[mono][interp] Implement tailcalls (#59799)

* [interp] Fix opcode dump

* [interp] Implement tailcalls

Before this commit we supported tailcalls only for calls to the same method. Tailcalls are implemented by copying the call arguments to the start of the stack space, followed by replacing of the current executing method.

* Re-enable test

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

@@ -3447,8 +3447,33 @@ interp_exec_method (InterpFrame *frame, ThreadContext *context, FrameClauseArgs
 			LOCAL_VAR (ip [1], gint64) = READ64 (ip + 2); /* note union usage */
 			ip += 6;
 			MINT_IN_BREAK;
+		MINT_IN_CASE(MINT_TAILCALL)
+		MINT_IN_CASE(MINT_TAILCALL_VIRT)
 		MINT_IN_CASE(MINT_JMP) {
-			InterpMethod *new_method = (InterpMethod*)frame->imethod->data_items [ip [1]];
+			gboolean is_tailcall = *ip != MINT_JMP;
+			InterpMethod *new_method;
+
+			if (is_tailcall) {
+				guint16 params_offset = ip [1];
+				guint16 params_size = ip [3];
+
+				// Copy the params to their location at the start of the frame
+				memmove (frame->stack, (guchar*)frame->stack + params_offset, params_size);
+				new_method = (InterpMethod*)frame->imethod->data_items [ip [2]];
+
+				if (*ip == MINT_TAILCALL_VIRT) {
+					gint16 slot = (gint16)ip [4];
+					MonoObject *this_arg = LOCAL_VAR (0, MonoObject*);
+					new_method = get_virtual_method_fast (new_method, this_arg->vtable, slot);
+					if (m_class_is_valuetype (this_arg->vtable->klass) && m_class_is_valuetype (new_method->method->klass)) {
+						/* unbox */
+						gpointer unboxed = mono_object_unbox_internal (this_arg);
+						LOCAL_VAR (0, gpointer) = unboxed;
+					}
+				}
+			} else {
+				new_method = (InterpMethod*)frame->imethod->data_items [ip [1]];
+			}
 
 			if (frame->imethod->prof_flags & MONO_PROFILER_CALL_INSTRUMENTATION_TAIL_CALL)
 				MONO_PROFILER_RAISE (method_tail_call, (frame->imethod->method, new_method->method));

src/mono/mono/mini/interp/mintops.def

@@ -670,6 +670,8 @@ OPDEF(MINT_CALLI_NAT_DYNAMIC, "calli.nat.dynamic", 5, 1, 2, MintOpMethodToken)
 OPDEF(MINT_CALLI_NAT_FAST, "calli.nat.fast", 7, 1, 2, MintOpMethodToken)
 OPDEF(MINT_CALL_VARARG, "call.vararg", 6, 1, 1, MintOpMethodToken)
 OPDEF(MINT_CALLRUN, "callrun", 5, 1, 1, MintOpNoArgs)
+OPDEF(MINT_TAILCALL, "tailcall", 4, 0, 1, MintOpMethodToken)
+OPDEF(MINT_TAILCALL_VIRT, "tailcall.virt", 5, 0, 1, MintOpMethodToken)
 
 OPDEF(MINT_ICALL_V_V, "mono_icall_v_v", 3, 0, 1, MintOpShortInt)
 OPDEF(MINT_ICALL_V_P, "mono_icall_v_p", 4, 1, 1, MintOpShortInt)

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

@@ -1424,6 +1424,7 @@ dump_interp_ins_data (InterpInst *ins, gint32 ins_offset, const guint16 *data, g
 			target = ins_offset + *(gint16*)(data + 1);
 			g_string_append_printf (str, " %u, IR_%04x", *(guint16*)data, target);
 		}
+		break;
 	case MintOpPair2:
 		g_string_append_printf (str, " %u <- %u, %u <- %u", data [0], data [1], data [2], data [3]);
 		break;
@@ -3141,6 +3142,24 @@ interp_emit_arg_conv (TransformData *td, MonoMethodSignature *csignature)
 		emit_convert (td, &arg_start [i], csignature->params [i]);
 }
 
+static gint16
+get_virt_method_slot (MonoMethod *method)
+{
+	if (mono_class_is_interface (method->klass))
+		return (gint16)(-2 * MONO_IMT_SIZE + mono_method_get_imt_slot (method));
+	else
+		return (gint16)mono_method_get_vtable_slot (method);
+}
+
+static int*
+create_call_args (TransformData *td, int num_args)
+{
+	int *call_args = (int*) mono_mempool_alloc (td->mempool, (num_args + 1) * sizeof (int));
+	for (int i = 0; i < num_args; i++)
+		call_args [i] = td->sp [i].local;
+	call_args [num_args] = -1;
+	return call_args;
+}
 /* Return FALSE if error, including inline failure */
 static gboolean
 interp_transform_call (TransformData *td, MonoMethod *method, MonoMethod *target_method, MonoGenericContext *generic_context, MonoClass *constrained_class, gboolean readonly, MonoError *error, gboolean check_visibility, gboolean save_last_error, gboolean tailcall)
@@ -3149,7 +3168,6 @@ interp_transform_call (TransformData *td, MonoMethod *method, MonoMethod *target
 	MonoMethodSignature *csignature;
 	int is_virtual = *td->ip == CEE_CALLVIRT;
 	int calli = *td->ip == CEE_CALLI || *td->ip == CEE_MONO_CALLI_EXTRA_ARG;
-	int i;
 	guint32 res_size = 0;
 	int op = -1;
 	int native = 0;
@@ -3300,26 +3318,44 @@ interp_transform_call (TransformData *td, MonoMethod *method, MonoMethod *target
 	}
 
