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"""A flow graph representation for Python bytecode"""
import dis
import types
import sys
from compiler import misc
from compiler.consts \
import CO_OPTIMIZED, CO_NEWLOCALS, CO_VARARGS, CO_VARKEYWORDS
class FlowGraph:
def __init__(self):
self.current = self.entry = Block()
self.exit = Block("exit")
self.blocks = misc.Set()
self.blocks.add(self.entry)
self.blocks.add(self.exit)
def startBlock(self, block):
if self._debug:
if self.current:
print "end", repr(self.current)
print " next", self.current.next
print " prev", self.current.prev
print " ", self.current.get_children()
print repr(block)
self.current = block
def nextBlock(self, block=None):
# XXX think we need to specify when there is implicit transfer
# from one block to the next. might be better to represent this
# with explicit JUMP_ABSOLUTE instructions that are optimized
# out when they are unnecessary.
#
# I think this strategy works: each block has a child
# designated as "next" which is returned as the last of the
# children. because the nodes in a graph are emitted in
# reverse post order, the "next" block will always be emitted
# immediately after its parent.
# Worry: maintaining this invariant could be tricky
if block is None:
block = self.newBlock()
# Note: If the current block ends with an unconditional control
# transfer, then it is techically incorrect to add an implicit
# transfer to the block graph. Doing so results in code generation
# for unreachable blocks. That doesn't appear to be very common
# with Python code and since the built-in compiler doesn't optimize
# it out we don't either.
self.current.addNext(block)
self.startBlock(block)
def newBlock(self):
b = Block()
self.blocks.add(b)
return b
def startExitBlock(self):
self.startBlock(self.exit)
_debug = 0
def _enable_debug(self):
self._debug = 1
def _disable_debug(self):
self._debug = 0
def emit(self, *inst):
if self._debug:
print "\t", inst
if len(inst) == 2 and isinstance(inst[1], Block):
self.current.addOutEdge(inst[1])
self.current.emit(inst)
def getBlocksInOrder(self):
"""Return the blocks in reverse postorder
i.e. each node appears before all of its successors
"""
order = order_blocks(self.entry, self.exit)
return order
def getBlocks(self):
return self.blocks.elements()
def getRoot(self):
"""Return nodes appropriate for use with dominator"""
return self.entry
def getContainedGraphs(self):
l = []
for b in self.getBlocks():
l.extend(b.getContainedGraphs())
return l
def order_blocks(start_block, exit_block):
"""Order blocks so that they are emitted in the right order"""
# Rules:
# - when a block has a next block, the next block must be emitted just after
# - when a block has followers (relative jumps), it must be emitted before
# them
# - all reachable blocks must be emitted
order = []
# Find all the blocks to be emitted.
remaining = set()
todo = [start_block]
while todo:
b = todo.pop()
if b in remaining:
continue
remaining.add(b)
for c in b.get_children():
if c not in remaining:
todo.append(c)
# A block is dominated by another block if that block must be emitted
# before it.
dominators = {}
for b in remaining:
if __debug__ and b.next:
assert b is b.next[0].prev[0], (b, b.next)
# Make sure every block appears in dominators, even if no
# other block must precede it.
dominators.setdefault(b, set())
# preceeding blocks dominate following blocks
for c in b.get_followers():
while 1:
dominators.setdefault(c, set()).add(b)
# Any block that has a next pointer leading to c is also
# dominated because the whole chain will be emitted at once.
# Walk backwards and add them all.
if c.prev and c.prev[0] is not b:
c = c.prev[0]
else:
break
def find_next():
