from rpython.jit.codewriter.effectinfo import EffectInfo
from rpython.jit.metainterp import jitprof
from rpython.jit.metainterp.history import (Const, ConstInt, getkind,
    INT, REF, FLOAT, AbstractDescr, IntFrontendOp, RefFrontendOp,
    FloatFrontendOp)
from rpython.jit.metainterp.resoperation import rop
from rpython.rlib import rarithmetic, rstack
from rpython.rlib.objectmodel import (we_are_translated, specialize,
        compute_unique_id)
from rpython.rlib.debug import ll_assert, debug_print
from rpython.rtyper import annlowlevel
from rpython.rtyper.lltypesystem import lltype, llmemory, rffi, rstr
from rpython.rtyper.rclass import OBJECTPTR
from rpython.jit.metainterp.walkvirtual import VirtualVisitor
from rpython.jit.metainterp import resumecode


# Logic to encode the chain of frames and the state of the boxes at a
# guard operation, and to decode it again.  This is a bit advanced,
# because it needs to support optimize.py which encodes virtuals with
# arbitrary cycles and also to compress the information

class VectorInfo(object):
    """
        prev: the previous VectorInfo or None
        failargs_pos: the index where to find it in the fail arguments
        location: the register location (an integer), specified by the backend
        variable: the original variable that lived at failargs_pos
    """
    _attrs_ = ('prev', 'failargs_pos', 'location', 'variable')
    prev = None
    failargs_pos = -1
    location = None
    variable = None

    def __init__(self, position, variable):
        self.failargs_pos = position
        self.variable = variable

    def getpos_in_failargs(self):
        return self.failargs_pos

    def next(self):
        return self.prev

    def getoriginal(self):
        return self.variable

    def clone(self):
        prev = None
        if self.prev:
            prev = self.prev.clone()
        return self.instance_clone(prev)

    def instance_clone(self, prev):
        raise NotImplementedError

class UnpackAtExitInfo(VectorInfo):
    def instance_clone(self, prev):
        info = UnpackAtExitInfo(self.failargs_pos, self.variable)
        info.prev = prev
        return info

class AccumInfo(VectorInfo):
    _attrs_ = ('accum_operation', 'scalar')

    def __init__(self, position, variable, operation):
        VectorInfo.__init__(self, position, variable)
        self.accum_operation = operation

    def instance_clone(self, prev):
        info = AccumInfo(self.failargs_pos, self.variable,
                         self.accum_operation)
        info.location = self.location
        info.prev = prev
        return info

    def __repr__(self):
        return 'AccumInfo(%s,%s,%s,%s,%s)' % (self.prev is None,
                                              self.accum_operation,
                                              self.failargs_pos,
                                              self.variable,
                                              self.location)

def _ensure_parent_resumedata(framestack, n, t, snapshot):
    if n == 0:
        return
    target = framestack[n]
    back = framestack[n - 1]
    if target.parent_snapshot:
        snapshot.prev = target.parent_snapshot
        return
    s = t.create_snapshot(back.jitcode, back.pc, back, True)
    snapshot.prev = s
    _ensure_parent_resumedata(framestack, n - 1, t, s)
    target.parent_snapshot = s

def capture_resumedata(framestack, virtualizable_boxes, virtualref_boxes, t):
    n = len(framestack) - 1
    result = t.length()
    if virtualizable_boxes is not None:
        virtualizable_boxes = ([virtualizable_boxes[-1]] +
                                virtualizable_boxes[:-1])
    else:
        virtualizable_boxes = []
    virtualref_boxes = virtualref_boxes[:]
    if n >= 0:
        top = framestack[n]
        snapshot = t.create_top_snapshot(top.jitcode, top.pc,
                    top, False, virtualizable_boxes,
                    virtualref_boxes)
        _ensure_parent_resumedata(framestack, n, t,snapshot)
    else:
        snapshot = t.create_empty_top_snapshot(
            virtualizable_boxes, virtualref_boxes)
    return result

PENDINGFIELDSTRUCT = lltype.Struct('PendingField',
                                   ('lldescr', OBJECTPTR),
                                   ('num', rffi.SHORT),
                                   ('fieldnum', rffi.SHORT),
                                   ('itemindex', rffi.INT))
PENDINGFIELDSP = lltype.Ptr(lltype.GcArray(PENDINGFIELDSTRUCT))

TAGMASK = 3

class TagOverflow(Exception):
    pass

def tag(value, tagbits):
    assert 0 <= tagbits <= 3
    sx = value >> 13
    if sx != 0 and sx != -1:
        raise TagOverflow
    return rffi.r_short(value<<2|tagbits)

def untag(value):
    value = rarithmetic.widen(value)
    tagbits = value & TAGMASK
    return value >> 2, tagbits

def tagged_eq(x, y):
    # please rpython :(
    return rarithmetic.widen(x) == rarithmetic.widen(y)

def tagged_list_eq(tl1, tl2):
    if len(tl1) != len(tl2):
        return False
    for i in range(len(tl1)):
        if not tagged_eq(tl1[i], tl2[i]):
            return False
    return True

TAGCONST    = 0
TAGINT      = 1
TAGBOX      = 2
TAGVIRTUAL  = 3

UNASSIGNED = tag(-1 << 13, TAGBOX)
UNASSIGNEDVIRTUAL = tag(-1 << 13, TAGVIRTUAL)
NULLREF = tag(-1, TAGCONST)
UNINITIALIZED = tag(-2, TAGCONST)   # used for uninitialized string characters
TAG_CONST_OFFSET = 0

class NumberingState(object):
    def __init__(self, size):
        self.liveboxes = {}
        self.current = [rffi.cast(rffi.SHORT, 0)] * size
        self._pos = 0
        self.num_boxes = 0
        self.num_virtuals = 0

    def append_short(self, item):
        self.current[self._pos] = item
        self._pos += 1

    def append_int(self, item):
        short = rffi.cast(rffi.SHORT, item)
        assert rffi.cast(lltype.Signed, short) == item
        return self.append_short(short)

    def create_numbering(self):
        return resumecode.create_numbering(self.current)

class ResumeDataLoopMemo(object):

    def __init__(self, metainterp_sd):
        self.metainterp_sd = metainterp_sd
        self.cpu = metainterp_sd.cpu
        self.consts = []
        self.large_ints = {}
        self.refs = self.cpu.ts.new_ref_dict_2()
        self.cached_boxes = {}
        self.cached_virtuals = {}

        self.nvirtuals = 0
        self.nvholes = 0
        self.nvreused = 0

    def getconst(self, const):
        if const.type == INT:
            val = const.getint()
            if not we_are_translated() and not isinstance(val, int):
                # unhappiness, probably a symbolic
                return self._newconst(const)
            try:
                return tag(val, TAGINT)
            except TagOverflow:
                pass
            tagged = self.large_ints.get(val, UNASSIGNED)
            if not tagged_eq(tagged, UNASSIGNED):
                return tagged
            tagged = self._newconst(const)
            self.large_ints[val] = tagged
            return tagged
        elif const.type == REF:
            val = const.getref_base()
            if not val:
                return NULLREF
            tagged = self.refs.get(val, UNASSIGNED)
            if not tagged_eq(tagged, UNASSIGNED):
                return tagged
            tagged = self._newconst(const)
            self.refs[val] = tagged
            return tagged
        return self._newconst(const)

    def _newconst(self, const):
        result = tag(len(self.consts) + TAG_CONST_OFFSET, TAGCONST)
        self.consts.append(const)
        return result

