path: root/pypy/interpreter/pyframe.py

""" PyFrame class implementation with the interpreter main loop.
"""

import sys
from rpython.rlib import jit, rweakref
from rpython.rlib.debug import make_sure_not_resized, check_nonneg
from rpython.rlib.debug import ll_assert_not_none
from rpython.rlib.jit import hint
from rpython.rlib.objectmodel import instantiate, specialize, we_are_translated
from rpython.rlib.objectmodel import not_rpython
from rpython.rlib.rarithmetic import intmask, r_uint
from rpython.tool.pairtype import extendabletype

from pypy.interpreter import pycode, pytraceback
from pypy.interpreter.argument import Arguments
from pypy.interpreter.astcompiler import consts
from pypy.interpreter.baseobjspace import W_Root
from pypy.interpreter.error import (
    OperationError, get_cleared_operation_error, oefmt)
from pypy.interpreter.executioncontext import ExecutionContext
from pypy.interpreter.nestedscope import Cell
from pypy.tool import stdlib_opcode

# Define some opcodes used
for op in '''DUP_TOP POP_TOP SETUP_EXCEPT SETUP_FINALLY SETUP_WITH
SETUP_ASYNC_WITH POP_BLOCK YIELD_VALUE
NOP FOR_ITER EXTENDED_ARG END_ASYNC_FOR LOAD_CONST
JUMP_IF_FALSE_OR_POP JUMP_IF_TRUE_OR_POP POP_JUMP_IF_FALSE POP_JUMP_IF_TRUE
JUMP_IF_NOT_EXC_MATCH JUMP_ABSOLUTE JUMP_FORWARD GET_ITER GET_AITER
RETURN_VALUE RERAISE RAISE_VARARGS POP_EXCEPT
'''.split():
    globals()[op] = stdlib_opcode.opmap[op]

class FrameDebugData(object):
    """ A small object that holds debug data for tracing
    """
    w_f_trace                = None
    instr_lb                 = 0
    instr_ub                 = 0
    instr_prev_plus_one      = 0
    f_lineno                 = 0      # current lineno for tracing
    is_being_profiled        = False
    is_in_line_tracing       = False
    f_trace_lines            = True
    f_trace_opcodes          = False
    w_locals                 = None
    hidden_operationerr      = None

    def __init__(self, pycode):
        self.f_lineno = pycode.co_firstlineno
        self.w_globals = pycode.w_globals

class PyFrame(W_Root):
    """Represents a frame for a regular Python function
    that needs to be interpreted.

    Public fields:
     * 'space' is the object space this frame is running in
     * 'code' is the PyCode object this frame runs
     * 'w_locals' is the locals dictionary to use, if needed, stored on a
       debug object
     * 'w_globals' is the attached globals dictionary
     * 'builtin' is the attached built-in module
     * 'valuestack_w', 'blockstack', control the interpretation

    Cell Vars:
        my local variables that are exposed to my inner functions
    Free Vars:
        variables coming from a parent function in which i'm nested
    'closure' is a list of Cell instances: the received free vars.
    """

    __metaclass__ = extendabletype

    frame_finished_execution = False
    f_generator_wref         = rweakref.dead_ref  # for generators/coroutines
    f_generator_nowref       = None               # (only one of the two attrs)
    w_yielding_from = None
    last_instr               = -1
    f_backref                = jit.vref_None

    escaped                  = False  # see mark_as_escaped()
    debugdata                = None

    pycode = None # code object executed by that frame
    locals_cells_stack_w = None # the list of all locals, cells and the valuestack
    valuestackdepth = 0 # number of items on valuestack
    lastblock = None

    # other fields:

    # builtin - builtin cache, only if honor__builtins__ is True
    # defaults to False

    # there is also self.space which is removed by the annotator

    # additionally JIT uses vable_token field that is representing
    # frame current virtualizable state as seen by the JIT

    def __init__(self, space, code, w_globals, outer_func):
        self = hint(self, access_directly=True, fresh_virtualizable=True)
        assert isinstance(code, pycode.PyCode)
        self.space = space
        self.pycode = code
        if code.frame_stores_global(w_globals):
            self.getorcreatedebug().w_globals = w_globals
        ncellvars = len(code.co_cellvars)
        nfreevars = len(code.co_freevars)
        size = code.co_nlocals + ncellvars + nfreevars + code.co_stacksize
        # the layout of this list is as follows:
        # | local vars | cells | stack |
        self.locals_cells_stack_w = [None] * size
        self.valuestackdepth = code.co_nlocals + ncellvars + nfreevars
        make_sure_not_resized(self.locals_cells_stack_w)
        check_nonneg(self.valuestackdepth)
        #
        if space.config.objspace.honor__builtins__:
            self.builtin = space.builtin.pick_builtin(w_globals)
        # regular functions always have CO_OPTIMIZED and CO_NEWLOCALS.
        # class bodies only have CO_NEWLOCALS.
        self.initialize_frame_scopes(outer_func, code)

