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478a1c09c4
cpython/Python/optimizer_analysis.c
mpage f978fb4f8d
gh-115999: Refactor LOAD_GLOBAL specializations to avoid reloading {globals, builtins} keys (gh-124953) 
Each of the `LOAD_GLOBAL` specializations is implemented roughly as:

1. Load keys version.
2. Load cached keys version.
3. Deopt if (1) and (2) don't match.
4. Load keys.
5. Load cached index into keys.
6. Load object from (4) at offset from (5).

This is not thread-safe in free-threaded builds; the keys object may be replaced
in between steps (3) and (4).

This change refactors the specializations to avoid reloading the keys object and
instead pass the keys object from guards to be consumed by downstream uops.
2024-10-09 15:18:25 +00:00

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#ifdef _Py_TIER2
/*
* This file contains the support code for CPython's uops optimizer.
* It also performs some simple optimizations.
* It performs a traditional data-flow analysis[1] over the trace of uops.
* Using the information gained, it chooses to emit, or skip certain instructions
* if possible.
*
* [1] For information on data-flow analysis, please see
* https://clang.llvm.org/docs/DataFlowAnalysisIntro.html
*
* */
#include "Python.h"
#include "opcode.h"
#include "pycore_dict.h"
#include "pycore_interp.h"
#include "pycore_opcode_metadata.h"
#include "pycore_opcode_utils.h"
#include "pycore_pystate.h" // _PyInterpreterState_GET()
#include "pycore_uop_metadata.h"
#include "pycore_dict.h"
#include "pycore_long.h"
#include "pycore_optimizer.h"
#include "pycore_object.h"
#include "pycore_dict.h"
#include "pycore_function.h"
#include "pycore_uop_metadata.h"
#include "pycore_uop_ids.h"
#include "pycore_range.h"
#include <stdarg.h>
#include <stdbool.h>
#include <stdint.h>
#include <stddef.h>
#ifdef Py_DEBUG
extern const char *_PyUOpName(int index);
extern void _PyUOpPrint(const _PyUOpInstruction *uop);
static const char *const DEBUG_ENV = "PYTHON_OPT_DEBUG";
static inline int get_lltrace(void) {
char *uop_debug = Py_GETENV(DEBUG_ENV);
int lltrace = 0;
if (uop_debug != NULL && *uop_debug >= '0') {
lltrace = *uop_debug - '0'; // TODO: Parse an int and all that
}
return lltrace;
}
#define DPRINTF(level, ...) \
if (get_lltrace() >= (level)) { printf(__VA_ARGS__); }
#else
#define DPRINTF(level, ...)
#endif
static int
get_mutations(PyObject* dict) {
assert(PyDict_CheckExact(dict));
PyDictObject *d = (PyDictObject *)dict;
return (d->_ma_watcher_tag >> DICT_MAX_WATCHERS) & ((1 << DICT_WATCHED_MUTATION_BITS)-1);
}
static void
increment_mutations(PyObject* dict) {
assert(PyDict_CheckExact(dict));
PyDictObject *d = (PyDictObject *)dict;
d->_ma_watcher_tag += (1 << DICT_MAX_WATCHERS);
}
/* The first two dict watcher IDs are reserved for CPython,
* so we don't need to check that they haven't been used */
#define BUILTINS_WATCHER_ID 0
#define GLOBALS_WATCHER_ID 1
#define TYPE_WATCHER_ID 0
static int
globals_watcher_callback(PyDict_WatchEvent event, PyObject* dict,
PyObject* key, PyObject* new_value)
{
RARE_EVENT_STAT_INC(watched_globals_modification);
