element index init with vptr (#4565)

Not sure if this is the most robust way to do it - I guess the
alternative is doing name lookup into the dest struct fields too?

toolchain/check/convert.cpp

@@ -168,30 +168,31 @@ static auto MakeElementAccessInst(Context& context, SemIR::LocId loc_id,
 // another aggregate.
 //
 // For the source: `src_id` is the source aggregate, `src_elem_type` is the
-// element type, `i` is the index, and `SourceAccessInstT` is the kind of
-// instruction used to access the source element.
+// element type, `src_field_index` is the index, and `SourceAccessInstT` is the
+// kind of instruction used to access the source element.
 //
 // For the target: `kind` is the kind of conversion or initialization,
 // `target_elem_type` is the element type. For initialization, `target_id` is
 // the destination, `target_block` is a pending block for target location
 // calculations that will be spliced as the return slot of the initializer if
-// necessary, `i` is the index, and `TargetAccessInstT` is the kind of
-// instruction used to access the destination element.
+// necessary, `target_field_index` is the index, and `TargetAccessInstT` is the
+// kind of instruction used to access the destination element.
 template <typename SourceAccessInstT, typename TargetAccessInstT>
 static auto ConvertAggregateElement(
     Context& context, SemIR::LocId loc_id, SemIR::InstId src_id,
     SemIR::TypeId src_elem_type,
     llvm::ArrayRef<SemIR::InstId> src_literal_elems,
     ConversionTarget::Kind kind, SemIR::InstId target_id,
-    SemIR::TypeId target_elem_type, PendingBlock* target_block, size_t i) {
+    SemIR::TypeId target_elem_type, PendingBlock* target_block,
+    size_t src_field_index, size_t target_field_index) {
   // Compute the location of the source element. This goes into the current code
   // block, not into the target block.
   // TODO: Ideally we would discard this instruction if it's unused.
-  auto src_elem_id =
-      !src_literal_elems.empty()
-          ? src_literal_elems[i]
-          : MakeElementAccessInst<SourceAccessInstT>(context, loc_id, src_id,
-                                                     src_elem_type, context, i);
+  auto src_elem_id = !src_literal_elems.empty()
+                         ? src_literal_elems[src_field_index]
+                         : MakeElementAccessInst<SourceAccessInstT>(
+                               context, loc_id, src_id, src_elem_type, context,
+                               src_field_index);
 
   // If we're performing a conversion rather than an initialization, we won't
   // have or need a target.
@@ -204,7 +205,8 @@ static auto ConvertAggregateElement(
   PendingBlock::DiscardUnusedInstsScope scope(target_block);
   target.init_block = target_block;
   target.init_id = MakeElementAccessInst<TargetAccessInstT>(
-      context, loc_id, target_id, target_elem_type, *target_block, i);
+      context, loc_id, target_id, target_elem_type, *target_block,
+      target_field_index);
   return Convert(context, loc_id, src_elem_id, target);
 }
 
@@ -275,7 +277,7 @@ static auto ConvertTupleToArray(Context& context, SemIR::TupleType tuple_type,
         ConvertAggregateElement<SemIR::TupleAccess, SemIR::ArrayIndex>(
             context, value_loc_id, value_id, src_type_id, literal_elems,
             ConversionTarget::FullInitializer, return_slot_id,
-            array_type.element_type_id, target_block, i);
+            array_type.element_type_id, target_block, i, i);
     if (init_id == SemIR::InstId::BuiltinErrorInst) {
       return SemIR::InstId::BuiltinErrorInst;
     }
@@ -356,7 +358,7 @@ static auto ConvertTupleToTuple(Context& context, SemIR::TupleType src_type,
     auto init_id =
         ConvertAggregateElement<SemIR::TupleAccess, SemIR::TupleAccess>(
             context, value_loc_id, value_id, src_type_id, literal_elems,
-            inner_kind, target.init_id, dest_type_id, target.init_block, i);
+            inner_kind, target.init_id, dest_type_id, target.init_block, i, i);
     if (init_id == SemIR::InstId::BuiltinErrorInst) {
       return SemIR::InstId::BuiltinErrorInst;
     }
@@ -394,7 +396,8 @@ static auto ConvertStructToStructOrClass(Context& context,
   auto dest_elem_fields = sem_ir.struct_type_fields().Get(dest_type.fields_id);
   bool dest_has_vptr = !dest_elem_fields.empty() &&
                        dest_elem_fields.front().name_id == SemIR::NameId::Vptr;
-  auto dest_elem_fields_size = dest_elem_fields.size() - dest_has_vptr;
+  int dest_vptr_offset = (dest_has_vptr ? 1 : 0);
+  auto dest_elem_fields_size = dest_elem_fields.size() - dest_vptr_offset;
 
