_own_vtable_entries(tcx, trait_ref);
if emit_vptr {
vtable_base += 1;
}
}
}
ControlFlow::Continue(())
}
};
if let Some(vtable_base) =
prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
{
vtable_base
} else {
bug!("Failed to find info for expected trait in vtable");
}
}
/// Find slot offset for trait vptr within vtable entries of another trait
pub fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
tcx: TyCtxt<'tcx>,
key: (
Ty<'tcx>, // trait object type whose trait owning vtable
Ty<'tcx>, // trait object for supertrait
),
) -> Option<usize> {
let (source, target) = key;
assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
// this has been typecked-before, so diagnostics is not really needed.
let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
let trait_ref = tcx.mk_trait_ref(unsize_trait_did, [source, target]);
match tcx.codegen_select_candidate((ty::ParamEnv::reveal_all(), ty::Binder::dummy(trait_ref))) {
Ok(ImplSource::TraitUpcasting(implsrc_traitcasting)) => {
implsrc_traitcasting.vtable_vptr_slot
}
otherwise => bug!("expected TraitUpcasting candidate, got {otherwise:?}"),
}
}
pub fn provide(providers: &mut ty::query::Providers) {
object_safety::provide(providers);
vtable::provide(providers);
*providers = ty::query::Providers {
specialization_graph_of: specialize::specialization_graph_provider,
specializes: specialize::specializes,
codegen_select_candidate: codegen::codegen_select_candidate,
own_existential_vtable_entries,
vtable_entries,
vtable_trait_upcasting_coercion_new_vptr_slot,
subst_and_check_impossible_predicates,
is_impossible_method,
..*providers

13
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View file

@ -19,6 +19,10 @@ use rustc_span::def_id::DefId;
use crate::traits::project::{normalize_with_depth, normalize_with_depth_to};
use crate::traits::util::{self, closure_trait_ref_and_return_type, predicate_for_trait_def};
use crate::traits::vtable::{
count_own_vtable_entries, prepare_vtable_segments, vtable_trait_first_method_offset,
VtblSegment,
};
use crate::traits::{
BuiltinDerivedObligation, ImplDerivedObligation, ImplDerivedObligationCause, ImplSource,
ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData,
@ -26,7 +30,7 @@ use crate::traits::{
ImplSourceGeneratorData, ImplSourceObjectData, ImplSourceTraitAliasData,
ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, ObjectCastObligation,
Obligation, ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection,
SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented, VtblSegment,
SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented,
};
use super::BuiltinImplConditions;
@ -583,7 +587,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
debug!(?nested, "object nested obligations");
let vtable_base = super::super::vtable_trait_first_method_offset(
let vtable_base = vtable_trait_first_method_offset(
tcx,
(unnormalized_upcast_trait_ref, ty::Binder::dummy(object_trait_ref)),
);
@ -904,7 +908,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
vptr_offset += util::count_own_vtable_entries(tcx, trait_ref);
vptr_offset += count_own_vtable_entries(tcx, trait_ref);
if trait_ref == upcast_trait_ref {
if emit_vptr {
return ControlFlow::Break(Some(vptr_offset));
@ -923,8 +927,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
};
let vtable_vptr_slot =
super::super::prepare_vtable_segments(tcx, source_trait_ref, vtable_segment_callback)
.unwrap();
prepare_vtable_segments(tcx, source_trait_ref, vtable_segment_callback).unwrap();
Ok(ImplSourceTraitUpcastingData { upcast_trait_ref, vtable_vptr_slot, nested })
}

10
compiler/rustc_trait_selection/src/traits/util.rs
View file

@ -261,16 +261,6 @@ pub fn upcast_choices<'tcx>(
supertraits(tcx, source_trait_ref).filter(|r| r.def_id() == target_trait_def_id).collect()
}
/// Given a trait `trait_ref`, returns the number of vtable entries
/// that come from `trait_ref`, excluding its supertraits. Used in
/// computing the vtable base for an upcast trait of a trait object.
pub fn count_own_vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
) -> usize {
tcx.own_existential_vtable_entries(trait_ref.def_id()).len()
}
/// Given an upcast trait object described by `object`, returns the
/// index of the method `method_def_id` (which should be part of
/// `object.upcast_trait_ref`) within the vtable for `object`.

