/pypy/jit/backend/x86/assembler.py

import sys, os
from pypy.jit.backend.llsupport import symbolic
from pypy.jit.backend.llsupport.asmmemmgr import MachineDataBlockWrapper
from pypy.jit.metainterp.history import Const, Box, BoxInt, ConstInt
from pypy.jit.metainterp.history import AbstractFailDescr, INT, REF, FLOAT
from pypy.jit.metainterp.history import JitCellToken
from pypy.rpython.lltypesystem import lltype, rffi, rstr, llmemory
from pypy.rpython.lltypesystem.lloperation import llop
from pypy.rpython.annlowlevel import llhelper
from pypy.rlib.jit import AsmInfo
from pypy.jit.backend.model import CompiledLoopToken
from pypy.jit.backend.x86.regalloc import (RegAlloc, get_ebp_ofs, _get_scale,
    gpr_reg_mgr_cls, _valid_addressing_size)

from pypy.jit.backend.x86.arch import (FRAME_FIXED_SIZE, FORCE_INDEX_OFS, WORD,
                                       IS_X86_32, IS_X86_64)

from pypy.jit.backend.x86.regloc import (eax, ecx, edx, ebx,
                                         esp, ebp, esi, edi,
                                         xmm0, xmm1, xmm2, xmm3,
                                         xmm4, xmm5, xmm6, xmm7,
                                         r8, r9, r10, r11,
                                         r12, r13, r14, r15,
                                         X86_64_SCRATCH_REG,
                                         X86_64_XMM_SCRATCH_REG,
                                         RegLoc, StackLoc, ConstFloatLoc,
                                         ImmedLoc, AddressLoc, imm,
                                         imm0, imm1, FloatImmedLoc)

from pypy.rlib.objectmodel import we_are_translated, specialize
from pypy.jit.backend.x86 import rx86, regloc, codebuf
from pypy.jit.metainterp.resoperation import rop, ResOperation
from pypy.jit.backend.x86.support import values_array
from pypy.jit.backend.x86 import support
from pypy.rlib.debug import (debug_print, debug_start, debug_stop,
                             have_debug_prints)
from pypy.rlib import rgc
from pypy.rlib.clibffi import FFI_DEFAULT_ABI
from pypy.jit.backend.x86.jump import remap_frame_layout
from pypy.jit.codewriter.effectinfo import EffectInfo
from pypy.jit.codewriter import longlong
from pypy.rlib.rarithmetic import intmask
from pypy.rlib.objectmodel import compute_unique_id

# darwin requires the stack to be 16 bytes aligned on calls. Same for gcc 4.5.0,
# better safe than sorry
CALL_ALIGN = 16 // WORD

def align_stack_words(words):
    return (words + CALL_ALIGN - 1) & ~(CALL_ALIGN-1)


class GuardToken(object):
    def __init__(self, faildescr, failargs, fail_locs, exc,
                 is_guard_not_invalidated):
        self.faildescr = faildescr
        self.failargs = failargs
        self.fail_locs = fail_locs
        self.exc = exc
        self.is_guard_not_invalidated = is_guard_not_invalidated

DEBUG_COUNTER = lltype.Struct('DEBUG_COUNTER', ('i', lltype.Signed),
                              ('type', lltype.Char), # 'b'ridge, 'l'abel or
                                                     # 'e'ntry point
                              ('number', lltype.Signed))

class Assembler386(object):
    _regalloc = None
    _output_loop_log = None

    def __init__(self, cpu, translate_support_code=False,
                            failargs_limit=1000):
        self.cpu = cpu
        self.verbose = False
        self.rtyper = cpu.rtyper
        self.fail_boxes_int = values_array(lltype.Signed, failargs_limit)
        self.fail_boxes_ptr = values_array(llmemory.GCREF, failargs_limit)
        self.fail_boxes_float = values_array(longlong.FLOATSTORAGE,
                                             failargs_limit)
        self.fail_ebp = 0
        self.loop_run_counters = []
        self.float_const_neg_addr = 0
        self.float_const_abs_addr = 0
        self.malloc_slowpath1 = 0
        self.malloc_slowpath2 = 0
        self.memcpy_addr = 0
        self.setup_failure_recovery()
        self._debug = False
        self.debug_counter_descr = cpu.fielddescrof(DEBUG_COUNTER, 'i')
        self.fail_boxes_count = 0
        self._current_depths_cache = (0, 0)
        self.datablockwrapper = None
        self.stack_check_slowpath = 0
        self.propagate_exception_path = 0
        self.gcrootmap_retaddr_forced = 0
        self.teardown()

    def leave_jitted_hook(self):
        ptrs = self.fail_boxes_ptr.ar
        llop.gc_assume_young_pointers(lltype.Void,
                                      llmemory.cast_ptr_to_adr(ptrs))