    # env numbering

    def _number_boxes(self, iter, arr, optimizer, numb_state):
        """ Number boxes from one snapshot
        """
        num_boxes = numb_state.num_boxes
        num_virtuals = numb_state.num_virtuals
        liveboxes = numb_state.liveboxes
        for item in arr:
            box = iter.get(rffi.cast(lltype.Signed, item))
            box = optimizer.get_box_replacement(box)

            if isinstance(box, Const):
                tagged = self.getconst(box)
            elif box in liveboxes:
                tagged = liveboxes[box]
            else:
                is_virtual = False
                if box.type == 'r':
                    info = optimizer.getptrinfo(box)
                    is_virtual = (info is not None and info.is_virtual())
                if box.type == 'i':
                    info = optimizer.getrawptrinfo(box, create=False)
                    is_virtual = (info is not None and info.is_virtual()) 
                if is_virtual:
                    tagged = tag(num_virtuals, TAGVIRTUAL)
                    num_virtuals += 1
                else:
                    tagged = tag(num_boxes, TAGBOX)
                    num_boxes += 1
                liveboxes[box] = tagged
            numb_state.append_short(tagged)
        numb_state.num_boxes = num_boxes
        numb_state.num_virtuals = num_virtuals

    def number(self, optimizer, position, trace):
        snapshot_iter = trace.get_snapshot_iter(position)
        numb_state = NumberingState(snapshot_iter.size)

        arr = snapshot_iter.vable_array

        numb_state.append_int(len(arr))
        self._number_boxes(snapshot_iter, arr, optimizer, numb_state)

        arr = snapshot_iter.vref_array
        n = len(arr)
        assert not (n & 1)
        numb_state.append_int(n >> 1)

        self._number_boxes(snapshot_iter, arr, optimizer, numb_state)

        for snapshot in snapshot_iter.framestack:
            jitcode_index, pc = snapshot_iter.unpack_jitcode_pc(snapshot)
            numb_state.append_int(jitcode_index)
            numb_state.append_int(pc)
            self._number_boxes(
                    snapshot_iter, snapshot.box_array, optimizer, numb_state)

        return numb_state


    # caching for virtuals and boxes inside them

    def num_cached_boxes(self):
        return len(self.cached_boxes)

    def assign_number_to_box(self, box, boxes):
        # returns a negative number
        if box in self.cached_boxes:
            num = self.cached_boxes[box]
            boxes[-num - 1] = box
        else:
            boxes.append(box)
            num = -len(boxes)
            self.cached_boxes[box] = num
        return num

    def num_cached_virtuals(self):
        return len(self.cached_virtuals)

    def assign_number_to_virtual(self, box):
        # returns a negative number
        if box in self.cached_virtuals:
            num = self.cached_virtuals[box]
        else:
            num = self.cached_virtuals[box] = -len(self.cached_virtuals) - 1
        return num

    def clear_box_virtual_numbers(self):
        self.cached_boxes.clear()
        self.cached_virtuals.clear()

    def update_counters(self, profiler):
        profiler.count(jitprof.Counters.NVIRTUALS, self.nvirtuals)
        profiler.count(jitprof.Counters.NVHOLES, self.nvholes)
        profiler.count(jitprof.Counters.NVREUSED, self.nvreused)

_frame_info_placeholder = (None, 0, 0)


class ResumeDataVirtualAdder(VirtualVisitor):

    def __init__(self, optimizer, storage, guard_op, trace, memo):
        self.optimizer = optimizer
        self.trace = trace
        self.storage = storage
        self.guard_op = guard_op
        self.memo = memo

    def make_virtual_info(self, info, fieldnums):
        assert fieldnums is not None
        vinfo = info._cached_vinfo
        if vinfo is not None and vinfo.equals(fieldnums):
            return vinfo
        vinfo = info.visitor_dispatch_virtual_type(self)
        vinfo.set_content(fieldnums)
        info._cached_vinfo = vinfo
        return vinfo

    def visit_not_virtual(self, value):
        assert 0, "unreachable"

    def visit_virtual(self, descr, fielddescrs):
        return VirtualInfo(descr, fielddescrs)

    def visit_vstruct(self, typedescr, fielddescrs):
        return VStructInfo(typedescr, fielddescrs)

    def visit_varray(self, arraydescr, clear):
        if clear:
            return VArrayInfoClear(arraydescr)
        else:
            return VArrayInfoNotClear(arraydescr)

    def visit_varraystruct(self, arraydescr, size, fielddescrs):
        return VArrayStructInfo(arraydescr, size, fielddescrs)

    def visit_vrawbuffer(self, func, size, offsets, descrs):
        return VRawBufferInfo(func, size, offsets, descrs)

    def visit_vrawslice(self, offset):
        return VRawSliceInfo(offset)

    def visit_vstrplain(self, is_unicode=False):
        if is_unicode:
            return VUniPlainInfo()
        else:
            return VStrPlainInfo()

    def visit_vstrconcat(self, is_unicode=False):
        if is_unicode:
            return VUniConcatInfo()
        else:
            return VStrConcatInfo()

    def visit_vstrslice(self, is_unicode=False):
        if is_unicode:
            return VUniSliceInfo()
        else:
            return VStrSliceInfo()

    def register_virtual_fields(self, virtualbox, _fieldboxes):
        tagged = self.liveboxes_from_env.get(virtualbox, UNASSIGNEDVIRTUAL)
        self.liveboxes[virtualbox] = tagged
        fieldboxes = []
        for box in _fieldboxes:
            if box is not None:
                box = self.optimizer.get_box_replacement(box)
            fieldboxes.append(box)
        self.vfieldboxes[virtualbox] = fieldboxes
        self._register_boxes(fieldboxes)

    def register_box(self, box):
        if (box is not None and not isinstance(box, Const)
            and box not in self.liveboxes_from_env
            and box not in self.liveboxes):
            self.liveboxes[box] = UNASSIGNED

    def _register_boxes(self, boxes):
        for box in boxes:
            self.register_box(box)

    def already_seen_virtual(self, virtualbox):
        if virtualbox not in self.liveboxes:
            assert virtualbox in self.liveboxes_from_env
            assert untag(self.liveboxes_from_env[virtualbox])[1] == TAGVIRTUAL
            return False
        tagged = self.liveboxes[virtualbox]
        _, tagbits = untag(tagged)
        return tagbits == TAGVIRTUAL

    def finish(self, pending_setfields=[]):
        optimizer = self.optimizer
        # compute the numbering
        storage = self.storage
        # make sure that nobody attached resume data to this guard yet
        assert not storage.rd_numb
        resume_position = self.guard_op.rd_resume_position
        assert resume_position >= 0
        # count stack depth
        numb_state = self.memo.number(optimizer,
            resume_position, optimizer.trace)
        self.liveboxes_from_env = liveboxes_from_env = numb_state.liveboxes
        num_virtuals = numb_state.num_virtuals
        self.liveboxes = {}

