Index: exceptiontransform.py
===================================================================
--- exceptiontransform.py	(revision 45847)
+++ exceptiontransform.py	(working copy)
@@ -283,6 +283,12 @@
             v_exc_type = self.gen_getfield('exc_type', llops)
             var_no_exc = self.gen_isnull(v_exc_type, llops)
 
+        # a hint that the backend can use for branch prediction
+        hints = {'expected': True}
+        c_hints = Constant(hints, lltype.Void)
+        var_no_exc = llops.genop('hint', [var_no_exc, c_hints],
+                                 resulttype = lltype.Bool)
+
         block.operations.extend(llops)
         
         block.exitswitch = var_no_exc
Index: c/src/support.h
===================================================================
--- c/src/support.h	(revision 45847)
+++ c/src/support.h	(working copy)
@@ -45,6 +45,12 @@
 #  define RPyAssert(x, msg)   /* nothing */
 #endif
 
+#ifdef __GNUC__
+#  define RPyHintExpected        __builtin_expect
+#else
+#  define RPyHintExpected(x, y)  (x)
+#endif
+
 #ifdef _RPyListOfString_New     /*  :-(  */
 #  define HAVE_RPY_LIST_OF_STRING
 #endif
Index: c/funcgen.py
===================================================================
--- c/funcgen.py	(revision 45847)
+++ c/funcgen.py	(working copy)
@@ -600,6 +600,13 @@
 
     def OP_HINT(self, op):
         hints = op.args[1].value
+        if 'expected' in hints:
+            # a hint for gcc.  only works for ints or bools
+            if isinstance(hints['expected'], int):
+                return '%s = RPyHintExpected(%s, %d);' % (
+                    self.expr(op.result),
+                    self.expr(op.args[0]),
+                    hints['expected'])
         return '%s\t/* hint: %r */' % (self.OP_SAME_AS(op), hints)
 
     def OP_KEEPALIVE(self, op): # xxx what should be the sematics consequences of this