Do no precompute when using vi mode.

IPython/terminal/interactiveshell.py

@@ -377,12 +377,24 b' class TerminalInteractiveShell(InteractiveShell):'
         """
         Return the current layout option for the current Terminal InteractiveShell
         """
+        def get_message():
+            return PygmentsTokens(self.prompts.in_prompt_tokens())
+
+        if self.editing_mode == 'emacs':
+            # with emacs mode the prompt is (usually) static, so we call only
+            # the function once. With VI mode it can toggle between [ins] and
+            # [nor] so we can't precompute.
+            # here I'm going to favor the default keybinding which almost
+            # everybody uses to decrease CPU usage.
+            # if we have issues with users with custom Prompts we can see how to
+            # work around this.
+            get_message = get_message()
 
         return {
                 'complete_in_thread': False,
                 'lexer':IPythonPTLexer(),
                 'reserve_space_for_menu':self.space_for_menu,
-                'message': PygmentsTokens(self.prompts.in_prompt_tokens()),
+                'message': get_message,
                 'prompt_continuation': (
                     lambda width, lineno, is_soft_wrap:
                         PygmentsTokens(self.prompts.continuation_prompt_tokens(width))),