    def set_debug(self, v):
        self._debug = v

    def setup_once(self):
        # the address of the function called by 'new'
        gc_ll_descr = self.cpu.gc_ll_descr
        gc_ll_descr.initialize()
        self.memcpy_addr = self.cpu.cast_ptr_to_int(support.memcpy_fn)
        self._build_failure_recovery(False)
        self._build_failure_recovery(True)
        if self.cpu.supports_floats:
            self._build_failure_recovery(False, withfloats=True)
            self._build_failure_recovery(True, withfloats=True)
            support.ensure_sse2_floats()
            self._build_float_constants()
        self._build_propagate_exception_path()
        if gc_ll_descr.get_malloc_slowpath_addr is not None:
            self._build_malloc_slowpath()
        self._build_stack_check_slowpath()
        if gc_ll_descr.gcrootmap:
            self._build_release_gil(gc_ll_descr.gcrootmap)
        debug_start('jit-backend-counts')
        self.set_debug(have_debug_prints())
        debug_stop('jit-backend-counts')

    def setup(self, looptoken):
        assert self.memcpy_addr != 0, "setup_once() not called?"
        self.current_clt = looptoken.compiled_loop_token
        self.pending_guard_tokens = []
        if WORD == 8:
            self.pending_memoryerror_trampoline_from = []
            self.error_trampoline_64 = 0
        self.mc = codebuf.MachineCodeBlockWrapper()
        #assert self.datablockwrapper is None --- but obscure case
        # possible, e.g. getting MemoryError and continuing
        allblocks = self.get_asmmemmgr_blocks(looptoken)
        self.datablockwrapper = MachineDataBlockWrapper(self.cpu.asmmemmgr,
                                                        allblocks)
        self.target_tokens_currently_compiling = {}

    def teardown(self):
        self.pending_guard_tokens = None
        if WORD == 8:
            self.pending_memoryerror_trampoline_from = None
        self.mc = None
        self.current_clt = None

    def finish_once(self):
        if self._debug:
            debug_start('jit-backend-counts')
            for i in range(len(self.loop_run_counters)):
                struct = self.loop_run_counters[i]
                if struct.type == 'l':
                    prefix = 'TargetToken(%d)' % struct.number
                elif struct.type == 'b':
                    prefix = 'bridge ' + str(struct.number)
                else:
                    prefix = 'entry ' + str(struct.number)
                debug_print(prefix + ':' + str(struct.i))
            debug_stop('jit-backend-counts')

    def _build_float_constants(self):
        datablockwrapper = MachineDataBlockWrapper(self.cpu.asmmemmgr, [])
        float_constants = datablockwrapper.malloc_aligned(32, alignment=16)
        datablockwrapper.done()
        addr = rffi.cast(rffi.CArrayPtr(lltype.Char), float_constants)
        qword_padding = '\x00\x00\x00\x00\x00\x00\x00\x00'
        # 0x8000000000000000
        neg_const = '\x00\x00\x00\x00\x00\x00\x00\x80'
        # 0x7FFFFFFFFFFFFFFF
        abs_const = '\xFF\xFF\xFF\xFF\xFF\xFF\xFF\x7F'
        data = neg_const + qword_padding + abs_const + qword_padding
        for i in range(len(data)):
            addr[i] = data[i]
        self.float_const_neg_addr = float_constants
        self.float_const_abs_addr = float_constants + 16

