764 lines
24 KiB
Python
764 lines
24 KiB
Python
"""A flow graph representation for Python bytecode"""
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import dis
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import types
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import sys
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from compiler import misc
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from compiler.consts \
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import CO_OPTIMIZED, CO_NEWLOCALS, CO_VARARGS, CO_VARKEYWORDS
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class FlowGraph:
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def __init__(self):
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self.current = self.entry = Block()
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self.exit = Block("exit")
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self.blocks = misc.Set()
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self.blocks.add(self.entry)
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self.blocks.add(self.exit)
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def startBlock(self, block):
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if self._debug:
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if self.current:
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print "end", repr(self.current)
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print " next", self.current.next
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print " prev", self.current.prev
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print " ", self.current.get_children()
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print repr(block)
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self.current = block
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def nextBlock(self, block=None):
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# XXX think we need to specify when there is implicit transfer
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# from one block to the next. might be better to represent this
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# with explicit JUMP_ABSOLUTE instructions that are optimized
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# out when they are unnecessary.
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#
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# I think this strategy works: each block has a child
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# designated as "next" which is returned as the last of the
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# children. because the nodes in a graph are emitted in
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# reverse post order, the "next" block will always be emitted
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# immediately after its parent.
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# Worry: maintaining this invariant could be tricky
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if block is None:
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block = self.newBlock()
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# Note: If the current block ends with an unconditional control
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# transfer, then it is techically incorrect to add an implicit
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# transfer to the block graph. Doing so results in code generation
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# for unreachable blocks. That doesn't appear to be very common
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# with Python code and since the built-in compiler doesn't optimize
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# it out we don't either.
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self.current.addNext(block)
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self.startBlock(block)
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def newBlock(self):
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b = Block()
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self.blocks.add(b)
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return b
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def startExitBlock(self):
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self.startBlock(self.exit)
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_debug = 0
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def _enable_debug(self):
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self._debug = 1
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def _disable_debug(self):
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self._debug = 0
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def emit(self, *inst):
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if self._debug:
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print "\t", inst
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if len(inst) == 2 and isinstance(inst[1], Block):
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self.current.addOutEdge(inst[1])
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self.current.emit(inst)
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def getBlocksInOrder(self):
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"""Return the blocks in reverse postorder
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i.e. each node appears before all of its successors
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"""
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order = order_blocks(self.entry, self.exit)
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return order
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def getBlocks(self):
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return self.blocks.elements()
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def getRoot(self):
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"""Return nodes appropriate for use with dominator"""
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return self.entry
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def getContainedGraphs(self):
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l = []
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for b in self.getBlocks():
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l.extend(b.getContainedGraphs())
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return l
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def order_blocks(start_block, exit_block):
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"""Order blocks so that they are emitted in the right order"""
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# Rules:
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# - when a block has a next block, the next block must be emitted just after
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# - when a block has followers (relative jumps), it must be emitted before
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# them
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# - all reachable blocks must be emitted
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order = []
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# Find all the blocks to be emitted.
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remaining = set()
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todo = [start_block]
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while todo:
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b = todo.pop()
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if b in remaining:
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continue
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remaining.add(b)
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for c in b.get_children():
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if c not in remaining:
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todo.append(c)
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# A block is dominated by another block if that block must be emitted
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# before it.
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dominators = {}
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for b in remaining:
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if __debug__ and b.next:
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assert b is b.next[0].prev[0], (b, b.next)
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# Make sure every block appears in dominators, even if no
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# other block must precede it.
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dominators.setdefault(b, set())
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# preceeding blocks dominate following blocks
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for c in b.get_followers():
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while 1:
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dominators.setdefault(c, set()).add(b)
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# Any block that has a next pointer leading to c is also
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# dominated because the whole chain will be emitted at once.
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# Walk backwards and add them all.
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if c.prev and c.prev[0] is not b:
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c = c.prev[0]
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else:
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break
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def find_next():
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# Find a block that can be emitted next.