        # collect liveboxes and virtuals
        n = len(liveboxes_from_env) - num_virtuals
        liveboxes = [None] * n
        self.vfieldboxes = {}
        for box, tagged in liveboxes_from_env.iteritems():
            i, tagbits = untag(tagged)
            if tagbits == TAGBOX:
                liveboxes[i] = box
            else:
                assert tagbits == TAGVIRTUAL
                if box.type == 'r':
                    info = optimizer.getptrinfo(box)
                else:
                    assert box.type == 'i'
                    info = optimizer.getrawptrinfo(box)
                assert info.is_virtual()
                info.visitor_walk_recursive(box, self, optimizer)

        for setfield_op in pending_setfields:
            box = setfield_op.getarg(0)
            box = optimizer.get_box_replacement(box)
            if setfield_op.getopnum() == rop.SETFIELD_GC:
                fieldbox = setfield_op.getarg(1)
            else:
                fieldbox = setfield_op.getarg(2)
            fieldbox = optimizer.get_box_replacement(fieldbox)
            self.register_box(box)
            self.register_box(fieldbox)
            info = optimizer.getptrinfo(fieldbox)
            assert info is not None and info.is_virtual()
            info.visitor_walk_recursive(fieldbox, self, optimizer)

        self._number_virtuals(liveboxes, optimizer, num_virtuals)
        self._add_pending_fields(optimizer, pending_setfields)

        storage.rd_numb = numb_state.create_numbering()
        storage.rd_consts = self.memo.consts
        return liveboxes[:]

    def _number_virtuals(self, liveboxes, optimizer, num_env_virtuals):
        from rpython.jit.metainterp.optimizeopt.info import AbstractVirtualPtrInfo
        
        # !! 'liveboxes' is a list that is extend()ed in-place !!
        memo = self.memo
        new_liveboxes = [None] * memo.num_cached_boxes()
        count = 0
        # So far, self.liveboxes should contain 'tagged' values that are
        # either UNASSIGNED, UNASSIGNEDVIRTUAL, or a *non-negative* value
        # with the TAGVIRTUAL.  The following loop removes the UNASSIGNED
        # and UNASSIGNEDVIRTUAL entries, and replaces them with real
        # negative values.
        for box, tagged in self.liveboxes.iteritems():
            i, tagbits = untag(tagged)
            if tagbits == TAGBOX:
                assert box not in self.liveboxes_from_env
                assert tagged_eq(tagged, UNASSIGNED)
                index = memo.assign_number_to_box(box, new_liveboxes)
                self.liveboxes[box] = tag(index, TAGBOX)
                count += 1
            else:
                assert tagbits == TAGVIRTUAL
                if tagged_eq(tagged, UNASSIGNEDVIRTUAL):
                    assert box not in self.liveboxes_from_env
                    index = memo.assign_number_to_virtual(box)
                    self.liveboxes[box] = tag(index, TAGVIRTUAL)
                else:
                    assert i >= 0
        new_liveboxes.reverse()
        liveboxes.extend(new_liveboxes)
        nholes = len(new_liveboxes) - count

        storage = self.storage
        storage.rd_virtuals = None
        vfieldboxes = self.vfieldboxes
        if vfieldboxes:
            length = num_env_virtuals + memo.num_cached_virtuals()
            virtuals = storage.rd_virtuals = [None] * length
            memo.nvirtuals += length
            memo.nvholes += length - len(vfieldboxes)
            for virtualbox, fieldboxes in vfieldboxes.iteritems():
                num, _ = untag(self.liveboxes[virtualbox])
                info = optimizer.getptrinfo(virtualbox)
                assert info.is_virtual()
                assert isinstance(info, AbstractVirtualPtrInfo)
                fieldnums = [self._gettagged(box)
                             for box in fieldboxes]
                vinfo = self.make_virtual_info(info, fieldnums)
                # if a new vinfo instance is made, we get the fieldnums list we
                # pass in as an attribute. hackish.
                if vinfo.fieldnums is not fieldnums:
                    memo.nvreused += 1
                virtuals[num] = vinfo

        if self._invalidation_needed(len(liveboxes), nholes):
            memo.clear_box_virtual_numbers()

    def _invalidation_needed(self, nliveboxes, nholes):
        memo = self.memo
        # xxx heuristic a bit out of thin air
        failargs_limit = memo.metainterp_sd.options.failargs_limit
        if nliveboxes > (failargs_limit // 2):
            if nholes > nliveboxes // 3:
                return True
        return False

    def _add_pending_fields(self, optimizer, pending_setfields):
        rd_pendingfields = lltype.nullptr(PENDINGFIELDSP.TO)
        if pending_setfields:
            n = len(pending_setfields)
            rd_pendingfields = lltype.malloc(PENDINGFIELDSP.TO, n)
            for i in range(n):
                op = pending_setfields[i]
                box = optimizer.get_box_replacement(op.getarg(0))
                descr = op.getdescr()
                opnum = op.getopnum()
                if opnum == rop.SETARRAYITEM_GC:
                    fieldbox = op.getarg(2)
                    boxindex = optimizer.get_box_replacement(op.getarg(1))
                    itemindex = boxindex.getint()
                    # sanity: it's impossible to run code with SETARRAYITEM_GC
                    # with negative index, so this guard cannot ever fail;
                    # but it's possible to try to *build* such invalid code
                    if itemindex < 0:
                        raise TagOverflow
                elif opnum == rop.SETFIELD_GC:
                    fieldbox = op.getarg(1)
                    itemindex = -1
                else:
                    raise AssertionError
                fieldbox = optimizer.get_box_replacement(fieldbox)
                #descr, box, fieldbox, itemindex = pending_setfields[i]
                lldescr = annlowlevel.cast_instance_to_base_ptr(descr)
                num = self._gettagged(box)
                fieldnum = self._gettagged(fieldbox)
                # the index is limited to 2147483647 (64-bit machines only)
                if itemindex > 2147483647:
                    raise TagOverflow
                #
                rd_pendingfields[i].lldescr = lldescr
                rd_pendingfields[i].num = num
                rd_pendingfields[i].fieldnum = fieldnum
                rd_pendingfields[i].itemindex = rffi.cast(rffi.INT, itemindex)
        self.storage.rd_pendingfields = rd_pendingfields

    def _gettagged(self, box):
        if box is None:
            return UNINITIALIZED
        if isinstance(box, Const):
            return self.memo.getconst(box)
        else:
            if box in self.liveboxes_from_env:
                return self.liveboxes_from_env[box]
            return self.liveboxes[box]

class AbstractVirtualInfo(object):
    kind = REF
    is_about_raw = False
    #def allocate(self, decoder, index):
    #    raise NotImplementedError
    def equals(self, fieldnums):
        return tagged_list_eq(self.fieldnums, fieldnums)

    def set_content(self, fieldnums):
        self.fieldnums = fieldnums

    def debug_prints(self):
        raise NotImplementedError


class AbstractVirtualStructInfo(AbstractVirtualInfo):
    def __init__(self, fielddescrs):
        self.fielddescrs = fielddescrs
        #self.fieldnums = ...

    @specialize.argtype(1)
    def setfields(self, decoder, struct):
        for i in range(len(self.fielddescrs)):
            descr = self.fielddescrs[i]
            num = self.fieldnums[i]
            if not tagged_eq(num, UNINITIALIZED):
                decoder.setfield(struct, num, descr)
        return struct

    def debug_prints(self):
        assert len(self.fielddescrs) == len(self.fieldnums)
        for i in range(len(self.fielddescrs)):
            debug_print("\t\t",
                        str(self.fielddescrs[i]),
                        str(untag(self.fieldnums[i])))

class VirtualInfo(AbstractVirtualStructInfo):
    def __init__(self, descr, fielddescrs):
        AbstractVirtualStructInfo.__init__(self, fielddescrs)
        self.descr = descr

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        struct = decoder.allocate_with_vtable(descr=self.descr)
        decoder.virtuals_cache.set_ptr(index, struct)
        return self.setfields(decoder, struct)

    def debug_prints(self):
        debug_print("\tvirtualinfo", self.known_class.repr_rpython(), " at ",  compute_unique_id(self))
        AbstractVirtualStructInfo.debug_prints(self)


class VStructInfo(AbstractVirtualStructInfo):
    def __init__(self, typedescr, fielddescrs):
        AbstractVirtualStructInfo.__init__(self, fielddescrs)
        self.typedescr = typedescr

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        struct = decoder.allocate_struct(self.typedescr)
        decoder.virtuals_cache.set_ptr(index, struct)
        return self.setfields(decoder, struct)

    def debug_prints(self):
        debug_print("\tvstructinfo", self.typedescr.repr_rpython(), " at ",  compute_unique_id(self))
        AbstractVirtualStructInfo.debug_prints(self)

class AbstractVArrayInfo(AbstractVirtualInfo):
    def __init__(self, arraydescr):
        assert arraydescr is not None
        self.arraydescr = arraydescr
        #self.fieldnums = ...

