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pytorch/torch/_dynamo/bytecode_transformation.py

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import dataclasses
import dis
import itertools
import sys
import types
from typing import Any, List, Optional
from .bytecode_analysis import (
propagate_line_nums,
remove_extra_line_nums,
stacksize_analysis,
)
@dataclasses.dataclass
class Instruction:
"""A mutable version of dis.Instruction"""
opcode: int
opname: str
arg: int
argval: Any
offset: Optional[int] = None
starts_line: Optional[int] = None
is_jump_target: bool = False
# extra fields to make modification easier:
target: Optional["Instruction"] = None
def __hash__(self):
return id(self)
def __eq__(self, other):
return id(self) == id(other)
def convert_instruction(i: dis.Instruction):
return Instruction(
i.opcode,
i.opname,
i.arg,
i.argval,
i.offset,
i.starts_line,
i.is_jump_target,
)
class _NotProvided:
pass
def create_instruction(name, arg=None, argval=_NotProvided, target=None):
if argval is _NotProvided:
argval = arg
return Instruction(
opcode=dis.opmap[name], opname=name, arg=arg, argval=argval, target=target
)
def lnotab_writer(lineno, byteno=0):
"""
Used to create typing.CodeType.co_lnotab
See https://github.com/python/cpython/blob/main/Objects/lnotab_notes.txt
This is the internal format of the line number table if Python < 3.10
"""
assert sys.version_info < (3, 10)
lnotab = []
def update(lineno_new, byteno_new):
nonlocal byteno, lineno
while byteno_new != byteno or lineno_new != lineno:
byte_offset = max(0, min(byteno_new - byteno, 255))
line_offset = max(-128, min(lineno_new - lineno, 127))
assert byte_offset != 0 or line_offset != 0
byteno += byte_offset
lineno += line_offset
lnotab.extend((byte_offset, line_offset & 0xFF))
return lnotab, update
def linetable_writer(first_lineno):
"""
Used to create typing.CodeType.co_linetable
See https://github.com/python/cpython/blob/main/Objects/lnotab_notes.txt
This is the internal format of the line number table if Python >= 3.10
"""
assert sys.version_info >= (3, 10)
linetable = []
lineno = first_lineno
lineno_delta = 0
byteno = 0
def _update(byteno_delta, lineno_delta):
while byteno_delta != 0 or lineno_delta != 0:
byte_offset = max(0, min(byteno_delta, 254))
line_offset = max(-127, min(lineno_delta, 127))
assert byte_offset != 0 or line_offset != 0
byteno_delta -= byte_offset
lineno_delta -= line_offset
linetable.extend((byte_offset, line_offset & 0xFF))
def update(lineno_new, byteno_new):
nonlocal lineno, lineno_delta, byteno
byteno_delta = byteno_new - byteno
byteno = byteno_new
_update(byteno_delta, lineno_delta)
lineno_delta = lineno_new - lineno
lineno = lineno_new
def end(total_bytes):
_update(total_bytes - byteno, lineno_delta)
return linetable, update, end
def assemble(instructions: List[Instruction], firstlineno):
"""Do the opposite of dis.get_instructions()"""
code = []
if sys.version_info < (3, 10):
lnotab, update_lineno = lnotab_writer(firstlineno)
else:
lnotab, update_lineno, end = linetable_writer(firstlineno)
for inst in instructions:
if inst.starts_line is not None:
update_lineno(inst.starts_line, len(code))
arg = inst.arg or 0
code.extend((inst.opcode, arg & 0xFF))
if sys.version_info >= (3, 11):
for _ in range(instruction_size(inst) // 2 - 1):
code.extend((0, 0))
if sys.version_info >= (3, 10):
end(len(code))
return bytes(code), bytes(lnotab)
def virtualize_jumps(instructions):
"""Replace jump targets with pointers to make editing easier"""
jump_targets = {inst.offset: inst for inst in instructions}
for inst in instructions:
if inst.opcode in dis.hasjabs or inst.opcode in dis.hasjrel:
for offset in (0, 2, 4, 6):
if jump_targets[inst.argval + offset].opcode != dis.EXTENDED_ARG:
inst.target = jump_targets[inst.argval + offset]
break
def devirtualize_jumps(instructions):
"""Fill in args for virtualized jump target after instructions may have moved"""