    def getdebug(self):
        return self.debugdata

    def getorcreatedebug(self):
        if self.debugdata is None:
            self.debugdata = FrameDebugData(self.pycode)
        return self.debugdata

    def get_w_globals(self):
        debugdata = self.getdebug()
        if debugdata is not None:
            return debugdata.w_globals
        return jit.promote(self.pycode).w_globals

    def get_w_f_trace(self):
        d = self.getdebug()
        if d is None:
            return None
        return d.w_f_trace

    def get_is_being_profiled(self):
        d = self.getdebug()
        if d is None:
            return False
        return d.is_being_profiled

    def get_w_locals(self):
        d = self.getdebug()
        if d is None:
            return None
        return d.w_locals

    def get_f_trace_lines(self):
        d = self.getdebug()
        if d is None:
            return True
        return d.f_trace_lines

    def get_f_trace_opcodes(self):
        d = self.getdebug()
        if d is None:
            return False
        return d.f_trace_opcodes

    @not_rpython
    def __repr__(self):
        # useful in tracebacks
        return "<%s.%s executing %s at line %s" % (
            self.__class__.__module__, self.__class__.__name__,
            self.pycode, self.get_last_lineno())

    def _getcell(self, varindex):
        cell = self.locals_cells_stack_w[varindex + self.pycode.co_nlocals]
        assert isinstance(cell, Cell)
        return cell

    def mark_as_escaped(self):
        """
        Must be called on frames that are exposed to applevel, e.g. by
        sys._getframe().  This ensures that the virtualref holding the frame
        is properly forced by ec.leave(), and thus the frame will be still
        accessible even after the corresponding C stack died.
        """
        self.escaped = True

    def append_block(self, block):
        assert block.previous is self.lastblock
        self.lastblock = block

    def pop_block(self):
        block = self.lastblock
        self.lastblock = block.previous
        return block

    def blockstack_non_empty(self):
        return self.lastblock is not None

    def get_blocklist(self):
        """Returns a list containing all the blocks in the frame"""
        lst = []
        block = self.lastblock
        while block is not None:
            lst.append(block)
            block = block.previous
        return lst

    def set_blocklist(self, lst):
        self.lastblock = None
        i = len(lst) - 1
        while i >= 0:
            block = lst[i]
            i -= 1
            block.previous = self.lastblock
            self.lastblock = block

    def get_builtin(self):
        if self.space.config.objspace.honor__builtins__:
            return self.builtin
        else:
            return self.space.builtin

    @jit.unroll_safe
    def initialize_frame_scopes(self, outer_func, code):
        # regular functions always have CO_OPTIMIZED and CO_NEWLOCALS.
        # class bodies only have CO_NEWLOCALS.
        # CO_NEWLOCALS: make a locals dict unless optimized is also set
        # CO_OPTIMIZED: no locals dict needed at all
        flags = code.co_flags
        if not (flags & pycode.CO_OPTIMIZED):
            if flags & pycode.CO_NEWLOCALS:
                self.getorcreatedebug().w_locals = self.space.newdict(module=True)
            else:
                w_globals = self.get_w_globals()
                assert w_globals is not None
                self.getorcreatedebug().w_locals = w_globals

        ncellvars = len(code.co_cellvars)
        nfreevars = len(code.co_freevars)
        if not nfreevars:
            if not ncellvars:
                return            # no cells needed - fast path
        elif outer_func is None:
            space = self.space
            raise oefmt(space.w_TypeError,
                        "directly executed code object may not contain free "
                        "variables")
        if outer_func and outer_func.closure:
            closure_size = len(outer_func.closure)
        else:
            closure_size = 0
        if closure_size != nfreevars:
            raise ValueError("code object received a closure with "
                                 "an unexpected number of free variables")
        index = code.co_nlocals
        for i in range(ncellvars):
            self.locals_cells_stack_w[index] = Cell(
                    None, self.pycode.cell_families[i])
            index += 1
        for i in range(nfreevars):
            self.locals_cells_stack_w[index] = outer_func.closure[i]
            index += 1

    def _is_generator_or_coroutine(self):
        return (self.getcode().co_flags & (pycode.CO_COROUTINE |
                                           pycode.CO_GENERATOR |
                                           pycode.CO_ASYNC_GENERATOR)) != 0