assert(get_mutations(dict) < _Py_MAX_ALLOWED_GLOBALS_MODIFICATIONS);
_Py_Executors_InvalidateDependency(_PyInterpreterState_GET(), dict, 1);
increment_mutations(dict);
PyDict_Unwatch(GLOBALS_WATCHER_ID, dict);
return 0;
}
static int
type_watcher_callback(PyTypeObject* type)
{
_Py_Executors_InvalidateDependency(_PyInterpreterState_GET(), type, 1);
PyType_Unwatch(TYPE_WATCHER_ID, (PyObject *)type);
return 0;
}
static PyObject *
convert_global_to_const(_PyUOpInstruction *inst, PyObject *obj)
{
assert(inst->opcode == _LOAD_GLOBAL_MODULE || inst->opcode == _LOAD_GLOBAL_BUILTINS || inst->opcode == _LOAD_ATTR_MODULE);
assert(PyDict_CheckExact(obj));
PyDictObject *dict = (PyDictObject *)obj;
assert(dict->ma_keys->dk_kind == DICT_KEYS_UNICODE);
PyDictUnicodeEntry *entries = DK_UNICODE_ENTRIES(dict->ma_keys);
assert(inst->operand <= UINT16_MAX);
if ((int)inst->operand >= dict->ma_keys->dk_nentries) {
return NULL;
}
PyObject *res = entries[inst->operand].me_value;
if (res == NULL) {
return NULL;
}
if (_Py_IsImmortal(res)) {
inst->opcode = (inst->oparg & 1) ? _LOAD_CONST_INLINE_BORROW_WITH_NULL : _LOAD_CONST_INLINE_BORROW;
}
else {
inst->opcode = (inst->oparg & 1) ? _LOAD_CONST_INLINE_WITH_NULL : _LOAD_CONST_INLINE;
}
inst->operand = (uint64_t)res;
return res;
}
static int
incorrect_keys(_PyUOpInstruction *inst, PyObject *obj)
{
if (!PyDict_CheckExact(obj)) {
return 1;
}
PyDictObject *dict = (PyDictObject *)obj;
if (dict->ma_keys->dk_version != inst->operand) {
return 1;
}
return 0;
}
static int
check_next_uop(_PyUOpInstruction *buffer, int size, int pc, uint16_t expected)
{
if (pc + 1 >= size) {
DPRINTF(1, "Cannot rewrite %s at pc %d: buffer too small\n",
_PyOpcode_uop_name[buffer[pc].opcode], pc);
return 0;
}
uint16_t next_opcode = buffer[pc + 1].opcode;
if (next_opcode != expected) {
DPRINTF(1,
"Cannot rewrite %s at pc %d: unexpected next opcode %s, "
"expected %s\n",
_PyOpcode_uop_name[buffer[pc].opcode], pc,
_PyOpcode_uop_name[next_opcode], _PyOpcode_uop_name[expected]);
return 0;
}
return 1;
}
/* Returns 1 if successfully optimized
* 0 if the trace is not suitable for optimization (yet)
* -1 if there was an error. */
static int
remove_globals(_PyInterpreterFrame *frame, _PyUOpInstruction *buffer,
int buffer_size, _PyBloomFilter *dependencies)
{
PyInterpreterState *interp = _PyInterpreterState_GET();
PyObject *builtins = frame->f_builtins;
if (builtins != interp->builtins) {
OPT_STAT_INC(remove_globals_builtins_changed);
return 1;
}
PyObject *globals = frame->f_globals;
PyFunctionObject *function = _PyFrame_GetFunction(frame);
assert(PyFunction_Check(function));
assert(function->func_builtins == builtins);
assert(function->func_globals == globals);
uint32_t function_version = _PyFunction_GetVersionForCurrentState(function);
/* In order to treat globals as constants, we need to
* know that the globals dict is the one we expected, and
* that it hasn't changed
* In order to treat builtins as constants, we need to
* know that the builtins dict is the one we expected, and
* that it hasn't changed and that the global dictionary's
* keys have not changed */
/* These values represent stacks of booleans (one bool per bit).