# Find a block that can be emitted next.
for b in remaining:
for c in dominators[b]:
if c in remaining:
break # can't emit yet, dominated by a remaining block
else:
return b
assert 0, 'circular dependency, cannot find next block'
b = start_block
while 1:
order.append(b)
remaining.discard(b)
if b.next:
b = b.next[0]
continue
elif b is not exit_block and not b.has_unconditional_transfer():
order.append(exit_block)
if not remaining:
break
b = find_next()
return order
class Block:
_count = 0
def __init__(self, label=''):
self.insts = []
self.outEdges = set()
self.label = label
self.bid = Block._count
self.next = []
self.prev = []
Block._count = Block._count + 1
def __repr__(self):
if self.label:
return "<block %s id=%d>" % (self.label, self.bid)
else:
return "<block id=%d>" % (self.bid)
def __str__(self):
insts = map(str, self.insts)
return "<block %s %d:\n%s>" % (self.label, self.bid,
'\n'.join(insts))
def emit(self, inst):
op = inst[0]
self.insts.append(inst)
def getInstructions(self):
return self.insts
def addOutEdge(self, block):
self.outEdges.add(block)
def addNext(self, block):
self.next.append(block)
assert len(self.next) == 1, map(str, self.next)
block.prev.append(self)
assert len(block.prev) == 1, map(str, block.prev)
_uncond_transfer = ('RETURN_VALUE', 'RAISE_VARARGS',
'JUMP_ABSOLUTE', 'JUMP_FORWARD', 'CONTINUE_LOOP',
)
def has_unconditional_transfer(self):
"""Returns True if there is an unconditional transfer to an other block
at the end of this block. This means there is no risk for the bytecode
executer to go past this block's bytecode."""
try:
op, arg = self.insts[-1]
except (IndexError, ValueError):
return
return op in self._uncond_transfer
def get_children(self):
return list(self.outEdges) + self.next
def get_followers(self):
"""Get the whole list of followers, including the next block."""
followers = set(self.next)
# Blocks that must be emitted *after* this one, because of
# bytecode offsets (e.g. relative jumps) pointing to them.
for inst in self.insts:
if inst[0] in PyFlowGraph.hasjrel:
followers.add(inst[1])
return followers
def getContainedGraphs(self):
"""Return all graphs contained within this block.
For example, a MAKE_FUNCTION block will contain a reference to
the graph for the function body.
"""
contained = []
for inst in self.insts:
if len(inst) == 1:
continue
op = inst[1]
if hasattr(op, 'graph'):
contained.append(op.graph)
return contained
# flags for code objects
# the FlowGraph is transformed in place; it exists in one of these states
RAW = "RAW"
FLAT = "FLAT"
CONV = "CONV"
DONE = "DONE"
class PyFlowGraph(FlowGraph):
super_init = FlowGraph.__init__
def __init__(self, name, filename, args=(), optimized=0, klass=None):
self.super_init()
self.name = name
self.filename = filename
self.docstring = None
self.args = args # XXX
self.argcount = getArgCount(args)
self.klass = klass
if optimized:
self.flags = CO_OPTIMIZED | CO_NEWLOCALS
else:
self.flags = 0
self.consts = []
self.names = []
# Free variables found by the symbol table scan, including
# variables used only in nested scopes, are included here.
self.freevars = []
self.cellvars = []
# The closure list is used to track the order of cell
# variables and free variables in the resulting code object.
# The offsets used by LOAD_CLOSURE/LOAD_DEREF refer to both
# kinds of variables.
self.closure = []
self.varnames = list(args) or []
for i in range(len(self.varnames)):
var = self.varnames[i]
if isinstance(var, TupleArg):
self.varnames[i] = var.getName()
self.stage = RAW
def setDocstring(self, doc):
self.docstring = doc
def setFlag(self, flag):
self.flags = self.flags | flag
if flag == CO_VARARGS:
self.argcount = self.argcount - 1
def checkFlag(self, flag):
if self.flags & flag:
return 1
def setFreeVars(self, names):
self.freevars = list(names)
def setCellVars(self, names):
self.cellvars = names
def getCode(self):
"""Get a Python code object"""
assert self.stage == RAW
self.computeStackDepth()
self.flattenGraph()
assert self.stage == FLAT
self.convertArgs()
assert self.stage == CONV
self.makeByteCode()
assert self.stage == DONE
return self.newCodeObject()
def dump(self, io=None):
if io:
save = sys.stdout
sys.stdout = io
pc = 0
for t in self.insts:
opname = t[0]
if opname == "SET_LINENO":
print
if len(t) == 1:
print "\t", "%3d" % pc, opname
pc = pc + 1
else:
print "\t", "%3d" % pc, opname, t[1]
pc = pc + 3
if io:
sys.stdout = save
def computeStackDepth(self):
"""Compute the max stack depth.
