[mono][swift-interop] Support for Swift struct lowering in direct P/Invoke returns (#104389)

* refactor struct lowering in method-to-ir.c

* [miniJIT][ARM64] Swift struct lowering in returns

* [interp][ARM64] Swift struct lowering in returns

Interpreter support for Swift struct lowering in returns on arm64 + LLVM fallback for ArgSwiftError and ArgSwiftVtypeLoweredRet ArgStorage types.

* enable SwiftRetAbiStress tests on Mono

* [miniJIT][x64] Swift struct lowering in returns

* [interp][x64] Swift struct lowering in returns

* refactoring arm64/x64

* more refactoring x64

* swift ret buffer: r10 to rax move for VCALL

* refactoring of swift ret. buffer handlig and more

* change byref of typedref to byref of klass

* replace spaces with tabs + formatting

* [arm64] move add_return_valuetype_swiftcall
out of add_valuetype and add it to get_call_info

* [x64] refactor add_return_valuetype_swiftcall

Author: matouskozak

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

@@ -7547,34 +7547,27 @@ mono_method_to_ir (MonoCompile *cfg, MonoMethod *method, MonoBasicBlock *start_b
 					// 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);
+						// Create a new local variable to store the base address of the struct
+						MonoInst *struct_base_address =  mono_compile_create_var (cfg, mono_get_int_type (), OP_LOCAL);
+						CHECK_ARG (idx_param);
+						NEW_ARGLOADA (cfg, struct_base_address, idx_param);
+						MONO_ADD_INS (cfg->cbb, struct_base_address);
 						if (!lowered_swift_struct.by_reference) {
-							// Create a new local variable to store the base address of the struct
-							MonoInst *struct_base_address =  mono_compile_create_var (cfg, mono_get_int_type (), OP_LOCAL);
-							CHECK_ARG (idx_param);
-							NEW_ARGLOADA (cfg, struct_base_address, idx_param);
-							MONO_ADD_INS (cfg->cbb, struct_base_address);
-
+							// Load the lowered elements of the struct
 							for (uint32_t idx_lowered = 0; idx_lowered < lowered_swift_struct.num_lowered_elements; ++idx_lowered) {
-								MonoInst *lowered_arg = NULL;
-								// Load the lowered elements of the struct
-								lowered_arg = mini_emit_memory_load (cfg, lowered_swift_struct.lowered_elements [idx_lowered], struct_base_address, lowered_swift_struct.offsets [idx_lowered], 0);
+								MonoInst *lowered_arg = mini_emit_memory_load (cfg, lowered_swift_struct.lowered_elements [idx_lowered], struct_base_address, lowered_swift_struct.offsets [idx_lowered], 0);
 								*sp++ = lowered_arg;
 
-								++new_param_count;
 								g_array_append_val (new_params, lowered_swift_struct.lowered_elements [idx_lowered]);
+								++new_param_count;
 							}
 						} 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);
-							// Load the address of the struct
-							MonoInst *struct_base_address =  mono_compile_create_var (cfg, mono_get_int_type (), OP_LOCAL);
-							CHECK_ARG (idx_param);
-							NEW_ARGLOADA (cfg, struct_base_address, idx_param);
-							MONO_ADD_INS (cfg->cbb, struct_base_address);
 							*sp++ = struct_base_address;
+							ptype = mono_class_get_byref_type (klass);
 
-							++new_param_count;
 							g_array_append_val (new_params, ptype);
+							++new_param_count;
 						}
 					} else {
 						// Copy over non-struct arguments