    def run(self, name=None, qualname=None):
        """Start this frame's execution."""
        if self._is_generator_or_coroutine():
            return self.initialize_as_generator(name, qualname)
        else:
            return self.execute_frame()
    run._always_inline_ = True

    def initialize_as_generator(self, name, qualname):
        space = self.space
        flags = self.getcode().co_flags
        if flags & pycode.CO_COROUTINE:
            from pypy.interpreter.generator import Coroutine
            gen = Coroutine(self, name, qualname)
            ec = space.getexecutioncontext()
            gen.capture_origin(ec)
        elif flags & pycode.CO_ASYNC_GENERATOR:
            from pypy.interpreter.generator import AsyncGenerator
            gen = AsyncGenerator(self, name, qualname)
        elif flags & pycode.CO_GENERATOR:
            from pypy.interpreter.generator import GeneratorIterator
            gen = GeneratorIterator(self, name, qualname)
        else:
            raise AssertionError("bad co_flags")

        if space.config.translation.rweakref:
            self.f_generator_wref = rweakref.ref(gen)
        else:
            self.f_generator_nowref = gen
        w_gen = gen
        return w_gen

    def resume_execute_frame(self, w_arg_or_err):
        # Called from execute_frame() just before resuming the bytecode
        # interpretation.
        from pypy.interpreter.pyopcode import SApplicationException
        space = self.space
        w_yf = self.w_yielding_from
        if w_yf is not None:
            self.w_yielding_from = None
            try:
                self.next_yield_from(w_yf, w_arg_or_err)
            except OperationError as operr:
                operr.record_context(space, space.getexecutioncontext())
                return self.handle_generator_error(operr)
            # Normal case: the call above raises Yield.
            # We reach this point if the iterable is exhausted.
            last_instr = jit.promote(self.last_instr)
            assert last_instr & 1 == 0
            assert last_instr >= 0
            return r_uint(last_instr + 2)

        if isinstance(w_arg_or_err, SApplicationException):
            return self.handle_generator_error(w_arg_or_err.operr)

        last_instr = jit.promote(self.last_instr)
        if last_instr != -1:
            assert last_instr & 1 == 0
            self.pushvalue(w_arg_or_err)
            return r_uint(last_instr + 2)
        else:
            return r_uint(0)

    def execute_frame(self, w_arg_or_err=None):
        """Execute this frame.  Main entry point to the interpreter.
        'w_arg_or_err' is non-None iff we are starting or resuming
        a generator or coroutine frame; in that case, w_arg_or_err
        is the input argument -or- an SApplicationException instance.
        """
        from pypy.interpreter import pyopcode as pyopcode
        # the following 'assert' is an annotation hint: it hides from
        # the annotator all methods that are defined in PyFrame but
        # overridden in the {,Host}FrameClass subclasses of PyFrame.
        assert (isinstance(self, self.space.FrameClass) or
                not self.space.config.translating)
        executioncontext = self.space.getexecutioncontext()
        executioncontext.enter(self)
        got_exception = True
        w_exitvalue = self.space.w_None
        try:
            executioncontext.call_trace(self)
            #
            # Execution starts just after the last_instr.  Initially,
            # last_instr is -1.  After a generator suspends it points to
            # the YIELD_VALUE/YIELD_FROM instruction.
            try:
                try:
                    if w_arg_or_err is None:
                        assert self.last_instr == -1
                        next_instr = r_uint(0)
                    else:
                        next_instr = self.resume_execute_frame(w_arg_or_err)
                except pyopcode.Yield:
                    w_exitvalue = self.popvalue()
                else:
                    w_exitvalue = self.dispatch(self.pycode, next_instr,
                                                executioncontext)
            except OperationError:
                raise
            except Exception as e:      # general fall-back
                raise self._convert_unexpected_exception(e)
            finally:
                executioncontext.return_trace(self, w_exitvalue)
            got_exception = False
        finally:
            executioncontext.leave(self, w_exitvalue, got_exception)
        return w_exitvalue
    execute_frame.insert_stack_check_here = True