386
compiler/rustc_trait_selection/src/traits/vtable.rs Normal file
View file

@ -0,0 +1,386 @@
use crate::errors::DumpVTableEntries;
use crate::traits::{impossible_predicates, is_vtable_safe_method};
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_infer::traits::util::PredicateSet;
use rustc_infer::traits::ImplSource;
use rustc_middle::ty::visit::TypeVisitable;
use rustc_middle::ty::InternalSubsts;
use rustc_middle::ty::{self, GenericParamDefKind, ToPredicate, Ty, TyCtxt, VtblEntry};
use rustc_span::{sym, Span};
use smallvec::SmallVec;
use std::fmt::Debug;
use std::ops::ControlFlow;
#[derive(Clone, Debug)]
pub(super) enum VtblSegment<'tcx> {
MetadataDSA,
TraitOwnEntries { trait_ref: ty::PolyTraitRef<'tcx>, emit_vptr: bool },
}
/// Prepare the segments for a vtable
pub(super) fn prepare_vtable_segments<'tcx, T>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
mut segment_visitor: impl FnMut(VtblSegment<'tcx>) -> ControlFlow<T>,
) -> Option<T> {
// The following constraints holds for the final arrangement.
// 1. The whole virtual table of the first direct super trait is included as the
// the prefix. If this trait doesn't have any super traits, then this step
// consists of the dsa metadata.
// 2. Then comes the proper pointer metadata(vptr) and all own methods for all
// other super traits except those already included as part of the first
// direct super trait virtual table.
// 3. finally, the own methods of this trait.
// This has the advantage that trait upcasting to the first direct super trait on each level
// is zero cost, and to another trait includes only replacing the pointer with one level indirection,
// while not using too much extra memory.
// For a single inheritance relationship like this,
// D --> C --> B --> A
// The resulting vtable will consists of these segments:
// DSA, A, B, C, D
// For a multiple inheritance relationship like this,
// D --> C --> A
// \-> B
// The resulting vtable will consists of these segments:
// DSA, A, B, B-vptr, C, D
// For a diamond inheritance relationship like this,
// D --> B --> A
// \-> C -/
// The resulting vtable will consists of these segments:
// DSA, A, B, C, C-vptr, D
// For a more complex inheritance relationship like this:
// O --> G --> C --> A
// \ \ \-> B
// | |-> F --> D
// | \-> E
// |-> N --> J --> H
// \ \-> I
// |-> M --> K
// \-> L
// The resulting vtable will consists of these segments:
// DSA, A, B, B-vptr, C, D, D-vptr, E, E-vptr, F, F-vptr, G,
// H, H-vptr, I, I-vptr, J, J-vptr, K, K-vptr, L, L-vptr, M, M-vptr,
// N, N-vptr, O
// emit dsa segment first.
if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::MetadataDSA) {
return Some(v);
}
let mut emit_vptr_on_new_entry = false;
let mut visited = PredicateSet::new(tcx);
let predicate = trait_ref.without_const().to_predicate(tcx);
let mut stack: SmallVec<[(ty::PolyTraitRef<'tcx>, _, _); 5]> =
smallvec![(trait_ref, emit_vptr_on_new_entry, None)];
visited.insert(predicate);
// the main traversal loop:
// basically we want to cut the inheritance directed graph into a few non-overlapping slices of nodes
// that each node is emitted after all its descendents have been emitted.
// so we convert the directed graph into a tree by skipping all previously visited nodes using a visited set.
// this is done on the fly.
// Each loop run emits a slice - it starts by find a "childless" unvisited node, backtracking upwards, and it
// stops after it finds a node that has a next-sibling node.
// This next-sibling node will used as the starting point of next slice.
// Example:
// For a diamond inheritance relationship like this,
// D#1 --> B#0 --> A#0
// \-> C#1 -/
// Starting point 0 stack [D]
// Loop run #0: Stack after diving in is [D B A], A is "childless"
// after this point, all newly visited nodes won't have a vtable that equals to a prefix of this one.
// Loop run #0: Emitting the slice [B A] (in reverse order), B has a next-sibling node, so this slice stops here.
