Index: ceval.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Python/ceval.c,v
retrieving revision 2.410
diff -c -r2.410 ceval.c
*** ceval.c	8 Jul 2004 01:49:00 -0000	2.410
--- ceval.c	1 Aug 2004 18:35:59 -0000
***************
*** 85,90 ****
--- 85,92 ----
  static void set_exc_info(PyThreadState *, PyObject *, PyObject *, PyObject *);
  static void reset_exc_info(PyThreadState *);
  static void format_exc_check_arg(PyObject *, char *, PyObject *);
+ static PyObject *string_concatenate(PyObject *, PyObject *,
+ 				    PyFrameObject *, unsigned char *);
  
  #define NAME_ERROR_MSG \
  	"name '%.200s' is not defined"
***************
*** 550,555 ****
--- 552,558 ----
  #define INSTR_OFFSET()	(next_instr - first_instr)
  #define NEXTOP()	(*next_instr++)
  #define NEXTARG()	(next_instr += 2, (next_instr[-1]<<8) + next_instr[-2])
+ #define PEEKARG()	((next_instr[2]<<8) + next_instr[1])
  #define JUMPTO(x)	(next_instr = first_instr + (x))
  #define JUMPBY(x)	(next_instr += (x))
  
***************
*** 580,587 ****
  #endif
  
  #define PREDICTED(op)		PRED_##op: next_instr++
! #define PREDICTED_WITH_ARG(op)	PRED_##op: oparg = (next_instr[2]<<8) + \
! 				next_instr[1]; next_instr += 3
  
  /* Stack manipulation macros */
  
--- 583,589 ----
  #endif
  
  #define PREDICTED(op)		PRED_##op: next_instr++
! #define PREDICTED_WITH_ARG(op)	PRED_##op: oparg = PEEKARG(); next_instr += 3
  
  /* Stack manipulation macros */
  
***************
*** 1066,1076 ****
--- 1068,1085 ----
  					goto slow_add;
  				x = PyInt_FromLong(i);
  			}
+ 			else if (PyString_CheckExact(v) &&
+ 				 PyString_CheckExact(w)) {
+ 				x = string_concatenate(v, w, f, next_instr);
+ 				/* string_concatenate consumed the ref to v */
+ 				goto skip_decref_vx;
+ 			}
  			else {
  			  slow_add:
  				x = PyNumber_Add(v, w);
  			}
  			Py_DECREF(v);
+ 		  skip_decref_vx:
  			Py_DECREF(w);
  			SET_TOP(x);
  			if (x != NULL) continue;
***************
*** 1261,1271 ****
--- 1270,1287 ----
  					goto slow_iadd;
  				x = PyInt_FromLong(i);
  			}
+ 			else if (PyString_CheckExact(v) &&
+ 				 PyString_CheckExact(w)) {
+ 				x = string_concatenate(v, w, f, next_instr);
+ 				/* string_concatenate consumed the ref to v */
+ 				goto skip_decref_v;
+ 			}
  			else {
  			  slow_iadd:
  				x = PyNumber_InPlaceAdd(v, w);
  			}
  			Py_DECREF(v);
+ 		  skip_decref_v:
  			Py_DECREF(w);
  			SET_TOP(x);
  			if (x != NULL) continue;
***************
*** 4189,4194 ****
--- 4205,4283 ----
  	PyErr_Format(exc, format_str, obj_str);
  }
  
+ static PyObject *
+ string_concatenate(PyObject *v, PyObject *w,
+ 		   PyFrameObject *f, unsigned char *next_instr)
+ {
+ 	/* This function implements 'variable += expr' when both arguments
+ 	   are strings. */
+ 	
+ 	if (v->ob_refcnt == 2) {
+ 		/* In the common case, there are 2 references to the value
+ 		 * stored in 'variable' when the += is performed: one on the
+ 		 * value stack (in 'v') and one still stored in the 'variable'.
+ 		 * We try to delete the variable now to reduce the refcnt to 1.
+ 		 */
+ 		switch (*next_instr) {
+ 		case STORE_FAST:
+ 		{
+ 			int oparg = PEEKARG();
+ 			PyObject **fastlocals = f->f_localsplus;
+ 			if (GETLOCAL(oparg) == v)
+ 				SETLOCAL(oparg, NULL);
+ 			break;
+ 		}
+ 		case STORE_DEREF:
+ 		{
+ 			PyObject **freevars = f->f_localsplus + f->f_nlocals;
+ 			PyObject *c = freevars[PEEKARG()];
+ 			if (PyCell_GET(c) == v)
+ 				PyCell_Set(c, NULL);
+ 			break;
+ 		}
+ 		case STORE_NAME:
+ 		{
+ 			PyObject *names = f->f_code->co_names;
+ 			PyObject *name = GETITEM(names, PEEKARG());
+ 			PyObject *locals = f->f_locals;
+ 			if (PyDict_CheckExact(locals) &&
+ 			    PyDict_GetItem(locals, name) == v) {
+ 				if (PyDict_DelItem(locals, name) != 0) {
+ 					PyErr_Clear();
+ 				}
+ 			}
+ 			break;
+ 		}
+ 		}
+ 	}
+ 
+ 	if (v->ob_refcnt == 1) {
+ 		/* Now we own the last reference to 'v', so we can resize it
+ 		 * in-place.
+ 		 */
+ 		int v_len = PyString_GET_SIZE(v);
+ 		int w_len = PyString_GET_SIZE(w);
+ 		if (_PyString_Resize(&v, v_len + w_len) != 0) {
+ 			/* XXX if _PyString_Resize() fails, 'v' has been
+ 			 * deallocated so it cannot be put back into 'variable'.
+ 			 * The MemoryError is raised when there is no value in
+ 			 * 'variable', which might (very remotely) be a cause
+ 			 * of incompatibilities.
+ 			 */
+ 			return NULL;
+ 		}
+ 		/* copy 'w' into the newly allocated area of 'v' */
+ 		memcpy(PyString_AS_STRING(v) + v_len,
+ 		       PyString_AS_STRING(w), w_len);
+ 		return v;
+ 	}
+ 	else {
+ 		/* When in-place resizing is not an option. */
+ 		PyString_Concat(&v, w);
+ 		return v;
+ 	}
+ }
+ 
  #ifdef DYNAMIC_EXECUTION_PROFILE
  
  static PyObject *