diff -r bc702c8c3881 -r 06894dd0d0be src/arch/isa_parser.py
--- a/src/arch/isa_parser.py	Sat Apr 21 15:08:35 2012 -0500
+++ b/src/arch/isa_parser.py	Sat Apr 21 15:09:58 2012 -0500
@@ -520,7 +520,11 @@
     def makeConstructor(self):
         c = ''
         if self.is_src:
+            if self.read_condition:
+               c += '\n\tif (%s) {' % (self.read_condition)
             c += '\n\t_srcRegIdx[_numSrcRegs++] = %s;'% (self.reg_spec)
+            if self.read_condition:
+               c += '\n\t}'
         if self.is_dest:
             c += '\n\t_destRegIdx[%d] = %s;' % \
                  (self.dest_reg_idx, self.reg_spec)
@@ -532,7 +536,13 @@
         if self.read_code != None:
             return self.buildReadCode('readIntRegOperand')
         int_reg_val = 'xc->readIntRegOperand(this, srcRegIndex++)'
-        return '%s = %s;\n' % (self.base_name, int_reg_val)
+        c = ''
+        if self.read_condition:
+           c += 'if (%s) {\n' % (self.read_condition)
+        c += '%s = %s;\n' % (self.base_name, int_reg_val)
+        if self.read_condition:
+           c += '}\n'
+        return c
 
     def makeWrite(self):
         if (self.ctype == 'float' or self.ctype == 'double'):
@@ -1797,6 +1807,14 @@
             else:
                 write_code = None
             if len(val) > 7:
+                read_condition = val[7]
+            else:
+                read_condition = None
+            if len(val) > 8:
+                write_condition = val[8]
+            else:
+                write_condition = None
+            if len(val) > 9:
                 error(lineno,
                       'error: too many attributes for operand "%s"' %
                       base_cls_name)
@@ -1823,8 +1841,8 @@
                          makeList(src_flags), makeList(dest_flags))
             # Accumulate attributes of new operand class in tmp_dict
             tmp_dict = {}
-            attrList = ['reg_spec', 'flags', 'sort_pri',
-                        'read_code', 'write_code']
+            attrList = ['reg_spec', 'flags', 'sort_pri', 'read_code',
+                        'write_code', 'read_condition', 'write_condition']
             if dflt_ext:
                 dflt_ctype = self.operandTypeMap[dflt_ext]
                 attrList.extend(['dflt_ctype', 'dflt_ext'])