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for b in remaining:
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for c in dominators[b]:
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if c in remaining:
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break # can't emit yet, dominated by a remaining block
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else:
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return b
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assert 0, 'circular dependency, cannot find next block'
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b = start_block
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while 1:
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order.append(b)
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remaining.discard(b)
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if b.next:
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b = b.next[0]
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continue
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elif b is not exit_block and not b.has_unconditional_transfer():
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order.append(exit_block)
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if not remaining:
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break
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b = find_next()
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return order
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class Block:
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_count = 0
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def __init__(self, label=''):
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self.insts = []
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self.outEdges = set()
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self.label = label
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self.bid = Block._count
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self.next = []
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self.prev = []
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Block._count = Block._count + 1
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def __repr__(self):
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if self.label:
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return "<block %s id=%d>" % (self.label, self.bid)
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else:
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return "<block id=%d>" % (self.bid)
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def __str__(self):
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insts = map(str, self.insts)
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return "<block %s %d:\n%s>" % (self.label, self.bid,
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'\n'.join(insts))
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def emit(self, inst):
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op = inst[0]
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self.insts.append(inst)
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def getInstructions(self):
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return self.insts
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def addOutEdge(self, block):
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self.outEdges.add(block)
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def addNext(self, block):
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self.next.append(block)
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assert len(self.next) == 1, map(str, self.next)
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block.prev.append(self)
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assert len(block.prev) == 1, map(str, block.prev)
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_uncond_transfer = ('RETURN_VALUE', 'RAISE_VARARGS',
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'JUMP_ABSOLUTE', 'JUMP_FORWARD', 'CONTINUE_LOOP',
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)
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def has_unconditional_transfer(self):
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"""Returns True if there is an unconditional transfer to an other block
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at the end of this block. This means there is no risk for the bytecode
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executer to go past this block's bytecode."""
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try:
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op, arg = self.insts[-1]
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except (IndexError, ValueError):
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return
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return op in self._uncond_transfer
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def get_children(self):
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return list(self.outEdges) + self.next
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def get_followers(self):
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"""Get the whole list of followers, including the next block."""
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followers = set(self.next)
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# Blocks that must be emitted *after* this one, because of
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# bytecode offsets (e.g. relative jumps) pointing to them.
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for inst in self.insts:
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if inst[0] in PyFlowGraph.hasjrel:
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followers.add(inst[1])
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return followers
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def getContainedGraphs(self):
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"""Return all graphs contained within this block.
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For example, a MAKE_FUNCTION block will contain a reference to
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the graph for the function body.
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"""
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contained = []
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for inst in self.insts:
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if len(inst) == 1:
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continue
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op = inst[1]
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if hasattr(op, 'graph'):
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contained.append(op.graph)
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return contained
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# flags for code objects
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# the FlowGraph is transformed in place; it exists in one of these states
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RAW = "RAW"
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FLAT = "FLAT"
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CONV = "CONV"
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DONE = "DONE"
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class PyFlowGraph(FlowGraph):
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super_init = FlowGraph.__init__
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def __init__(self, name, filename, args=(), optimized=0, klass=None):
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self.super_init()
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self.name = name
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self.filename = filename
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self.docstring = None
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self.args = args # XXX
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self.argcount = getArgCount(args)
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self.klass = klass
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if optimized:
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self.flags = CO_OPTIMIZED | CO_NEWLOCALS
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else:
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self.flags = 0
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self.consts = []
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self.names = []
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# Free variables found by the symbol table scan, including
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# variables used only in nested scopes, are included here.
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self.freevars = []
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self.cellvars = []
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# The closure list is used to track the order of cell
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# variables and free variables in the resulting code object.
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# The offsets used by LOAD_CLOSURE/LOAD_DEREF refer to both
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# kinds of variables.