    def _build_malloc_slowpath(self):
        # With asmgcc, we need two helpers, so that we can write two CALL
        # instructions in assembler, with a mark_gc_roots in between.
        # With shadowstack, this is not needed, so we produce a single helper.
        gcrootmap = self.cpu.gc_ll_descr.gcrootmap
        shadow_stack = (gcrootmap is not None and gcrootmap.is_shadow_stack)
        #
        # ---------- first helper for the slow path of malloc ----------
        mc = codebuf.MachineCodeBlockWrapper()
        if self.cpu.supports_floats:          # save the XMM registers in
            for i in range(self.cpu.NUM_REGS):# the *caller* frame, from esp+8
                mc.MOVSD_sx((WORD*2)+8*i, i)
        mc.SUB_rr(edx.value, eax.value)       # compute the size we want
        addr = self.cpu.gc_ll_descr.get_malloc_slowpath_addr()
        #
        # The registers to save in the copy area: with shadowstack, most
        # registers need to be saved.  With asmgcc, the callee-saved registers
        # don't need to.
        save_in_copy_area = gpr_reg_mgr_cls.REGLOC_TO_COPY_AREA_OFS.items()
        if not shadow_stack:
            save_in_copy_area = [(reg, ofs) for (reg, ofs) in save_in_copy_area
                   if reg not in gpr_reg_mgr_cls.REGLOC_TO_GCROOTMAP_REG_INDEX]
        #
        for reg, ofs in save_in_copy_area:
            mc.MOV_br(ofs, reg.value)
        #
        if shadow_stack:
            # ---- shadowstack ----
            mc.SUB_ri(esp.value, 16 - WORD)      # stack alignment of 16 bytes
            if IS_X86_32:
                mc.MOV_sr(0, edx.value)          # push argument
            elif IS_X86_64:
                mc.MOV_rr(edi.value, edx.value)
            mc.CALL(imm(addr))
            mc.ADD_ri(esp.value, 16 - WORD)
        else:
            # ---- asmgcc ----
            if IS_X86_32:
                mc.MOV_sr(WORD, edx.value)       # save it as the new argument
            elif IS_X86_64:
                # rdi can be clobbered: its content was saved in the
                # copy area of the stack
                mc.MOV_rr(edi.value, edx.value)
            mc.JMP(imm(addr))                    # tail call to the real malloc
            rawstart = mc.materialize(self.cpu.asmmemmgr, [])
            self.malloc_slowpath1 = rawstart
            # ---------- second helper for the slow path of malloc ----------
            mc = codebuf.MachineCodeBlockWrapper()
        #
        for reg, ofs in save_in_copy_area:
            mc.MOV_rb(reg.value, ofs)
            assert reg is not eax and reg is not edx
        #
        if self.cpu.supports_floats:          # restore the XMM registers
            for i in range(self.cpu.NUM_REGS):# from where they were saved
                mc.MOVSD_xs(i, (WORD*2)+8*i)
        #
        # Note: we check this after the code above, just because the code
        # above is more than 127 bytes on 64-bits...
        mc.TEST_rr(eax.value, eax.value)
        mc.J_il8(rx86.Conditions['Z'], 0) # patched later
        jz_location = mc.get_relative_pos()
        #
        nursery_free_adr = self.cpu.gc_ll_descr.get_nursery_free_addr()
        mc.MOV(edx, heap(nursery_free_adr))   # load this in EDX
        mc.RET()
        #
        # If the slowpath malloc failed, we raise a MemoryError that
        # always interrupts the current loop, as a "good enough"
        # approximation.  Also note that we didn't RET from this helper;
        # but the code we jump to will actually restore the stack
        # position based on EBP, which will get us out of here for free.
        offset = mc.get_relative_pos() - jz_location
        assert 0 < offset <= 127
        mc.overwrite(jz_location-1, chr(offset))
        mc.JMP(imm(self.propagate_exception_path))
        #
        rawstart = mc.materialize(self.cpu.asmmemmgr, [])
        self.malloc_slowpath2 = rawstart

    def _build_propagate_exception_path(self):
        if self.cpu.propagate_exception_v < 0:
            return      # not supported (for tests, or non-translated)
        #
        self.mc = codebuf.MachineCodeBlockWrapper()
        # call on_leave_jitted_save_exc()
        addr = self.cpu.get_on_leave_jitted_int(save_exception=True,
                                                default_to_memoryerror=True)
        self.mc.CALL(imm(addr))
        self.mc.MOV_ri(eax.value, self.cpu.propagate_exception_v)
        self._call_footer()
        rawstart = self.mc.materialize(self.cpu.asmmemmgr, [])
        self.propagate_exception_path = rawstart
        self.mc = None

    def _build_stack_check_slowpath(self):
        _, _, slowpathaddr = self.cpu.insert_stack_check()
        if slowpathaddr == 0 or self.cpu.propagate_exception_v < 0:
            return      # no stack check (for tests, or non-translated)
        #
        # make a "function" that is called immediately at the start of
        # an assembler function.  In particular, the stack looks like:
        #
        #    |  ...                |    <-- aligned to a multiple of 16
        #    |  retaddr of caller  |
        #    |  my own retaddr     |    <-- esp
        #    +---------------------+
        #
        mc = codebuf.MachineCodeBlockWrapper()
        #
        stack_size = WORD
        if IS_X86_64:
            # on the x86_64, we have to save all the registers that may
            # have been used to pass arguments
            stack_size += 6*WORD + 8*8
            for reg in [edi, esi, edx, ecx, r8, r9]:
                mc.PUSH_r(reg.value)
            mc.SUB_ri(esp.value, 8*8)
            for i in range(8):
                mc.MOVSD_sx(8*i, i)     # xmm0 to xmm7
        #
        if IS_X86_32:
            stack_size += 2*WORD
            mc.PUSH_r(eax.value)        # alignment
            mc.PUSH_r(esp.value)
        elif IS_X86_64:
            mc.MOV_rr(edi.value, esp.value)
        #
        # esp is now aligned to a multiple of 16 again
        mc.CALL(imm(slowpathaddr))
        #
        mc.MOV(eax, heap(self.cpu.pos_exception()))
        mc.TEST_rr(eax.value, eax.value)
        mc.J_il8(rx86.Conditions['NZ'], 0)
        jnz_location = mc.get_relative_pos()
        #
        if IS_X86_32:
            mc.ADD_ri(esp.value, 2*WORD)    # cancel the two PUSHes above
        elif IS_X86_64:
            # restore the registers
            for i in range(7, -1, -1):
                mc.MOVSD_xs(i, 8*i)
            mc.ADD_ri(esp.value, 8*8)
            for reg in [r9, r8, ecx, edx, esi, edi]:
                mc.POP_r(reg.value)
        #
        mc.RET()
        #
        # patch the JNZ above
        offset = mc.get_relative_pos() - jnz_location
        assert 0 < offset <= 127
        mc.overwrite(jnz_location-1, chr(offset))
        # call on_leave_jitted_save_exc()
        addr = self.cpu.get_on_leave_jitted_int(save_exception=True)
        mc.CALL(imm(addr))
        #
        mc.MOV_ri(eax.value, self.cpu.propagate_exception_v)
        #
        # footer -- note the ADD, which skips the return address of this
        # function, and will instead return to the caller's caller.  Note
        # also that we completely ignore the saved arguments, because we
        # are interrupting the function.
        mc.ADD_ri(esp.value, stack_size)
        mc.RET()
        #
        rawstart = mc.materialize(self.cpu.asmmemmgr, [])
        self.stack_check_slowpath = rawstart