* Pushing a frame shifts left, popping a frame shifts right. */
uint32_t function_checked = 0;
uint32_t builtins_watched = 0;
uint32_t globals_watched = 0;
uint32_t prechecked_function_version = 0;
if (interp->dict_state.watchers[GLOBALS_WATCHER_ID] == NULL) {
interp->dict_state.watchers[GLOBALS_WATCHER_ID] = globals_watcher_callback;
}
if (interp->type_watchers[TYPE_WATCHER_ID] == NULL) {
interp->type_watchers[TYPE_WATCHER_ID] = type_watcher_callback;
}
for (int pc = 0; pc < buffer_size; pc++) {
_PyUOpInstruction *inst = &buffer[pc];
int opcode = inst->opcode;
switch(opcode) {
case _GUARD_BUILTINS_VERSION_PUSH_KEYS:
if (incorrect_keys(inst, builtins)) {
OPT_STAT_INC(remove_globals_incorrect_keys);
return 0;
}
if (interp->rare_events.builtin_dict >= _Py_MAX_ALLOWED_BUILTINS_MODIFICATIONS) {
continue;
}
if (!check_next_uop(buffer, buffer_size, pc,
_LOAD_GLOBAL_BUILTINS_FROM_KEYS)) {
continue;
}
if ((builtins_watched & 1) == 0) {
PyDict_Watch(BUILTINS_WATCHER_ID, builtins);
builtins_watched |= 1;
}
if (function_checked & 1) {
buffer[pc].opcode = NOP;
}
else {
buffer[pc].opcode = _CHECK_FUNCTION;
buffer[pc].operand = function_version;
function_checked |= 1;
}
// We're no longer pushing the builtins keys; rewrite the
// instruction that consumed the keys to load them from the
// frame.
buffer[pc + 1].opcode = _LOAD_GLOBAL_BUILTINS;
break;
case _GUARD_GLOBALS_VERSION:
case _GUARD_GLOBALS_VERSION_PUSH_KEYS:
if (incorrect_keys(inst, globals)) {
OPT_STAT_INC(remove_globals_incorrect_keys);
return 0;
}
uint64_t watched_mutations = get_mutations(globals);
if (watched_mutations >= _Py_MAX_ALLOWED_GLOBALS_MODIFICATIONS) {
continue;
}
if (opcode == _GUARD_GLOBALS_VERSION_PUSH_KEYS &&
!check_next_uop(buffer, buffer_size, pc,
_LOAD_GLOBAL_MODULE_FROM_KEYS)) {
continue;
}
if ((globals_watched & 1) == 0) {
PyDict_Watch(GLOBALS_WATCHER_ID, globals);
_Py_BloomFilter_Add(dependencies, globals);
globals_watched |= 1;
}
if (function_checked & 1) {
buffer[pc].opcode = NOP;
}
else {
buffer[pc].opcode = _CHECK_FUNCTION;
buffer[pc].operand = function_version;
function_checked |= 1;
}
if (opcode == _GUARD_GLOBALS_VERSION_PUSH_KEYS) {
// We're no longer pushing the globals keys; rewrite the
// instruction that consumed the keys to load them from the
// frame.
buffer[pc + 1].opcode = _LOAD_GLOBAL_MODULE;
}
break;
case _LOAD_GLOBAL_BUILTINS:
if (function_checked & globals_watched & builtins_watched & 1) {
convert_global_to_const(inst, builtins);
}
break;
case _LOAD_GLOBAL_MODULE:
if (function_checked & globals_watched & 1) {
convert_global_to_const(inst, globals);
}
break;
case _PUSH_FRAME:
{
builtins_watched <<= 1;
globals_watched <<= 1;
function_checked <<= 1;
uint64_t operand = buffer[pc].operand;
if (operand == 0 || (operand & 1)) {
// It's either a code object or NULL, so bail
return 1;
}
PyFunctionObject *func = (PyFunctionObject *)operand;
if (func == NULL) {
return 1;
}
assert(PyFunction_Check(func));
function_version = func->func_version;
if (prechecked_function_version == function_version) {
function_checked |= 1;
}
prechecked_function_version = 0;
globals = func->func_globals;
builtins = func->func_builtins;