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self.closure = []
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self.varnames = list(args) or []
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for i in range(len(self.varnames)):
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var = self.varnames[i]
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if isinstance(var, TupleArg):
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self.varnames[i] = var.getName()
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self.stage = RAW
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def setDocstring(self, doc):
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self.docstring = doc
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def setFlag(self, flag):
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self.flags = self.flags | flag
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if flag == CO_VARARGS:
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self.argcount = self.argcount - 1
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def checkFlag(self, flag):
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if self.flags & flag:
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return 1
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def setFreeVars(self, names):
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self.freevars = list(names)
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def setCellVars(self, names):
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self.cellvars = names
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def getCode(self):
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"""Get a Python code object"""
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assert self.stage == RAW
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self.computeStackDepth()
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self.flattenGraph()
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assert self.stage == FLAT
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self.convertArgs()
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assert self.stage == CONV
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self.makeByteCode()
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assert self.stage == DONE
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return self.newCodeObject()
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def dump(self, io=None):
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if io:
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save = sys.stdout
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sys.stdout = io
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pc = 0
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for t in self.insts:
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opname = t[0]
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if opname == "SET_LINENO":
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print
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if len(t) == 1:
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print "\t", "%3d" % pc, opname
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pc = pc + 1
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else:
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print "\t", "%3d" % pc, opname, t[1]
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pc = pc + 3
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if io:
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sys.stdout = save
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def computeStackDepth(self):
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"""Compute the max stack depth.
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Approach is to compute the stack effect of each basic block.
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Then find the path through the code with the largest total
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effect.
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"""
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depth = {}
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exit = None
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for b in self.getBlocks():
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depth[b] = findDepth(b.getInstructions())
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seen = {}
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def max_depth(b, d):
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if b in seen:
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return d
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seen[b] = 1
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d = d + depth[b]
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children = b.get_children()
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if children:
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return max([max_depth(c, d) for c in children])
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else:
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if not b.label == "exit":
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return max_depth(self.exit, d)
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else:
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return d
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self.stacksize = max_depth(self.entry, 0)
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def flattenGraph(self):
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"""Arrange the blocks in order and resolve jumps"""
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assert self.stage == RAW
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self.insts = insts = []
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pc = 0
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begin = {}
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end = {}
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for b in self.getBlocksInOrder():
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begin[b] = pc
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for inst in b.getInstructions():
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insts.append(inst)
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if len(inst) == 1:
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pc = pc + 1
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elif inst[0] != "SET_LINENO":
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# arg takes 2 bytes
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pc = pc + 3
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end[b] = pc
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pc = 0
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for i in range(len(insts)):
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inst = insts[i]
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if len(inst) == 1:
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pc = pc + 1
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elif inst[0] != "SET_LINENO":
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pc = pc + 3
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opname = inst[0]
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if opname in self.hasjrel:
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oparg = inst[1]
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offset = begin[oparg] - pc
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insts[i] = opname, offset
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elif opname in self.hasjabs:
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insts[i] = opname, begin[inst[1]]
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self.stage = FLAT
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hasjrel = set()
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for i in dis.hasjrel:
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hasjrel.add(dis.opname[i])
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hasjabs = set()
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for i in dis.hasjabs:
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hasjabs.add(dis.opname[i])
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def convertArgs(self):
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"""Convert arguments from symbolic to concrete form"""
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assert self.stage == FLAT
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self.consts.insert(0, self.docstring)
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self.sort_cellvars()
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for i in range(len(self.insts)):
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t = self.insts[i]
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if len(t) == 2:
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opname, oparg = t
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conv = self._converters.get(opname, None)
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if conv:
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self.insts[i] = opname, conv(self, oparg)
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self.stage = CONV
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def sort_cellvars(self):
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"""Sort cellvars in the order of varnames and prune from freevars.
