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Refactor vtable format.

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This commit is contained in:
Charles Lew 2021-06-17 12:20:18 +08:00
parent da7d405357
commit d2dc4276fd
5 changed files with 311 additions and 58 deletions
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6
compiler/rustc_infer/src/traits/util.rs
View File

@ -14,17 +14,17 @@ pub fn anonymize_predicate<'tcx>(
tcx.reuse_or_mk_predicate(pred, new)
}
struct PredicateSet<'tcx> {
pub struct PredicateSet<'tcx> {
tcx: TyCtxt<'tcx>,
set: FxHashSet<ty::Predicate<'tcx>>,
}
impl PredicateSet<'tcx> {
fn new(tcx: TyCtxt<'tcx>) -> Self {
pub fn new(tcx: TyCtxt<'tcx>) -> Self {
Self { tcx, set: Default::default() }
}
fn insert(&mut self, pred: ty::Predicate<'tcx>) -> bool {
pub fn insert(&mut self, pred: ty::Predicate<'tcx>) -> bool {
// We have to be careful here because we want
//
// for<'a> Foo<&'a i32>

8
compiler/rustc_middle/src/ty/vtable.rs
View File

@ -2,7 +2,7 @@
use crate::mir::interpret::{alloc_range, AllocId, Allocation, Pointer, Scalar, ScalarMaybeUninit};
use crate::ty::fold::TypeFoldable;
use crate::ty::{self, DefId, SubstsRef, Ty, TyCtxt};
use crate::ty::{self, DefId, PolyExistentialTraitRef, SubstsRef, Ty, TyCtxt};
use rustc_ast::Mutability;
#[derive(Clone, Copy, Debug, PartialEq, HashStable)]
@ -12,6 +12,7 @@ pub enum VtblEntry<'tcx> {
MetadataAlign,
Vacant,
Method(DefId, SubstsRef<'tcx>),
TraitVPtr(PolyExistentialTraitRef<'tcx>),
}
pub const COMMON_VTABLE_ENTRIES: &[VtblEntry<'_>] =
@ -92,6 +93,11 @@ pub fn vtable_allocation(
let fn_ptr = Pointer::from(fn_alloc_id);
ScalarMaybeUninit::from_pointer(fn_ptr, &tcx)
}
VtblEntry::TraitVPtr(trait_ref) => {
let supertrait_alloc_id = self.vtable_allocation(ty, Some(*trait_ref));
let vptr = Pointer::from(supertrait_alloc_id);
ScalarMaybeUninit::from_pointer(vptr, &tcx)
}
};
vtable
.write_scalar(&tcx, alloc_range(ptr_size * idx, ptr_size), scalar)

4
compiler/rustc_mir/src/monomorphize/collector.rs
View File

@ -1116,6 +1116,10 @@ fn create_mono_items_for_vtable_methods<'tcx>(
| VtblEntry::MetadataSize
| VtblEntry::MetadataAlign
| VtblEntry::Vacant => None,
VtblEntry::TraitVPtr(_) => {
// all super trait items already covered, so skip them.
None
}
VtblEntry::Method(def_id, substs) => ty::Instance::resolve_for_vtable(
tcx,
ty::ParamEnv::reveal_all(),

2
compiler/rustc_trait_selection/src/lib.rs
View File

@ -31,6 +31,8 @@
extern crate tracing;
#[macro_use]
extern crate rustc_middle;
#[macro_use]
extern crate smallvec;
pub mod autoderef;
pub mod infer;