    # stack manipulation helpers
    def pushvalue(self, w_object):
        depth = self.valuestackdepth
        self.locals_cells_stack_w[depth] = ll_assert_not_none(w_object)
        self.valuestackdepth = depth + 1

    def pushvalue_none(self):
        depth = self.valuestackdepth
        # the entry is already None, and remains None
        assert self.locals_cells_stack_w[depth] is None
        self.valuestackdepth = depth + 1

    def pushvalue_maybe_none(self, w_object):
        depth = self.valuestackdepth
        self.locals_cells_stack_w[depth] = w_object
        self.valuestackdepth = depth + 1

    def assert_stack_index(self, index):
        if we_are_translated():
            return
        if not self._check_stack_index(index):
            #import pdb; pdb.set_trace()
            assert 0

    def _check_stack_index(self, index):
        code = self.pycode
        ncellvars = len(code.co_cellvars)
        nfreevars = len(code.co_freevars)
        stackstart = code.co_nlocals + ncellvars + nfreevars
        return index >= stackstart

    def popvalue(self):
        return ll_assert_not_none(self.popvalue_maybe_none())

    def popvalue_maybe_none(self):
        depth = self.valuestackdepth - 1
        self.assert_stack_index(depth)
        assert depth >= 0
        w_object = self.locals_cells_stack_w[depth]
        self.locals_cells_stack_w[depth] = None
        self.valuestackdepth = depth
        return w_object


    # we need two popvalues that return different data types:
    # one in case we want list another in case of tuple
    def _new_popvalues():
        @jit.unroll_safe
        def popvalues(self, n):
            values_w = [None] * n
            while True:
                n -= 1
                if n < 0:
                    break
                values_w[n] = self.popvalue()
            return values_w
        return popvalues
    popvalues = _new_popvalues()
    popvalues_mutable = _new_popvalues()
    del _new_popvalues

    @jit.unroll_safe
    def peekvalues(self, n):
        values_w = [None] * n
        base = self.valuestackdepth - n
        self.assert_stack_index(base)
        assert base >= 0
        while True:
            n -= 1
            if n < 0:
                break
            values_w[n] = self.locals_cells_stack_w[base+n]
        return values_w

    @jit.unroll_safe
    def dropvalues(self, n):
        n = hint(n, promote=True)
        finaldepth = self.valuestackdepth - n
        self.assert_stack_index(finaldepth)
        assert finaldepth >= 0
        while True:
            n -= 1
            if n < 0:
                break
            self.locals_cells_stack_w[finaldepth+n] = None
        self.valuestackdepth = finaldepth

    @jit.unroll_safe
    def pushrevvalues(self, n, values_w): # n should be len(values_w)
        make_sure_not_resized(values_w)
        while True:
            n -= 1
            if n < 0:
                break
            self.pushvalue(values_w[n])

    @jit.unroll_safe
    def dupvalues(self, n):
        delta = n-1
        while True:
            n -= 1
            if n < 0:
                break
            w_value = self.peekvalue(delta)
            self.pushvalue(w_value)

    def peekvalue(self, index_from_top=0):
        # NOTE: top of the stack is peekvalue(0).
        # Contrast this with CPython where it's PEEK(-1).
        return ll_assert_not_none(self.peekvalue_maybe_none(index_from_top))

    def peekvalue_maybe_none(self, index_from_top=0):
        index_from_top = hint(index_from_top, promote=True)
        index = self.valuestackdepth + ~index_from_top
        self.assert_stack_index(index)
        assert index >= 0
        return self.locals_cells_stack_w[index]

    def settopvalue(self, w_object, index_from_top=0):
        index_from_top = hint(index_from_top, promote=True)
        index = self.valuestackdepth + ~index_from_top
        self.assert_stack_index(index)
        assert index >= 0
        self.locals_cells_stack_w[index] = ll_assert_not_none(w_object)

    @jit.unroll_safe
    def dropvaluesuntil(self, finaldepth):
        depth = self.valuestackdepth - 1
        finaldepth = hint(finaldepth, promote=True)
        assert finaldepth >= 0
        while depth >= finaldepth:
            self.locals_cells_stack_w[depth] = None
            depth -= 1
        self.valuestackdepth = finaldepth

    def _guess_function_name_parens(self, fnname=None, w_function=None):
        """ Returns 'funcname()' from either a function name fnname or a
        wrapped callable w_function. If it's not a function or a method, returns
        'Classname object'"""
        # XXX this is super annoying to compute every time we do a function call!
        # CPython has a similar function, PyEval_GetFuncName
        from pypy.interpreter.function import Function, _Method
        if fnname is not None:
            return fnname + '()'
        if w_function is None:
            return None
        if isinstance(w_function, Function):
            return w_function.name + '()'
        if isinstance(w_function, _Method):
            return self._guess_function_name_parens(None, w_function.w_function)
        return self.space.type(w_function).getname(self.space) + ' object'

    def make_arguments(self, nargs, methodcall=False, w_function=None, fnname=None):
        fnname_parens = self._guess_function_name_parens(fnname, w_function)
        return Arguments(
                self.space, self.peekvalues(nargs), methodcall=methodcall, fnname_parens=fnname_parens)

    def argument_factory(self, arguments, keywords, keywords_w, w_star, w_starstar, methodcall=False, w_function=None, fnname=None):
        fnname_parens = self._guess_function_name_parens(fnname, w_function)
        return Arguments(
                self.space, arguments, keywords, keywords_w, w_star,
                w_starstar, methodcall=methodcall, fnname_parens=fnname_parens)

    def hide(self):
        return self.pycode.hidden_applevel

    def getcode(self):
        return hint(self.pycode, promote=True)