    @staticmethod
    @rgc.no_collect
    def _release_gil_asmgcc(css):
        # similar to trackgcroot.py:pypy_asm_stackwalk, first part
        from pypy.rpython.memory.gctransform import asmgcroot
        new = rffi.cast(asmgcroot.ASM_FRAMEDATA_HEAD_PTR, css)
        next = asmgcroot.gcrootanchor.next
        new.next = next
        new.prev = asmgcroot.gcrootanchor
        asmgcroot.gcrootanchor.next = new
        next.prev = new
        # and now release the GIL
        before = rffi.aroundstate.before
        if before:
            before()

    @staticmethod
    @rgc.no_collect
    def _reacquire_gil_asmgcc(css):
        # first reacquire the GIL
        after = rffi.aroundstate.after
        if after:
            after()
        # similar to trackgcroot.py:pypy_asm_stackwalk, second part
        from pypy.rpython.memory.gctransform import asmgcroot
        old = rffi.cast(asmgcroot.ASM_FRAMEDATA_HEAD_PTR, css)
        prev = old.prev
        next = old.next
        prev.next = next
        next.prev = prev

    @staticmethod
    @rgc.no_collect
    def _release_gil_shadowstack():
        before = rffi.aroundstate.before
        if before:
            before()

    @staticmethod
    @rgc.no_collect
    def _reacquire_gil_shadowstack():
        after = rffi.aroundstate.after
        if after:
            after()

    _NOARG_FUNC = lltype.Ptr(lltype.FuncType([], lltype.Void))
    _CLOSESTACK_FUNC = lltype.Ptr(lltype.FuncType([rffi.LONGP],
                                                  lltype.Void))

    def _build_release_gil(self, gcrootmap):
        if gcrootmap.is_shadow_stack:
            releasegil_func = llhelper(self._NOARG_FUNC,
                                       self._release_gil_shadowstack)
            reacqgil_func = llhelper(self._NOARG_FUNC,
                                     self._reacquire_gil_shadowstack)
        else:
            releasegil_func = llhelper(self._CLOSESTACK_FUNC,
                                       self._release_gil_asmgcc)
            reacqgil_func = llhelper(self._CLOSESTACK_FUNC,
                                     self._reacquire_gil_asmgcc)
        self.releasegil_addr  = self.cpu.cast_ptr_to_int(releasegil_func)
        self.reacqgil_addr = self.cpu.cast_ptr_to_int(reacqgil_func)

    def assemble_loop(self, loopname, inputargs, operations, looptoken, log):
        '''adds the following attributes to looptoken:
               _x86_function_addr   (address of the generated func, as an int)
               _x86_loop_code       (debug: addr of the start of the ResOps)
               _x86_fullsize        (debug: full size including failure)
               _x86_debug_checksum
        '''
        # XXX this function is too longish and contains some code
        # duplication with assemble_bridge().  Also, we should think
        # about not storing on 'self' attributes that will live only
        # for the duration of compiling one loop or a one bridge.

        clt = CompiledLoopToken(self.cpu, looptoken.number)
        clt.allgcrefs = []
        looptoken.compiled_loop_token = clt
        if not we_are_translated():
            # Arguments should be unique
            assert len(set(inputargs)) == len(inputargs)

        self.setup(looptoken)
        if log:
            operations = self._inject_debugging_code(looptoken, operations,
                                                     'e', looptoken.number)

