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Initialize vptrs to point to vtables (#5244)

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Adds a mapping to keep track of vtable LLVM IR decls/defs for use.
Adds the vtable_id to the vtable_ptr initialize instruction for lookup.
Adds emission of vtable declarations for use outside the file that
defines the vtable. (this isn't done lazily, it's done for any imported
class - it could be done lazily & maybe eventually has to be lazy to
handle generics)
This commit is contained in:
David Blaikie
2025-04-05 06:11:34 +00:00
committed by GitHub
parent 8c113c1241
commit 8e7bb2f953
8 changed files with 218 additions and 63 deletions
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toolchain/lower/file_context.cpp
+22 -10
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@@ -69,7 +69,9 @@ auto FileContext::Run() -> std::unique_ptr<llvm::Module> {
}
for (const auto& class_info : sem_ir_->classes().array_ref()) {
BuildVtable(class_info);
if (auto* llvm_vtable = BuildVtable(class_info)) {
global_variables_.Insert(class_info.vtable_id, llvm_vtable);
}
}
// Specific functions are lowered when we emit a reference to them.
@@ -707,24 +709,35 @@ auto FileContext::GetLocForDI(SemIR::InstId inst_id) -> LocForDI {
}
}
auto FileContext::BuildVtable(const SemIR::Class& class_info) -> void {
auto FileContext::BuildVtable(const SemIR::Class& class_info)
-> llvm::GlobalVariable* {
// Bail out if this class is not dynamic (this will account for classes that
// are declared-and-not-defined (including extern declarations) as well).
if (!class_info.is_dynamic) {
return;
return nullptr;
}
Mangler m(*this);
std::string mangled_name = m.MangleVTable(class_info);
auto first_owning_decl_loc =
sem_ir().insts().GetLocId(class_info.first_owning_decl_id);
if (first_owning_decl_loc.is_import_ir_inst_id()) {
return;
// Emit a declaration of an imported vtable using a(n opaque) pointer type.
// This doesn't have to match the definition that appears elsewhere, it'll
// still get merged correctly.
auto* gv = new llvm::GlobalVariable(
llvm_module(),
llvm::PointerType::get(llvm_context(), /*AddressSpace=*/0),
/*isConstant=*/true, llvm::GlobalValue::ExternalLinkage, nullptr,
mangled_name);
gv->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
return gv;
}
auto canonical_vtable_id =
sem_ir().constant_values().GetConstantInstId(class_info.vtable_id);
if (canonical_vtable_id == SemIR::ErrorInst::SingletonInstId) {
return;
}
auto vtable_inst_block =
sem_ir().inst_blocks().Get(sem_ir()
.insts()
@@ -734,9 +747,6 @@ auto FileContext::BuildVtable(const SemIR::Class& class_info) -> void {
auto* entry_type = llvm::IntegerType::getInt32Ty(llvm_context());
auto* table_type = llvm::ArrayType::get(entry_type, vtable_inst_block.size());
Mangler m(*this);
std::string mangled_name = m.MangleVTable(class_info);
auto* llvm_vtable = new llvm::GlobalVariable(
llvm_module(), table_type, /*isConstant=*/true,
llvm::GlobalValue::ExternalLinkage, nullptr, mangled_name);
@@ -763,6 +773,8 @@ auto FileContext::BuildVtable(const SemIR::Class& class_info) -> void {
llvm_vtable->setInitializer(llvm::ConstantArray::get(table_type, vfuncs));
llvm_vtable->setUnnamedAddr(llvm::GlobalValue::UnnamedAddr::Global);
return llvm_vtable;
}
} // namespace Carbon::Lower