if (builtins != interp->builtins) {
OPT_STAT_INC(remove_globals_builtins_changed);
return 1;
}
break;
}
case _RETURN_VALUE:
{
builtins_watched >>= 1;
globals_watched >>= 1;
function_checked >>= 1;
uint64_t operand = buffer[pc].operand;
if (operand == 0 || (operand & 1)) {
// It's either a code object or NULL, so bail
return 1;
}
PyFunctionObject *func = (PyFunctionObject *)operand;
if (func == NULL) {
return 1;
}
assert(PyFunction_Check(func));
function_version = func->func_version;
globals = func->func_globals;
builtins = func->func_builtins;
break;
}
case _CHECK_FUNCTION_EXACT_ARGS:
prechecked_function_version = (uint32_t)buffer[pc].operand;
break;
default:
if (is_terminator(inst)) {
return 1;
}
break;
}
}
return 0;
}
#define STACK_LEVEL() ((int)(stack_pointer - ctx->frame->stack))
#define STACK_SIZE() ((int)(ctx->frame->stack_len))
#define WITHIN_STACK_BOUNDS() \
(STACK_LEVEL() >= 0 && STACK_LEVEL() <= STACK_SIZE())
#define GETLOCAL(idx) ((ctx->frame->locals[idx]))
#define REPLACE_OP(INST, OP, ARG, OPERAND) \
INST->opcode = OP; \
INST->oparg = ARG; \
INST->operand = OPERAND;
/* Shortened forms for convenience, used in optimizer_bytecodes.c */
#define sym_is_not_null _Py_uop_sym_is_not_null
#define sym_is_const _Py_uop_sym_is_const
#define sym_get_const _Py_uop_sym_get_const
#define sym_new_unknown _Py_uop_sym_new_unknown
#define sym_new_not_null _Py_uop_sym_new_not_null
#define sym_new_type _Py_uop_sym_new_type
#define sym_is_null _Py_uop_sym_is_null
#define sym_new_const _Py_uop_sym_new_const
#define sym_new_null _Py_uop_sym_new_null
#define sym_has_type _Py_uop_sym_has_type
#define sym_get_type _Py_uop_sym_get_type
#define sym_matches_type _Py_uop_sym_matches_type
#define sym_matches_type_version _Py_uop_sym_matches_type_version
#define sym_set_null(SYM) _Py_uop_sym_set_null(ctx, SYM)
#define sym_set_non_null(SYM) _Py_uop_sym_set_non_null(ctx, SYM)
#define sym_set_type(SYM, TYPE) _Py_uop_sym_set_type(ctx, SYM, TYPE)
#define sym_set_type_version(SYM, VERSION) _Py_uop_sym_set_type_version(ctx, SYM, VERSION)
#define sym_set_const(SYM, CNST) _Py_uop_sym_set_const(ctx, SYM, CNST)
#define sym_is_bottom _Py_uop_sym_is_bottom
#define sym_truthiness _Py_uop_sym_truthiness
#define frame_new _Py_uop_frame_new
#define frame_pop _Py_uop_frame_pop
static int
optimize_to_bool(
_PyUOpInstruction *this_instr,
_Py_UOpsContext *ctx,
_Py_UopsSymbol *value,
_Py_UopsSymbol **result_ptr)
{
if (sym_matches_type(value, &PyBool_Type)) {
REPLACE_OP(this_instr, _NOP, 0, 0);
*result_ptr = value;
return 1;
}
int truthiness = sym_truthiness(value);
if (truthiness >= 0) {
PyObject *load = truthiness ? Py_True : Py_False;
REPLACE_OP(this_instr, _POP_TOP_LOAD_CONST_INLINE_BORROW, 0, (uintptr_t)load);
*result_ptr = sym_new_const(ctx, load);
return 1;
}
return 0;
}
static void
eliminate_pop_guard(_PyUOpInstruction *this_instr, bool exit)
{
REPLACE_OP(this_instr, _POP_TOP, 0, 0);
if (exit) {
REPLACE_OP((this_instr+1), _EXIT_TRACE, 0, 0);
this_instr[1].target = this_instr->target;
}
}
/* _PUSH_FRAME/_RETURN_VALUE's operand can be 0, a PyFunctionObject *, or a
* PyCodeObject *. Retrieve the code object if possible.
