commit fd7ed407d79b797e20d0a6fe69e18f9ba9354979
Author: Raymond Hettinger <python@rcn.com>
Date:   Tue Dec 18 21:24:09 2007 +0000

    Give meaning to the oparg for BUILD_MAP:  estimated size of the dictionary.
    
    Allows dictionaries to be pre-sized (upto 255 elements) saving time lost
    to re-sizes with their attendant mallocs and re-insertions.
    
    Has zero effect on small dictionaries (5 elements or fewer), a slight
    benefit for dicts upto 22 elements (because they had to resize once
    anyway), and more benefit for dicts upto 255 elements (saving multiple
    resizes during the build-up and reducing the number of collisions on
    the first insertions).  Beyond 255 elements, there is no addional benefit.

diff --git a/Python/compile.c b/Python/compile.c
index 3b0c53fb19..36ad8a48e0 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2922,11 +2922,9 @@ compiler_visit_expr(struct compiler *c, expr_ty e)
        case IfExp_kind:
                return compiler_ifexp(c, e);
        case Dict_kind:
-               /* XXX get rid of arg? */
-               ADDOP_I(c, BUILD_MAP, 0);
                n = asdl_seq_LEN(e->v.Dict.values);
-               /* We must arrange things just right for STORE_SUBSCR.
-                  It wants the stack to look like (value) (dict) (key) */
+               ADDOP_I(c, BUILD_MAP, (n>255 ? 255 : n));
+               n = asdl_seq_LEN(e->v.Dict.values);
                for (i = 0; i < n; i++) {
                        VISIT(c, expr, 
                                (expr_ty)asdl_seq_GET(e->v.Dict.values, i));