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lazy field index (#4514)

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We considered a couple of other options for this:
* https://github.com/carbon-language/carbon-lang/pull/4515 Keep the
`ElementIndex` numbering vptr-ignorant, and do +1 offsets as needed -
seems subtle/easy to miss
* https://github.com/carbon-language/carbon-lang/pull/4517 Always have a
zeroth element in the object representation, make it zero-size in the
case of no-vptr - @zygoloid was concerned this would add overhead
especially to stateless objects used in type-trait-like things.

But currently moving forward with this direction - of initializing field
indexes with an invalid value until the end of the class definition,
then assigning field indexes during construction of the class's object
representation struct type. This direction might reinforce/help avoid
premature access to the object representation before the class is
complete, and give a single place where class layout is done (at class
completion) if we want to add more options there, such as class layout
optimizations, etc.

This patch still has problems with object initialization (that #4515
does not have/does address) but does address normal `obj.member` access
correctly.

---------

Co-authored-by: Richard Smith <richard@metafoo.co.uk>
This commit is contained in:
David Blaikie
2024-11-26 18:16:25 +00:00
committed by GitHub
co-authored by Richard Smith
parent 9c71151e34
commit f921923b4b
9 changed files with 358 additions and 118 deletions
Download Patch File Download Diff File Expand all files Collapse all files
toolchain/check/handle_class.cpp
+57 -32
View File
@@ -295,7 +295,7 @@ auto HandleParseNode(Context& context, Parse::ClassDefinitionStartId node_id)
context.inst_block_stack().Push();
context.node_stack().Push(node_id, class_id);
context.struct_type_fields_stack().PushArray();
context.field_decls_stack().PushArray();
// TODO: Handle the case where there's control flow in the class body. For
// example:
@@ -512,7 +512,7 @@ auto HandleParseNode(Context& context, Parse::BaseDeclId node_id) -> bool {
return true;
}
if (!context.struct_type_fields_stack().PeekArray().empty()) {
if (!context.field_decls_stack().PeekArray().empty()) {
// TODO: Add note that includes the first field location as an example.
CARBON_DIAGNOSTIC(
BaseDeclAfterFieldDecl, Error,
@@ -523,6 +523,8 @@ auto HandleParseNode(Context& context, Parse::BaseDeclId node_id) -> bool {
auto base_info = CheckBaseType(context, base_type_node_id, base_type_expr_id);
// TODO: Should we diagnose if there are already any fields?
// The `base` value in the class scope has an unbound element type. Instance
// binding will be performed when it's found by name lookup into an instance.
auto field_type_id =
@@ -530,8 +532,7 @@ auto HandleParseNode(Context& context, Parse::BaseDeclId node_id) -> bool {
class_info.base_id = context.AddInst<SemIR::BaseDecl>(
node_id, {.type_id = field_type_id,
.base_type_id = base_info.type_id,
.index = SemIR::ElementIndex(
context.struct_type_fields_stack().PeekArray().size())});
.index = SemIR::ElementIndex::Invalid});
if (base_info.type_id != SemIR::TypeId::Error) {
auto base_class_info = context.classes().Get(
@@ -539,12 +540,6 @@ auto HandleParseNode(Context& context, Parse::BaseDeclId node_id) -> bool {
class_info.is_dynamic |= base_class_info.is_dynamic;
}
// Add a corresponding field to the object representation of the class.
// TODO: Consider whether we want to use `partial T` here.
// TODO: Should we diagnose if there are already any fields?
context.struct_type_fields_stack().AppendToTop(
{.name_id = SemIR::NameId::Base, .type_id = base_info.type_id});
// Bind the name `base` in the class to the base field.
context.decl_name_stack().AddNameOrDiagnoseDuplicate(
context.decl_name_stack().MakeUnqualifiedName(node_id,
@@ -567,8 +562,7 @@ auto HandleParseNode(Context& context, Parse::BaseDeclId node_id) -> bool {
// returns a corresponding complete type witness instruction.
static auto CheckCompleteAdapterClassType(Context& context,
Parse::NodeId node_id,
SemIR::ClassId class_id,
SemIR::StructTypeFieldsId fields_id)
SemIR::ClassId class_id)
-> SemIR::InstId {
const auto& class_info = context.classes().Get(class_id);
if (class_info.base_id.is_valid()) {
@@ -581,17 +575,14 @@ static auto CheckCompleteAdapterClassType(Context& context,
return SemIR::InstId::BuiltinErrorInst;
}
if (auto fields = context.struct_type_fields().Get(fields_id);
!fields.empty()) {
auto [first_field_inst_id, _] = context.LookupNameInExactScope(