*/
static PyCodeObject *
get_code(_PyUOpInstruction *op)
{
assert(op->opcode == _PUSH_FRAME || op->opcode == _RETURN_VALUE || op->opcode == _RETURN_GENERATOR);
PyCodeObject *co = NULL;
uint64_t operand = op->operand;
if (operand == 0) {
return NULL;
}
if (operand & 1) {
co = (PyCodeObject *)(operand & ~1);
}
else {
PyFunctionObject *func = (PyFunctionObject *)operand;
assert(PyFunction_Check(func));
co = (PyCodeObject *)func->func_code;
}
assert(PyCode_Check(co));
return co;
}
static PyCodeObject *
get_code_with_logging(_PyUOpInstruction *op)
{
PyCodeObject *co = NULL;
uint64_t push_operand = op->operand;
if (push_operand & 1) {
co = (PyCodeObject *)(push_operand & ~1);
DPRINTF(3, "code=%p ", co);
assert(PyCode_Check(co));
}
else {
PyFunctionObject *func = (PyFunctionObject *)push_operand;
DPRINTF(3, "func=%p ", func);
if (func == NULL) {
DPRINTF(3, "\n");
DPRINTF(1, "Missing function\n");
return NULL;
}
co = (PyCodeObject *)func->func_code;
DPRINTF(3, "code=%p ", co);
}
return co;
}
/* 1 for success, 0 for not ready, cannot error at the moment. */
static int
optimize_uops(
PyCodeObject *co,
_PyUOpInstruction *trace,
int trace_len,
int curr_stacklen,
_PyBloomFilter *dependencies
)
{
_Py_UOpsContext context;
_Py_UOpsContext *ctx = &context;
uint32_t opcode = UINT16_MAX;
int curr_space = 0;
int max_space = 0;
_PyUOpInstruction *first_valid_check_stack = NULL;
_PyUOpInstruction *corresponding_check_stack = NULL;
_Py_uop_abstractcontext_init(ctx);
_Py_UOpsAbstractFrame *frame = _Py_uop_frame_new(ctx, co, curr_stacklen, NULL, 0);
if (frame == NULL) {
return -1;
}
ctx->curr_frame_depth++;
ctx->frame = frame;
ctx->done = false;
ctx->out_of_space = false;
ctx->contradiction = false;
_PyUOpInstruction *this_instr = NULL;
for (int i = 0; !ctx->done; i++) {
assert(i < trace_len);
this_instr = &trace[i];
int oparg = this_instr->oparg;
opcode = this_instr->opcode;
_Py_UopsSymbol **stack_pointer = ctx->frame->stack_pointer;
#ifdef Py_DEBUG
if (get_lltrace() >= 3) {
printf("%4d abs: ", (int)(this_instr - trace));
_PyUOpPrint(this_instr);
printf(" ");
}
#endif
switch (opcode) {
#include "optimizer_cases.c.h"
default:
DPRINTF(1, "\nUnknown opcode in abstract interpreter\n");
Py_UNREACHABLE();
}
assert(ctx->frame != NULL);
DPRINTF(3, " stack_level %d\n", STACK_LEVEL());
ctx->frame->stack_pointer = stack_pointer;
assert(STACK_LEVEL() >= 0);
}
if (ctx->out_of_space) {
DPRINTF(3, "\n");
DPRINTF(1, "Out of space in abstract interpreter\n");
}
if (ctx->contradiction) {
// Attempted to push a "bottom" (contradiction) symbol onto the stack.
// This means that the abstract interpreter has hit unreachable code.
// We *could* generate an _EXIT_TRACE or _FATAL_ERROR here, but hitting
// bottom indicates type instability, so we are probably better off
// retrying later.
