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cpython/Python/optimizer_analysis.c

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/*
* This file contains the support code for CPython's uops redundancy eliminator.
* 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 "cpython/optimizer.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>
// Holds locals, stack, locals, stack ... co_consts (in that order)
#define MAX_ABSTRACT_INTERP_SIZE 4096
#define OVERALLOCATE_FACTOR 5
#define TY_ARENA_SIZE (UOP_MAX_TRACE_LENGTH * OVERALLOCATE_FACTOR)
// Need extras for root frame and for overflow frame (see TRACE_STACK_PUSH())
#define MAX_ABSTRACT_FRAME_DEPTH (TRACE_STACK_SIZE + 2)
#ifdef Py_DEBUG
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
// Flags for below.
#define KNOWN 1 << 0
#define TRUE_CONST 1 << 1
#define IS_NULL 1 << 2
#define NOT_NULL 1 << 3
typedef struct {
int flags;
PyTypeObject *typ;
// constant propagated value (might be NULL)
PyObject *const_val;
} _Py_UOpsSymType;
typedef struct _Py_UOpsAbstractFrame {
// Max stacklen
int stack_len;
int locals_len;
_Py_UOpsSymType **stack_pointer;
_Py_UOpsSymType **stack;
_Py_UOpsSymType **locals;
} _Py_UOpsAbstractFrame;
typedef struct ty_arena {
int ty_curr_number;
int ty_max_number;
_Py_UOpsSymType arena[TY_ARENA_SIZE];
} ty_arena;
// Tier 2 types meta interpreter
typedef struct _Py_UOpsAbstractInterpContext {
PyObject_HEAD
// The current "executing" frame.
_Py_UOpsAbstractFrame *frame;
_Py_UOpsAbstractFrame frames[MAX_ABSTRACT_FRAME_DEPTH];
int curr_frame_depth;
// Arena for the symbolic types.
ty_arena t_arena;
_Py_UOpsSymType **n_consumed;
_Py_UOpsSymType **limit;
_Py_UOpsSymType *locals_and_stack[MAX_ABSTRACT_INTERP_SIZE];
} _Py_UOpsAbstractInterpContext;
static inline _Py_UOpsSymType* sym_new_unknown(_Py_UOpsAbstractInterpContext *ctx);
// 0 on success, -1 on error.
static _Py_UOpsAbstractFrame *
ctx_frame_new(
_Py_UOpsAbstractInterpContext *ctx,
PyCodeObject *co,
_Py_UOpsSymType **localsplus_start,
int n_locals_already_filled,
int curr_stackentries
)
{
assert(ctx->curr_frame_depth < MAX_ABSTRACT_FRAME_DEPTH);
_Py_UOpsAbstractFrame *frame = &ctx->frames[ctx->curr_frame_depth];
frame->stack_len = co->co_stacksize;
frame->locals_len = co->co_nlocalsplus;
frame->locals = localsplus_start;
frame->stack = frame->locals + co->co_nlocalsplus;
frame->stack_pointer = frame->stack + curr_stackentries;
ctx->n_consumed = localsplus_start + (co->co_nlocalsplus + co->co_stacksize);
if (ctx->n_consumed >= ctx->limit) {
return NULL;
}
// Initialize with the initial state of all local variables
for (int i = n_locals_already_filled; i < co->co_nlocalsplus; i++) {
_Py_UOpsSymType *local = sym_new_unknown(ctx);
if (local == NULL) {
return NULL;
}
frame->locals[i] = local;
}
// Initialize the stack as well
for (int i = 0; i < curr_stackentries; i++) {
_Py_UOpsSymType *stackvar = sym_new_unknown(ctx);
if (stackvar == NULL) {
return NULL;
}
frame->stack[i] = stackvar;
}
return frame;
}
static void
abstractcontext_fini(_Py_UOpsAbstractInterpContext *ctx)
{
if (ctx == NULL) {
return;
}
ctx->curr_frame_depth = 0;
int tys = ctx->t_arena.ty_curr_number;
for (int i = 0; i < tys; i++) {
Py_CLEAR(ctx->t_arena.arena[i].const_val);
}
}
static int
abstractcontext_init(
_Py_UOpsAbstractInterpContext *ctx,
PyCodeObject *co,
int curr_stacklen,
int ir_entries
)
{
ctx->limit = ctx->locals_and_stack + MAX_ABSTRACT_INTERP_SIZE;
ctx->n_consumed = ctx->locals_and_stack;
#ifdef Py_DEBUG // Aids debugging a little. There should never be NULL in the abstract interpreter.