Approach is to compute the stack effect of each basic block.
Then find the path through the code with the largest total
effect.
"""
depth = {}
exit = None
for b in self.getBlocks():
depth[b] = findDepth(b.getInstructions())
seen = {}
def max_depth(b, d):
if b in seen:
return d
seen[b] = 1
d = d + depth[b]
children = b.get_children()
if children:
return max([max_depth(c, d) for c in children])
else:
if not b.label == "exit":
return max_depth(self.exit, d)
else:
return d
self.stacksize = max_depth(self.entry, 0)
def flattenGraph(self):
"""Arrange the blocks in order and resolve jumps"""
assert self.stage == RAW
self.insts = insts = []
pc = 0
begin = {}
end = {}
for b in self.getBlocksInOrder():
begin[b] = pc
for inst in b.getInstructions():
insts.append(inst)
if len(inst) == 1:
pc = pc + 1
elif inst[0] != "SET_LINENO":
# arg takes 2 bytes
pc = pc + 3
end[b] = pc
pc = 0
for i in range(len(insts)):
inst = insts[i]
if len(inst) == 1:
pc = pc + 1
elif inst[0] != "SET_LINENO":
pc = pc + 3
opname = inst[0]
if opname in self.hasjrel:
oparg = inst[1]
offset = begin[oparg] - pc
insts[i] = opname, offset
elif opname in self.hasjabs:
insts[i] = opname, begin[inst[1]]
self.stage = FLAT
hasjrel = set()
for i in dis.hasjrel:
hasjrel.add(dis.opname[i])
hasjabs = set()
for i in dis.hasjabs:
hasjabs.add(dis.opname[i])
def convertArgs(self):
"""Convert arguments from symbolic to concrete form"""
assert self.stage == FLAT
self.consts.insert(0, self.docstring)
self.sort_cellvars()
for i in range(len(self.insts)):
t = self.insts[i]
if len(t) == 2:
opname, oparg = t
conv = self._converters.get(opname, None)
if conv:
self.insts[i] = opname, conv(self, oparg)
self.stage = CONV
def sort_cellvars(self):
"""Sort cellvars in the order of varnames and prune from freevars.
"""
cells = {}
for name in self.cellvars:
cells[name] = 1
self.cellvars = [name for name in self.varnames
if name in cells]
for name in self.cellvars:
del cells[name]
self.cellvars = self.cellvars + cells.keys()
self.closure = self.cellvars + self.freevars
def _lookupName(self, name, list):
"""Return index of name in list, appending if necessary
This routine uses a list instead of a dictionary, because a
dictionary can't store two different keys if the keys have the
same value but different types, e.g. 2 and 2L. The compiler
must treat these two separately, so it does an explicit type
comparison before comparing the values.
"""
t = type(name)
for i in range(len(list)):
if t == type(list[i]) and list[i] == name:
return i
end = len(list)
list.append(name)
return end
_converters = {}
def _convert_LOAD_CONST(self, arg):
if hasattr(arg, 'getCode'):
arg = arg.getCode()
return self._lookupName(arg, self.consts)
def _convert_LOAD_FAST(self, arg):
self._lookupName(arg, self.names)
return self._lookupName(arg, self.varnames)
_convert_STORE_FAST = _convert_LOAD_FAST
_convert_DELETE_FAST = _convert_LOAD_FAST
def _convert_LOAD_NAME(self, arg):
if self.klass is None:
self._lookupName(arg, self.varnames)
return self._lookupName(arg, self.names)
def _convert_NAME(self, arg):
if self.klass is None:
self._lookupName(arg, self.varnames)
return self._lookupName(arg, self.names)
_convert_STORE_NAME = _convert_NAME
_convert_DELETE_NAME = _convert_NAME
_convert_IMPORT_NAME = _convert_NAME
_convert_IMPORT_FROM = _convert_NAME
_convert_STORE_ATTR = _convert_NAME
_convert_LOAD_ATTR = _convert_NAME
_convert_DELETE_ATTR = _convert_NAME
_convert_LOAD_GLOBAL = _convert_NAME
_convert_STORE_GLOBAL = _convert_NAME
_convert_DELETE_GLOBAL = _convert_NAME
def _convert_DEREF(self, arg):
self._lookupName(arg, self.names)
self._lookupName(arg, self.varnames)
return self._lookupName(arg, self.closure)
_convert_LOAD_DEREF = _convert_DEREF
_convert_STORE_DEREF = _convert_DEREF
def _convert_LOAD_CLOSURE(self, arg):
self._lookupName(arg, self.varnames)
return self._lookupName(arg, self.closure)
_cmp = list(dis.cmp_op)
def _convert_COMPARE_OP(self, arg):
return self._cmp.index(arg)
