Issue #2183: Simplify and optimize bytecode for list comprehensions.
diff --git a/Doc/library/dis.rst b/Doc/library/dis.rst
index 84a0c25..e9cbb13 100644
--- a/Doc/library/dis.rst
+++ b/Doc/library/dis.rst
@@ -463,9 +463,11 @@
address to jump to (which should be a ``FOR_ITER`` instruction).
-.. opcode:: LIST_APPEND ()
+.. opcode:: LIST_APPEND (i)
- Calls ``list.append(TOS1, TOS)``. Used to implement list comprehensions.
+ Calls ``list.append(TOS[-i], TOS)``. Used to implement list comprehensions.
+ While the appended value is popped off, the list object remains on the
+ stack so that it is available for further iterations of the loop.
.. opcode:: LOAD_LOCALS ()
diff --git a/Include/opcode.h b/Include/opcode.h
index 9f20b56..5e6fba0 100644
--- a/Include/opcode.h
+++ b/Include/opcode.h
@@ -22,7 +22,6 @@
#define UNARY_INVERT 15
-#define LIST_APPEND 18
#define BINARY_POWER 19
#define BINARY_MULTIPLY 20
@@ -89,6 +88,7 @@
#define DELETE_NAME 91 /* "" */
#define UNPACK_SEQUENCE 92 /* Number of sequence items */
#define FOR_ITER 93
+#define LIST_APPEND 94
#define STORE_ATTR 95 /* Index in name list */
#define DELETE_ATTR 96 /* "" */
diff --git a/Lib/compiler/pycodegen.py b/Lib/compiler/pycodegen.py
index 61b9fe9..5d5dca0 100644
--- a/Lib/compiler/pycodegen.py
+++ b/Lib/compiler/pycodegen.py
@@ -570,16 +570,10 @@
self.nextBlock(end)
# list comprehensions
- __list_count = 0
-
def visitListComp(self, node):
self.set_lineno(node)
# setup list
- tmpname = "$list%d" % self.__list_count
- self.__list_count = self.__list_count + 1
self.emit('BUILD_LIST', 0)
- self.emit('DUP_TOP')
- self._implicitNameOp('STORE', tmpname)
stack = []
for i, for_ in zip(range(len(node.quals)), node.quals):
@@ -591,9 +585,8 @@
self.visit(if_, cont)
stack.insert(0, (start, cont, anchor))
- self._implicitNameOp('LOAD', tmpname)
self.visit(node.expr)
- self.emit('LIST_APPEND')
+ self.emit('LIST_APPEND', len(node.quals) + 1)
for start, cont, anchor in stack:
if cont:
@@ -604,9 +597,6 @@
self.nextBlock(skip_one)
self.emit('JUMP_ABSOLUTE', start)
self.startBlock(anchor)
- self._implicitNameOp('DELETE', tmpname)
-
- self.__list_count = self.__list_count - 1
def visitListCompFor(self, node):
start = self.newBlock()
diff --git a/Lib/opcode.py b/Lib/opcode.py
index cee5057..d41383b 100644
--- a/Lib/opcode.py
+++ b/Lib/opcode.py
@@ -58,7 +58,6 @@
def_op('UNARY_INVERT', 15)
-def_op('LIST_APPEND', 18)
def_op('BINARY_POWER', 19)
def_op('BINARY_MULTIPLY', 20)
def_op('BINARY_DIVIDE', 21)
@@ -128,7 +127,7 @@
name_op('DELETE_NAME', 91) # ""
def_op('UNPACK_SEQUENCE', 92) # Number of tuple items
jrel_op('FOR_ITER', 93)
-
+def_op('LIST_APPEND', 94)
name_op('STORE_ATTR', 95) # Index in name list
name_op('DELETE_ATTR', 96) # ""
name_op('STORE_GLOBAL', 97) # ""
diff --git a/Lib/test/test_dis.py b/Lib/test/test_dis.py
index fd508a9..6fa437b 100644
--- a/Lib/test/test_dis.py
+++ b/Lib/test/test_dis.py
@@ -54,29 +54,25 @@
dis_bug1333982 = """\
%-4d 0 LOAD_CONST 1 (0)
- 3 JUMP_IF_TRUE 41 (to 47)
+ 3 JUMP_IF_TRUE 33 (to 39)
6 POP_TOP
7 LOAD_GLOBAL 0 (AssertionError)
10 BUILD_LIST 0
- 13 DUP_TOP
- 14 STORE_FAST 1 (_[1])
- 17 LOAD_FAST 0 (x)
- 20 GET_ITER
- >> 21 FOR_ITER 13 (to 37)
- 24 STORE_FAST 2 (s)
- 27 LOAD_FAST 1 (_[1])
- 30 LOAD_FAST 2 (s)
- 33 LIST_APPEND
- 34 JUMP_ABSOLUTE 21
- >> 37 DELETE_FAST 1 (_[1])
+ 13 LOAD_FAST 0 (x)
+ 16 GET_ITER
+ >> 17 FOR_ITER 12 (to 32)
+ 20 STORE_FAST 1 (s)
+ 23 LOAD_FAST 1 (s)
+ 26 LIST_APPEND 2
+ 29 JUMP_ABSOLUTE 17
- %-4d 40 LOAD_CONST 2 (1)
- 43 BINARY_ADD
- 44 RAISE_VARARGS 2
- >> 47 POP_TOP
+ %-4d >> 32 LOAD_CONST 2 (1)
+ 35 BINARY_ADD
+ 36 RAISE_VARARGS 2
+ >> 39 POP_TOP
- %-4d 48 LOAD_CONST 0 (None)
- 51 RETURN_VALUE
+ %-4d 40 LOAD_CONST 0 (None)
+ 43 RETURN_VALUE
"""%(bug1333982.func_code.co_firstlineno + 1,
bug1333982.func_code.co_firstlineno + 2,
bug1333982.func_code.co_firstlineno + 3)
diff --git a/Misc/NEWS b/Misc/NEWS
index 9567505..9e499ae 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
Core and Builtins
-----------------
+- Issue #2183: Simplify and optimize bytecode for list comprehensions.