for (int i = 0 ; i < MAX_ABSTRACT_INTERP_SIZE; i++) {
ctx->locals_and_stack[i] = NULL;
}
#endif
// Setup the arena for sym expressions.
ctx->t_arena.ty_curr_number = 0;
ctx->t_arena.ty_max_number = TY_ARENA_SIZE;
// Frame setup
ctx->curr_frame_depth = 0;
_Py_UOpsAbstractFrame *frame = ctx_frame_new(ctx, co, ctx->n_consumed, 0, curr_stacklen);
if (frame == NULL) {
return -1;
}
ctx->curr_frame_depth++;
ctx->frame = frame;
return 0;
}
static int
ctx_frame_pop(
_Py_UOpsAbstractInterpContext *ctx
)
{
_Py_UOpsAbstractFrame *frame = ctx->frame;
ctx->n_consumed = frame->locals;
ctx->curr_frame_depth--;
assert(ctx->curr_frame_depth >= 1);
ctx->frame = &ctx->frames[ctx->curr_frame_depth - 1];
return 0;
}
// Takes a borrowed reference to const_val, turns that into a strong reference.
static _Py_UOpsSymType*
sym_new(_Py_UOpsAbstractInterpContext *ctx,
PyObject *const_val)
{
_Py_UOpsSymType *self = &ctx->t_arena.arena[ctx->t_arena.ty_curr_number];
if (ctx->t_arena.ty_curr_number >= ctx->t_arena.ty_max_number) {
OPT_STAT_INC(optimizer_failure_reason_no_memory);
DPRINTF(1, "out of space for symbolic expression type\n");
return NULL;
}
ctx->t_arena.ty_curr_number++;
self->const_val = NULL;
self->typ = NULL;
self->flags = 0;
if (const_val != NULL) {
self->const_val = Py_NewRef(const_val);
}
return self;
}
static inline void
sym_set_flag(_Py_UOpsSymType *sym, int flag)
{
sym->flags |= flag;
}
static inline void
sym_clear_flag(_Py_UOpsSymType *sym, int flag)
{
sym->flags &= (~flag);
}
static inline bool
sym_has_flag(_Py_UOpsSymType *sym, int flag)
{
return (sym->flags & flag) != 0;
}
static inline bool
sym_is_known(_Py_UOpsSymType *sym)
{
return sym_has_flag(sym, KNOWN);
}
static inline bool
sym_is_not_null(_Py_UOpsSymType *sym)
{
return (sym->flags & (IS_NULL | NOT_NULL)) == NOT_NULL;
}
static inline bool
sym_is_null(_Py_UOpsSymType *sym)
{
return (sym->flags & (IS_NULL | NOT_NULL)) == IS_NULL;
}
static inline void
sym_set_type(_Py_UOpsSymType *sym, PyTypeObject *tp)
{
assert(PyType_Check(tp));
sym->typ = tp;
sym_set_flag(sym, KNOWN);
sym_set_flag(sym, NOT_NULL);
}
static inline void
sym_set_null(_Py_UOpsSymType *sym)
{
sym_set_flag(sym, IS_NULL);
sym_set_flag(sym, KNOWN);
}
static inline _Py_UOpsSymType*
sym_new_unknown(_Py_UOpsAbstractInterpContext *ctx)
{
return sym_new(ctx,NULL);
}
static inline _Py_UOpsSymType*
sym_new_known_notnull(_Py_UOpsAbstractInterpContext *ctx)
{
_Py_UOpsSymType *res = sym_new_unknown(ctx);
if (res == NULL) {
return NULL;
}
sym_set_flag(res, NOT_NULL);
return res;
}
static inline _Py_UOpsSymType*
sym_new_known_type(_Py_UOpsAbstractInterpContext *ctx,
PyTypeObject *typ)
{
_Py_UOpsSymType *res = sym_new(ctx,NULL);
if (res == NULL) {
return NULL;
}
sym_set_type(res, typ);
return res;
}
// Takes a borrowed reference to const_val.
