Fix vm_getivar to handle module with TOO_COMPLEX shape

test/ruby/test_shapes.rb

@@ -275,6 +275,25 @@ class TestShapes < Test::Unit::TestCase
     end;
   end
 
+  def test_run_out_of_shape_for_module_ivar
+    assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
+    begin;
+      o = Object.new
+      i = 0
+      while RubyVM::Shape.shapes_available > 0
+        o.instance_variable_set(:"@i#{i}", 1)
+        i += 1
+      end
+
+      module Foo
+        @a = 1
+        @b = 2
+        assert_equal 1, @a
+        assert_equal 2, @b
+      end
+    end;
+  end
+
   def test_run_out_of_shape_for_class_cvar
     assert_separately([], "#{<<~"begin;"}\n#{<<~'end;'}")
     begin;

vm_insnhelper.c

@@ -1289,7 +1289,27 @@ vm_getivar(VALUE obj, ID id, const rb_iseq_t *iseq, IVC ic, const struct rb_call
         rb_shape_t *shape = rb_shape_get_shape_by_id(shape_id);
 
         if (shape_id == OBJ_TOO_COMPLEX_SHAPE_ID) {
-            if (!st_lookup(ROBJECT_IV_HASH(obj), id, &val)) {
+            st_table *table = NULL;
+            switch (BUILTIN_TYPE(obj)) {
+              case T_CLASS:
+              case T_MODULE:
+                table = (st_table *)RCLASS_IVPTR(obj);
+                break;
+
+              case T_OBJECT:
+                table = ROBJECT_IV_HASH(obj);
+                break;
+
+              default: {
+                struct gen_ivtbl *ivtbl;
+                if (rb_gen_ivtbl_get(obj, 0, &ivtbl)) {
+                    table = ivtbl->as.complex.table;
+                }
+                break;
+              }
+            }
+
+            if (!table || !st_lookup(table, id, &val)) {
                 val = default_value;
             }
         }