| """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()) |
| # preceding 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 |