    @jit.look_inside_iff(lambda self, scope_w: jit.isvirtual(scope_w))
    def setfastscope(self, scope_w):
        """Initialize the fast locals from a list of values,
        where the order is according to self.pycode.signature()."""
        scope_len = len(scope_w)
        if scope_len > self.pycode.co_nlocals:
            raise ValueError("new fastscope is longer than the allocated area")
        # don't assign directly to 'locals_cells_stack_w[:scope_len]' to be
        # virtualizable-friendly
        for i in range(scope_len):
            self.locals_cells_stack_w[i] = scope_w[i]
        self.init_cells()

    def getdictscope(self):
        """
        Get the locals as a dictionary
        """
        self.fast2locals()
        return self.debugdata.w_locals

    def setdictscope(self, w_locals):
        """
        Initialize the locals from a dictionary.
        """
        self.getorcreatedebug().w_locals = w_locals
        self.locals2fast()

    @jit.unroll_safe
    def fast2locals(self):
        # Copy values from the fastlocals to self.w_locals
        d = self.getorcreatedebug()
        if d.w_locals is None:
            d.w_locals = self.space.newdict(module=True)
        varnames = self.getcode().getvarnames()
        for i in range(min(len(varnames), self.getcode().co_nlocals)):
            name = varnames[i]
            w_value = self.locals_cells_stack_w[i]
            if w_value is not None:
                self.space.setitem_str(d.w_locals, name, w_value)
            else:
                w_name = self.space.newtext(name)
                try:
                    self.space.delitem(d.w_locals, w_name)
                except OperationError as e:
                    if not e.match(self.space, self.space.w_KeyError):
                        raise

        # cellvars are values exported to inner scopes
        # freevars are values coming from outer scopes
        # (see locals2fast for why CO_OPTIMIZED)
        freevarnames = self.pycode.co_cellvars
        if self.pycode.co_flags & consts.CO_OPTIMIZED:
            freevarnames = freevarnames + self.pycode.co_freevars
        for i in range(len(freevarnames)):
            name = freevarnames[i]
            cell = self._getcell(i)
            try:
                w_value = cell.get()
            except ValueError:
                w_name = self.space.newtext(name)
                try:
                    self.space.delitem(d.w_locals, w_name)
                except OperationError as e:
                    if not e.match(self.space, self.space.w_KeyError):
                        raise
            else:
                self.space.setitem_str(d.w_locals, name, w_value)


    @jit.unroll_safe
    def locals2fast(self):
        # Copy values from self.w_locals to the fastlocals
        w_locals = self.getorcreatedebug().w_locals
        assert w_locals is not None
        varnames = self.getcode().getvarnames()
        numlocals = self.getcode().co_nlocals

        new_fastlocals_w = [None] * numlocals

        for i in range(min(len(varnames), numlocals)):
            name = varnames[i]
            w_value = self.space.finditem_str(w_locals, name)
            if w_value is not None:
                new_fastlocals_w[i] = w_value

        self.setfastscope(new_fastlocals_w)

        freevarnames = self.pycode.co_cellvars
        if self.pycode.co_flags & consts.CO_OPTIMIZED:
            freevarnames = freevarnames + self.pycode.co_freevars
            # If the namespace is unoptimized, then one of the
            # following cases applies:
            # 1. It does not contain free variables, because it
            #    uses import * or is a top-level namespace.
            # 2. It is a class namespace.
            # We don't want to accidentally copy free variables
            # into the locals dict used by the class.
        for i in range(len(freevarnames)):
            name = freevarnames[i]
            cell = self._getcell(i)
            w_value = self.space.finditem_str(w_locals, name)
            if w_value is not None:
                cell.set(w_value)
            else:
                cell.set(None)