# similarly for other opcodes...
for name, obj in locals().items():
if name[:9] == "_convert_":
opname = name[9:]
_converters[opname] = obj
del name, obj, opname
def makeByteCode(self):
assert self.stage == CONV
self.lnotab = lnotab = LineAddrTable()
for t in self.insts:
opname = t[0]
if len(t) == 1:
lnotab.addCode(self.opnum[opname])
else:
oparg = t[1]
if opname == "SET_LINENO":
lnotab.nextLine(oparg)
continue
hi, lo = twobyte(oparg)
try:
lnotab.addCode(self.opnum[opname], lo, hi)
except ValueError:
print opname, oparg
print self.opnum[opname], lo, hi
raise
self.stage = DONE
opnum = {}
for num in range(len(dis.opname)):
opnum[dis.opname[num]] = num
del num
def newCodeObject(self):
assert self.stage == DONE
if (self.flags & CO_NEWLOCALS) == 0:
nlocals = 0
else:
nlocals = len(self.varnames)
argcount = self.argcount
if self.flags & CO_VARKEYWORDS:
argcount = argcount - 1
return types.CodeType(argcount, nlocals, self.stacksize, self.flags,
self.lnotab.getCode(), self.getConsts(),
tuple(self.names), tuple(self.varnames),
self.filename, self.name, self.lnotab.firstline,
self.lnotab.getTable(), tuple(self.freevars),
tuple(self.cellvars))
def getConsts(self):
"""Return a tuple for the const slot of the code object
Must convert references to code (MAKE_FUNCTION) to code
objects recursively.
"""
l = []
for elt in self.consts:
if isinstance(elt, PyFlowGraph):
elt = elt.getCode()
l.append(elt)
return tuple(l)
def isJump(opname):
if opname[:4] == 'JUMP':
return 1
class TupleArg:
"""Helper for marking func defs with nested tuples in arglist"""
def __init__(self, count, names):
self.count = count
self.names = names
def __repr__(self):
return "TupleArg(%s, %s)" % (self.count, self.names)
def getName(self):
return ".%d" % self.count
def getArgCount(args):
argcount = len(args)
if args:
for arg in args:
if isinstance(arg, TupleArg):
numNames = len(misc.flatten(arg.names))
argcount = argcount - numNames
return argcount
def twobyte(val):
"""Convert an int argument into high and low bytes"""
assert isinstance(val, int)
return divmod(val, 256)
class LineAddrTable:
"""lnotab
This class builds the lnotab, which is documented in compile.c.
Here's a brief recap:
For each SET_LINENO instruction after the first one, two bytes are
added to lnotab. (In some cases, multiple two-byte entries are
added.) The first byte is the distance in bytes between the
instruction for the last SET_LINENO and the current SET_LINENO.
The second byte is offset in line numbers. If either offset is
greater than 255, multiple two-byte entries are added -- see
compile.c for the delicate details.
