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gh-126835: Move constant subscript folding to CFG (#129568)

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Move folding of constant subscription from AST optimizer to CFG.

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
This commit is contained in:
Yan Yanchii 2025-02-04 09:10:55 +01:00 • committed by GitHub
parent bb5c6875d6
commit 0664c1af9b
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6 changed files with 138 additions and 31 deletions
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82
Python/flowgraph.c
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@ -6,6 +6,7 @@
#include "pycore_compile.h"
#include "pycore_intrinsics.h"
#include "pycore_pymem.h" // _PyMem_IsPtrFreed()
#include "pycore_long.h" // _PY_IS_SMALL_INT()
#include "pycore_opcode_utils.h"
#include "pycore_opcode_metadata.h" // OPCODE_HAS_ARG, etc
@ -1443,6 +1444,84 @@ optimize_if_const_list_or_set(PyObject *const_cache, cfg_instr* inst, int n, PyO
return SUCCESS;
}
/*
Walk basic block upwards 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,
PyObject *const_cache, int *newopcode, int *newoparg)
{
if (PyLong_CheckExact(newconst)) {
int overflow;
long val = PyLong_AsLongAndOverflow(newconst, &overflow);
if (!overflow && _PY_IS_SMALL_INT(val)) {
*newopcode = LOAD_SMALL_INT;
*newoparg = val;
return SUCCESS;
}
}
*newopcode = LOAD_CONST;
*newoparg = add_const(newconst, consts, const_cache);
RETURN_IF_ERROR(*newoparg);
return SUCCESS;
}
static int
optimize_if_const_subscr(basicblock *bb, int n, PyObject *consts, PyObject *const_cache)
{
cfg_instr *subscr = &bb->b_instr[n];
assert(subscr->i_opcode == BINARY_SUBSCR);
cfg_instr *arg, *idx;
if (!find_load_const_pair(bb, n-1, &arg, &idx)) {
return SUCCESS;
}
PyObject *o, *key;
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)
{
return ERROR;
}
PyObject *newconst = PyObject_GetItem(o, key);
if (newconst == NULL) {
if (PyErr_ExceptionMatches(PyExc_KeyboardInterrupt)) {
return ERROR;
}
PyErr_Clear();
return SUCCESS;
}
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);
return SUCCESS;
}
#define VISITED (-1)
// Replace an arbitrary run of SWAPs and NOPs with an optimal one that has the
@ -1948,6 +2027,9 @@ optimize_basic_block(PyObject *const_cache, basicblock *bb, PyObject *consts)
INSTR_SET_OP0(inst, NOP);
}
break;
case BINARY_SUBSCR:
RETURN_IF_ERROR(optimize_if_const_subscr(bb, i, consts, const_cache));
break;
}
}