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        length = len(self.fieldnums)
        arraydescr = self.arraydescr
        array = decoder.allocate_array(length, arraydescr, self.clear)
        decoder.virtuals_cache.set_ptr(index, array)
        # NB. the check for the kind of array elements is moved out of the loop
        if arraydescr.is_array_of_pointers():
            for i in range(length):
                num = self.fieldnums[i]
                if not tagged_eq(num, UNINITIALIZED):
                    decoder.setarrayitem_ref(array, i, num, arraydescr)
        elif arraydescr.is_array_of_floats():
            for i in range(length):
                num = self.fieldnums[i]
                if not tagged_eq(num, UNINITIALIZED):
                    decoder.setarrayitem_float(array, i, num, arraydescr)
        else:
            for i in range(length):
                num = self.fieldnums[i]
                if not tagged_eq(num, UNINITIALIZED):
                    decoder.setarrayitem_int(array, i, num, arraydescr)
        return array

    def debug_prints(self):
        debug_print("\tvarrayinfo", self.arraydescr, " at ",
                    compute_unique_id(self), " clear=", self.clear)
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))


class VArrayInfoClear(AbstractVArrayInfo):
    clear = True

class VArrayInfoNotClear(AbstractVArrayInfo):
    clear = False


class VAbstractRawInfo(AbstractVirtualInfo):
    kind = INT
    is_about_raw = True


class VRawBufferInfo(VAbstractRawInfo):

    def __init__(self, func, size, offsets, descrs):
        self.func = func
        self.size = size
        self.offsets = offsets
        self.descrs = descrs

    @specialize.argtype(1)
    def allocate_int(self, decoder, index):
        length = len(self.fieldnums)
        buffer = decoder.allocate_raw_buffer(self.func, self.size)
        decoder.virtuals_cache.set_int(index, buffer)
        for i in range(len(self.offsets)):
            offset = self.offsets[i]
            descr = self.descrs[i]
            decoder.setrawbuffer_item(buffer, self.fieldnums[i], offset, descr)
        return buffer

    def debug_prints(self):
        debug_print("\tvrawbufferinfo", " at ",  compute_unique_id(self))
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))


class VRawSliceInfo(VAbstractRawInfo):

    def __init__(self, offset):
        self.offset = offset

    @specialize.argtype(1)
    def allocate_int(self, decoder, index):
        assert len(self.fieldnums) == 1
        base_buffer = decoder.decode_int(self.fieldnums[0])
        buffer = decoder.int_add_const(base_buffer, self.offset)
        decoder.virtuals_cache.set_int(index, buffer)
        return buffer

    def debug_prints(self):
        debug_print("\tvrawsliceinfo", " at ",  compute_unique_id(self))
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))


class VArrayStructInfo(AbstractVirtualInfo):
    def __init__(self, arraydescr, size, fielddescrs):
        self.size = size
        self.arraydescr = arraydescr
        self.fielddescrs = fielddescrs

    def debug_prints(self):
        debug_print("\tvarraystructinfo", self.arraydescr, " at ",  compute_unique_id(self))
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        array = decoder.allocate_array(self.size, self.arraydescr,
                                       clear=True)
        decoder.virtuals_cache.set_ptr(index, array)
        p = 0
        for i in range(self.size):
            for j in range(len(self.fielddescrs)):
                num = self.fieldnums[p]
                if not tagged_eq(num, UNINITIALIZED):
                    decoder.setinteriorfield(i, array, num,
                                             self.fielddescrs[j])
                p += 1
        return array


class VStrPlainInfo(AbstractVirtualInfo):
    """Stands for the string made out of the characters of all fieldnums."""

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        length = len(self.fieldnums)
        string = decoder.allocate_string(length)
        decoder.virtuals_cache.set_ptr(index, string)
        for i in range(length):
            charnum = self.fieldnums[i]
            if not tagged_eq(charnum, UNINITIALIZED):
                decoder.string_setitem(string, i, charnum)
        return string

    def debug_prints(self):
        debug_print("\tvstrplaininfo length", len(self.fieldnums), " at ",  compute_unique_id(self))


class VStrConcatInfo(AbstractVirtualInfo):
    """Stands for the string made out of the concatenation of two
    other strings."""

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        # xxx for blackhole resuming, this will build all intermediate
        # strings and throw them away immediately, which is a bit sub-
        # efficient.  Not sure we care.
        left, right = self.fieldnums
        string = decoder.concat_strings(left, right)
        decoder.virtuals_cache.set_ptr(index, string)
        return string

    def debug_prints(self):
        debug_print("\tvstrconcatinfo at ",  compute_unique_id(self))
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))


class VStrSliceInfo(AbstractVirtualInfo):
    """Stands for the string made out of slicing another string."""

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        largerstr, start, length = self.fieldnums
        string = decoder.slice_string(largerstr, start, length)
        decoder.virtuals_cache.set_ptr(index, string)
        return string

    def debug_prints(self):
        debug_print("\tvstrsliceinfo at ",  compute_unique_id(self))
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))


class VUniPlainInfo(AbstractVirtualInfo):
    """Stands for the unicode string made out of the characters of all
    fieldnums."""

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        length = len(self.fieldnums)
        string = decoder.allocate_unicode(length)
        decoder.virtuals_cache.set_ptr(index, string)
        for i in range(length):
            charnum = self.fieldnums[i]
            if not tagged_eq(charnum, UNINITIALIZED):
                decoder.unicode_setitem(string, i, charnum)
        return string

    def debug_prints(self):
        debug_print("\tvuniplaininfo length", len(self.fieldnums), " at ",  compute_unique_id(self))


class VUniConcatInfo(AbstractVirtualInfo):
    """Stands for the unicode string made out of the concatenation of two
    other unicode strings."""

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        # xxx for blackhole resuming, this will build all intermediate
        # strings and throw them away immediately, which is a bit sub-
        # efficient.  Not sure we care.
        left, right = self.fieldnums
        string = decoder.concat_unicodes(left, right)
        decoder.virtuals_cache.set_ptr(index, string)
        return string

    def debug_prints(self):
        debug_print("\tvuniconcatinfo at ",  compute_unique_id(self))
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))


class VUniSliceInfo(AbstractVirtualInfo):
    """Stands for the unicode string made out of slicing another
    unicode string."""