"""
def __init__(self):
self.code = []
self.codeOffset = 0
self.firstline = 0
self.lastline = 0
self.lastoff = 0
self.lnotab = []
def addCode(self, *args):
for arg in args:
self.code.append(chr(arg))
self.codeOffset = self.codeOffset + len(args)
def nextLine(self, lineno):
if self.firstline == 0:
self.firstline = lineno
self.lastline = lineno
else:
# compute deltas
addr = self.codeOffset - self.lastoff
line = lineno - self.lastline
# Python assumes that lineno always increases with
# increasing bytecode address (lnotab is unsigned char).
# Depending on when SET_LINENO instructions are emitted
# this is not always true. Consider the code:
# a = (1,
# b)
# In the bytecode stream, the assignment to "a" occurs
# after the loading of "b". This works with the C Python
# compiler because it only generates a SET_LINENO instruction
# for the assignment.
if line >= 0:
push = self.lnotab.append
while addr > 255:
push(255); push(0)
addr -= 255
while line > 255:
push(addr); push(255)
line -= 255
addr = 0
if addr > 0 or line > 0:
push(addr); push(line)
self.lastline = lineno
self.lastoff = self.codeOffset
def getCode(self):
return ''.join(self.code)
def getTable(self):
return ''.join(map(chr, self.lnotab))
class StackDepthTracker:
# XXX 1. need to keep track of stack depth on jumps
# XXX 2. at least partly as a result, this code is broken
def findDepth(self, insts, debug=0):
depth = 0
maxDepth = 0
for i in insts:
opname = i[0]
if debug:
print i,
delta = self.effect.get(opname, None)
if delta is not None:
depth = depth + delta
else:
# now check patterns
for pat, pat_delta in self.patterns:
if opname[:len(pat)] == pat:
delta = pat_delta
depth = depth + delta
break
# if we still haven't found a match
if delta is None:
meth = getattr(self, opname, None)
if meth is not None:
depth = depth + meth(i[1])
if depth > maxDepth:
maxDepth = depth
if debug:
print depth, maxDepth
return maxDepth
effect = {
'POP_TOP': -1,
'DUP_TOP': 1,
'LIST_APPEND': -1,
'SET_ADD': -1,
'MAP_ADD': -2,
'SLICE+1': -1,
'SLICE+2': -1,
'SLICE+3': -2,
'STORE_SLICE+0': -1,
'STORE_SLICE+1': -2,
'STORE_SLICE+2': -2,
'STORE_SLICE+3': -3,
'DELETE_SLICE+0': -1,
'DELETE_SLICE+1': -2,
'DELETE_SLICE+2': -2,
'DELETE_SLICE+3': -3,
'STORE_SUBSCR': -3,
'DELETE_SUBSCR': -2,
# PRINT_EXPR?
'PRINT_ITEM': -1,
'RETURN_VALUE': -1,
'YIELD_VALUE': -1,
'EXEC_STMT': -3,
'BUILD_CLASS': -2,
'STORE_NAME': -1,
'STORE_ATTR': -2,
'DELETE_ATTR': -1,
'STORE_GLOBAL': -1,
'BUILD_MAP': 1,
'COMPARE_OP': -1,
'STORE_FAST': -1,
'IMPORT_STAR': -1,
'IMPORT_NAME': -1,
'IMPORT_FROM': 1,
'LOAD_ATTR': 0, # unlike other loads
# close enough...
'SETUP_EXCEPT': 3,
'SETUP_FINALLY': 3,
'FOR_ITER': 1,
'WITH_CLEANUP': -1,
}
# use pattern match
patterns = [
('BINARY_', -1),
('LOAD_', 1),
]
def UNPACK_SEQUENCE(self, count):
return count-1
def BUILD_TUPLE(self, count):
return -count+1
def BUILD_LIST(self, count):
return -count+1
def BUILD_SET(self, count):
return -count+1
def CALL_FUNCTION(self, argc):
hi, lo = divmod(argc, 256)
return -(lo + hi * 2)
def CALL_FUNCTION_VAR(self, argc):
return self.CALL_FUNCTION(argc)-1
def CALL_FUNCTION_KW(self, argc):
return self.CALL_FUNCTION(argc)-1
def CALL_FUNCTION_VAR_KW(self, argc):
return self.CALL_FUNCTION(argc)-2
def MAKE_FUNCTION(self, argc):
return -argc
def MAKE_CLOSURE(self, argc):
# XXX need to account for free variables too!
return -argc
def BUILD_SLICE(self, argc):
if argc == 2:
return -1
elif argc == 3:
return -2
def DUP_TOPX(self, argc):
return argc
findDepth = StackDepthTracker().findDepth