Speed-up dictionary constructor by about 10%.

New opcode, STORE_MAP saves the compiler from awkward stack manipulations
and specializes for dicts using PyDict_SetItem instead of PyObject_SetItem.

Old disassembly:
              0 BUILD_MAP                0
              3 DUP_TOP
              4 LOAD_CONST               1 (1)
              7 ROT_TWO
              8 LOAD_CONST               2 ('x')
             11 STORE_SUBSCR
             12 DUP_TOP
             13 LOAD_CONST               3 (2)
             16 ROT_TWO
             17 LOAD_CONST               4 ('y')
             20 STORE_SUBSCR

New disassembly:
              0 BUILD_MAP                0
              3 LOAD_CONST               1 (1)
              6 LOAD_CONST               2 ('x')
              9 STORE_MAP
             10 LOAD_CONST               3 (2)
             13 LOAD_CONST               4 ('y')
             16 STORE_MAP

Include/opcode.h

@@ -45,6 +45,7 @@ extern "C" {
 #define DELETE_SLICE	50
 /* Also uses 51-53 */
 
+#define STORE_MAP	54
 #define INPLACE_ADD	55
 #define INPLACE_SUBTRACT	56
 #define INPLACE_MULTIPLY	57

Lib/opcode.py

@@ -85,6 +85,7 @@ def jabs_op(name, op):
 def_op('DELETE_SLICE+2', 52)
 def_op('DELETE_SLICE+3', 53)
 
+def_op('STORE_MAP', 54)
 def_op('INPLACE_ADD', 55)
 def_op('INPLACE_SUBTRACT', 56)
 def_op('INPLACE_MULTIPLY', 57)

Python/ceval.c

@@ -2002,6 +2002,18 @@ PyEval_EvalFrameEx(PyFrameObject *f, int throwflag)
 			if (x != NULL) continue;
 			break;
 
+		case STORE_MAP:
+			w = TOP();     /* key */
+			u = SECOND();  /* value */
+			v = THIRD();   /* dict */
+			STACKADJ(-2);
+			assert (PyDict_CheckExact(v));
+			err = PyDict_SetItem(v, w, u);  /* v[w] = u */
+			Py_DECREF(u);
+			Py_DECREF(w);
+			if (err == 0) continue;
+			break;
+
 		case LOAD_ATTR:
 			w = GETITEM(names, oparg);
 			v = TOP();

Python/compile.c

@@ -729,6 +729,8 @@ opcode_stack_effect(int opcode, int oparg)
 			return -1;
 		case STORE_SUBSCR:
 			return -3;
+		case STORE_MAP:
+			return -2;
 		case DELETE_SUBSCR:
 			return -2;
 
@@ -2926,13 +2928,11 @@ compiler_visit_expr(struct compiler *c, expr_ty e)
 		/* We must arrange things just right for STORE_SUBSCR.
 		   It wants the stack to look like (value) (dict) (key) */
 		for (i = 0; i < n; i++) {
-			ADDOP(c, DUP_TOP);
 			VISIT(c, expr, 
 				(expr_ty)asdl_seq_GET(e->v.Dict.values, i));
-			ADDOP(c, ROT_TWO);
 			VISIT(c, expr, 
 				(expr_ty)asdl_seq_GET(e->v.Dict.keys, i));
-			ADDOP(c, STORE_SUBSCR);
+			ADDOP(c, STORE_MAP);
 		}
 		break;
 	case ListComp_kind:

Python/import.c

@@ -66,10 +66,10 @@ extern time_t PyOS_GetLastModificationTime(char *, FILE *);
        Python 2.5c1: 62121 (fix wrong lnotab with for loops and
        			    storing constants that should have been removed)
        Python 2.5c2: 62131 (fix wrong code: for x, in ... in listcomp/genexp)
-       Python 2.6a0: 62141 (peephole optimizations)
+       Python 2.6a0: 62151 (peephole optimizations and STORE_MAP opcode)
 .
 */
-#define MAGIC (62141 | ((long)'\r'<<16) | ((long)'\n'<<24))
+#define MAGIC (62151 | ((long)'\r'<<16) | ((long)'\n'<<24))
 
 /* Magic word as global; note that _PyImport_Init() can change the
    value of this global to accommodate for alterations of how the