Add support for SwiftSelf<T> in Mono JIT and Interpreter (#104171)

This PR adds Mono support for SwiftSelf<T> in the Swift calling convention. This type enables the correct passing of frozen value types in instance methods in Swift.

Author: kotlarmilos

src/mono/mono/metadata/marshal.c

@@ -130,8 +130,9 @@ static GENERATE_TRY_GET_CLASS_WITH_CACHE (suppress_gc_transition_attribute, "Sys
 static GENERATE_TRY_GET_CLASS_WITH_CACHE (unmanaged_callers_only_attribute, "System.Runtime.InteropServices", "UnmanagedCallersOnlyAttribute")
 static GENERATE_TRY_GET_CLASS_WITH_CACHE (unmanaged_callconv_attribute, "System.Runtime.InteropServices", "UnmanagedCallConvAttribute")
 
-GENERATE_TRY_GET_CLASS_WITH_CACHE (swift_error, "System.Runtime.InteropServices.Swift", "SwiftError")
 GENERATE_TRY_GET_CLASS_WITH_CACHE (swift_self, "System.Runtime.InteropServices.Swift", "SwiftSelf")
+GENERATE_TRY_GET_CLASS_WITH_CACHE (swift_self_t, "System.Runtime.InteropServices.Swift", "SwiftSelf`1");
+GENERATE_TRY_GET_CLASS_WITH_CACHE (swift_error, "System.Runtime.InteropServices.Swift", "SwiftError")
 GENERATE_TRY_GET_CLASS_WITH_CACHE (swift_indirect_result, "System.Runtime.InteropServices.Swift", "SwiftIndirectResult")
 
 static gboolean type_is_blittable (MonoType *type);
@@ -3698,20 +3699,30 @@ mono_marshal_get_native_wrapper (MonoMethod *method, gboolean check_exceptions,
 
 		if (mono_method_signature_has_ext_callconv (csig, MONO_EXT_CALLCONV_SWIFTCALL)) {
 			MonoClass *swift_self = mono_class_try_get_swift_self_class ();
+			MonoClass *swift_self_t = mono_class_try_get_swift_self_t_class ();
 			MonoClass *swift_error = mono_class_try_get_swift_error_class ();
 			MonoClass *swift_indirect_result = mono_class_try_get_swift_indirect_result_class ();
 			MonoClass *swift_error_ptr = mono_class_create_ptr (m_class_get_this_arg (swift_error));
 			int swift_error_args = 0, swift_self_args = 0, swift_indirect_result_args = 0;
 			for (int i = 0; i < method->signature->param_count; ++i) {
 				MonoClass *param_klass = mono_class_from_mono_type_internal (method->signature->params [i]);
+				MonoGenericClass *param_gklass = mono_class_try_get_generic_class (param_klass);
 				if (param_klass) {
 					if (param_klass == swift_error && !m_type_is_byref (method->signature->params [i])) {
 						swift_error_args = swift_self_args = 0;
 						mono_error_set_generic_error (emitted_error, "System", "InvalidProgramException", "SwiftError argument must be passed by reference.");
 						break;
 					} else if (param_klass == swift_error || param_klass == swift_error_ptr) {
 						swift_error_args++;
-					} else if (param_klass == swift_self) {
+					} else if (param_gklass && (param_gklass->container_class == swift_self_t) && i > 0) {
+						swift_error_args = swift_self_args = 0;
+						mono_error_set_generic_error (emitted_error, "System", "InvalidProgramException", "SwiftSelf<T> must be the first argument in the signature.");
+						break;
+					} else if (param_gklass && (param_gklass->container_class == swift_self_t) && m_type_is_byref (method->signature->params [i])) {
+						swift_error_args = swift_self_args = 0;
+						mono_error_set_generic_error (emitted_error, "System", "InvalidProgramException", "Expected SwiftSelf<T> struct, got pointer/reference.");
+						break;
+					} else if (param_klass == swift_self || (param_gklass && (param_gklass->container_class == swift_self_t))) {
 						swift_self_args++;
 					} else if (param_klass == swift_indirect_result) {
 						swift_indirect_result_args++;

src/mono/mono/metadata/marshal.h

@@ -753,6 +753,7 @@ IlgenCallbacksToMono*
 mono_marshal_get_mono_callbacks_for_ilgen (void);
 
