diff -r 2e7aa74993f9 -r 73d1e7e4bfff src/arch/isa_parser.py
--- a/src/arch/isa_parser.py	Thu Jun 12 14:49:52 2014 -0500
+++ b/src/arch/isa_parser.py	Thu Jun 12 14:49:54 2014 -0500
@@ -1119,17 +1119,7 @@
 
         self.flags = self.operands.concatAttrLists('flags')
 
-        # Make a basic guess on the operand class (function unit type).
-        # These are good enough for most cases, and can be overridden
-        # later otherwise.
-        if 'IsStore' in self.flags:
-            self.op_class = 'MemWriteOp'
-        elif 'IsLoad' in self.flags or 'IsPrefetch' in self.flags:
-            self.op_class = 'MemReadOp'
-        elif 'IsFloating' in self.flags:
-            self.op_class = 'FloatAddOp'
-        else:
-            self.op_class = 'IntAluOp'
+        self.op_class = ""
 
         # Optional arguments are assumed to be either StaticInst flags
         # or an OpClass value.  To avoid having to import a complete
@@ -1144,6 +1134,18 @@
                 error('InstObjParams: optional arg "%s" not recognized '
                       'as StaticInst::Flag or OpClass.' % oa)
 
+        # Make a basic guess on the operand class if not set.
+        # These are good enough for most cases.
+        if not self.op_class:
+            if 'IsStore' in self.flags:
+                self.op_class = 'MemWriteOp'
+            elif 'IsLoad' in self.flags or 'IsPrefetch' in self.flags:
+                self.op_class = 'MemReadOp'
+            elif 'IsFloating' in self.flags:
+                self.op_class = 'FloatAddOp'
+            else:
+                self.op_class = 'IntAluOp'
+
         # add flag initialization to contructor here to include
         # any flags added via opt_args
         self.constructor += makeFlagConstructor(self.flags)