    @specialize.argtype(1)
    def allocate(self, decoder, index):
        largerstr, start, length = self.fieldnums
        string = decoder.slice_unicode(largerstr, start, length)
        decoder.virtuals_cache.set_ptr(index, string)
        return string

    def debug_prints(self):
        debug_print("\tvunisliceinfo at ",  compute_unique_id(self))
        for i in self.fieldnums:
            debug_print("\t\t", str(untag(i)))

# ____________________________________________________________

class AbstractVirtualCache(object):
    pass

def get_VirtualCache_class(suffix):
    # we need to create two copy of this class, because virtuals_*_cache will
    # be lists of different types (one for ResumeDataDirectReader and one for
    # ResumeDataBoxReader)
    class VirtualCache(AbstractVirtualCache):
        def __init__(self, virtuals_ptr_cache, virtuals_int_cache):
            self.virtuals_ptr_cache = virtuals_ptr_cache
            self.virtuals_int_cache = virtuals_int_cache

        def get_ptr(self, i):
            return self.virtuals_ptr_cache[i]

        def get_int(self, i):
            return self.virtuals_int_cache[i]

        def set_ptr(self, i, v):
            self.virtuals_ptr_cache[i] = v

        def set_int(self, i, v):
            self.virtuals_int_cache[i] = v

    VirtualCache.__name__ += suffix
    return VirtualCache

class AbstractResumeDataReader(object):
    """A base mixin containing the logic to reconstruct virtuals out of
    guard failure.  There are two implementations of this mixin:
    ResumeDataBoxReader for when we are compiling (i.e. when we have a
    metainterp), and ResumeDataDirectReader for when we are merely
    blackholing and want the best performance.
    """
    _mixin_ = True
    rd_virtuals = None
    virtuals_cache = None
    virtual_ptr_default = None
    virtual_int_default = None


    def _init(self, cpu, storage):
        self.cpu = cpu
        self.numb = storage.rd_numb
        self.cur_index = 0
        self.count = storage.rd_count
        self.consts = storage.rd_consts

    def _prepare(self, storage):
        self._prepare_virtuals(storage.rd_virtuals)
        self._prepare_pendingfields(storage.rd_pendingfields)

    def read_jitcode_pos_pc(self):
        jitcode_pos, self.cur_index = resumecode.numb_next_item(self.numb,
            self.cur_index)
        pc, self.cur_index = resumecode.numb_next_item(self.numb,
            self.cur_index)
        return jitcode_pos, pc

    def done_reading(self):
        return self.cur_index >= len(self.numb.code)

    def getvirtual_ptr(self, index):
        # Returns the index'th virtual, building it lazily if needed.
        # Note that this may be called recursively; that's why the
        # allocate() methods must fill in the cache as soon as they
        # have the object, before they fill its fields.
        assert self.virtuals_cache is not None
        v = self.virtuals_cache.get_ptr(index)
        if not v:
            assert self.rd_virtuals is not None
            v = self.rd_virtuals[index].allocate(self, index)
            ll_assert(v == self.virtuals_cache.get_ptr(index), "resume.py: bad cache")
        return v

    def getvirtual_int(self, index):
        assert self.virtuals_cache is not None
        v = self.virtuals_cache.get_int(index)
        if not v:
            v = self.rd_virtuals[index]
            ll_assert(bool(v), "resume.py: null rd_virtuals[index]")
            assert v.is_about_raw and isinstance(v, VAbstractRawInfo)
            v = v.allocate_int(self, index)
            ll_assert(v == self.virtuals_cache.get_int(index), "resume.py: bad cache")
        return v

    def force_all_virtuals(self):
        rd_virtuals = self.rd_virtuals
        if rd_virtuals:
            for i in range(len(rd_virtuals)):
                rd_virtual = rd_virtuals[i]
                if rd_virtual is not None:
                    if rd_virtual.kind == REF:
                        self.getvirtual_ptr(i)
                    elif rd_virtual.kind == INT:
                        self.getvirtual_int(i)
                    else:
                        assert False
        return self.virtuals_cache

    def _prepare_virtuals(self, virtuals):
        if virtuals:
            self.rd_virtuals = virtuals
            # XXX: this is suboptimal, because we are creating two lists, one
            # for REFs and one for INTs: but for each index, we are using
            # either one or the other, so we should think of a way to
            # "compact" them
            self.virtuals_cache = self.VirtualCache([self.virtual_ptr_default] * len(virtuals),
                                                    [self.virtual_int_default] * len(virtuals))

    def _prepare_pendingfields(self, pendingfields):
        if pendingfields:
            for i in range(len(pendingfields)):
                lldescr = pendingfields[i].lldescr
                num = pendingfields[i].num
                fieldnum = pendingfields[i].fieldnum
                itemindex = pendingfields[i].itemindex
                descr = annlowlevel.cast_base_ptr_to_instance(AbstractDescr,
                                                              lldescr)
                struct = self.decode_ref(num)
                itemindex = rffi.cast(lltype.Signed, itemindex)
                if itemindex < 0:
                    self.setfield(struct, fieldnum, descr)
                else:
                    self.setarrayitem(struct, itemindex, fieldnum, descr)

    def setarrayitem(self, array, index, fieldnum, arraydescr):
        if arraydescr.is_array_of_pointers():
            self.setarrayitem_ref(array, index, fieldnum, arraydescr)
        elif arraydescr.is_array_of_floats():
            self.setarrayitem_float(array, index, fieldnum, arraydescr)
        else:
            self.setarrayitem_int(array, index, fieldnum, arraydescr)

    def _prepare_next_section(self, info):
        # Use info.enumerate_vars(), normally dispatching to
        # rpython.jit.codewriter.jitcode.  Some tests give a different 'info'.
        self.cur_index = info.enumerate_vars(self._callback_i,
                                        self._callback_r,
                                        self._callback_f,
                                        self.unique_id,  # <-- annotation hack
                                        self.cur_index)

    def _callback_i(self, index, register_index):
        item, index = resumecode.numb_next_item(self.numb, index)
        value = self.decode_int(item)
        self.write_an_int(register_index, value)
        return index

    def _callback_r(self, index, register_index):
        item, index = resumecode.numb_next_item(self.numb, index)
        value = self.decode_ref(item)
        self.write_a_ref(register_index, value)
        return index

    def _callback_f(self, index, register_index):
        item, index = resumecode.numb_next_item(self.numb, index)
        value = self.decode_float(item)
        self.write_a_float(register_index, value)
        return index

# ---------- when resuming for pyjitpl.py, make boxes ----------

def rebuild_from_resumedata(metainterp, storage, deadframe,
                            virtualizable_info, greenfield_info):
    resumereader = ResumeDataBoxReader(storage, deadframe, metainterp)
    boxes = resumereader.consume_vref_and_vable_boxes(virtualizable_info,
                                                      greenfield_info)
    virtualizable_boxes, virtualref_boxes = boxes
    while not resumereader.done_reading():
        jitcode_pos, pc = resumereader.read_jitcode_pos_pc()
        jitcode = metainterp.staticdata.jitcodes[jitcode_pos]
        f = metainterp.newframe(jitcode)
        f.setup_resume_at_op(pc)
        resumereader.consume_boxes(f.get_current_position_info(),
                                   f.registers_i, f.registers_r, f.registers_f)
        f.handle_rvmprof_enter_on_resume()
    return resumereader.liveboxes, virtualizable_boxes, virtualref_boxes


class ResumeDataBoxReader(AbstractResumeDataReader):
    unique_id = lambda: None
    VirtualCache = get_VirtualCache_class('BoxReader')

    def __init__(self, storage, deadframe, metainterp):
        self._init(metainterp.cpu, storage)
        self.deadframe = deadframe
        self.metainterp = metainterp
        self.liveboxes = [None] * storage.rd_count
        self._prepare(storage)

    def consume_boxes(self, info, boxes_i, boxes_r, boxes_f):
        self.boxes_i = boxes_i
        self.boxes_r = boxes_r
        self.boxes_f = boxes_f
        self._prepare_next_section(info)