node_id, fields.front().name_id, class_info.scope_id,
context.name_scopes().Get(class_info.scope_id));
auto field_decls = context.field_decls_stack().PeekArray();
if (!field_decls.empty()) {
CARBON_DIAGNOSTIC(AdaptWithFields, Error, "adapter with fields");
CARBON_DIAGNOSTIC(AdaptWithFieldHere, Note,
"first field declaration is here");
context.emitter()
.Build(class_info.adapt_id, AdaptWithFields)
.Note(first_field_inst_id, AdaptWithFieldHere)
.Note(field_decls.front(), AdaptWithFieldHere)
.Emit();
return SemIR::InstId::BuiltinErrorInst;
}
@@ -637,6 +628,31 @@ static auto CheckCompleteAdapterClassType(Context& context,
{.type_id = context.GetBuiltinType(SemIR::BuiltinInstKind::WitnessType),
.object_repr_id = adapted_type_id});
}
static auto AddStructTypeFields(
Context& context,
llvm::SmallVector<SemIR::StructTypeField>& struct_type_fields)
-> SemIR::StructTypeFieldsId {
for (auto field_decl_id : context.field_decls_stack().PeekArray()) {
auto field_decl = context.insts().GetAs<SemIR::FieldDecl>(field_decl_id);
field_decl.index =
SemIR::ElementIndex{static_cast<int>(struct_type_fields.size())};
context.ReplaceInstPreservingConstantValue(field_decl_id, field_decl);
if (field_decl.type_id == SemIR::TypeId::Error) {
struct_type_fields.push_back(
{.name_id = field_decl.name_id, .type_id = SemIR::TypeId::Error});
continue;
}
auto unbound_element_type =
context.sem_ir().types().GetAs<SemIR::UnboundElementType>(
field_decl.type_id);
struct_type_fields.push_back(
{.name_id = field_decl.name_id,
.type_id = unbound_element_type.element_type_id});
}
auto fields_id =
context.struct_type_fields().AddCanonical(struct_type_fields);
return fields_id;
}
// Checks that the specified finished class definition is valid and builds and
// returns a corresponding complete type witness instruction.
@@ -644,39 +660,47 @@ static auto CheckCompleteClassType(Context& context, Parse::NodeId node_id,
SemIR::ClassId class_id) -> SemIR::InstId {
auto& class_info = context.classes().Get(class_id);
if (class_info.adapt_id.is_valid()) {
auto fields_id = context.struct_type_fields().AddCanonical(
context.struct_type_fields_stack().PeekArray());
context.struct_type_fields_stack().PopArray();
return CheckCompleteAdapterClassType(context, node_id, class_id, fields_id);
return CheckCompleteAdapterClassType(context, node_id, class_id);
}
bool defining_vtable_ptr = class_info.is_dynamic;
bool defining_vptr = class_info.is_dynamic;
if (class_info.base_id.is_valid()) {
auto base_info = context.insts().GetAs<SemIR::BaseDecl>(class_info.base_id);
// TODO: If the base class is template dependent, we will need to decide
// whether to add a vptr as part of instantiation.
if (auto* base_class_info = TryGetAsClass(context, base_info.base_type_id);
base_class_info && base_class_info->is_dynamic) {
defining_vtable_ptr = false;
defining_vptr = false;
}
}
if (defining_vtable_ptr) {
context.struct_type_fields_stack().PrependToTop(
auto field_decls = context.field_decls_stack().PeekArray();
llvm::SmallVector<SemIR::StructTypeField> struct_type_fields;
struct_type_fields.reserve(defining_vptr + class_info.base_id.is_valid() +
field_decls.size());
if (defining_vptr) {
struct_type_fields.push_back(
{.name_id = SemIR::NameId::Vptr,
.type_id = context.GetPointerType(
context.GetBuiltinType(SemIR::BuiltinInstKind::VtableType))});
}
auto fields_id = context.struct_type_fields().AddCanonical(
context.struct_type_fields_stack().PeekArray());
context.struct_type_fields_stack().PopArray();
if (class_info.base_id.is_valid()) {
auto base_decl = context.insts().GetAs<SemIR::BaseDecl>(class_info.base_id);
base_decl.index =
SemIR::ElementIndex{static_cast<int>(struct_type_fields.size())};
context.ReplaceInstPreservingConstantValue(class_info.base_id, base_decl);
struct_type_fields.push_back(
{.name_id = SemIR::NameId::Base,
.type_id = context.insts()
.GetAs<SemIR::BaseDecl>(class_info.base_id)
.base_type_id});
}
return context.AddInst<SemIR::CompleteTypeWitness>(
node_id,
{.type_id = context.GetBuiltinType(SemIR::BuiltinInstKind::WitnessType),
.object_repr_id = context.GetStructType(fields_id)});
.object_repr_id = context.GetStructType(
AddStructTypeFields(context, struct_type_fields))});
}
auto HandleParseNode(Context& context, Parse::ClassDefinitionId node_id)
@@ -691,6 +715,7 @@ auto HandleParseNode(Context& context, Parse::ClassDefinitionId node_id)
class_info.complete_type_witness_id = complete_type_witness_id;
context.inst_block_stack().Pop();
context.field_decls_stack().PopArray();
FinishGenericDefinition(context, class_info.generic_id);