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"""
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cells = {}
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for name in self.cellvars:
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cells[name] = 1
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self.cellvars = [name for name in self.varnames
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if name in cells]
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for name in self.cellvars:
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del cells[name]
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self.cellvars = self.cellvars + cells.keys()
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self.closure = self.cellvars + self.freevars
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def _lookupName(self, name, list):
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"""Return index of name in list, appending if necessary
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This routine uses a list instead of a dictionary, because a
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dictionary can't store two different keys if the keys have the
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same value but different types, e.g. 2 and 2L. The compiler
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must treat these two separately, so it does an explicit type
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comparison before comparing the values.
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"""
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t = type(name)
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for i in range(len(list)):
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if t == type(list[i]) and list[i] == name:
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return i
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end = len(list)
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list.append(name)
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return end
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_converters = {}
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def _convert_LOAD_CONST(self, arg):
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if hasattr(arg, 'getCode'):
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arg = arg.getCode()
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return self._lookupName(arg, self.consts)
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def _convert_LOAD_FAST(self, arg):
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self._lookupName(arg, self.names)
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return self._lookupName(arg, self.varnames)
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_convert_STORE_FAST = _convert_LOAD_FAST
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_convert_DELETE_FAST = _convert_LOAD_FAST
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def _convert_LOAD_NAME(self, arg):
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if self.klass is None:
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self._lookupName(arg, self.varnames)
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return self._lookupName(arg, self.names)
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def _convert_NAME(self, arg):
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if self.klass is None:
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self._lookupName(arg, self.varnames)
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return self._lookupName(arg, self.names)
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_convert_STORE_NAME = _convert_NAME
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_convert_DELETE_NAME = _convert_NAME
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_convert_IMPORT_NAME = _convert_NAME
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_convert_IMPORT_FROM = _convert_NAME
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_convert_STORE_ATTR = _convert_NAME
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_convert_LOAD_ATTR = _convert_NAME
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_convert_DELETE_ATTR = _convert_NAME
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_convert_LOAD_GLOBAL = _convert_NAME
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_convert_STORE_GLOBAL = _convert_NAME
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_convert_DELETE_GLOBAL = _convert_NAME
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def _convert_DEREF(self, arg):
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self._lookupName(arg, self.names)
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self._lookupName(arg, self.varnames)
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return self._lookupName(arg, self.closure)
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_convert_LOAD_DEREF = _convert_DEREF
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_convert_STORE_DEREF = _convert_DEREF
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def _convert_LOAD_CLOSURE(self, arg):
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self._lookupName(arg, self.varnames)
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return self._lookupName(arg, self.closure)
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_cmp = list(dis.cmp_op)
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def _convert_COMPARE_OP(self, arg):
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return self._cmp.index(arg)
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# similarly for other opcodes...
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for name, obj in locals().items():
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if name[:9] == "_convert_":
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opname = name[9:]
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_converters[opname] = obj
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del name, obj, opname
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def makeByteCode(self):
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assert self.stage == CONV
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self.lnotab = lnotab = LineAddrTable()
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for t in self.insts:
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opname = t[0]
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if len(t) == 1:
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lnotab.addCode(self.opnum[opname])
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else:
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oparg = t[1]
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if opname == "SET_LINENO":
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lnotab.nextLine(oparg)
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continue
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hi, lo = twobyte(oparg)
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try:
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lnotab.addCode(self.opnum[opname], lo, hi)
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except ValueError:
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print opname, oparg
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print self.opnum[opname], lo, hi
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raise
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self.stage = DONE
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opnum = {}
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for num in range(len(dis.opname)):
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opnum[dis.opname[num]] = num
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del num
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def newCodeObject(self):
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assert self.stage == DONE
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if (self.flags & CO_NEWLOCALS) == 0:
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nlocals = 0
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else:
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nlocals = len(self.varnames)
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argcount = self.argcount
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if self.flags & CO_VARKEYWORDS:
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argcount = argcount - 1
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return types.CodeType(argcount, nlocals, self.stacksize, self.flags,
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self.lnotab.getCode(), self.getConsts(),
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tuple(self.names), tuple(self.varnames),
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self.filename, self.name, self.lnotab.firstline,
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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
|