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Split the witness table into a separate ImplWitnessTable instruction (#5272)

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This allows us to import the table for a given impl only once, while we
can import many ImplWitness instructions with different specifics for a
generic impl.

For example in convert_facet_value_to_narrowed_facet_type.carbon we see
that a single witness table is imported for the BitAnd interface, with
multiple witnesses (for different specifics) imported and sharing the
same table.

The ImplWitnessTable now contains a back-link to the Impl the witness is
for, allowing inst namer to name that interface in the textual semir,
and allowing the interface to be found when debugging from a witness.

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>
This commit is contained in:
Dana Jansens
2025-04-11 20:30:04 +00:00
committed by GitHub
co-authored by Richard Smith
parent c34a8d0a3a
commit 0e8d354567
273 changed files with 4091 additions and 3391 deletions
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toolchain/check/impl.cpp
+33 -7
View File
@@ -11,6 +11,7 @@
#include "toolchain/check/function.h"
#include "toolchain/check/generic.h"
#include "toolchain/check/import_ref.h"
#include "toolchain/check/inst.h"
#include "toolchain/check/interface.h"
#include "toolchain/check/name_lookup.h"
#include "toolchain/check/type.h"
@@ -108,14 +109,17 @@ auto ImplWitnessStartDefinition(Context& context, SemIR::Impl& impl) -> void {
return;
}
auto witness = context.insts().GetAs<SemIR::ImplWitness>(impl.witness_id);
auto witness_block = context.inst_blocks().GetMutable(witness.elements_id);
// `witness.elements_id` will be `SemIR::InstBlockId::Empty` when the
auto witness_table =
context.insts().GetAs<SemIR::ImplWitnessTable>(witness.witness_table_id);
auto witness_block =
context.inst_blocks().GetMutable(witness_table.elements_id);
// `witness_table.elements_id` will be `SemIR::InstBlockId::Empty` when the
// definition is the first declaration and the interface has no members. The
// other case where `witness_block` will be empty is when we are using a
// placeholder witness. This happens when there is a forward declaration of
// the impl and the facet type has no rewrite constraints and so it wasn't
// required to be complete.
if (witness.elements_id != SemIR::InstBlockId::Empty &&
if (witness_table.elements_id != SemIR::InstBlockId::Empty &&
witness_block.empty()) {
if (!RequireCompleteFacetTypeForImplDefinition(
context, impl.latest_decl_id(), impl.constraint_id)) {
@@ -123,8 +127,8 @@ auto ImplWitnessStartDefinition(Context& context, SemIR::Impl& impl) -> void {
}
AllocateFacetTypeImplWitness(context, impl.interface.interface_id,
witness.elements_id);
witness_block = context.inst_blocks().GetMutable(witness.elements_id);
witness_table.elements_id);
witness_block = context.inst_blocks().GetMutable(witness_table.elements_id);
}
const auto& interface = context.interfaces().Get(impl.interface.interface_id);
auto assoc_entities =
@@ -171,7 +175,10 @@ auto FinishImplWitness(Context& context, SemIR::Impl& impl) -> void {
return;
}
auto witness = context.insts().GetAs<SemIR::ImplWitness>(impl.witness_id);
auto witness_block = context.inst_blocks().GetMutable(witness.elements_id);
auto witness_table =
context.insts().GetAs<SemIR::ImplWitnessTable>(witness.witness_table_id);
auto witness_block =
context.inst_blocks().GetMutable(witness_table.elements_id);
auto& impl_scope = context.name_scopes().Get(impl.scope_id);
auto self_type_id = context.types().GetTypeIdForTypeInstId(impl.self_id);
const auto& interface = context.interfaces().Get(impl.interface.interface_id);
@@ -240,7 +247,10 @@ auto FillImplWitnessWithErrors(Context& context, SemIR::Impl& impl) -> void {
if (impl.witness_id.has_value() &&
impl.witness_id != SemIR::ErrorInst::SingletonInstId) {
auto witness = context.insts().GetAs<SemIR::ImplWitness>(impl.witness_id);
auto witness_block = context.inst_blocks().GetMutable(witness.elements_id);
auto witness_table = context.insts().GetAs<SemIR::ImplWitnessTable>(
witness.witness_table_id);
auto witness_block =
context.inst_blocks().GetMutable(witness_table.elements_id);
for (auto& elem : witness_block) {
if (elem == SemIR::ImplWitnessTablePlaceholder::SingletonInstId) {
elem = SemIR::ErrorInst::SingletonInstId;
@@ -249,6 +259,22 @@ auto FillImplWitnessWithErrors(Context& context, SemIR::Impl& impl) -> void {
}
}
auto AssignImplIdInWitness(Context& context, SemIR::ImplId impl_id,
SemIR::InstId witness_id) -> void {
if (witness_id == SemIR::ErrorInst::SingletonInstId) {
return;
}
auto witness = context.insts().GetAs<SemIR::ImplWitness>(witness_id);
auto witness_table =
context.insts().GetAs<SemIR::ImplWitnessTable>(witness.witness_table_id);
witness_table.impl_id = impl_id;
// Note: The `ImplWitnessTable` instruction is `Unique`, so while this marks
// the instruction as being a dependent instruction of a generic impl, it will
// not be substituted into the eval block.
ReplaceInstBeforeConstantUse(context, witness.witness_table_id,
witness_table);
}
auto IsImplEffectivelyFinal(Context& context, const SemIR::Impl& impl) -> bool {
return impl.is_final ||
(context.constant_values().Get(impl.self_id).is_concrete() &&