[Polly] Revert changes to isl Python code

This partially reverts b605dab,
dropping the changes to isl. This is an external library, so
we shouldn't modify it unless strictly necessary.

polly/lib/External/isl/interface/python.cc

@@ -347,7 +347,7 @@ static void print_persistent_callback_failure_check(int indent,
 		printf(fmt, 0);
 		printf(", '%s') and ", callback_name.c_str());
 		printf(fmt, 0);
-		printf(".%s['exc_info'] is not None:\n", callback_name.c_str());
+		printf(".%s['exc_info'] != None:\n", callback_name.c_str());
 		print_indent(indent, "    exc_info = ");
 		printf(fmt, 0);
 		printf(".%s['exc_info'][0]\n", callback_name.c_str());

polly/lib/External/isl/libisl-gdb.py

@@ -70,7 +70,7 @@ def invoke(self, arg, from_tty):
         arg = gdb.parse_and_eval(arg)
         printer = str_lookup_function(arg)
 
-        if printer is None:
+        if printer == None:
             print("No isl printer for this type")
             return
 
@@ -90,7 +90,7 @@ def str_lookup_function(val):
     lookup_tag = val.type.target()
     regex = re.compile("^isl_(.*)$")
 
-    if lookup_tag is None:
+    if lookup_tag == None:
         return None
 
     m = regex.match(str(lookup_tag))

polly/lib/External/isl/python/isl.py.top

@@ -3,7 +3,7 @@ from ctypes import *
 from ctypes.util import find_library
 
 isl_dyld_library_path = os.environ.get('ISL_DYLD_LIBRARY_PATH')
-if isl_dyld_library_path is not None:
+if isl_dyld_library_path != None:
     os.environ['DYLD_LIBRARY_PATH'] =  isl_dyld_library_path
 try:
     isl = cdll.LoadLibrary(isl_dlname)
@@ -29,7 +29,7 @@ class Context:
 
     @staticmethod
     def getDefaultInstance():
-        if Context.defaultInstance is None:
+        if Context.defaultInstance == None:
             Context.defaultInstance = Context()
         return Context.defaultInstance