Incorporate header files and compiler flags into object cache hash

Ensure that code is recompiled when one of our custom headers is changed or the compiler flags are modified.

pystencils/cpu/cpujit.py

@@ -205,10 +205,23 @@ def read_config():
     if config['cache']['object_cache'] is not False:
         config['cache']['object_cache'] = os.path.expanduser(config['cache']['object_cache']).format(pid=os.getpid())
 
-        if config['cache']['clear_cache_on_start']:
+        clear_cache = False
+        cache_status_file = os.path.join(config['cache']['object_cache'], 'last_config.json')
+        if os.path.exists(cache_status_file):
+            # check if compiler config has changed
+            last_config = json.load(open(cache_status_file, 'r'))
+            if set(last_config.items()) != set(config['compiler'].items()):
+                clear_cache = True
+            else:
+                for key in last_config.keys():
+                    if last_config[key] != config['compiler'][key]:
+                        clear_cache = True
+
+        if config['cache']['clear_cache_on_start'] or clear_cache:
             shutil.rmtree(config['cache']['object_cache'], ignore_errors=True)
 
         create_folder(config['cache']['object_cache'], False)
+        json.dump(config['compiler'], open(cache_status_file, 'w'), indent=4)
 
     if config['compiler']['os'] == 'windows':
         from pystencils.cpu.msvc_detection import get_environment