[issue6133] LOAD_CONST followed by LOAD_ATTR can be optimized to just be a LOAD_COST

[Raymond Hettinger]

Raymond Hettinger <rhettinger at users.sourceforge.net> added the comment:

I'm working a better patch now.  Will give to collin to review when it's
ready.  Here's a draft of the new opcode:

		TARGET(LOAD_CONST_ATTR)
			u = GETLOCAL(oparg);	/* Cached attribute or NULL */
			t = TOP();				/* t = (obj, name) where obj is constant */
			if (u != NULL) {		/* If cache is non-null, use it */
				Py_INCREF(u);
				SET_TOP(u);
				Py_DECREF(t);
				FAST_DISPATCH();
			}
			/* Cache is empty, do regular attribute lookup */
			assert(PyTuple_CheckExact(t) && Py_SIZE(t) == 2);
			v = PyTuple_GET_ITEM(t, 0);
			w = PyTuple_GET_ITEM(t, 1);
			x = PyObject_GetAttr(v, w);
			Py_DECREF(t);
			if (x != NULL) {		/* Successful lookup; cache it and return */
				SETLOCAL(oparg, x);
				Py_INCREF(x);
				SET_TOP(x);
				break;
			}
			STACKADJ(-1);			/* Attribute not found; goto err handler */
			break;

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<http://bugs.python.org/issue6133>
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