    def consume_virtualizable_boxes(self, vinfo, index):
        # we have to ignore the initial part of 'nums' (containing vrefs),
        # find the virtualizable from nums[-1], and use it to know how many
        # boxes of which type we have to return.  This does not write
        # anything into the virtualizable.
        numb = self.numb
        item, index = resumecode.numb_next_item(numb, index)
        virtualizablebox = self.decode_ref(item)
        virtualizable = vinfo.unwrap_virtualizable_box(virtualizablebox)
        return vinfo.load_list_of_boxes(virtualizable, self, virtualizablebox,
            numb, index)

    def consume_virtualref_boxes(self, index):
        # Returns a list of boxes, assumed to be all BoxPtrs.
        # We leave up to the caller to call vrefinfo.continue_tracing().
        size, index = resumecode.numb_next_item(self.numb, index)
        if size == 0:
            return [], index
        lst = []
        for i in range(size * 2):
            item, index = resumecode.numb_next_item(self.numb, index)
            lst.append(self.decode_ref(item))
        return lst, index

    def consume_vref_and_vable_boxes(self, vinfo, ginfo):
        vable_size, index = resumecode.numb_next_item(self.numb, 0)
        if vinfo is not None:
            virtualizable_boxes, index = self.consume_virtualizable_boxes(vinfo,
                                                                          index)
        elif ginfo is not None:
            item, index = resumecode.numb_next_item(self.numb, index)
            virtualizable_boxes = [self.decode_ref(item)]
        else:
            virtualizable_boxes = None
        virtualref_boxes, index = self.consume_virtualref_boxes(index)
        self.cur_index = index
        return virtualizable_boxes, virtualref_boxes

    def allocate_with_vtable(self, descr=None):
        return self.metainterp.execute_new_with_vtable(descr=descr)

    def allocate_struct(self, typedescr):
        return self.metainterp.execute_new(typedescr)

    def allocate_array(self, length, arraydescr, clear):
        lengthbox = ConstInt(length)
        if clear:
            return self.metainterp.execute_new_array_clear(arraydescr,
                                                           lengthbox)
        return self.metainterp.execute_new_array(arraydescr, lengthbox)

    def allocate_raw_buffer(self, func, size):
        cic = self.metainterp.staticdata.callinfocollection
        calldescr, _ = cic.callinfo_for_oopspec(EffectInfo.OS_RAW_MALLOC_VARSIZE_CHAR)
        # Can't use 'func' from callinfo_for_oopspec(), because we have
        # several variants (zero/non-zero, memory-pressure or not, etc.)
        # and we have to pick the correct one here; that's why we save
        # it in the VRawBufferInfo.
        return self.metainterp.execute_and_record_varargs(
            rop.CALL_I, [ConstInt(func), ConstInt(size)], calldescr)

    def allocate_string(self, length):
        return self.metainterp.execute_and_record(rop.NEWSTR,
                                                  None, ConstInt(length))

    def string_setitem(self, strbox, index, charnum):
        charbox = self.decode_box(charnum, INT)
        self.metainterp.execute_and_record(rop.STRSETITEM, None,
                                           strbox, ConstInt(index), charbox)

    def concat_strings(self, str1num, str2num):
        cic = self.metainterp.staticdata.callinfocollection
        calldescr, func = cic.callinfo_for_oopspec(EffectInfo.OS_STR_CONCAT)
        str1box = self.decode_box(str1num, REF)
        str2box = self.decode_box(str2num, REF)
        return self.metainterp.execute_and_record_varargs(
            rop.CALL_R, [ConstInt(func), str1box, str2box], calldescr)

    def slice_string(self, strnum, startnum, lengthnum):
        cic = self.metainterp.staticdata.callinfocollection
        calldescr, func = cic.callinfo_for_oopspec(EffectInfo.OS_STR_SLICE)
        strbox = self.decode_box(strnum, REF)
        startbox = self.decode_box(startnum, INT)
        lengthbox = self.decode_box(lengthnum, INT)
        stopbox = self.metainterp.execute_and_record(rop.INT_ADD, None,
                                                     startbox, lengthbox)
        return self.metainterp.execute_and_record_varargs(
            rop.CALL_R, [ConstInt(func), strbox, startbox, stopbox], calldescr)

    def allocate_unicode(self, length):
        return self.metainterp.execute_and_record(rop.NEWUNICODE,
                                                  None, ConstInt(length))

    def unicode_setitem(self, strbox, index, charnum):
        charbox = self.decode_box(charnum, INT)
        self.metainterp.execute_and_record(rop.UNICODESETITEM, None,
                                           strbox, ConstInt(index), charbox)

    def concat_unicodes(self, str1num, str2num):
        cic = self.metainterp.staticdata.callinfocollection
        calldescr, func = cic.callinfo_for_oopspec(EffectInfo.OS_UNI_CONCAT)
        str1box = self.decode_box(str1num, REF)
        str2box = self.decode_box(str2num, REF)
        return self.metainterp.execute_and_record_varargs(
            rop.CALL_R, [ConstInt(func), str1box, str2box], calldescr)

    def slice_unicode(self, strnum, startnum, lengthnum):
        cic = self.metainterp.staticdata.callinfocollection
        calldescr, func = cic.callinfo_for_oopspec(EffectInfo.OS_UNI_SLICE)
        strbox = self.decode_box(strnum, REF)
        startbox = self.decode_box(startnum, INT)
        lengthbox = self.decode_box(lengthnum, INT)
        stopbox = self.metainterp.execute_and_record(rop.INT_ADD, None,
                                                     startbox, lengthbox)
        return self.metainterp.execute_and_record_varargs(
            rop.CALL_R, [ConstInt(func), strbox, startbox, stopbox], calldescr)

    def setfield(self, structbox, fieldnum, descr):
        if descr.is_pointer_field():
            kind = REF
        elif descr.is_float_field():
            kind = FLOAT
        else:
            kind = INT
        fieldbox = self.decode_box(fieldnum, kind)
        self.metainterp.execute_setfield_gc(descr, structbox, fieldbox)

    def setinteriorfield(self, index, array, fieldnum, descr):
        if descr.is_pointer_field():
            kind = REF
        elif descr.is_float_field():
            kind = FLOAT
        else:
            kind = INT
        fieldbox = self.decode_box(fieldnum, kind)
        self.metainterp.execute_setinteriorfield_gc(descr, array,
                                                    ConstInt(index), fieldbox)

    def setarrayitem_int(self, arraybox, index, fieldnum, arraydescr):
        self._setarrayitem(arraybox, index, fieldnum, arraydescr, INT)

    def setarrayitem_ref(self, arraybox, index, fieldnum, arraydescr):
        self._setarrayitem(arraybox, index, fieldnum, arraydescr, REF)

    def setarrayitem_float(self, arraybox, index, fieldnum, arraydescr):
        self._setarrayitem(arraybox, index, fieldnum, arraydescr, FLOAT)

    def _setarrayitem(self, arraybox, index, fieldnum, arraydescr, kind):
        itembox = self.decode_box(fieldnum, kind)
        self.metainterp.execute_setarrayitem_gc(arraydescr, arraybox,
                                                ConstInt(index), itembox)

    def setrawbuffer_item(self, bufferbox, fieldnum, offset, arraydescr):
        if arraydescr.is_array_of_pointers():
            kind = REF
        elif arraydescr.is_array_of_floats():
            kind = FLOAT
        else:
            kind = INT
        itembox = self.decode_box(fieldnum, kind)
        self.metainterp.execute_raw_store(arraydescr, bufferbox,
                                          ConstInt(offset), itembox)

    def decode_int(self, tagged):
        return self.decode_box(tagged, INT)

    def decode_ref(self, tagged):
        return self.decode_box(tagged, REF)

    def decode_float(self, tagged):
        return self.decode_box(tagged, FLOAT)