    @jit.unroll_safe
    def init_cells(self):
        """
        Initialize cellvars from self.locals_cells_stack_w.
        """
        args_to_copy = self.pycode._args_as_cellvars
        index = self.pycode.co_nlocals
        for i in range(len(args_to_copy)):
            argnum = args_to_copy[i]
            if argnum >= 0:
                cell = self.locals_cells_stack_w[index]
                assert isinstance(cell, Cell)
                cell.set(self.locals_cells_stack_w[argnum])
            index += 1

    def getclosure(self):
        return None

    def fget_code(self, space):
        return self.getcode()

    def fget_getdictscope(self, space):
        return self.getdictscope()

    def fget_w_globals(self, space):
        # bit silly, but GetSetProperty passes a space
        return self.get_w_globals()


    ### line numbers ###

    def fget_f_lineno(self, space):
        "Returns the line number of the instruction currently being executed."
        if self.get_w_f_trace() is None:
            return space.newint(self.get_last_lineno())
        else:
            return space.newint(self.getorcreatedebug().f_lineno)

    def fset_f_lineno(self, space, w_new_lineno):
        "Change the line number of the instruction currently being executed."
        try:
            new_lineno = space.int_w(w_new_lineno)
        except OperationError:
            raise oefmt(space.w_ValueError, "lineno must be an integer")

        # You can only do this from within a trace function, not via
        # _getframe or similar hackery.
        if space.int_w(self.fget_f_lasti(space)) == -1:
            raise oefmt(space.w_ValueError,
                        "can't jump from the 'call' trace event of a new frame")
        if self.get_w_f_trace() is None:
            raise oefmt(space.w_ValueError,
                        "f_lineno can only be set by a trace function")

        code = self.pycode.co_code
        if ord(code[self.last_instr]) == YIELD_VALUE:
            raise oefmt(space.w_ValueError,
                        "can't jump from a yield statement")

        # Only allow jumps when we're tracing a line event.
        d = self.getorcreatedebug()
        if not d.is_in_line_tracing:
            raise oefmt(space.w_ValueError,
                        "can only jump from a 'line' trace event")

        line = self.pycode.co_firstlineno
        if new_lineno < line:
            raise oefmt(space.w_ValueError,
                        "line %d comes before the current code block", new_lineno)

        lines = marklines(self.pycode)
        x = first_line_not_before(lines, new_lineno)


        # If we didn't reach the requested line, return an error.
        if x == -1:
            raise oefmt(space.w_ValueError,
                        "line %d comes after the current code block", new_lineno)
        new_lineno = x

        blocks = markblocks(self.pycode)
        start_block_stack = blocks[self.last_instr // 2]
        best_block_stack = None

        error = "cannot find bytecode for specified line"
        best_addr = -1
        for i in range(len(lines)):
            if lines[i] == new_lineno:
                target_block_stack = blocks[i]
                if compatible_block_stack(start_block_stack, target_block_stack):
                    error = None
                    if best_block_stack is None or len(target_block_stack) > len(best_block_stack):
                        best_block_stack = target_block_stack
                        best_addr = i * 2
                elif error is not None:
                    if target_block_stack:
                        error = explain_incompatible_block_stack(target_block_stack)
                    else:
                        error = "code may be unreachable"
        if error is not None:
            raise OperationError(space.w_ValueError, space.newtext(error))

        while len(start_block_stack) > len(best_block_stack):
            kind = start_block_stack[-1]
            if kind == JUMP_BLOCKSTACK_LOOP:
                self.popvalue()
            elif kind == JUMP_BLOCKSTACK_TRY:
                self.pop_block().cleanupstack(self)
            elif kind == JUMP_BLOCKSTACK_WITH:
                self.pop_block().cleanupstack(self)
                self.popvalue()
            else:
                assert kind == JUMP_BLOCKSTACK_EXCEPT
                raise OperationError(space.w_ValueError, space.newtext(
                    "can't jump out of an 'except' block"))
            start_block_stack = pop_simulated_stack(start_block_stack)

        d.f_lineno = new_lineno
        assert best_addr & 1 == 0
        self.last_instr = best_addr

    def get_last_lineno(self):
        "Returns the line number of the instruction currently being executed."
        return pytraceback.offset2lineno(self.pycode, self.last_instr)

    def fget_f_builtins(self, space):
        return self.get_builtin().getdict(space)

    def get_f_back(self):
        return ExecutionContext.getnextframe_nohidden(self)

    def fget_f_back(self, space):
        return self.get_f_back()

    def fget_f_lasti(self, space):
        return self.space.newint(self.last_instr)

    def fget_f_trace(self, space):
        return self.get_w_f_trace()

    def fset_f_trace(self, space, w_trace):
        if space.is_w(w_trace, space.w_None):
            self.getorcreatedebug().w_f_trace = None
        else:
            d = self.getorcreatedebug()
            d.w_f_trace = w_trace
            d.f_lineno = self.get_last_lineno()