 GENERATE_TRY_GET_CLASS_WITH_CACHE_DECL (swift_self)
+GENERATE_TRY_GET_CLASS_WITH_CACHE_DECL (swift_self_t);
 GENERATE_TRY_GET_CLASS_WITH_CACHE_DECL (swift_error)
 GENERATE_TRY_GET_CLASS_WITH_CACHE_DECL (swift_indirect_result)
 

src/mono/mono/mini/interp/transform.c

@@ -3356,6 +3356,7 @@ interp_emit_swiftcall_struct_lowering (TransformData *td, MonoMethodSignature *c
 	uint32_t new_param_count = 0;
 	int align;
 	MonoClass *swift_self = mono_class_try_get_swift_self_class ();
+	MonoClass *swift_self_t = mono_class_try_get_swift_self_t_class ();
 	MonoClass *swift_error = mono_class_try_get_swift_error_class ();
 	MonoClass *swift_indirect_result = mono_class_try_get_swift_indirect_result_class ();
 	/*
@@ -3366,6 +3367,8 @@ interp_emit_swiftcall_struct_lowering (TransformData *td, MonoMethodSignature *c
 	for (int idx_param = 0; idx_param < csignature->param_count; ++idx_param) {
 		MonoType *ptype = csignature->params [idx_param];
 		MonoClass *klass = mono_class_from_mono_type_internal (ptype);
+		MonoGenericClass *gklass = mono_class_try_get_generic_class (klass);
+
 		// SwiftSelf, SwiftError, and SwiftIndirectResult are special cases where we need to preserve the class information for the codegen to handle them correctly.
 		if (mono_type_is_struct (ptype) && !(klass == swift_self || klass == swift_error || klass == swift_indirect_result)) {
 			SwiftPhysicalLowering lowered_swift_struct = mono_marshal_get_swift_physical_lowering (ptype, FALSE);
@@ -3386,8 +3389,13 @@ interp_emit_swiftcall_struct_lowering (TransformData *td, MonoMethodSignature *c
 					g_array_append_val (new_params, lowered_swift_struct.lowered_elements [idx_lowered]);
 				}
 			} else {
-				// For structs that cannot be lowered, we change the argument to byref type
-				ptype = mono_class_get_byref_type (mono_defaults.typed_reference_class);
+				// For structs that cannot be lowered, we change the argument to a pointer-like argument type.
+				// If SwiftSelf<T> can't be lowered, it should be passed in the same manner as SwiftSelf, via the context register.
+				if (gklass && (gklass->container_class == swift_self_t))
+					ptype = mono_class_get_byref_type (swift_self);
+				else
+					ptype = mono_class_get_byref_type (klass);
+
 				// Load the address of the struct
 				interp_add_ins (td, MINT_LDLOCA_S);
 				interp_ins_set_sreg (td->last_ins, sp_old_params [idx_param].var);

src/mono/mono/mini/method-to-ir.c

@@ -7533,6 +7533,7 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 				GArray *new_params = g_array_sized_new (FALSE, FALSE, sizeof (MonoType*), n);
 				uint32_t new_param_count = 0;
 				MonoClass *swift_self = mono_class_try_get_swift_self_class ();
+				MonoClass *swift_self_t = mono_class_try_get_swift_self_t_class ();
 				MonoClass *swift_error = mono_class_try_get_swift_error_class ();
 				MonoClass *swift_indirect_result = mono_class_try_get_swift_indirect_result_class ();
 				/*
@@ -7543,6 +7544,7 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 				for (int idx_param = 0; idx_param < n; ++idx_param) {
 					MonoType *ptype = fsig->params [idx_param];
 					MonoClass *klass = mono_class_from_mono_type_internal (ptype);
+					MonoGenericClass *gklass = mono_class_try_get_generic_class (klass);
 