        regalloc = RegAlloc(self, self.cpu.translate_support_code)
        #
        self._call_header_with_stack_check()
        stackadjustpos = self._patchable_stackadjust()
        clt._debug_nbargs = len(inputargs)
        operations = regalloc.prepare_loop(inputargs, operations,
                                           looptoken, clt.allgcrefs)
        looppos = self.mc.get_relative_pos()
        looptoken._x86_loop_code = looppos
        clt.frame_depth = -1     # temporarily
        clt.param_depth = -1     # temporarily
        frame_depth, param_depth = self._assemble(regalloc, operations)
        clt.frame_depth = frame_depth
        clt.param_depth = param_depth
        #
        size_excluding_failure_stuff = self.mc.get_relative_pos()
        self.write_pending_failure_recoveries()
        full_size = self.mc.get_relative_pos()
        #
        rawstart = self.materialize_loop(looptoken)
        debug_start("jit-backend-addr")
        debug_print("Loop %d (%s) has address %x to %x (bootstrap %x)" % (
            looptoken.number, loopname,
            rawstart + looppos,
            rawstart + size_excluding_failure_stuff,
            rawstart))
        debug_stop("jit-backend-addr")
        self._patch_stackadjust(rawstart + stackadjustpos,
                                frame_depth + param_depth)
        self.patch_pending_failure_recoveries(rawstart)
        #
        ops_offset = self.mc.ops_offset
        if not we_are_translated():
            # used only by looptoken.dump() -- useful in tests
            looptoken._x86_rawstart = rawstart
            looptoken._x86_fullsize = full_size
            looptoken._x86_ops_offset = ops_offset
        looptoken._x86_function_addr = rawstart

        self.fixup_target_tokens(rawstart)
        self.teardown()
        # oprofile support
        if self.cpu.profile_agent is not None:
            name = "Loop # %s: %s" % (looptoken.number, loopname)
            self.cpu.profile_agent.native_code_written(name,
                                                       rawstart, full_size)
        return AsmInfo(ops_offset, rawstart + looppos,
                       size_excluding_failure_stuff - looppos)

    def assemble_bridge(self, faildescr, inputargs, operations,
                        original_loop_token, log):
        if not we_are_translated():
            # Arguments should be unique
            assert len(set(inputargs)) == len(inputargs)

        descr_number = self.cpu.get_fail_descr_number(faildescr)
        failure_recovery = self._find_failure_recovery_bytecode(faildescr)

        self.setup(original_loop_token)
        if log:
            operations = self._inject_debugging_code(faildescr, operations,
                                                     'b', descr_number)

        arglocs = self.rebuild_faillocs_from_descr(failure_recovery)
        if not we_are_translated():
            assert ([loc.assembler() for loc in arglocs] ==
                    [loc.assembler() for loc in faildescr._x86_debug_faillocs])
        regalloc = RegAlloc(self, self.cpu.translate_support_code)
        fail_depths = faildescr._x86_current_depths
        startpos = self.mc.get_relative_pos()
        operations = regalloc.prepare_bridge(fail_depths, inputargs, arglocs,
                                             operations,
                                             self.current_clt.allgcrefs)

        stackadjustpos = self._patchable_stackadjust()
        frame_depth, param_depth = self._assemble(regalloc, operations)
        codeendpos = self.mc.get_relative_pos()
        self.write_pending_failure_recoveries()
        fullsize = self.mc.get_relative_pos()
        #
        rawstart = self.materialize_loop(original_loop_token)
        debug_start("jit-backend-addr")
        debug_print("bridge out of Guard %d has address %x to %x" %
                    (descr_number, rawstart, rawstart + codeendpos))
        debug_stop("jit-backend-addr")
        self._patch_stackadjust(rawstart + stackadjustpos,
                                frame_depth + param_depth)
        self.patch_pending_failure_recoveries(rawstart)
        if not we_are_translated():
            # for the benefit of tests
            faildescr._x86_bridge_frame_depth = frame_depth
            faildescr._x86_bridge_param_depth = param_depth
        # patch the jump from original guard
        self.patch_jump_for_descr(faildescr, rawstart)
        ops_offset = self.mc.ops_offset
        self.fixup_target_tokens(rawstart)
        self.current_clt.frame_depth = max(self.current_clt.frame_depth, frame_depth)
        self.current_clt.param_depth = max(self.current_clt.param_depth, param_depth)
        self.teardown()
        # oprofile support
        if self.cpu.profile_agent is not None:
            name = "Bridge # %s" % (descr_number,)
            self.cpu.profile_agent.native_code_written(name,
                                                       rawstart, fullsize)
        return AsmInfo(ops_offset, startpos + rawstart, codeendpos - startpos)

    def write_pending_failure_recoveries(self):
        # for each pending guard, generate the code of the recovery stub
        # at the end of self.mc.
        for tok in self.pending_guard_tokens:
            tok.pos_recovery_stub = self.generate_quick_failure(tok)
        if WORD == 8 and len(self.pending_memoryerror_trampoline_from) > 0:
            self.error_trampoline_64 = self.generate_propagate_error_64()