indexof = {id(inst): i for i, inst, in enumerate(instructions)}
jumps = set(dis.hasjabs).union(set(dis.hasjrel))
for inst in instructions:
if inst.opcode in jumps:
target = inst.target
target_index = indexof[id(target)]
for offset in (1, 2, 3):
if (
target_index >= offset
and instructions[target_index - offset].opcode == dis.EXTENDED_ARG
):
target = instructions[target_index - offset]
else:
break
if inst.opcode in dis.hasjabs:
if sys.version_info < (3, 10):
inst.arg = target.offset
else:
# arg is offset of the instruction line rather than the bytecode
# for all jabs/jrel since python 3.10
inst.arg = int(target.offset / 2)
else: # relative jump
if sys.version_info < (3, 10):
inst.arg = target.offset - inst.offset - instruction_size(inst)
else:
inst.arg = int(
(target.offset - inst.offset - instruction_size(inst)) / 2
)
inst.argval = target.offset
inst.argrepr = f"to {target.offset}"
def strip_extended_args(instructions: List[Instruction]):
instructions[:] = [i for i in instructions if i.opcode != dis.EXTENDED_ARG]
def remove_load_call_method(instructions: List[Instruction]):
"""LOAD_METHOD puts a NULL on the stack which causes issues, so remove it"""
rewrites = {"LOAD_METHOD": "LOAD_ATTR", "CALL_METHOD": "CALL_FUNCTION"}
for inst in instructions:
if inst.opname in rewrites:
inst.opname = rewrites[inst.opname]
inst.opcode = dis.opmap[inst.opname]
return instructions
def explicit_super(code: types.CodeType, instructions: List[Instruction]):
"""convert super() with no args into explict arg form"""
cell_and_free = (code.co_cellvars or tuple()) + (code.co_freevars or tuple())
output = []
for idx, inst in enumerate(instructions):
output.append(inst)
if inst.opname == "LOAD_GLOBAL" and inst.argval == "super":
nexti = instructions[idx + 1]
if nexti.opname == "CALL_FUNCTION" and nexti.arg == 0:
assert "__class__" in cell_and_free
output.append(
create_instruction(
"LOAD_DEREF", cell_and_free.index("__class__"), "__class__"
)
)
first_var = code.co_varnames[0]
if first_var in cell_and_free:
output.append(
create_instruction(
"LOAD_DEREF", cell_and_free.index(first_var), first_var
)
)
else:
output.append(create_instruction("LOAD_FAST", 0, first_var))
nexti.arg = 2
nexti.argval = 2
instructions[:] = output
def fix_extended_args(instructions: List[Instruction]):
"""Fill in correct argvals for EXTENDED_ARG ops"""
output = []
def maybe_pop_n(n):
for _ in range(n):
if output and output[-1].opcode == dis.EXTENDED_ARG:
output.pop()
for i, inst in enumerate(instructions):
if inst.opcode == dis.EXTENDED_ARG:
# Leave this instruction alone for now so we never shrink code
inst.arg = 0
elif inst.arg and inst.arg > 0xFFFFFF:
maybe_pop_n(3)
output.append(create_instruction("EXTENDED_ARG", inst.arg >> 24))
output.append(create_instruction("EXTENDED_ARG", inst.arg >> 16))
output.append(create_instruction("EXTENDED_ARG", inst.arg >> 8))
elif inst.arg and inst.arg > 0xFFFF:
maybe_pop_n(2)
output.append(create_instruction("EXTENDED_ARG", inst.arg >> 16))
output.append(create_instruction("EXTENDED_ARG", inst.arg >> 8))
elif inst.arg and inst.arg > 0xFF:
maybe_pop_n(1)
output.append(create_instruction("EXTENDED_ARG", inst.arg >> 8))
output.append(inst)
added = len(output) - len(instructions)
assert added >= 0
instructions[:] = output
return added
# from https://github.com/python/cpython/blob/v3.11.1/Include/internal/pycore_opcode.h#L41
# TODO use the actual object instead, can interface from eval_frame.c
_PYOPCODE_CACHES = {
"BINARY_SUBSCR": 4,
"STORE_SUBSCR": 1,
"UNPACK_SEQUENCE": 1,
"STORE_ATTR": 4,
"LOAD_ATTR": 4,
"COMPARE_OP": 2,
"LOAD_GLOBAL": 5,
"BINARY_OP": 1,
"LOAD_METHOD": 10,
"PRECALL": 1,
"CALL": 4,
}
def instruction_size(inst):
if sys.version_info >= (3, 11):
return 2 * (_PYOPCODE_CACHES.get(dis.opname[inst.opcode], 0) + 1)
return 2
def check_offsets(instructions):
offset = 0