+ Original patch by Neal Norwitz.
+
- Issue #4597: Fixed exception handling when the __exit__ function of a
context manager returns a value that cannot be converted to a bool.
diff --git a/Python/ceval.c b/Python/ceval.c
index bd35185..09501af 100644
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -1294,9 +1294,8 @@
case LIST_APPEND:
w = POP();
- v = POP();
+ v = stack_pointer[-oparg];
err = PyList_Append(v, w);
- Py_DECREF(v);
Py_DECREF(w);
if (err == 0) {
PREDICT(JUMP_ABSOLUTE);
diff --git a/Python/compile.c b/Python/compile.c
index 88d54ab..756a903 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -693,7 +693,7 @@
return 0;
case LIST_APPEND:
- return -2;
+ return -1;
case BINARY_POWER:
case BINARY_MULTIPLY:
@@ -2599,9 +2599,8 @@
}
static int
-compiler_listcomp_generator(struct compiler *c, PyObject *tmpname,
- asdl_seq *generators, int gen_index,
- expr_ty elt)
+compiler_listcomp_generator(struct compiler *c, asdl_seq *generators,
+ int gen_index, expr_ty elt)
{
/* generate code for the iterator, then each of the ifs,
and then write to the element */
@@ -2638,16 +2637,13 @@
}
if (++gen_index < asdl_seq_LEN(generators))
- if (!compiler_listcomp_generator(c, tmpname,
- generators, gen_index, elt))
+ if (!compiler_listcomp_generator(c, generators, gen_index, elt))
return 0;
/* only append after the last for generator */
if (gen_index >= asdl_seq_LEN(generators)) {
- if (!compiler_nameop(c, tmpname, Load))
- return 0;
VISIT(c, expr, elt);
- ADDOP(c, LIST_APPEND);
+ ADDOP_I(c, LIST_APPEND, gen_index+1);
compiler_use_next_block(c, skip);
}
@@ -2659,10 +2655,6 @@
}
ADDOP_JABS(c, JUMP_ABSOLUTE, start);
compiler_use_next_block(c, anchor);
- /* delete the temporary list name added to locals */
- if (gen_index == 1)
- if (!compiler_nameop(c, tmpname, Del))
- return 0;
return 1;
}
@@ -2670,21 +2662,10 @@
static int
compiler_listcomp(struct compiler *c, expr_ty e)
{
- identifier tmp;
- int rc = 0;
- asdl_seq *generators = e->v.ListComp.generators;
-
assert(e->kind == ListComp_kind);
- tmp = compiler_new_tmpname(c);
- if (!tmp)
- return 0;
ADDOP_I(c, BUILD_LIST, 0);
- ADDOP(c, DUP_TOP);
- if (compiler_nameop(c, tmp, Store))
- rc = compiler_listcomp_generator(c, tmp, generators, 0,
- e->v.ListComp.elt);
- Py_DECREF(tmp);
- return rc;
+ return compiler_listcomp_generator(c, e->v.ListComp.generators, 0,
+ e->v.ListComp.elt);
}
static int
diff --git a/Python/import.c b/Python/import.c
index 781bb48..40fc018 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -73,9 +73,10 @@
Python 2.5c2: 62131 (fix wrong code: for x, in ... in listcomp/genexp)
Python 2.6a0: 62151 (peephole optimizations and STORE_MAP opcode)
Python 2.6a1: 62161 (WITH_CLEANUP optimization)
+ Python 2.7a0: 62171 (optimize list comprehensions/change LIST_APPEND)
.
*/
-#define MAGIC (62161 | ((long)'\r'<<16) | ((long)'\n'<<24))
+#define MAGIC (62171 | ((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