   auto value = sem_ir.insts().Get(value_id);
   auto value_loc_id = sem_ir.insts().GetLocId(value_id);
@@ -496,7 +499,7 @@ static auto ConvertStructToStructOrClass(Context& context,
         ConvertAggregateElement<SemIR::StructAccess, TargetAccessInstT>(
             context, value_loc_id, value_id, src_field.type_id, literal_elems,
             inner_kind, target.init_id, dest_field.type_id, target.init_block,
-            src_field_index);
+            src_field_index, src_field_index + dest_vptr_offset);
     if (init_id == SemIR::InstId::BuiltinErrorInst) {
       return SemIR::InstId::BuiltinErrorInst;
     }

toolchain/check/testdata/class/virtual_modifiers.carbon

@@ -47,6 +47,20 @@ fn F() {
   var v: Modifiers.Base = {};
 }
 
+// --- init_members.carbon
+
+package InitMembers;
+
+base class Base {
+  virtual fn F();
+  var m1: i32;
+  var m2: i32;
+}
+
+fn F() {
+  var v: Base = {.m2 = 3, .m1 = 5};
+}
+
 // CHECK:STDOUT: --- modifiers.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
@@ -235,3 +249,105 @@ fn F() {
 // CHECK:STDOUT:   return
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
+// CHECK:STDOUT: --- init_members.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %Base: type = class_type @Base [template]
+// CHECK:STDOUT:   %F.type.1: type = fn_type @F.1 [template]
+// CHECK:STDOUT:   %F.1: %F.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.1: Core.IntLiteral = int_value 32 [template]
+// CHECK:STDOUT:   %Int.type: type = fn_type @Int [template]
+// CHECK:STDOUT:   %Int: %Int.type = struct_value () [template]
+// CHECK:STDOUT:   %i32: type = int_type signed, %.1 [template]
+// CHECK:STDOUT:   %.2: type = unbound_element_type %Base, %i32 [template]
+// CHECK:STDOUT:   %.3: type = ptr_type <vtable> [template]
+// CHECK:STDOUT:   %.4: type = struct_type {.<vptr>: %.3, .m1: %i32, .m2: %i32} [template]
+// CHECK:STDOUT:   %.5: <witness> = complete_type_witness %.4 [template]
+// CHECK:STDOUT:   %F.type.2: type = fn_type @F.2 [template]
+// CHECK:STDOUT:   %F.2: %F.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.7: Core.IntLiteral = int_value 3 [template]
+// CHECK:STDOUT:   %.8: Core.IntLiteral = int_value 5 [template]
+// CHECK:STDOUT:   %.9: type = struct_type {.m2: Core.IntLiteral, .m1: Core.IntLiteral} [template]
+// CHECK:STDOUT:   %Convert.type.2: type = fn_type @Convert.1, @ImplicitAs(%i32) [template]
+// CHECK:STDOUT:   %Convert.type.14: type = fn_type @Convert.2, @impl.1(%.1) [template]
+// CHECK:STDOUT:   %Convert.14: %Convert.type.14 = struct_value () [template]
+// CHECK:STDOUT:   %.33: <witness> = interface_witness (%Convert.14) [template]
+// CHECK:STDOUT:   %.34: <bound method> = bound_method %.8, %Convert.14 [template]
+// CHECK:STDOUT:   %.35: <specific function> = specific_function %.34, @Convert.2(%.1) [template]
+// CHECK:STDOUT:   %.36: %i32 = int_value 5 [template]
+// CHECK:STDOUT:   %.37: <bound method> = bound_method %.7, %Convert.14 [template]
+// CHECK:STDOUT:   %.38: <specific function> = specific_function %.37, @Convert.2(%.1) [template]
+// CHECK:STDOUT:   %.39: %i32 = int_value 3 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     .Int = %import_ref.1
+// CHECK:STDOUT:     .ImplicitAs = %import_ref.2
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .Base = %Base.decl
+// CHECK:STDOUT:     .F = %F.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %Base.decl: type = class_decl @Base [template = constants.%Base] {} {}
+// CHECK:STDOUT:   %F.decl: %F.type.2 = fn_decl @F.2 [template = constants.%F.2] {} {}
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @Base {
+// CHECK:STDOUT:   %F.decl: %F.type.1 = fn_decl @F.1 [template = constants.%F.1] {} {}
+// CHECK:STDOUT:   %.loc6_11.1: Core.IntLiteral = int_value 32 [template = constants.%.1]