    def fdel_f_trace(self, space):
        self.getorcreatedebug().w_f_trace = None

    def fget_f_trace_lines(self, space):
        return space.newbool(self.get_f_trace_lines())

    def fset_f_trace_lines(self, space, w_trace):
        self.getorcreatedebug().f_trace_lines = space.is_true(w_trace)

    def fget_f_trace_opcodes(self, space):
        return space.newbool(self.get_f_trace_opcodes())

    def fset_f_trace_opcodes(self, space, w_trace):
        self.getorcreatedebug().f_trace_opcodes = space.is_true(w_trace)

    def get_generator(self):
        if self.space.config.translation.rweakref:
            return self.f_generator_wref()
        else:
            return self.f_generator_nowref

    def descr_clear(self, space):
        """F.clear(): clear most references held by the frame"""
        # Clears a random subset of the attributes: the local variables
        # and the w_locals.  Note that CPython doesn't clear f_locals
        # (which can create leaks) but it's hard to notice because
        # the next Python-level read of 'frame.f_locals' will clear it.
        if not self.frame_finished_execution:
            if not self._is_generator_or_coroutine():
                raise oefmt(space.w_RuntimeError,
                            "cannot clear an executing frame")
            gen = self.get_generator()
            if gen is not None:
                if gen.running:
                    raise oefmt(space.w_RuntimeError,
                                "cannot clear an executing frame")
                # xxx CPython raises the RuntimeWarning "coroutine was never
                # awaited" in this case too.  Does it make any sense?
                gen.descr_close()

        debug = self.getdebug()
        if debug is not None:
            debug.w_f_trace = None
            if debug.w_locals is not None:
                debug.w_locals = space.newdict()

        # clear the locals, including the cell/free vars, and the stack
        for i in range(len(self.locals_cells_stack_w)):
            w_oldvalue = self.locals_cells_stack_w[i]
            if isinstance(w_oldvalue, Cell):
                # we can't mutate w_oldvalue here, because that could still be
                # shared by an inner/outer function
                w_newvalue = Cell(
                    None, w_oldvalue.family)
            else:
                w_newvalue = None
            self.locals_cells_stack_w[i] = w_newvalue
        self.valuestackdepth = 0
        self.lastblock = None    # the FrameBlock chained list

    def _convert_unexpected_exception(self, e):
        from pypy.interpreter import error

        operr = error.get_converted_unexpected_exception(self.space, e)
        pytraceback.record_application_traceback(
            self.space, operr, self, self.last_instr)
        raise operr

    def descr_repr(self, space):
        code = self.pycode
        moreinfo = ", file '%s', line %s, code %s" % (
            code.co_filename, self.get_last_lineno(), code.co_name)
        return self.getrepr(space, "frame", moreinfo)

# ____________________________________________________________

JUMP_BLOCKSTACK_WITH = 'w'
JUMP_BLOCKSTACK_LOOP = 'l'
JUMP_BLOCKSTACK_TRY = 't'
JUMP_BLOCKSTACK_EXCEPT = 'e'

def marklines(code):
    res = [-1] * (len(code.co_code) // 2)

    lnotab = code.co_lnotab
    addr = 0
    line = code.co_firstlineno
    res[0] = line
    for offset in xrange(0, len(lnotab), 2):
        addr += ord(lnotab[offset])
        line_offset = ord(lnotab[offset + 1])
        if line_offset >= 0x80:
            line_offset -= 0x100
        line += line_offset
        res[addr // 2] = line
    return res

def first_line_not_before(lines, line):
    result = sys.maxint
    for index, l in enumerate(lines):
        if l < result and l >= line:
            result = l
    if result == sys.maxint:
        return -1
    return result

