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Do not fold a constant if a large sequence will result.

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Saves space in the presence of code like: (None,)*10000
This commit is contained in:
Raymond Hettinger 2005-01-26 12:50:05 +00:00
parent c560a00966
commit 9feb267caf
2 changed files with 19 additions and 5 deletions
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4
Lib/test/test_peepholer.py
View file

@ -129,6 +129,10 @@ class TestTranforms(unittest.TestCase):
self.assert_('(2)' in asm)
self.assert_("('b')" in asm)
# Verify that large sequences do not result from folding
asm = dis_single('a="x"*1000')
self.assert_('(1000)' in asm)
def test_elim_extra_return(self):
# RETURN LOAD_CONST None RETURN --> RETURN
def f(x):

20
Python/compile.c
View file

@ -444,12 +444,16 @@ tuple_of_constants(unsigned char *codestr, int n, PyObject *consts)
The consts table must still be in list form so that the
new constant can be appended.
Called with codestr pointing to the first LOAD_CONST.
Abandons the transformation if the folding fails (i.e. 1+'a'). */
Abandons the transformation if the folding fails (i.e. 1+'a').
If the new constant is a sequence, only folds when the size
is below a threshold value. That keeps pyc files from
becoming large in the presence of code like: (None,)*1000.
*/
static int
fold_binops_on_constants(unsigned char *codestr, PyObject *consts)
{
PyObject *newconst, *v, *w;
int len_consts, opcode;
int len_consts, opcode, size;
/* Pre-conditions */
assert(PyList_CheckExact(consts));
@ -468,8 +472,8 @@ fold_binops_on_constants(unsigned char *codestr, PyObject *consts)
newconst = PyNumber_Multiply(v, w);
break;
case BINARY_DIVIDE:
/* XXX care is needed to fold this operation statically:
the result might depend on the run-time presence of the -Qnew flag */
/* Cannot fold this operation statically since
the result can depend on the run-time presence of the -Qnew flag */
return 0;
case BINARY_TRUE_DIVIDE:
newconst = PyNumber_TrueDivide(v, w);
@ -513,6 +517,13 @@ fold_binops_on_constants(unsigned char *codestr, PyObject *consts)
PyErr_Clear();
return 0;
}
size = PyObject_Size(newconst);
if (size == -1)
PyErr_Clear();
else if (size > 20) {
Py_DECREF(newconst);
return 0;
}
/* Append folded constant into consts table */
len_consts = PyList_GET_SIZE(consts);
@ -733,7 +744,6 @@ optimize_code(PyObject *code, PyObject* consts, PyObject *names, PyObject *linen
LOAD_CONST c1 LOAD_CONST c2 BINOP --> LOAD_CONST binop(c1,c2) */
case BINARY_POWER:
case BINARY_MULTIPLY:
case BINARY_DIVIDE:
case BINARY_TRUE_DIVIDE:
case BINARY_FLOOR_DIVIDE:
case BINARY_MODULO: