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cpython/Python/optimizer_analysis.c

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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_version_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_version_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;
}
/* 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 = (PyFunctionObject *)frame->f_funcobj;
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:
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 ((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;
}
break;
case _GUARD_GLOBALS_VERSION:
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 ((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;
}
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;
}
/* 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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