def markblocks(code):
    blocks = [None] * ((len(code.co_code) // 2) + 1)
    blocks[0] = ''
    todo = True
    while todo:
        todo = False
        for i in range(0, len(code.co_code), 2):
            block_stack = blocks[i // 2]
            if block_stack is None:
                continue
            opcode = ord(code.co_code[i])
            if (
                opcode == JUMP_IF_FALSE_OR_POP or
                opcode == JUMP_IF_TRUE_OR_POP or
                opcode == POP_JUMP_IF_FALSE or
                opcode == POP_JUMP_IF_TRUE or
                opcode == JUMP_IF_NOT_EXC_MATCH
            ):
                j = _get_arg(code.co_code, i)
                if blocks[j // 2] is None and j < i:
                    todo = True
                assert blocks[j // 2] is None or blocks[j // 2] == block_stack
                blocks[j // 2] = block_stack
                blocks[i // 2 + 1] = block_stack
            elif opcode == JUMP_ABSOLUTE:
                j = _get_arg(code.co_code, i)
                if blocks[j // 2] is None and j < i:
                    todo = True
                assert blocks[j // 2] is None or blocks[j // 2] == block_stack
                blocks[j // 2] = block_stack
            elif (
                opcode == SETUP_FINALLY or
                opcode == SETUP_EXCEPT
            ):
                j = _get_arg(code.co_code, i) + i + 2
                stack = block_stack + JUMP_BLOCKSTACK_EXCEPT
                assert blocks[j // 2] is None or blocks[j // 2] == stack
                blocks[j // 2] = stack
                block_stack = block_stack + JUMP_BLOCKSTACK_TRY
                blocks[i // 2 + 1] = block_stack
            elif (
                opcode == SETUP_WITH or
                opcode == SETUP_ASYNC_WITH
            ):
                j = _get_arg(code.co_code, i) + i + 2
                stack = block_stack + JUMP_BLOCKSTACK_EXCEPT
                assert blocks[j // 2] is None or blocks[j // 2] == stack
                blocks[j // 2] = stack
                block_stack = block_stack + JUMP_BLOCKSTACK_WITH
                blocks[i // 2 + 1] = block_stack
            elif opcode == JUMP_FORWARD:
                j = _get_arg(code.co_code, i) + i + 2
                assert blocks[j // 2] is None or blocks[j // 2] == block_stack
                blocks[j // 2] = block_stack
            elif (
                opcode == GET_ITER or
                opcode == GET_AITER
            ):
                block_stack = block_stack + JUMP_BLOCKSTACK_LOOP
                blocks[i // 2 + 1] = block_stack
            elif opcode == FOR_ITER:
                blocks[i // 2 + 1] = block_stack
                block_stack = pop_simulated_stack(block_stack)
                j = _get_arg(code.co_code, i) + i + 2
                assert blocks[j // 2] is None or blocks[j // 2] == block_stack
                blocks[j // 2] = block_stack
            elif (
                opcode == POP_BLOCK or
                opcode == POP_EXCEPT
            ):
                block_stack = pop_simulated_stack(block_stack)
                blocks[i // 2 + 1] = block_stack
            elif opcode == END_ASYNC_FOR:
                block_stack = pop_simulated_stack(block_stack, 2)
                blocks[i // 2 + 1] = block_stack
            elif (
                opcode == RETURN_VALUE or
                opcode == RAISE_VARARGS or
                opcode == RERAISE
            ):
                pass
            else:
                blocks[i // 2 + 1] = block_stack
    return blocks

def pop_simulated_stack(stack, offset=1):
    end = len(stack) - offset
    assert end >= 0
    return stack[:end]

def _get_arg(code, addr):
    # read backwards for EXTENDED_ARG
    oparg = ord(code[addr + 1])
    if addr >= 2 and ord(code[addr - 2]) == EXTENDED_ARG:
        oparg |= ord(code[addr - 1]) << 8
        if addr >= 4 and ord(code[addr - 4]) == EXTENDED_ARG:
            raise ValueError("fix me please!")
    return oparg

def compatible_block_stack(from_stack, to_stack):
    if to_stack is None:
        return False
    return from_stack[:len(to_stack)] == to_stack

def explain_incompatible_block_stack(to_stack):
    kind = to_stack[-1]
    if kind == JUMP_BLOCKSTACK_LOOP:
        return "can't jump into the body of a for loop"
    elif kind == JUMP_BLOCKSTACK_TRY:
        return "can't jump into the body of a try statement"
    elif kind == JUMP_BLOCKSTACK_WITH:
        return "can't jump into the body of a with statement"
    else:
        assert kind == JUMP_BLOCKSTACK_EXCEPT
        return "can't jump into an 'except' block as there's no exception"
# ____________________________________________________________

def get_block_class(opname):
    # select the appropriate kind of block
    from pypy.interpreter.pyopcode import block_classes
    return block_classes[opname]

def unpickle_block(space, w_tup):
    w_opname, w_handlerposition, w_valuestackdepth = space.unpackiterable(w_tup)
    opname = space.text_w(w_opname)
    handlerposition = space.int_w(w_handlerposition)
    valuestackdepth = space.int_w(w_valuestackdepth)
    assert valuestackdepth >= 0
    assert handlerposition >= 0
    blk = instantiate(get_block_class(opname))
    blk.handlerposition = handlerposition
    blk.valuestackdepth = valuestackdepth
    return blk