    def patch_pending_failure_recoveries(self, rawstart):
        # after we wrote the assembler to raw memory, set up
        # tok.faildescr._x86_adr_jump_offset to contain the raw address of
        # the 4-byte target field in the JMP/Jcond instruction, and patch
        # the field in question to point (initially) to the recovery stub
        clt = self.current_clt
        for tok in self.pending_guard_tokens:
            addr = rawstart + tok.pos_jump_offset
            tok.faildescr._x86_adr_jump_offset = addr
            relative_target = tok.pos_recovery_stub - (tok.pos_jump_offset + 4)
            assert rx86.fits_in_32bits(relative_target)
            #
            if not tok.is_guard_not_invalidated:
                mc = codebuf.MachineCodeBlockWrapper()
                mc.writeimm32(relative_target)
                mc.copy_to_raw_memory(addr)
            else:
                # GUARD_NOT_INVALIDATED, record an entry in
                # clt.invalidate_positions of the form:
                #     (addr-in-the-code-of-the-not-yet-written-jump-target,
                #      relative-target-to-use)
                relpos = tok.pos_jump_offset
                clt.invalidate_positions.append((rawstart + relpos,
                                                 relative_target))
                # General idea: Although no code was generated by this
                # guard, the code might be patched with a "JMP rel32" to
                # the guard recovery code.  This recovery code is
                # already generated, and looks like the recovery code
                # for any guard, even if at first it has no jump to it.
                # So we may later write 5 bytes overriding the existing
                # instructions; this works because a CALL instruction
                # would also take at least 5 bytes.  If it could take
                # less, we would run into the issue that overwriting the
                # 5 bytes here might get a few nonsense bytes at the
                # return address of the following CALL.
        if WORD == 8:
            for pos_after_jz in self.pending_memoryerror_trampoline_from:
                assert self.error_trampoline_64 != 0     # only if non-empty
                mc = codebuf.MachineCodeBlockWrapper()
                mc.writeimm32(self.error_trampoline_64 - pos_after_jz)
                mc.copy_to_raw_memory(rawstart + pos_after_jz - 4)

    def get_asmmemmgr_blocks(self, looptoken):
        clt = looptoken.compiled_loop_token
        if clt.asmmemmgr_blocks is None:
            clt.asmmemmgr_blocks = []
        return clt.asmmemmgr_blocks

    def materialize_loop(self, looptoken):
        self.datablockwrapper.done()      # finish using cpu.asmmemmgr
        self.datablockwrapper = None
        allblocks = self.get_asmmemmgr_blocks(looptoken)
        return self.mc.materialize(self.cpu.asmmemmgr, allblocks,
                                   self.cpu.gc_ll_descr.gcrootmap)

    def _register_counter(self, tp, number, token):
        # YYY very minor leak -- we need the counters to stay alive
        # forever, just because we want to report them at the end
        # of the process
        struct = lltype.malloc(DEBUG_COUNTER, flavor='raw',
                               track_allocation=False)
        struct.i = 0
        struct.type = tp
        if tp == 'b' or tp == 'e':
            struct.number = number
        else:
            assert token
            struct.number = compute_unique_id(token)
        self.loop_run_counters.append(struct)            
        return struct

    def _find_failure_recovery_bytecode(self, faildescr):
        adr_jump_offset = faildescr._x86_adr_jump_offset
        if adr_jump_offset == 0:
            # This case should be prevented by the logic in compile.py:
            # look for CNT_BUSY_FLAG, which disables tracing from a guard
            # when another tracing from the same guard is already in progress.
            raise BridgeAlreadyCompiled
        # follow the JMP/Jcond
        p = rffi.cast(rffi.INTP, adr_jump_offset)
        adr_target = adr_jump_offset + 4 + rffi.cast(lltype.Signed, p[0])
        # skip the CALL
        if WORD == 4:
            adr_target += 5     # CALL imm
        else:
            adr_target += 13    # MOV r11, imm-as-8-bytes; CALL *r11 xxxxxxxxxx
        return adr_target

    def patch_jump_for_descr(self, faildescr, adr_new_target):
        adr_jump_offset = faildescr._x86_adr_jump_offset
        assert adr_jump_offset != 0
        offset = adr_new_target - (adr_jump_offset + 4)
        # If the new target fits within a rel32 of the jump, just patch
        # that. Otherwise, leave the original rel32 to the recovery stub in
        # place, but clobber the recovery stub with a jump to the real
        # target.
        mc = codebuf.MachineCodeBlockWrapper()
        if rx86.fits_in_32bits(offset):
            mc.writeimm32(offset)
            mc.copy_to_raw_memory(adr_jump_offset)
        else:
            # "mov r11, addr; jmp r11" is up to 13 bytes, which fits in there
            # because we always write "mov r11, imm-as-8-bytes; call *r11" in
            # the first place.
            mc.MOV_ri(X86_64_SCRATCH_REG.value, adr_new_target)
            mc.JMP_r(X86_64_SCRATCH_REG.value)
            p = rffi.cast(rffi.INTP, adr_jump_offset)
            adr_target = adr_jump_offset + 4 + rffi.cast(lltype.Signed, p[0])
            mc.copy_to_raw_memory(adr_target)
        faildescr._x86_adr_jump_offset = 0    # means "patched"

    def fixup_target_tokens(self, rawstart):
        for targettoken in self.target_tokens_currently_compiling:
            targettoken._x86_loop_code += rawstart
        self.target_tokens_currently_compiling = None

    def _append_debugging_code(self, operations, tp, number, token):
        counter = self._register_counter(tp, number, token)
        c_adr = ConstInt(rffi.cast(lltype.Signed, counter))
        box = BoxInt()
        box2 = BoxInt()
        ops = [ResOperation(rop.GETFIELD_RAW, [c_adr],
                            box, descr=self.debug_counter_descr),
               ResOperation(rop.INT_ADD, [box, ConstInt(1)], box2),
               ResOperation(rop.SETFIELD_RAW, [c_adr, box2],
                            None, descr=self.debug_counter_descr)]
        operations.extend(ops)
        