// Loop run #0: Stack after exiting out is [D C], C is the next starting point.
// Loop run #1: Stack after diving in is [D C], C is "childless", since its child A is skipped(already emitted).
// Loop run #1: Emitting the slice [D C] (in reverse order). No one has a next-sibling node.
// Loop run #1: Stack after exiting out is []. Now the function exits.
loop {
// dive deeper into the stack, recording the path
'diving_in: loop {
if let Some((inner_most_trait_ref, _, _)) = stack.last() {
let inner_most_trait_ref = *inner_most_trait_ref;
let mut direct_super_traits_iter = tcx
.super_predicates_of(inner_most_trait_ref.def_id())
.predicates
.into_iter()
.filter_map(move |(pred, _)| {
pred.subst_supertrait(tcx, &inner_most_trait_ref).to_opt_poly_trait_pred()
});
'diving_in_skip_visited_traits: loop {
if let Some(next_super_trait) = direct_super_traits_iter.next() {
if visited.insert(next_super_trait.to_predicate(tcx)) {
// We're throwing away potential constness of super traits here.
// FIXME: handle ~const super traits
let next_super_trait = next_super_trait.map_bound(|t| t.trait_ref);
stack.push((
next_super_trait,
emit_vptr_on_new_entry,
Some(direct_super_traits_iter),
));
break 'diving_in_skip_visited_traits;
} else {
continue 'diving_in_skip_visited_traits;
}
} else {
break 'diving_in;
}
}
}
}
// Other than the left-most path, vptr should be emitted for each trait.
emit_vptr_on_new_entry = true;
// emit innermost item, move to next sibling and stop there if possible, otherwise jump to outer level.
'exiting_out: loop {
if let Some((inner_most_trait_ref, emit_vptr, siblings_opt)) = stack.last_mut() {
if let ControlFlow::Break(v) = (segment_visitor)(VtblSegment::TraitOwnEntries {
trait_ref: *inner_most_trait_ref,
emit_vptr: *emit_vptr,
}) {
return Some(v);
}
'exiting_out_skip_visited_traits: loop {
if let Some(siblings) = siblings_opt {
if let Some(next_inner_most_trait_ref) = siblings.next() {
if visited.insert(next_inner_most_trait_ref.to_predicate(tcx)) {
// We're throwing away potential constness of super traits here.
// FIXME: handle ~const super traits
let next_inner_most_trait_ref =
next_inner_most_trait_ref.map_bound(|t| t.trait_ref);
*inner_most_trait_ref = next_inner_most_trait_ref;
*emit_vptr = emit_vptr_on_new_entry;
break 'exiting_out;
} else {
continue 'exiting_out_skip_visited_traits;
}
}
}
stack.pop();
continue 'exiting_out;
}
}
// all done
return None;
}
}
}
fn dump_vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
sp: Span,
trait_ref: ty::PolyTraitRef<'tcx>,
entries: &[VtblEntry<'tcx>],
) {
tcx.sess.emit_err(DumpVTableEntries {
span: sp,
trait_ref,
entries: format!("{:#?}", entries),
});
}
fn own_existential_vtable_entries<'tcx>(tcx: TyCtxt<'tcx>, trait_def_id: DefId) -> &'tcx [DefId] {
let trait_methods = tcx
.associated_items(trait_def_id)
.in_definition_order()
.filter(|item| item.kind == ty::AssocKind::Fn);
// Now list each method's DefId (for within its trait).
let own_entries = trait_methods.filter_map(move |trait_method| {
debug!("own_existential_vtable_entry: 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_def_id, &trait_method) {
debug!("own_existential_vtable_entry: not vtable safe");
return None;
}
Some(def_id)
});
tcx.arena.alloc_from_iter(own_entries.into_iter())
}
/// Given a trait `trait_ref`, iterates the vtable entries
/// that come from `trait_ref`, including its supertraits.
fn vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
) -> &'tcx [VtblEntry<'tcx>] {
debug!("vtable_entries({:?})", trait_ref);
let mut entries = vec![];
let vtable_segment_callback = |segment| -> ControlFlow<()> {
match segment {
VtblSegment::MetadataDSA => {
entries.extend(TyCtxt::COMMON_VTABLE_ENTRIES);
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
let existential_trait_ref = trait_ref
.map_bound(|trait_ref| ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref));
// Lookup the shape of vtable for the trait.