static inline _Py_UOpsSymType*
sym_new_const(_Py_UOpsAbstractInterpContext *ctx, PyObject *const_val)
{
assert(const_val != NULL);
_Py_UOpsSymType *temp = sym_new(
ctx,
const_val
);
if (temp == NULL) {
return NULL;
}
sym_set_type(temp, Py_TYPE(const_val));
sym_set_flag(temp, TRUE_CONST);
sym_set_flag(temp, KNOWN);
sym_set_flag(temp, NOT_NULL);
return temp;
}
static inline bool
is_const(_Py_UOpsSymType *sym)
{
return sym->const_val != NULL;
}
static inline PyObject *
get_const(_Py_UOpsSymType *sym)
{
return sym->const_val;
}
static _Py_UOpsSymType*
sym_new_null(_Py_UOpsAbstractInterpContext *ctx)
{
_Py_UOpsSymType *null_sym = sym_new_unknown(ctx);
if (null_sym == NULL) {
return NULL;
}
sym_set_null(null_sym);
return null_sym;
}
static inline bool
sym_matches_type(_Py_UOpsSymType *sym, PyTypeObject *typ)
{
assert(typ == NULL || PyType_Check(typ));
if (!sym_has_flag(sym, KNOWN)) {
return false;
}
return sym->typ == typ;
}
static inline bool
op_is_end(uint32_t opcode)
{
return opcode == _EXIT_TRACE || opcode == _JUMP_TO_TOP;
}
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
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);
increment_mutations(dict);
PyDict_Unwatch(GLOBALS_WATCHER_ID, dict);
return 0;
}
static void
global_to_const(_PyUOpInstruction *inst, PyObject *obj)
{
assert(inst->opcode == _LOAD_GLOBAL_MODULE || inst->opcode == _LOAD_GLOBAL_BUILTINS);
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);
PyObject *res = entries[inst->operand].me_value;
if (res == NULL) {
return;
}
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;
}
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) {
return 1;
}
PyObject *globals = frame->f_globals;
assert(PyFunction_Check(((PyFunctionObject *)frame->f_funcobj)));
assert(((PyFunctionObject *)frame->f_funcobj)->func_builtins == builtins);
assert(((PyFunctionObject *)frame->f_funcobj)->func_globals == globals);
/* 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 builtins_checked = 0;
uint32_t builtins_watched = 0;
uint32_t globals_checked = 0;
uint32_t globals_watched = 0;
if (interp->dict_state.watchers[GLOBALS_WATCHER_ID] == NULL) {
interp->dict_state.watchers[GLOBALS_WATCHER_ID] = globals_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)) {
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 (builtins_checked & 1) {
buffer[pc].opcode = NOP;
}
else {
buffer[pc].opcode = _CHECK_BUILTINS;
buffer[pc].operand = (uintptr_t)builtins;
builtins_checked |= 1;
}
break;
case _GUARD_GLOBALS_VERSION:
if (incorrect_keys(inst, globals)) {
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 (globals_checked & 1) {
buffer[pc].opcode = NOP;
}
else {
buffer[pc].opcode = _CHECK_GLOBALS;
buffer[pc].operand = (uintptr_t)globals;
globals_checked |= 1;
}
break;
case _LOAD_GLOBAL_BUILTINS:
if (globals_checked & builtins_checked & globals_watched & builtins_watched & 1) {
global_to_const(inst, builtins);
}
break;
case _LOAD_GLOBAL_MODULE:
if (globals_checked & globals_watched & 1) {
global_to_const(inst, globals);
}
break;
case _PUSH_FRAME:
{
globals_checked <<= 1;
globals_watched <<= 1;
builtins_checked <<= 1;
builtins_watched <<= 1;
PyFunctionObject *func = (PyFunctionObject *)buffer[pc].operand;
if (func == NULL) {
return 1;
}
assert(PyFunction_Check(func));
globals = func->func_globals;
builtins = func->func_builtins;
if (builtins != interp->builtins) {
return 1;
}
break;
}
case _POP_FRAME:
{
globals_checked >>= 1;
globals_watched >>= 1;
builtins_checked >>= 1;
builtins_watched >>= 1;
PyFunctionObject *func = (PyFunctionObject *)buffer[pc].operand;
assert(PyFunction_Check(func));
globals = func->func_globals;
builtins = func->func_builtins;
break;
}
default:
if (op_is_end(opcode)) {
return 1;
}
break;
}
}
return 0;
}
#define STACK_LEVEL() ((int)(stack_pointer - ctx->frame->stack))
#define GETLOCAL(idx) ((ctx->frame->locals[idx]))
