8000 gh-126835: Set location for noped out instructions after constant folding in CFG. by WolframAlph · Pull Request #130109 · python/cpython · GitHub
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gh-126835: Set location for noped out instructions after constant folding in CFG. #130109

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Merged
merged 4 commits into from
Feb 14, 2025
Merged

gh-126835: Set location for noped out instructions after constant folding in CFG. #130109

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ef68aaa
set location for noped out instructions after optimizations
WolframAlph Feb 14, 2025
0f95636
use NO_LOCATION
WolframAlph Feb 14, 2025
bdae73b
update tests
WolframAlph Feb 14, 2025
cdf427a
set location for BUILD_SET/BUILD_LIST
WolframAlph Feb 14, 2025
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set location for noped out instructions after optimizations
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@WolframAlph
WolframAlph committed Feb 14, 2025
commit ef68aaa5e7b27cc05bb434f1a8a304ca52b562f5
77 changes: 77 additions & 0 deletions Lib/test/test_peepholer.py
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Original file line number Diff line number Diff line change
Expand Up @@ -535,6 +535,83 @@ def test_folding_subscript(self):
self.assertInBytecode(code, 'BINARY_OP', argval=subscr_argval)
self.check_lnotab(code)

def test_constant_folding_reset_nop_location(self):
sources = [
"""
(-
-
-
1)
""",

"""
(1
+
2
+
3)
""",

"""
(1,
2,
3)[0]
""",

"""
[1,
2,
3]
""",

"""
{1,
2,
3}
""",

"""
1 in [
1,
2,
3
]
""",

"""
1 in {
1,
2,
3
}
""",

"""
for _ in [1,
2,
3]:
pass
""",

"""
for _ in [1,
2,
x]:
pass
""",

"""
for _ in {1,
2,
3}:
pass
"""
]

for source in sources:
code = compile(textwrap.dedent(source), '', 'single')
self.assertNotInBytecode(code, 'NOP')

def test_in_literal_list(self):
def containtest():
return x in [a, b]
Expand Down
90 changes: 33 additions & 57 deletions Python/flowgraph.c
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Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,12 @@ is_jump(cfg_instr *i)
_instr__ptr_->i_oparg = 0; \
} while (0);

#define INSTR_SET_LOC(I, LOC) \
do { \
cfg_instr *_instr__ptr_ = (I); \
_instr__ptr_->i_loc = (LOC); \
} while (0);

/***** Blocks *****/

/* Returns the offset of the next instruction in the current block's
Expand Down Expand Up @@ -1382,18 +1388,22 @@ get_constant_sequence(basicblock *bb, int start, int size,

/*
Walk basic block backwards starting from "start" and change "count" number of
non-NOP instructions to NOP's.
non-NOP instructions to NOP's and set their i_loc info to "location" if provided.
*/
static void
nop_out(basicblock *bb, int start, int count)
nop_out(basicblock *bb, int start, int count, _Py_SourceLocation *location)
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Just set the location to NO_LOCATION. Then the NOP will be discarded.

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Right, I forgot about NO_LOCATION. Thanks!

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@WolframAlph WolframAlph Feb 14, 2025 •
edited
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If we set NO_LOCATION, there is 1 test failing in test_dis.

cpython/Lib/test/test_dis.py

Lines 891 to 912 in 140e69c

dis_loop_test_quickened_code = """\
%3d RESUME_CHECK 0
%3d BUILD_LIST 0
LOAD_CONST_MORTAL 1 ((1, 2, 3))
LIST_EXTEND 1
LOAD_SMALL_INT 3
BINARY_OP 5 (*)
GET_ITER
L1: FOR_ITER_LIST 14 (to L2)
STORE_FAST 0 (i)
%3d LOAD_GLOBAL_MODULE 1 (load_test + NULL)
LOAD_FAST 0 (i)
CALL_PY_GENERAL 1
POP_TOP
JUMP_BACKWARD_{: <6} 16 (to L1)
%3d L2: END_FOR
POP_ITER
LOAD_CONST_IMMORTAL 0 (None)
RETURN_VALUE

There is a bit of a difference in emitted dis, original is (showing only diff part):

887           RESUME_CHECK             0

888           BUILD_LIST               0
              LOAD_CONST_MORTAL        1 ((1, 2, 3))
              LIST_EXTEND              1
              LOAD_SMALL_INT           3
              BINARY_OP                5 (*)
              GET_ITER
      L1:     FOR_ITER_LIST           14 (to L2)
              STORE_FAST               0 (i)

and new dis:

887           RESUME_CHECK             0
              BUILD_LIST               0
              LOAD_CONST_MORTAL        1 ((1, 2, 3))

888           LIST_EXTEND              1
              LOAD_SMALL_INT           3
              BINARY_OP                5 (*)
              GET_ITER
      L1:     FOR_ITER_LIST           14 (to L2)
              STORE_FAST               0 (i)

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Maybe we need to set the locations on the BUILD_LIST and LOAD_CONST (but don't worry about the NOPs).

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Yes, it would help. I wonder if that's cleaner than the proposed solution.

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Anyway, I've updated the PR.