for inst in instructions:
assert inst.offset == offset
offset += instruction_size(inst)
def update_offsets(instructions):
offset = 0
for inst in instructions:
inst.offset = offset
offset += instruction_size(inst)
def debug_bytes(*args):
index = range(max(map(len, args)))
result = []
for arg in (
[index] + list(args) + [[int(a != b) for a, b in zip(args[-1], args[-2])]]
):
result.append(" ".join(f"{x:03}" for x in arg))
return "bytes mismatch\n" + "\n".join(result)
def debug_checks(code):
"""Make sure our assembler produces same bytes as we start with"""
dode = transform_code_object(code, lambda x, y: None, safe=True)
assert code.co_code == dode.co_code, debug_bytes(code.co_code, dode.co_code)
assert code.co_lnotab == dode.co_lnotab, debug_bytes(code.co_lnotab, dode.co_lnotab)
HAS_LOCAL = set(dis.haslocal)
HAS_NAME = set(dis.hasname)
def fix_vars(instructions: List[Instruction], code_options):
varnames = {name: idx for idx, name in enumerate(code_options["co_varnames"])}
names = {name: idx for idx, name in enumerate(code_options["co_names"])}
for i in range(len(instructions)):
if instructions[i].opcode in HAS_LOCAL:
instructions[i].arg = varnames[instructions[i].argval]
elif instructions[i].opcode in HAS_NAME:
instructions[i].arg = names[instructions[i].argval]
def transform_code_object(code, transformations, safe=False):
# Python 3.11 changes to code keys are not fully documented.
# See https://github.com/python/cpython/blob/3.11/Objects/clinic/codeobject.c.h#L24
# for new format.
keys = ["co_argcount"]
if sys.version_info >= (3, 8):
keys.append("co_posonlyargcount")
keys.extend(
[
"co_kwonlyargcount",
"co_nlocals",
"co_stacksize",
"co_flags",
"co_code",
"co_consts",
"co_names",
"co_varnames",
"co_filename",
"co_name",
]
)
if sys.version_info >= (3, 11):
keys.append("co_qualname")
keys.append("co_firstlineno")
if sys.version_info >= (3, 10):
keys.append("co_linetable")
else:
keys.append("co_lnotab")
if sys.version_info >= (3, 11):
# not documented, but introduced in https://github.com/python/cpython/issues/84403
keys.append("co_exceptiontable")
keys.extend(
[
"co_freevars",
"co_cellvars",
]
)
code_options = {k: getattr(code, k) for k in keys}
assert len(code_options["co_varnames"]) == code_options["co_nlocals"]
instructions = cleaned_instructions(code, safe)
propagate_line_nums(instructions)
transformations(instructions, code_options)
fix_vars(instructions, code_options)
dirty = True
while dirty:
update_offsets(instructions)
devirtualize_jumps(instructions)
# this pass might change offsets, if so we need to try again
dirty = fix_extended_args(instructions)
remove_extra_line_nums(instructions)
bytecode, lnotab = assemble(instructions, code_options["co_firstlineno"])
if sys.version_info < (3, 10):
code_options["co_lnotab"] = lnotab
else:
code_options["co_linetable"] = lnotab
code_options["co_code"] = bytecode
code_options["co_nlocals"] = len(code_options["co_varnames"])
code_options["co_stacksize"] = stacksize_analysis(instructions)
assert set(keys) - {"co_posonlyargcount"} == set(code_options.keys()) - {
"co_posonlyargcount"
}
if sys.version_info >= (3, 11):
# generated code doesn't contain exceptions, so leave exception table empty
code_options["co_exceptiontable"] = b""
return types.CodeType(*[code_options[k] for k in keys])
def cleaned_instructions(code, safe=False):
instructions = list(map(convert_instruction, dis.get_instructions(code)))
check_offsets(instructions)
virtualize_jumps(instructions)
strip_extended_args(instructions)
if not safe:
remove_load_call_method(instructions)
explicit_super(code, instructions)
return instructions
_unique_id_counter = itertools.count()
def unique_id(name):
return f"{name}_{next(_unique_id_counter)}"
def is_generator(code: types.CodeType):
co_generator = 0x20
return (code.co_flags & co_generator) > 0
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