    def decode_box(self, tagged, kind):
        num, tag = untag(tagged)
        if tag == TAGCONST:
            if tagged_eq(tagged, NULLREF):
                box = self.cpu.ts.CONST_NULL
            else:
                box = self.consts[num - TAG_CONST_OFFSET]
        elif tag == TAGVIRTUAL:
            if kind == INT:
                box = self.getvirtual_int(num)
            else:
                box = self.getvirtual_ptr(num)
        elif tag == TAGINT:
            box = ConstInt(num)
        else:
            assert tag == TAGBOX
            box = self.liveboxes[num]
            if box is None:
                box = self.load_box_from_cpu(num, kind)
        assert box.type == kind
        return box

    def load_box_from_cpu(self, num, kind):
        if num < 0:
            num += len(self.liveboxes)
            assert num >= 0
        if kind == INT:
            box = IntFrontendOp(0)
            box.setint(self.cpu.get_int_value(self.deadframe, num))
        elif kind == REF:
            box = RefFrontendOp(0)
            box.setref_base(self.cpu.get_ref_value(self.deadframe, num))
        elif kind == FLOAT:
            box = FloatFrontendOp(0)
            box.setfloatstorage(self.cpu.get_float_value(self.deadframe, num))
        else:
            assert 0, "bad kind: %d" % ord(kind)
        self.liveboxes[num] = box
        return box

    def decode_box_of_type(self, TYPE, tagged):
        kind = getkind(TYPE)
        if kind == 'int':
            kind = INT
        elif kind == 'ref':
            kind = REF
        elif kind == 'float':
            kind = FLOAT
        else:
            raise AssertionError(kind)
        return self.decode_box(tagged, kind)
    decode_box_of_type._annspecialcase_ = 'specialize:arg(1)'

    def write_an_int(self, index, box):
        self.boxes_i[index] = box

    def write_a_ref(self, index, box):
        self.boxes_r[index] = box

    def write_a_float(self, index, box):
        self.boxes_f[index] = box

    def int_add_const(self, intbox, offset):
        return self.metainterp.execute_and_record(rop.INT_ADD, None, intbox,
                                                  ConstInt(offset))

# ---------- when resuming for blackholing, get direct values ----------

def blackhole_from_resumedata(blackholeinterpbuilder, jitcodes,
                              jitdriver_sd, storage,
                              deadframe, all_virtuals=None):
    # The initialization is stack-critical code: it must not be interrupted by
    # StackOverflow, otherwise the jit_virtual_refs are left in a dangling state.
    rstack._stack_criticalcode_start()
    try:
        resumereader = ResumeDataDirectReader(blackholeinterpbuilder.metainterp_sd,
                                              storage, deadframe, all_virtuals)
        vinfo = jitdriver_sd.virtualizable_info
        ginfo = jitdriver_sd.greenfield_info
        vrefinfo = blackholeinterpbuilder.metainterp_sd.virtualref_info
        resumereader.consume_vref_and_vable(vrefinfo, vinfo, ginfo)
    finally:
        rstack._stack_criticalcode_stop()
    #
    # First get a chain of blackhole interpreters whose length is given
    # by the positions in the numbering.  The first one we get must be
    # the bottom one, i.e. the last one in the chain, in order to make
    # the comment in BlackholeInterpreter.setposition() valid.
    curbh = None
    while not resumereader.done_reading():
        nextbh = blackholeinterpbuilder.acquire_interp()
        nextbh.nextblackholeinterp = curbh
        curbh = nextbh
        jitcode_pos, pc = resumereader.read_jitcode_pos_pc()
        jitcode = jitcodes[jitcode_pos]
        curbh.setposition(jitcode, pc)
        resumereader.consume_one_section(curbh)
        curbh.handle_rvmprof_enter()
    return curbh

def force_from_resumedata(metainterp_sd, storage, deadframe, vinfo, ginfo):
    resumereader = ResumeDataDirectReader(metainterp_sd, storage, deadframe)
    resumereader.handling_async_forcing()
    vrefinfo = metainterp_sd.virtualref_info
    resumereader.consume_vref_and_vable(vrefinfo, vinfo, ginfo)
    return resumereader.force_all_virtuals()


class ResumeDataDirectReader(AbstractResumeDataReader):
    unique_id = lambda: None
    virtual_ptr_default = lltype.nullptr(llmemory.GCREF.TO)
    virtual_int_default = 0
    resume_after_guard_not_forced = 0
    VirtualCache = get_VirtualCache_class('DirectReader')
    #             0: not a GUARD_NOT_FORCED
    #             1: in handle_async_forcing
    #             2: resuming from the GUARD_NOT_FORCED

    def __init__(self, metainterp_sd, storage, deadframe, all_virtuals=None):
        self._init(metainterp_sd.cpu, storage)
        self.deadframe = deadframe
        self.callinfocollection = metainterp_sd.callinfocollection
        if all_virtuals is None:        # common case
            self._prepare(storage)
        else:
            # special case for resuming after a GUARD_NOT_FORCED: we already
            # have the virtuals
            self.resume_after_guard_not_forced = 2
            self.virtuals_cache = all_virtuals
            # self.rd_virtuals can remain None, because virtuals_cache is
            # already filled

    def handling_async_forcing(self):
        self.resume_after_guard_not_forced = 1

    def consume_one_section(self, blackholeinterp):
        self.blackholeinterp = blackholeinterp
        info = blackholeinterp.get_current_position_info()
        self._prepare_next_section(info)

    def consume_virtualref_info(self, vrefinfo, index):
        # we have to decode a list of references containing pairs
        # [..., virtual, vref, ...] and returns the index at the end
        size, index = resumecode.numb_next_item(self.numb, index)
        if vrefinfo is None or size == 0:
            assert size == 0
            return index
        for i in range(size):
            virtual_item, index = resumecode.numb_next_item(
                self.numb, index)
            vref_item, index = resumecode.numb_next_item(
                self.numb, index)
            virtual = self.decode_ref(virtual_item)
            vref = self.decode_ref(vref_item)
            # For each pair, we store the virtual inside the vref.
            vrefinfo.continue_tracing(vref, virtual)
        return index

    def consume_vable_info(self, vinfo, index):
        # we have to ignore the initial part of 'nums' (containing vrefs),
        # find the virtualizable from nums[-1], load all other values
        # from the CPU stack, and copy them into the virtualizable
        numb = self.numb
        item, index = resumecode.numb_next_item(self.numb, index)
        virtualizable = self.decode_ref(item)
        # just reset the token, we'll force it later
        vinfo.reset_token_gcref(virtualizable)
        index = vinfo.write_from_resume_data_partial(virtualizable, self,
            index, numb)
        return index

    def load_value_of_type(self, TYPE, tagged):
        from rpython.jit.metainterp.warmstate import specialize_value
        kind = getkind(TYPE)
        if kind == 'int':
            x = self.decode_int(tagged)
        elif kind == 'ref':
            x = self.decode_ref(tagged)
        elif kind == 'float':
            x = self.decode_float(tagged)
        else:
            raise AssertionError(kind)
        return specialize_value(TYPE, x)
    load_value_of_type._annspecialcase_ = 'specialize:arg(1)'

    def consume_vref_and_vable(self, vrefinfo, vinfo, ginfo):
        vable_size, index = resumecode.numb_next_item(self.numb, 0)
        if self.resume_after_guard_not_forced != 2:
            if vinfo is not None:
                index = self.consume_vable_info(vinfo, index)
            if ginfo is not None:
                _, index = resumecode.numb_next_item(self.numb, index)
            index = self.consume_virtualref_info(vrefinfo, index)
        else:
            index = resumecode.numb_next_n_items(self.numb, vable_size, index)
            vref_size, index = resumecode.numb_next_item(self.numb, index)
            index = resumecode.numb_next_n_items(self.numb, vref_size * 2, index)
        self.cur_index = index 

