Move vtable methods into its own module

Author: compiler-errors

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -20,25 +20,21 @@ 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 _;
 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