DPRINTF(3, "\n");
DPRINTF(1, "Hit bottom in abstract interpreter\n");
_Py_uop_abstractcontext_fini(ctx);
return 0;
}
/* Either reached the end or cannot optimize further, but there
* would be no benefit in retrying later */
_Py_uop_abstractcontext_fini(ctx);
if (first_valid_check_stack != NULL) {
assert(first_valid_check_stack->opcode == _CHECK_STACK_SPACE);
assert(max_space > 0);
assert(max_space <= INT_MAX);
assert(max_space <= INT32_MAX);
first_valid_check_stack->opcode = _CHECK_STACK_SPACE_OPERAND;
first_valid_check_stack->operand = max_space;
}
return trace_len;
error:
DPRINTF(3, "\n");
DPRINTF(1, "Encountered error in abstract interpreter\n");
if (opcode <= MAX_UOP_ID) {
OPT_ERROR_IN_OPCODE(opcode);
}
_Py_uop_abstractcontext_fini(ctx);
return -1;
}
static int
remove_unneeded_uops(_PyUOpInstruction *buffer, int buffer_size)
{
/* Remove _SET_IP and _CHECK_VALIDITY where possible.
* _SET_IP is needed if the following instruction escapes or
* could error. _CHECK_VALIDITY is needed if the previous
* instruction could have escaped. */
int last_set_ip = -1;
bool may_have_escaped = true;
for (int pc = 0; pc < buffer_size; pc++) {
int opcode = buffer[pc].opcode;
switch (opcode) {
case _START_EXECUTOR:
may_have_escaped = false;
break;
case _SET_IP:
buffer[pc].opcode = _NOP;
last_set_ip = pc;
break;
case _CHECK_VALIDITY:
if (may_have_escaped) {
may_have_escaped = false;
}
else {
buffer[pc].opcode = _NOP;
}
break;
case _CHECK_VALIDITY_AND_SET_IP:
if (may_have_escaped) {
may_have_escaped = false;
buffer[pc].opcode = _CHECK_VALIDITY;
}
else {
buffer[pc].opcode = _NOP;
}
last_set_ip = pc;
break;
case _POP_TOP:
{
_PyUOpInstruction *last = &buffer[pc-1];
while (last->opcode == _NOP) {
last--;
}
if (last->opcode == _LOAD_CONST_INLINE ||
last->opcode == _LOAD_CONST_INLINE_BORROW ||
last->opcode == _LOAD_FAST ||
last->opcode == _COPY
) {
last->opcode = _NOP;
buffer[pc].opcode = _NOP;
}
if (last->opcode == _REPLACE_WITH_TRUE) {
last->opcode = _NOP;
}
break;
}
case _JUMP_TO_TOP:
case _EXIT_TRACE:
case _DYNAMIC_EXIT:
return pc + 1;
default:
{
/* _PUSH_FRAME doesn't escape or error, but it
* does need the IP for the return address */
bool needs_ip = opcode == _PUSH_FRAME;
if (_PyUop_Flags[opcode] & HAS_ESCAPES_FLAG) {
needs_ip = true;
may_have_escaped = true;
}
if (needs_ip && last_set_ip >= 0) {
if (buffer[last_set_ip].opcode == _CHECK_VALIDITY) {
buffer[last_set_ip].opcode = _CHECK_VALIDITY_AND_SET_IP;
}
else {
assert(buffer[last_set_ip].opcode == _NOP);
buffer[last_set_ip].opcode = _SET_IP;
}
last_set_ip = -1;
}
}
}
}
Py_UNREACHABLE();
}
// 0 - failure, no error raised, just fall back to Tier 1
// -1 - failure, and raise error
// > 0 - length of optimized trace
int
_Py_uop_analyze_and_optimize(
_PyInterpreterFrame *frame,
_PyUOpInstruction *buffer,
int length,
int curr_stacklen,
_PyBloomFilter *dependencies
)
{
OPT_STAT_INC(optimizer_attempts);
int err = remove_globals(frame, buffer, length, dependencies);
if (err <= 0) {
return err;
}
length = optimize_uops(
_PyFrame_GetCode(frame), buffer,
length, curr_stacklen, dependencies);
if (length <= 0) {
return length;
}
length = remove_unneeded_uops(buffer, length);
assert(length > 0);
OPT_STAT_INC(optimizer_successes);
return length;
}
#endif /* _Py_TIER2 */
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