    @specialize.argtype(1)
    def _inject_debugging_code(self, looptoken, operations, tp, number):
        if self._debug:
            # before doing anything, let's increase a counter
            s = 0
            for op in operations:
                s += op.getopnum()
            looptoken._x86_debug_checksum = s

            newoperations = []
            self._append_debugging_code(newoperations, tp, number,
                                        None)
            for op in operations:
                newoperations.append(op)
                if op.getopnum() == rop.LABEL:
                    self._append_debugging_code(newoperations, 'l', number,
                                                op.getdescr())
            operations = newoperations
        return operations

    def _assemble(self, regalloc, operations):
        self._regalloc = regalloc
        regalloc.compute_hint_frame_locations(operations)
        regalloc.walk_operations(operations)
        if we_are_translated() or self.cpu.dont_keepalive_stuff:
            self._regalloc = None   # else keep it around for debugging
        frame_depth = regalloc.fm.get_frame_depth()
        param_depth = regalloc.param_depth
        jump_target_descr = regalloc.jump_target_descr
        if jump_target_descr is not None:
            target_frame_depth = jump_target_descr._x86_clt.frame_depth
            target_param_depth = jump_target_descr._x86_clt.param_depth
            frame_depth = max(frame_depth, target_frame_depth)
            param_depth = max(param_depth, target_param_depth)
        return frame_depth, param_depth

    def _patchable_stackadjust(self):
        # stack adjustment LEA
        self.mc.LEA32_rb(esp.value, 0)
        return self.mc.get_relative_pos() - 4

    def _patch_stackadjust(self, adr_lea, allocated_depth):
        # patch stack adjustment LEA
        mc = codebuf.MachineCodeBlockWrapper()
        # Compute the correct offset for the instruction LEA ESP, [EBP-4*words]
        mc.writeimm32(self._get_offset_of_ebp_from_esp(allocated_depth))
        mc.copy_to_raw_memory(adr_lea)

    def _get_offset_of_ebp_from_esp(self, allocated_depth):
        # Given that [EBP] is where we saved EBP, i.e. in the last word
        # of our fixed frame, then the 'words' value is:
        words = (FRAME_FIXED_SIZE - 1) + allocated_depth
        # align, e.g. for Mac OS X
        aligned_words = align_stack_words(words+2)-2 # 2 = EIP+EBP
        return -WORD * aligned_words

    def _call_header(self):
        # NB. the shape of the frame is hard-coded in get_basic_shape() too.
        # Also, make sure this is consistent with FRAME_FIXED_SIZE.
        self.mc.PUSH_r(ebp.value)
        self.mc.MOV_rr(ebp.value, esp.value)
        for loc in self.cpu.CALLEE_SAVE_REGISTERS:
            self.mc.PUSH_r(loc.value)

        gcrootmap = self.cpu.gc_ll_descr.gcrootmap
        if gcrootmap and gcrootmap.is_shadow_stack:
            self._call_header_shadowstack(gcrootmap)

    def _call_header_with_stack_check(self):
        if self.stack_check_slowpath == 0:
            pass                # no stack check (e.g. not translated)
        else:
            endaddr, lengthaddr, _ = self.cpu.insert_stack_check()
            self.mc.MOV(eax, heap(endaddr))             # MOV eax, [start]
            self.mc.SUB(eax, esp)                       # SUB eax, current
            self.mc.CMP(eax, heap(lengthaddr))          # CMP eax, [length]
            self.mc.J_il8(rx86.Conditions['BE'], 0)     # JBE .skip
            jb_location = self.mc.get_relative_pos()
            self.mc.CALL(imm(self.stack_check_slowpath))# CALL slowpath
            # patch the JB above                        # .skip:
            offset = self.mc.get_relative_pos() - jb_location
            assert 0 < offset <= 127
            self.mc.overwrite(jb_location-1, chr(offset))
            #
        self._call_header()

    def _call_footer(self):
        self.mc.LEA_rb(esp.value, -len(self.cpu.CALLEE_SAVE_REGISTERS) * WORD)

        gcrootmap = self.cpu.gc_ll_descr.gcrootmap
        if gcrootmap and gcrootmap.is_shadow_stack:
            self._call_footer_shadowstack(gcrootmap)