285
compiler/rustc_trait_selection/src/traits/mod.rs
View File

@ -35,8 +35,10 @@
COMMON_VTABLE_ENTRIES,
};
use rustc_span::Span;
use smallvec::SmallVec;
use std::fmt::Debug;
use std::ops::ControlFlow;
pub use self::FulfillmentErrorCode::*;
pub use self::ImplSource::*;
@ -454,6 +456,164 @@ fn subst_and_check_impossible_predicates<'tcx>(
result
}
#[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 emited after all its descendents have been emitted.
// so we convert the directed graph into a tree by skipping all previously visted 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: Emiting 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: Emiting 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_ref()
});
'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)) {
stack.push((
next_super_trait.value,
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)) {
*inner_most_trait_ref = next_inner_most_trait_ref.value;
*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;
}
}
}
/// Given a trait `trait_ref`, iterates the vtable entries
/// that come from `trait_ref`, including its supertraits.
fn vtable_entries<'tcx>(
@ -462,16 +622,21 @@ fn vtable_entries<'tcx>(
) -> &'tcx [VtblEntry<'tcx>] {
debug!("vtable_entries({:?})", trait_ref);
let entries = COMMON_VTABLE_ENTRIES.iter().cloned().chain(
supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
let mut entries = vec![];
let vtable_segment_callback = |segment| -> ControlFlow<()> {
match segment {
VtblSegment::MetadataDSA => {
entries.extend(COMMON_VTABLE_ENTRIES);
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
let trait_methods = tcx
.associated_items(trait_ref.def_id())
.in_definition_order()
.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`.
trait_methods.map(move |trait_method| {
let own_entries = trait_methods.map(move |trait_method| {
debug!("vtable_entries: trait_method={:?}", trait_method);
let def_id = trait_method.def_id;
@ -485,7 +650,8 @@ fn vtable_entries<'tcx>(
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 { .. } => {
GenericParamDefKind::Type { .. }
| GenericParamDefKind::Const { .. } => {
trait_ref.substs[param.index as usize]
}
})
@ -494,8 +660,8 @@ fn vtable_entries<'tcx>(
// 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);
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.
@ -508,11 +674,24 @@ fn vtable_entries<'tcx>(
}
VtblEntry::Method(def_id, substs)
})
}),
);
});
tcx.arena.alloc_from_iter(entries)
entries.extend(own_entries);
if emit_vptr {
let trait_ref = trait_ref.map_bound(|trait_ref| {
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
});
entries.push(VtblEntry::TraitVPtr(trait_ref));
}
}
}
ControlFlow::Continue(())
};
let _ = prepare_vtable_segments(tcx, trait_ref, vtable_segment_callback);
tcx.arena.alloc_from_iter(entries.into_iter())
}
/// Find slot base for trait methods within vtable entries of another trait
@ -525,20 +704,82 @@ fn vtable_trait_first_method_offset<'tcx>(
) -> usize {
let (trait_to_be_found, trait_owning_vtable) = key;
let mut supertraits = util::supertraits(tcx, trait_owning_vtable);
let vtable_segment_callback = {
let mut vtable_base = 0;
// For each of the non-matching predicates that
// we pass over, we sum up the set of number of vtable
// entries, so that we can compute the offset for the selected
// trait.
let vtable_base = ty::COMMON_VTABLE_ENTRIES.len()
+ supertraits
.by_ref()
.take_while(|t| *t != trait_to_be_found)
.map(|t| util::count_own_vtable_entries(tcx, t))
.sum::<usize>();
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vtable_base += COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
if trait_ref == trait_to_be_found {
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
/// FIXME: This function is not yet used. Remove `#[allow(dead_code)]` when it's used in upcoming pr.
#[allow(dead_code)]
fn vtable_trait_vptr_slot_offset<'tcx>(
tcx: TyCtxt<'tcx>,
key: (
ty::PolyTraitRef<'tcx>, // trait_to_be_found
ty::PolyTraitRef<'tcx>, // trait_owning_vtable
),
) -> Option<usize> {
let (trait_to_be_found, trait_owning_vtable) = key;
let vtable_segment_callback = {
let mut vptr_offset = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vptr_offset += COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
vptr_offset += util::count_own_vtable_entries(tcx, trait_ref);
if trait_ref == trait_to_be_found {
if emit_vptr {
return ControlFlow::Break(Some(vptr_offset));
} else {
return ControlFlow::Break(None);
}
}
if emit_vptr {
vptr_offset += 1;
}
}
}
ControlFlow::Continue(())
}
};
if let Some(vptr_offset) =
prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
{
vptr_offset
} else {
bug!("Failed to find info for expected trait in vtable");
}
}
pub fn provide(providers: &mut ty::query::Providers) {