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"""A flow graph representation for Python bytecode"""
import dis
import new
import string
import types
from compiler import misc
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):
self.current = block
def nextBlock(self, block=None):
if block is None:
block = self.newBlock()
# XXX think we need to specify when there is implicit transfer
# from one block to the next
#
# 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
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)
def emit(self, *inst):
# XXX should jump instructions implicitly call nextBlock?
if inst[0] == 'RETURN_VALUE':
self.current.addOutEdge(self.exit)
self.current.emit(inst)
def getBlocks(self):
"""Return the blocks in reverse postorder
i.e. each node appears before all of its successors
"""
# XXX make sure every node that doesn't have an explicit next
# is set so that next points to exit
for b in self.blocks.elements():
if b is self.exit:
continue
if not b.next:
b.addNext(self.exit)
order = dfs_postorder(self.entry, {})
order.reverse()
# hack alert
if not self.exit in order:
order.append(self.exit)
return order
def dfs_postorder(b, seen):
"""Depth-first search of tree rooted at b, return in postorder"""
order = []
seen[b] = b
for c in b.children():
if seen.has_key(c):
continue
order = order + dfs_postorder(c, seen)
order.append(b)
return order
class Block:
_count = 0
def __init__(self, label=''):
self.insts = []
self.inEdges = misc.Set()
self.outEdges = misc.Set()
self.label = label
self.bid = Block._count
self.next = []
Block._count = Block._count + 1
def __repr__(self):
if self.label:
return "<block %s id=%d len=%d>" % (self.label, self.bid,
len(self.insts))
else:
return "<block id=%d len=%d>" % (self.bid, len(self.insts))
def __str__(self):
insts = map(str, self.insts)
return "<block %s %d:\n%s>" % (self.label, self.bid,
string.join(insts, '\n'))
def emit(self, inst):
op = inst[0]
if op[:4] == 'JUMP':
self.outEdges.add(inst[1])
self.insts.append(inst)
def getInstructions(self):
return self.insts
def addInEdge(self, block):
self.inEdges.add(block)
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)
def children(self):
return self.outEdges.elements() + self.next
# flags for code objects
CO_OPTIMIZED = 0x0001
CO_NEWLOCALS = 0x0002
CO_VARARGS = 0x0004
CO_VARKEYWORDS = 0x0008
# 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):
self.super_init()
self.name = name
self.filename = filename
self.docstring = None
self.args = args # XXX
self.argcount = getArgCount(args)
if optimized:
self.flags = CO_OPTIMIZED | CO_NEWLOCALS
else:
self.flags = 0
self.consts = []
self.names = []
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
self.consts.insert(0, doc)
def setFlag(self, flag):
self.flags = self.flags | flag
if flag == CO_VARARGS:
self.argcount = self.argcount - 1
def getCode(self):
"""Get a Python code object"""
if self.stage == RAW:
self.flattenGraph()
if self.stage == FLAT:
self.convertArgs()
if self.stage == CONV:
self.makeByteCode()
if self.stage == DONE:
return self.newCodeObject()
raise RuntimeError, "inconsistent PyFlowGraph state"
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 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.getBlocks():
begin[b] = pc
for inst in b.getInstructions():
insts.append(inst)
if len(inst) == 1:
pc = pc + 1
else:
# 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
else:
pc = pc + 3
opname = inst[0]
if self.hasjrel.has_elt(opname):
oparg = inst[1]
offset = begin[oparg] - pc
insts[i] = opname, offset
elif self.hasjabs.has_elt(opname):
insts[i] = opname, begin[inst[1]]
self.stacksize = findDepth(self.insts)
self.stage = FLAT
hasjrel = misc.Set()
for i in dis.hasjrel:
hasjrel.add(dis.opname[i])
hasjabs = misc.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
for i in range(len(self.insts)):
t = self.insts[i]
if len(t) == 2:
opname = t[0]
oparg = t[1]
conv = self._converters.get(opname, None)
if conv:
self.insts[i] = opname, conv(self, oparg)
self.stage = CONV
def _lookupName(self, name, list):
"""Return index of name in list, appending if necessary"""
if name in list:
i = list.index(name)
# this is cheap, but incorrect in some cases, e.g 2 vs. 2L
if type(name) == type(list[i]):
return i
for i in range(len(list)):
elt = list[i]
if type(elt) == type(name) and elt == name:
return i
end = len(list)
list.append(name)
return end
_converters = {}
def _convert_LOAD_CONST(self, arg):
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_NAME(self, arg):
return self._lookupName(arg, self.names)
_convert_LOAD_NAME = _convert_NAME
_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
_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)
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 == 0:
nlocals = 0
else:
nlocals = len(self.varnames)
argcount = self.argcount
if self.flags & CO_VARKEYWORDS:
argcount = argcount - 1
return new.code(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())
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 ".nested%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 type(val) == types.IntType
return divmod(val, 256)
class LineAddrTable:
"""lnotab
This class builds the lnotab, which is undocumented but described
by com_set_lineno in compile.c. Here's an attempt at explanation:
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 -- one entry
for each factor of 255.
"""
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:
while addr > 0 or line > 0:
# write the values in 1-byte chunks that sum
# to desired value
trunc_addr = addr
trunc_line = line
if trunc_addr > 255:
trunc_addr = 255
if trunc_line > 255:
trunc_line = 255
self.lnotab.append(trunc_addr)
self.lnotab.append(trunc_line)
addr = addr - trunc_addr
line = line - trunc_line
self.lastline = lineno
self.lastoff = self.codeOffset
def getCode(self):
return string.join(self.code, '')
def getTable(self):
return string.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):
depth = 0
maxDepth = 0
for i in insts:
opname = i[0]
delta = self.effect.get(opname, 0)
if delta > 1:
depth = depth + delta
elif delta < 0:
if depth > maxDepth:
maxDepth = depth
depth = depth + delta
else:
if depth > maxDepth:
maxDepth = depth
# 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 == 0:
meth = getattr(self, opname, None)
if meth is not None:
depth = depth + meth(i[1])
if depth < 0:
depth = 0
return maxDepth
effect = {
'POP_TOP': -1,
'DUP_TOP': 1,
'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,
'LOAD_LOCALS': 1,
'RETURN_VALUE': -1,
'EXEC_STMT': -2,
'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': 0,
'IMPORT_FROM': 1,
}
# use pattern match
patterns = [
('BINARY_', -1),
('LOAD_', 1),
]
# special cases:
# UNPACK_SEQUENCE, BUILD_TUPLE,
# BUILD_LIST, CALL_FUNCTION, MAKE_FUNCTION, BUILD_SLICE
def UNPACK_SEQUENCE(self, count):
return count
def BUILD_TUPLE(self, count):
return -count
def BUILD_LIST(self, count):
return -count
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 BUILD_SLICE(self, argc):
if argc == 2:
return -1
elif argc == 3:
return -2
findDepth = StackDepthTracker().findDepth
|