+// CHECK:STDOUT:   %int.make_type_signed.loc6: init type = call constants.%Int(%.loc6_11.1) [template = constants.%i32]
+// CHECK:STDOUT:   %.loc6_11.2: type = value_of_initializer %int.make_type_signed.loc6 [template = constants.%i32]
+// CHECK:STDOUT:   %.loc6_11.3: type = converted %int.make_type_signed.loc6, %.loc6_11.2 [template = constants.%i32]
+// CHECK:STDOUT:   %.loc6_9: %.2 = field_decl m1, element0 [template]
+// CHECK:STDOUT:   %.loc7_11.1: Core.IntLiteral = int_value 32 [template = constants.%.1]
+// CHECK:STDOUT:   %int.make_type_signed.loc7: init type = call constants.%Int(%.loc7_11.1) [template = constants.%i32]
+// CHECK:STDOUT:   %.loc7_11.2: type = value_of_initializer %int.make_type_signed.loc7 [template = constants.%i32]
+// CHECK:STDOUT:   %.loc7_11.3: type = converted %int.make_type_signed.loc7, %.loc7_11.2 [template = constants.%i32]
+// CHECK:STDOUT:   %.loc7_9: %.2 = field_decl m2, element1 [template]
+// CHECK:STDOUT:   %.loc8: <witness> = complete_type_witness %.4 [template = constants.%.5]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%Base
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   .m1 = %.loc6_9
+// CHECK:STDOUT:   .m2 = %.loc7_9
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: virtual fn @F.1();
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F.2() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %Base.ref: type = name_ref Base, file.%Base.decl [template = constants.%Base]
+// CHECK:STDOUT:   %v.var: ref %Base = var v
+// CHECK:STDOUT:   %v: ref %Base = bind_name v, %v.var
+// CHECK:STDOUT:   %.loc11_24: Core.IntLiteral = int_value 3 [template = constants.%.7]
+// CHECK:STDOUT:   %.loc11_33: Core.IntLiteral = int_value 5 [template = constants.%.8]
+// CHECK:STDOUT:   %.loc11_34.1: %.9 = struct_literal (%.loc11_24, %.loc11_33)
+// CHECK:STDOUT:   %.loc11_34.2: %Convert.type.2 = interface_witness_access constants.%.33, element0 [template = constants.%Convert.14]
+// CHECK:STDOUT:   %.loc11_34.3: <bound method> = bound_method %.loc11_33, %.loc11_34.2 [template = constants.%.34]
+// CHECK:STDOUT:   %.loc11_34.4: <specific function> = specific_function %.loc11_34.3, @Convert.2(constants.%.1) [template = constants.%.35]
+// CHECK:STDOUT:   %int.convert_checked.loc11_34.1: init %i32 = call %.loc11_34.4(%.loc11_33) [template = constants.%.36]
+// CHECK:STDOUT:   %.loc11_34.5: init %i32 = converted %.loc11_33, %int.convert_checked.loc11_34.1 [template = constants.%.36]
+// CHECK:STDOUT:   %.loc11_34.6: ref %i32 = class_element_access %v.var, element2
+// CHECK:STDOUT:   %.loc11_34.7: init %i32 = initialize_from %.loc11_34.5 to %.loc11_34.6 [template = constants.%.36]
+// CHECK:STDOUT:   %.loc11_34.8: %Convert.type.2 = interface_witness_access constants.%.33, element0 [template = constants.%Convert.14]
+// CHECK:STDOUT:   %.loc11_34.9: <bound method> = bound_method %.loc11_24, %.loc11_34.8 [template = constants.%.37]
+// CHECK:STDOUT:   %.loc11_34.10: <specific function> = specific_function %.loc11_34.9, @Convert.2(constants.%.1) [template = constants.%.38]
+// CHECK:STDOUT:   %int.convert_checked.loc11_34.2: init %i32 = call %.loc11_34.10(%.loc11_24) [template = constants.%.39]
+// CHECK:STDOUT:   %.loc11_34.11: init %i32 = converted %.loc11_24, %int.convert_checked.loc11_34.2 [template = constants.%.39]
+// CHECK:STDOUT:   %.loc11_34.12: ref %i32 = class_element_access %v.var, element1
+// CHECK:STDOUT:   %.loc11_34.13: init %i32 = initialize_from %.loc11_34.11 to %.loc11_34.12 [template = constants.%.39]
+// CHECK:STDOUT:   %.loc11_34.14: init %Base = class_init (<error>, %.loc11_34.7, %.loc11_34.13), %v.var [template = <error>]
+// CHECK:STDOUT:   %.loc11_35: init %Base = converted %.loc11_34.1, %.loc11_34.14 [template = <error>]
+// CHECK:STDOUT:   assign %v.var, %.loc11_35
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT: