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bpo-38328: Speed up the creation time of constant set literals. #16878

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bpo-38328: Speed up the creation time of constant set literals. #16878

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e79e0a8
Fold constant list literals into frozensets.
brandtbucher Oct 22, 2019
ed747fc
📜🤖 Added by blurb_it.
blurb-it[bot] Oct 22, 2019
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2019-10-22-00-55-25.bpo-38328.pW0jsL.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Sped up the creation time of constant :class:`set` literals. Patch by Brandt Bucher.
24 changes: 22 additions & 2 deletions Python/peephole.c
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Expand Up @@ -126,11 +126,12 @@ copy_op_arg(_Py_CODEUNIT *codestr, Py_ssize_t i, unsigned char op,
The consts table must still be in list form so that the
new constant (c1, c2, ... cn) can be appended.
Called with codestr pointing to the first LOAD_CONST.
If frozenset is nonzero, do the same thing with BUILD_SET and a frozenset.
*/
static Py_ssize_t
fold_tuple_on_constants(_Py_CODEUNIT *codestr, Py_ssize_t codelen,
Py_ssize_t c_start, Py_ssize_t opcode_end,
PyObject *consts, int n)
PyObject *consts, int n, int frozenset)
{
/* Pre-conditions */
assert(PyList_CheckExact(consts));
Expand Down Expand Up @@ -161,6 +162,15 @@ fold_tuple_on_constants(_Py_CODEUNIT *codestr, Py_ssize_t codelen,
}
#endif

if (frozenset) {
PyObject *tmp = newconst;
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I'm pretty sure Py_SETREF() should be used here instead of this temporary variable.

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Is Py_SETREF(newconst, PyFrozenSet_New(newconst)) really clearer and safer? I can add it if you think so, but I personally don’t...

newconst = PyFrozenSet_New(tmp);
Py_DECREF(tmp);
if (!newconst) {
return -1;
}
}

/* Append folded constant onto consts */
if (PyList_Append(consts, newconst)) {
Py_DECREF(newconst);
Expand Down Expand Up @@ -321,16 +331,26 @@ PyCode_Optimize(PyObject *code, PyObject* consts, PyObject *names,
break;

/* Try to fold tuples of constants.
Sets of constants are loaded as frozensets and unpacked.
Skip over BUILD_SEQN 1 UNPACK_SEQN 1.
Replace BUILD_SEQN 2 UNPACK_SEQN 2 with ROT2.
Replace BUILD_SEQN 3 UNPACK_SEQN 3 with ROT3 ROT2. */
case BUILD_TUPLE:
case BUILD_SET:
j = get_arg(codestr, i);
int is_tuple = opcode == BUILD_TUPLE;
if (!is_tuple && j <= 1) {
break;
}
if (j > 0 && lastlc >= j) {
h = lastn_const_start(codestr, op_start, j);
if (ISBASICBLOCK(blocks, h, op_start)) {
h = fold_tuple_on_constants(codestr, codelen,
h, i+1, consts, j);
h, i+is_tuple, consts, j,
!is_tuple);
if (!is_tuple && h >= 0) {
codestr[i] = PACKOPARG(BUILD_SET_UNPACK, 1);
}
break;
}
}
Expand Down