#define REPLACE_OP(INST, OP, ARG, OPERAND) \
INST->opcode = OP; \
INST->oparg = ARG; \
INST->operand = OPERAND;
#define OUT_OF_SPACE_IF_NULL(EXPR) \
do { \
if ((EXPR) == NULL) { \
goto out_of_space; \
} \
} while (0);
#define _LOAD_ATTR_NOT_NULL \
do { \
OUT_OF_SPACE_IF_NULL(attr = sym_new_known_notnull(ctx)); \
OUT_OF_SPACE_IF_NULL(null = sym_new_null(ctx)); \
} while (0);
/* 1 for success, 0 for not ready, cannot error at the moment. */
static int
uop_redundancy_eliminator(
PyCodeObject *co,
_PyUOpInstruction *trace,
int trace_len,
int curr_stacklen
)
{
_Py_UOpsAbstractInterpContext context;
_Py_UOpsAbstractInterpContext *ctx = &context;
if (abstractcontext_init(
ctx,
co, curr_stacklen,
trace_len) < 0) {
goto out_of_space;
}
for (_PyUOpInstruction *this_instr = trace;
this_instr < trace + trace_len && !op_is_end(this_instr->opcode);
this_instr++) {
int oparg = this_instr->oparg;
uint32_t opcode = this_instr->opcode;
_Py_UOpsSymType **stack_pointer = ctx->frame->stack_pointer;
DPRINTF(3, "Abstract interpreting %s:%d ",
_PyOpcode_uop_name[opcode],
oparg);
switch (opcode) {
#include "tier2_redundancy_eliminator_cases.c.h"
default:
DPRINTF(1, "Unknown 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);
}
abstractcontext_fini(ctx);
return 1;
out_of_space:
DPRINTF(1, "Out of space in abstract interpreter\n");
abstractcontext_fini(ctx);
return 0;
error:
DPRINTF(1, "Encountered error in abstract interpreter\n");
abstractcontext_fini(ctx);
return 0;
}
static void
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 = false;
for (int pc = 0; pc < buffer_size; pc++) {
int opcode = buffer[pc].opcode;
switch (opcode) {
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 _JUMP_TO_TOP:
case _EXIT_TRACE:
return;
default:
{
bool needs_ip = false;
if (_PyUop_Flags[opcode] & HAS_ESCAPES_FLAG) {
needs_ip = true;
may_have_escaped = true;
}
if (_PyUop_Flags[opcode] & HAS_ERROR_FLAG) {
needs_ip = true;
}
if (opcode == _PUSH_FRAME) {
needs_ip = 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;
}
}
}
}
}
static void
peephole_opt(_PyInterpreterFrame *frame, _PyUOpInstruction *buffer, int buffer_size)
{
PyCodeObject *co = (PyCodeObject *)frame->f_executable;
for (int pc = 0; pc < buffer_size; pc++) {
int opcode = buffer[pc].opcode;
switch(opcode) {
case _LOAD_CONST: {
assert(co != NULL);
PyObject *val = PyTuple_GET_ITEM(co->co_consts, buffer[pc].oparg);
buffer[pc].opcode = _Py_IsImmortal(val) ? _LOAD_CONST_INLINE_BORROW : _LOAD_CONST_INLINE;
buffer[pc].operand = (uintptr_t)val;
break;
}
case _CHECK_PEP_523:
{
/* Setting the eval frame function invalidates
* all executors, so no need to check dynamically */
if (_PyInterpreterState_GET()->eval_frame == NULL) {
buffer[pc].opcode = _NOP;
}
break;
}
case _PUSH_FRAME:
case _POP_FRAME:
{
PyFunctionObject *func = (PyFunctionObject *)buffer[pc].operand;
if (func == NULL) {
co = NULL;
}
else {
assert(PyFunction_Check(func));
co = (PyCodeObject *)func->func_code;
}
break;
}
case _JUMP_TO_TOP:
case _EXIT_TRACE:
return;
}
}
}
// 0 - failure, no error raised, just fall back to Tier 1
// -1 - failure, and raise error
// 1 - optimizer success
int
_Py_uop_analyze_and_optimize(
_PyInterpreterFrame *frame,
_PyUOpInstruction *buffer,
int buffer_size,
int curr_stacklen,
_PyBloomFilter *dependencies
)
{
OPT_STAT_INC(optimizer_attempts);
int err = remove_globals(frame, buffer, buffer_size, dependencies);
if (err == 0) {
goto not_ready;
}
if (err < 0) {
goto error;
}
peephole_opt(frame, buffer, buffer_size);
err = uop_redundancy_eliminator(
(PyCodeObject *)frame->f_executable, buffer,
buffer_size, curr_stacklen);
if (err == 0) {
goto not_ready;
}
assert(err == 1);
remove_unneeded_uops(buffer, buffer_size);
OPT_STAT_INC(optimizer_successes);
return 1;
not_ready:
return 0;
error:
return -1;
}
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