Add string conversions for predicates and encodings.

This is just used for printing better comments in generated code.

meta/cretonne/predicates.py

@@ -65,6 +65,14 @@ class Predicate(object):
                 (p.predicate_context() for p in parts))
         assert self.context, "Incompatible predicate parts"
 
+    def __str__(self):
+        s = '{}({})'.format(
+                type(self).__name__,
+                ' ,'.join(map(str, self.parts)))
+        if self.name:
+            s = '{}={}'.format(self.name, s)
+        return s
+
     def predicate_context(self):
         return self.context
 
@@ -164,6 +172,10 @@ class FieldPredicate(object):
         self.function = function
         self.args = args
 
+    def __str__(self):
+        args = (self.field.name,) + tuple(map(str, self.args))
+        return '{}({})'.format(self.function, ', '.join(args))
+
     def predicate_context(self):
         """
         This predicate can be evaluated in the context of an instruction