{
assert(start < bb->b_iused);
for (; count > 0; start--) {
assert(start >= 0);
if (bb->b_instr[start].i_opcode == NOP) {
cfg_instr *instr = &bb->b_instr[start];
if (instr->i_opcode == NOP) {
continue;
}
INSTR_SET_OP0(&bb->b_instr[start], NOP);
INSTR_SET_OP0(instr, NOP);
if (location != NULL) {
INSTR_SET_LOC(instr, *location);
}
count--;
}
}
Expand Down Expand Up @@ -1422,8 +1432,8 @@ fold_tuple_of_constants(basicblock *bb, int n, PyObject *consts, PyObject *const
assert(PyTuple_CheckExact(newconst) && PyTuple_GET_SIZE(newconst) == seq_size);
int index = add_const(newconst, consts, const_cache);
RETURN_IF_ERROR(index);
nop_out(bb, n-1, seq_size);
INSTR_SET_OP1(&bb->b_instr[n], LOAD_CONST, index);
nop_out(bb, n-1, seq_size, &instr->i_loc);
INSTR_SET_OP1(instr, LOAD_CONST, index);
return SUCCESS;
}

Expand Down Expand Up @@ -1472,7 +1482,7 @@ optimize_lists_and_sets(basicblock *bb, int i, int nextop,
}
int index = add_const(newconst, consts, const_cache);
RETURN_IF_ERROR(index);
nop_out(bb, i-1, seq_size);
nop_out(bb, i-1, seq_size, &instr->i_loc);
if (contains_or_iter) {
INSTR_SET_OP1(instr, LOAD_CONST, index);
}
Expand All @@ -1486,33 +1496,6 @@ optimize_lists_and_sets(basicblock *bb, int i, int nextop,
return SUCCESS;
}

/*
Walk basic block backwards starting from "start" to collect instruction pair
that loads consts skipping NOP's in between.
*/
static bool
find_load_const_pair(basicblock *bb, int start, cfg_instr **first, cfg_instr **second)
{
cfg_instr *second_load_const = NULL;
while (start >= 0) {
cfg_instr *inst = &bb->b_instr[start--];
if (inst->i_opcode == NOP) {
continue;
}
if (!loads_const(inst->i_opcode)) {
return false;
}
if (second_load_const == NULL) {
second_load_const = inst;
continue;
}
*first = inst;
*second = second_load_const;
return true;
}
return false;
}

/* Determine opcode & oparg for freshly folded constant. */
static int
newop_from_folded(PyObject *newconst, PyObject *consts,
Expand All @@ -1534,27 +1517,25 @@ newop_from_folded(PyObject *newconst, PyObject *consts,
}

static int
optimize_if_const_op(basicblock *bb, int n, PyObject *consts, PyObject *const_cache)
optimize_if_const_binop(basicblock *bb, int i, PyObject *consts, PyObject *const_cache)
{
cfg_instr *subscr = &bb->b_instr[n];
assert(subscr->i_opcode == BINARY_OP);
if (subscr->i_oparg != NB_SUBSCR) {
cfg_instr *binop = &bb->b_instr[i];
assert(binop->i_opcode == BINARY_OP);
if (binop->i_oparg != NB_SUBSCR) {
/* TODO: support other binary ops */
return SUCCESS;
}
cfg_instr *arg, *idx;
if (!find_load_const_pair(bb, n-1, &arg, &idx)) {
PyObject *pair;
RETURN_IF_ERROR(get_constant_sequence(bb, i-1, 2, consts, &pair));
if (pair == NULL) {
return SUCCESS;
}
PyObject *o = NULL, *key = NULL;
if ((o = get_const_value(arg->i_opcode, arg->i_oparg, consts)) == NULL
|| (key = get_const_value(idx->i_opcode, idx->i_oparg, consts)) == NULL)
{
goto error;
}
PyObject *newconst = PyObject_GetItem(o, key);
Py_DECREF(o);
Py_DECREF(key);
assert(PyTuple_CheckExact(pair) && PyTuple_Size(pair) == 2);
PyObject *left = PyTuple_GET_ITEM(pair, 0);
PyObject *right = PyTuple_GET_ITEM(pair, 1);
assert(left != NULL && right != NULL);
PyObject *newconst = PyObject_GetItem(left, right);
Comment on lines +1535 to +1538
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Suggested change
F438
PyObject *left = PyTuple_GET_ITEM(pair, 0);
PyObject *right = PyTuple_GET_ITEM(pair, 1);
assert(left != NULL && right != NULL);
PyObject *newconst = PyObject_GetItem(left, right);
PyObject *obj = PyTuple_GET_ITEM(pair, 0);
PyObject *attr = PyTuple_GET_ITEM(pair, 1);
assert(obj != NULL && attr != NULL);
PyObject *newconst = PyObject_GetItem(obj, attr);

I this clearer?

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For subscript yes, but eventually there will be other binary ops as well. I could apply if you want.

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Ok, leave it.

Py_DECREF(pair);
if (newconst == NULL) {
if (PyErr_ExceptionMatches(PyExc_KeyboardInterrupt)) {
return ERROR;
Expand All @@ -1564,14 +1545,9 @@ optimize_if_const_op(basicblock *bb, int n, PyObject *consts, PyObject *const_ca
}
int newopcode, newoparg;
RETURN_IF_ERROR(newop_from_folded(newconst, consts, const_cache, &newopcode, &newoparg));
INSTR_SET_OP1(subscr, newopcode, newoparg);
INSTR_SET_OP0(arg, NOP);
INSTR_SET_OP0(idx, NOP);
nop_out(bb, i-1, 2, &binop->i_loc);
INSTR_SET_OP1(binop, newopcode, newoparg);
return SUCCESS;
error:
Py_XDECREF(o);
Py_XDECREF(key);
return ERROR;
}

#define VISITED (-1)
Expand Down Expand Up @@ -2072,7 +2048,7 @@ optimize_basic_block(PyObject *const_cache, basicblock *bb, PyObject *consts)
}
break;
case BINARY_OP:
RETURN_IF_ERROR(optimize_if_const_op(bb, i, consts, const_cache));
RETURN_IF_ERROR(optimize_if_const_binop(bb, i, consts, const_cache));
break;
}
}
Expand Down
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