 					// SwiftSelf, SwiftError, and SwiftIndirectResult are special cases where we need to preserve the class information for the codegen to handle them correctly.
 					if (mono_type_is_struct (ptype) && !(klass == swift_self || klass == swift_error || klass == swift_indirect_result)) {
@@ -7562,9 +7564,17 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 								++new_param_count;
 							}
 						} else {
-							// For structs that cannot be lowered, we change the argument to byref type
+							// For structs that cannot be lowered, we change the argument to a pointer-like argument type.
+							// If SwiftSelf<T> can't be lowered, it should be passed in the same manner as SwiftSelf, via the context register.
+							if (gklass && (gklass->container_class == swift_self_t)) {
+								ptype = mono_class_get_byref_type (swift_self);
+								// The ARGLOADA should be a pointer-like type.
+								struct_base_address->klass = mono_defaults.int_class;
+							} else {
+								ptype = mono_class_get_byref_type (klass);
+							}
+
 							*sp++ = struct_base_address;
-							ptype = mono_class_get_byref_type (klass);
 
 							g_array_append_val (new_params, ptype);
 							++new_param_count;

src/mono/mono/mini/mini-amd64.c

@@ -1096,8 +1096,7 @@ get_call_info (MonoMemPool *mp, MonoMethodSignature *sig)
 
 			if ((klass == swift_self || klass == swift_indirect_result) && sig->pinvoke) {
 				guint32 size = mini_type_stack_size_full (m_class_get_byval_arg (klass), NULL, sig->pinvoke && !sig->marshalling_disabled);
-				g_assert (size == 8);
-
+				g_assert (size == TARGET_SIZEOF_VOID_P);
 				ainfo->storage = ArgValuetypeInReg;
 				ainfo->pair_storage [0] = ArgInIReg;
 				ainfo->pair_storage [1] = ArgNone;

src/mono/mono/mini/mini-arm64.c

@@ -1922,8 +1922,7 @@ get_call_info (MonoMemPool *mp, MonoMethodSignature *sig)
 				guint32 align;
 				MonoType *ptype = mini_get_underlying_type (sig->params [pindex]);
 				int size = mini_type_stack_size_full (ptype, &align, cinfo->pinvoke);
-				g_assert (size == 8);
-
+				g_assert (size == TARGET_SIZEOF_VOID_P);
 				ainfo->storage = ArgVtypeInIRegs;
 				ainfo->reg = (klass == swift_self) ? ARMREG_R20 : ARMREG_R8;
 				ainfo->nregs = 1;

src/tests/Interop/Swift/SwiftSelfContext/SwiftSelfContext.cs

@@ -69,15 +69,13 @@ public struct FrozenNonEnregisteredStruct
     public static extern long SumFrozenNonEnregisteredStruct(SwiftSelf<FrozenNonEnregisteredStruct> self);
 
     [Fact]
-    [SkipOnMono("SwiftSelf<T> is not supported on Mono")]
     public unsafe static void TestSelfIsFrozenEnregisteredStruct()
     {
         long sum = SumFrozenEnregisteredStruct(new SwiftSelf<FrozenEnregisteredStruct>(new FrozenEnregisteredStruct { A = 10, B = 20 }));
         Assert.Equal(30, sum);
     }
 
     [Fact]
-    [SkipOnMono("SwiftSelf<T> is not supported on Mono")]
     public unsafe static void TestSelfIsFrozenNonEnregisteredStruct()
     {
         long sum = SumFrozenNonEnregisteredStruct(new SwiftSelf<FrozenNonEnregisteredStruct>(new FrozenNonEnregisteredStruct { A = 10, B = 20, C = 30, D = 40, E = 50 }));