 	CHECK_STACK (td, csignature->param_count + csignature->hasthis);
-	if (tailcall && !td->gen_sdb_seq_points && !calli && op == -1 && (!is_virtual || (target_method->flags & METHOD_ATTRIBUTE_VIRTUAL) == 0) &&
+	if (tailcall && !td->gen_sdb_seq_points && !calli && op == -1 &&
 		(target_method->flags & METHOD_ATTRIBUTE_PINVOKE_IMPL) == 0 && 
 		(target_method->iflags & METHOD_IMPL_ATTRIBUTE_INTERNAL_CALL) == 0 &&
 		!(target_method->iflags & METHOD_IMPL_ATTRIBUTE_NOINLINING)) {
 		(void)mono_class_vtable_checked (target_method->klass, error);
 		return_val_if_nok (error, FALSE);
 
-		if (method == target_method && *(td->ip + 5) == CEE_RET && !(csignature->hasthis && m_class_is_valuetype (target_method->klass))) {
+		if (*(td->ip + 5) == CEE_RET) {
 			if (td->inlined_method)
 				return FALSE;
 
 			if (td->verbose_level)
 				g_print ("Optimize tail call of %s.%s\n", m_class_get_name (target_method->klass), target_method->name);
 
-			for (i = csignature->param_count - 1 + !!csignature->hasthis; i >= 0; --i)
-				store_arg (td, i);
+			int num_args = csignature->param_count + !!csignature->hasthis;
+			td->sp -= num_args;
+			guint32 params_stack_size = get_stack_size (td->sp, num_args);
+
+			int *call_args = create_call_args (td, num_args);
+
+			if (is_virtual) {
+				interp_add_ins (td, MINT_CKNULL);
+				interp_ins_set_sreg (td->last_ins, td->sp->local);
+				set_simple_type_and_local (td, td->sp, td->sp->type);
+				interp_ins_set_dreg (td->last_ins, td->sp->local);
+
+				interp_add_ins (td, MINT_TAILCALL_VIRT);
+				td->last_ins->data [2] = get_virt_method_slot (target_method);
+			} else {
+				interp_add_ins (td, MINT_TAILCALL);
+			}
+			interp_ins_set_sreg (td->last_ins, MINT_CALL_ARGS_SREG);
+			td->last_ins->data [0] = get_data_item_index (td, mono_interp_get_imethod (target_method, error));
+			return_val_if_nok (error, FALSE);
+			td->last_ins->data [1] = params_stack_size;
+			td->last_ins->flags |= INTERP_INST_FLAG_CALL;
+			td->last_ins->info.call_args = call_args;
 
-			interp_add_ins (td, MINT_BR);
-			// We are branching to the beginning of the method
-			td->last_ins->info.target_bb = td->entry_bb;
 			int in_offset = td->ip - td->il_code;
 			if (interp_ip_in_cbb (td, in_offset + 5))
 				++td->ip; /* gobble the CEE_RET if it isn't branched to */				
@@ -3375,10 +3411,7 @@ interp_transform_call (TransformData *td, MonoMethod *method, MonoMethod *target
 	td->sp -= num_args;
 	guint32 params_stack_size = get_stack_size (td->sp, num_args);
 
-	int *call_args = (int*) mono_mempool_alloc (td->mempool, (num_args + 1) * sizeof (int));
-	for (int i = 0; i < num_args; i++)
-		call_args [i] = td->sp [i].local;
-	call_args [num_args] = -1;
+	int *call_args = create_call_args (td, num_args);
 
 	// We overwrite it with the return local, save it for future use
 	if (csignature->param_count || csignature->hasthis)
@@ -3517,10 +3550,7 @@ interp_transform_call (TransformData *td, MonoMethod *method, MonoMethod *target
 				td->last_ins->data [2] = params_stack_size;
 			} else if (is_virtual) {
 				interp_add_ins (td, MINT_CALLVIRT_FAST);
-				if (mono_class_is_interface (target_method->klass))
-					td->last_ins->data [1] = -2 * MONO_IMT_SIZE + mono_method_get_imt_slot (target_method);
-				else
-					td->last_ins->data [1] = mono_method_get_vtable_slot (target_method);
+				td->last_ins->data [1] = get_virt_method_slot (target_method);
 			} else if (is_virtual) {
 				interp_add_ins (td, MINT_CALLVIRT);
 			} else {

src/tests/issues.targets

@@ -1805,9 +1805,6 @@
         <ExcludeList Include = "$(XunitTestBinBase)/JIT/IL_Conformance/Old/Conformance_Base/div_r8/**">
             <Issue>https://github.com/dotnet/runtime/issues/54375</Issue>
         </ExcludeList>
-        <ExcludeList Include = "$(XunitTestBinBase)/JIT/Directed/tailcall/tailcall/**">
-            <Issue>https://github.com/dotnet/runtime/issues/54374</Issue>
-        </ExcludeList>
         <ExcludeList Include = "$(XunitTestBinBase)/JIT/Methodical/Invoke/deep/_il_reldeep1/**">
             <Issue>needs triage</Issue>
         </ExcludeList>