    def allocate_with_vtable(self, descr=None):
        from rpython.jit.metainterp.executor import exec_new_with_vtable
        return exec_new_with_vtable(self.cpu, descr)

    def allocate_struct(self, typedescr):
        return self.cpu.bh_new(typedescr)

    def allocate_array(self, length, arraydescr, clear):
        if clear:
            return self.cpu.bh_new_array_clear(length, arraydescr)
        return self.cpu.bh_new_array(length, arraydescr)

    def allocate_string(self, length):
        return self.cpu.bh_newstr(length)

    def allocate_raw_buffer(self, func, size):
        from rpython.jit.codewriter import heaptracker
        cic = self.callinfocollection
        calldescr, _ = cic.callinfo_for_oopspec(EffectInfo.OS_RAW_MALLOC_VARSIZE_CHAR)
        return self.cpu.bh_call_i(func, [size], None, None, calldescr)

    def string_setitem(self, str, index, charnum):
        char = self.decode_int(charnum)
        self.cpu.bh_strsetitem(str, index, char)

    def concat_strings(self, str1num, str2num):
        str1 = self.decode_ref(str1num)
        str2 = self.decode_ref(str2num)
        str1 = lltype.cast_opaque_ptr(lltype.Ptr(rstr.STR), str1)
        str2 = lltype.cast_opaque_ptr(lltype.Ptr(rstr.STR), str2)
        cic = self.callinfocollection
        funcptr = cic.funcptr_for_oopspec(EffectInfo.OS_STR_CONCAT)
        result = funcptr(str1, str2)
        return lltype.cast_opaque_ptr(llmemory.GCREF, result)

    def slice_string(self, strnum, startnum, lengthnum):
        str = self.decode_ref(strnum)
        start = self.decode_int(startnum)
        length = self.decode_int(lengthnum)
        str = lltype.cast_opaque_ptr(lltype.Ptr(rstr.STR), str)
        cic = self.callinfocollection
        funcptr = cic.funcptr_for_oopspec(EffectInfo.OS_STR_SLICE)
        result = funcptr(str, start, start + length)
        return lltype.cast_opaque_ptr(llmemory.GCREF, result)

    def allocate_unicode(self, length):
        return self.cpu.bh_newunicode(length)

    def unicode_setitem(self, str, index, charnum):
        char = self.decode_int(charnum)
        self.cpu.bh_unicodesetitem(str, index, char)

    def concat_unicodes(self, str1num, str2num):
        str1 = self.decode_ref(str1num)
        str2 = self.decode_ref(str2num)
        str1 = lltype.cast_opaque_ptr(lltype.Ptr(rstr.UNICODE), str1)
        str2 = lltype.cast_opaque_ptr(lltype.Ptr(rstr.UNICODE), str2)
        cic = self.callinfocollection
        funcptr = cic.funcptr_for_oopspec(EffectInfo.OS_UNI_CONCAT)
        result = funcptr(str1, str2)
        return lltype.cast_opaque_ptr(llmemory.GCREF, result)

    def slice_unicode(self, strnum, startnum, lengthnum):
        str = self.decode_ref(strnum)
        start = self.decode_int(startnum)
        length = self.decode_int(lengthnum)
        str = lltype.cast_opaque_ptr(lltype.Ptr(rstr.UNICODE), str)
        cic = self.callinfocollection
        funcptr = cic.funcptr_for_oopspec(EffectInfo.OS_UNI_SLICE)
        result = funcptr(str, start, start + length)
        return lltype.cast_opaque_ptr(llmemory.GCREF, result)

    def setfield(self, struct, fieldnum, descr):
        if descr.is_pointer_field():
            newvalue = self.decode_ref(fieldnum)
            self.cpu.bh_setfield_gc_r(struct, newvalue, descr)
        elif descr.is_float_field():
            newvalue = self.decode_float(fieldnum)
            self.cpu.bh_setfield_gc_f(struct, newvalue, descr)
        else:
            newvalue = self.decode_int(fieldnum)
            self.cpu.bh_setfield_gc_i(struct, newvalue, descr)

    def setinteriorfield(self, index, array, fieldnum, descr):
        if descr.is_pointer_field():
            newvalue = self.decode_ref(fieldnum)
            self.cpu.bh_setinteriorfield_gc_r(array, index, newvalue, descr)
        elif descr.is_float_field():
            newvalue = self.decode_float(fieldnum)
            self.cpu.bh_setinteriorfield_gc_f(array, index, newvalue, descr)
        else:
            newvalue = self.decode_int(fieldnum)
            self.cpu.bh_setinteriorfield_gc_i(array, index, newvalue, descr)

    def setarrayitem_int(self, array, index, fieldnum, arraydescr):
        newvalue = self.decode_int(fieldnum)
        self.cpu.bh_setarrayitem_gc_i(array, index, newvalue, arraydescr)

    def setarrayitem_ref(self, array, index, fieldnum, arraydescr):
        newvalue = self.decode_ref(fieldnum)
        self.cpu.bh_setarrayitem_gc_r(array, index, newvalue, arraydescr)

    def setarrayitem_float(self, array, index, fieldnum, arraydescr):
        newvalue = self.decode_float(fieldnum)
        self.cpu.bh_setarrayitem_gc_f(array, index, newvalue, arraydescr)

    def setrawbuffer_item(self, buffer, fieldnum, offset, descr):
        assert not descr.is_array_of_pointers()
        if descr.is_array_of_floats():
            newvalue = self.decode_float(fieldnum)
            self.cpu.bh_raw_store_f(buffer, offset, newvalue, descr)
        else:
            newvalue = self.decode_int(fieldnum)
            self.cpu.bh_raw_store_i(buffer, offset, newvalue, descr)

    def decode_int(self, tagged):
        num, tag = untag(tagged)
        if tag == TAGCONST:
            return self.consts[num - TAG_CONST_OFFSET].getint()
        elif tag == TAGINT:
            return num
        elif tag == TAGVIRTUAL:
            return self.getvirtual_int(num)
        else:
            assert tag == TAGBOX
            if num < 0:
                num += self.count
            return self.cpu.get_int_value(self.deadframe, num)

    def decode_ref(self, tagged):
        num, tag = untag(tagged)
        if tag == TAGCONST:
            if tagged_eq(tagged, NULLREF):
                return self.cpu.ts.NULLREF
            return self.consts[num - TAG_CONST_OFFSET].getref_base()
        elif tag == TAGVIRTUAL:
            return self.getvirtual_ptr(num)
        else:
            assert tag == TAGBOX
            if num < 0:
                num += self.count
            return self.cpu.get_ref_value(self.deadframe, num)

    def decode_float(self, tagged):
        num, tag = untag(tagged)
        if tag == TAGCONST:
            return self.consts[num - TAG_CONST_OFFSET].getfloatstorage()
        else:
            assert tag == TAGBOX
            if num < 0:
                num += self.count
            return self.cpu.get_float_value(self.deadframe, num)

    def write_an_int(self, index, int):
        self.blackholeinterp.setarg_i(index, int)

    def write_a_ref(self, index, ref):
        self.blackholeinterp.setarg_r(index, ref)

    def write_a_float(self, index, float):
        self.blackholeinterp.setarg_f(index, float)

    def int_add_const(self, base, offset):
        return base + offset