let own_existential_entries =
tcx.own_existential_vtable_entries(existential_trait_ref.def_id());
let own_entries = own_existential_entries.iter().copied().map(|def_id| {
debug!("vtable_entries: trait_method={:?}", def_id);
// The method may have some early-bound lifetimes; add regions for those.
let substs = trait_ref.map_bound(|trait_ref| {
InternalSubsts::for_item(tcx, def_id, |param, _| match param.kind {
GenericParamDefKind::Lifetime => tcx.lifetimes.re_erased.into(),
GenericParamDefKind::Type { .. }
| GenericParamDefKind::Const { .. } => {
trait_ref.substs[param.index as usize]
}
})
});
// The trait type may have higher-ranked lifetimes in it;
// erase them if they appear, so that we get the type
// at some particular call site.
let substs = tcx
.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), substs);
// It's possible that the method relies on where-clauses that
// do not hold for this particular set of type parameters.
// Note that this method could then never be called, so we
// do not want to try and codegen it, in that case (see #23435).
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;
}
let instance = ty::Instance::resolve_for_vtable(
tcx,
ty::ParamEnv::reveal_all(),
def_id,
substs,
)
.expect("resolution failed during building vtable representation");
VtblEntry::Method(instance)
});
entries.extend(own_entries);
if emit_vptr {
entries.push(VtblEntry::TraitVPtr(trait_ref));
}
}
}
ControlFlow::Continue(())
};
let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
if tcx.has_attr(trait_ref.def_id(), sym::rustc_dump_vtable) {
let sp = tcx.def_span(trait_ref.def_id());
dump_vtable_entries(tcx, sp, trait_ref, &entries);
}
tcx.arena.alloc_from_iter(entries.into_iter())
}
/// Find slot base for trait methods within vtable entries of another trait
pub(super) fn vtable_trait_first_method_offset<'tcx>(
tcx: TyCtxt<'tcx>,
key: (
ty::PolyTraitRef<'tcx>, // trait_to_be_found
ty::PolyTraitRef<'tcx>, // trait_owning_vtable
),
) -> usize {
let (trait_to_be_found, trait_owning_vtable) = key;
// #90177
let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
let vtable_segment_callback = {
let mut vtable_base = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
return ControlFlow::Break(vtable_base);
}
vtable_base += count_own_vtable_entries(tcx, trait_ref);
if emit_vptr {
vtable_base += 1;
}
}
}
ControlFlow::Continue(())
}
};
if let Some(vtable_base) =
prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
{
vtable_base
} else {
bug!("Failed to find info for expected trait in vtable");
}
}
/// Find slot offset for trait vptr within vtable entries of another trait
pub(crate) fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
tcx: TyCtxt<'tcx>,
key: (
Ty<'tcx>, // trait object type whose trait owning vtable
Ty<'tcx>, // trait object for supertrait
),
) -> Option<usize> {
let (source, target) = key;
assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.needs_infer());
assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.needs_infer());
// this has been typecked-before, so diagnostics is not really needed.
let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
let trait_ref = tcx.mk_trait_ref(unsize_trait_did, [source, target]);
match tcx.codegen_select_candidate((ty::ParamEnv::reveal_all(), ty::Binder::dummy(trait_ref))) {
Ok(ImplSource::TraitUpcasting(implsrc_traitcasting)) => {
implsrc_traitcasting.vtable_vptr_slot
}
otherwise => bug!("expected TraitUpcasting candidate, got {otherwise:?}"),
}
}
/// Given a trait `trait_ref`, returns the number of vtable entries
/// that come from `trait_ref`, excluding its supertraits. Used in
/// computing the vtable base for an upcast trait of a trait object.
pub(crate) fn count_own_vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
) -> usize {
tcx.own_existential_vtable_entries(trait_ref.def_id()).len()
}
pub(super) fn provide(providers: &mut ty::query::Providers) {
*providers = ty::query::Providers {
own_existential_vtable_entries,
vtable_entries,
vtable_trait_upcasting_coercion_new_vptr_slot,
..*providers
};
}