[mono] Miscellaneous startup optimizations (dotnet#101263)

* Optimize out an unnecessary memset under g_slist_prepend
* Don't inline constructors of Exception or its descendants into interpreter method bodies

Author: kg

src/mono/mono/eglib/gslist.c

@@ -52,7 +52,8 @@ g_slist_append (GSList *list, gpointer data)
 GSList*
 g_slist_prepend (GSList *list, gpointer data)
 {
-	GSList *head = g_slist_alloc ();
+	// We don't need to zero the allocation using g_slist_alloc since we fully initialize the node
+	GSList *head = g_new (GSList, 1);
 	head->data = data;
 	head->next = list;
 

src/mono/mono/metadata/class-getters.h

@@ -48,6 +48,7 @@ MONO_CLASS_GETTER(m_class_is_interfaces_inited, gboolean, , MonoClass, interface
 MONO_CLASS_GETTER(m_class_is_simd_type, gboolean, , MonoClass, simd_type)
 MONO_CLASS_GETTER(m_class_is_has_finalize_inited, gboolean, , MonoClass, has_finalize_inited)
 MONO_CLASS_GETTER(m_class_is_fields_inited, gboolean, , MonoClass, fields_inited)
+MONO_CLASS_GETTER(m_class_is_exception_class, gboolean, , MonoClass, is_exception_class)
 MONO_CLASS_GETTER(m_class_has_failure, gboolean, , MonoClass, has_failure)
 MONO_CLASS_GETTER(m_class_has_deferred_failure, gboolean, , MonoClass, has_deferred_failure)
 MONO_CLASS_GETTER(m_class_has_weak_fields, gboolean, , MonoClass, has_weak_fields)

src/mono/mono/metadata/class-init.c

@@ -735,6 +735,17 @@ mono_class_create_from_typedef (MonoImage *image, guint32 type_token, MonoError
 		}
 	}
 
+	// compute is_exception_class, used by interp to avoid inlining exception handling code
+	if (
+		klass->parent && !m_class_is_valuetype (klass) &&
+		!m_class_is_interface (klass)
+	) {
+		if (m_class_is_exception_class (klass->parent))
+			klass->is_exception_class = 1;
+		else if (!strcmp (klass->name, "Exception") && !strcmp(klass->name_space, "System"))
+			klass->is_exception_class = 1;
+	}
+
 	mono_loader_unlock ();
 
 	MONO_PROFILER_RAISE (class_loaded, (klass));
@@ -926,6 +937,7 @@ mono_class_create_generic_inst (MonoGenericClass *gclass)
 	klass->this_arg.byref__ = TRUE;
 	klass->is_inlinearray = gklass->is_inlinearray;
 	klass->inlinearray_value = gklass->inlinearray_value;
+	klass->is_exception_class = gklass->is_exception_class;
 	klass->enumtype = gklass->enumtype;
 	klass->valuetype = gklass->valuetype;
 

src/mono/mono/metadata/class-private-definition.h

@@ -68,9 +68,8 @@ struct _MonoClass {
 	guint no_special_static_fields : 1; /* has no thread/context static fields */
 
 	guint nested_classes_inited : 1; /* Whenever nested_class is initialized */
-
-	/* next byte*/
 	guint interfaces_inited : 1; /* interfaces is initialized */
+	/* next byte*/
 	guint simd_type : 1; /* class is a simd intrinsic type */
 	guint has_finalize_inited    : 1; /* has_finalize is initialized */
 	guint fields_inited : 1; /* setup_fields () has finished */
@@ -79,6 +78,8 @@ struct _MonoClass {
 	guint has_dim_conflicts : 1; /* Class has conflicting default interface methods */
 	guint any_field_has_auto_layout : 1; /* a field in this type's layout uses auto-layout */
 	guint has_deferred_failure : 1;
+	/* next byte*/
+	guint is_exception_class : 1; /* is System.Exception or derived from it */
 
 	MonoClass  *parent;
 	MonoClass  *nested_in;

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

@@ -2907,6 +2907,9 @@ interp_method_check_inlining (TransformData *td, MonoMethod *method, MonoMethodS
 	if (g_list_find (td->dont_inline, method))
 		return FALSE;
 
+	if (m_class_is_exception_class (method->klass) && !strcmp (method->name, ".ctor"))
+		return FALSE;
+
 	return TRUE;
 }