        for i in range(len(self.cpu.CALLEE_SAVE_REGISTERS)-1, -1, -1):
            self.mc.POP_r(self.cpu.CALLEE_SAVE_REGISTERS[i].value)

        self.mc.POP_r(ebp.value)
        self.mc.RET()

    def _call_header_shadowstack(self, gcrootmap):
        # we need to put two words into the shadowstack: the MARKER_FRAME
        # and the address of the frame (ebp, actually)
        rst = gcrootmap.get_root_stack_top_addr()
        if rx86.fits_in_32bits(rst):
            self.mc.MOV_rj(eax.value, rst)            # MOV eax, [rootstacktop]
        else:
            self.mc.MOV_ri(r13.value, rst)            # MOV r13, rootstacktop
            self.mc.MOV_rm(eax.value, (r13.value, 0)) # MOV eax, [r13]
        #
        MARKER = gcrootmap.MARKER_FRAME
        self.mc.LEA_rm(ebx.value, (eax.value, 2*WORD)) # LEA ebx, [eax+2*WORD]
        self.mc.MOV_mi((eax.value, WORD), MARKER)      # MOV [eax+WORD], MARKER
        self.mc.MOV_mr((eax.value, 0), ebp.value)      # MOV [eax], ebp
        #
        if rx86.fits_in_32bits(rst):
            self.mc.MOV_jr(rst, ebx.value)            # MOV [rootstacktop], ebx
        else:
            self.mc.MOV_mr((r13.value, 0), ebx.value) # MOV [r13], ebx

    def _call_footer_shadowstack(self, gcrootmap):
        rst = gcrootmap.get_root_stack_top_addr()
        if rx86.fits_in_32bits(rst):
            self.mc.SUB_ji8(rst, 2*WORD)       # SUB [rootstacktop], 2*WORD
        else:
            self.mc.MOV_ri(ebx.value, rst)           # MOV ebx, rootstacktop
            self.mc.SUB_mi8((ebx.value, 0), 2*WORD)  # SUB [ebx], 2*WORD

    def redirect_call_assembler(self, oldlooptoken, newlooptoken):
        # some minimal sanity checking
        old_nbargs = oldlooptoken.compiled_loop_token._debug_nbargs
        new_nbargs = newlooptoken.compiled_loop_token._debug_nbargs
        assert old_nbargs == new_nbargs
        # we overwrite the instructions at the old _x86_direct_bootstrap_code
        # to start with a JMP to the new _x86_direct_bootstrap_code.
        # Ideally we should rather patch all existing CALLs, but well.
        oldadr = oldlooptoken._x86_function_addr
        target = newlooptoken._x86_function_addr
        mc = codebuf.MachineCodeBlockWrapper()
        mc.JMP(imm(target))
        if WORD == 4:         # keep in sync with prepare_loop()
            assert mc.get_relative_pos() == 5
        else:
            assert mc.get_relative_pos() <= 13
        mc.copy_to_raw_memory(oldadr)

    def dump(self, text):
        if not self.verbose:
            return
        _prev = Box._extended_display
        try:
            Box._extended_display = False
            pos = self.mc.get_relative_pos()
            print >> sys.stderr, ' 0x%x  %s' % (pos, text)
        finally:
            Box._extended_display = _prev

    # ------------------------------------------------------------

    def mov(self, from_loc, to_loc):
        if (isinstance(from_loc, RegLoc) and from_loc.is_xmm) or (isinstance(to_loc, RegLoc) and to_loc.is_xmm):
            self.mc.MOVSD(to_loc, from_loc)
        else:
            assert to_loc is not ebp
            self.mc.MOV(to_loc, from_loc)

    regalloc_mov = mov # legacy interface

    def regalloc_push(self, loc):
        if isinstance(loc, RegLoc) and loc.is_xmm:
            self.mc.SUB_ri(esp.value, 8)   # = size of doubles
            self.mc.MOVSD_sx(0, loc.value)
        elif WORD == 4 and isinstance(loc, StackLoc) and loc.get_width() == 8:
            # XXX evil trick
            self.mc.PUSH_b(get_ebp_ofs(loc.position))
            self.mc.PUSH_b(get_ebp_ofs(loc.position + 1))
        else:
            self.mc.PUSH(loc)

    def regalloc_pop(self, loc):
        if isinstance(loc, RegLoc) and loc.is_xmm:
            self.mc.MOVSD_xs(loc.value, 0)
            self.mc.ADD_ri(esp.value, 8)   # = size of doubles
        elif WORD == 4 and isinstance(loc, StackLoc) and loc.get_width() == 8:
            # XXX evil trick
            self.mc.POP_b(get_ebp_ofs(loc.position + 1))
            self.mc.POP_b(get_ebp_ofs(loc.position))
        else:
            self.mc.POP(loc)

    def regalloc_immedmem2mem(self, from_loc, to_loc):
        # move a ConstFloatLoc directly to a StackLoc, as two MOVs
        # (even on x86-64, because the immediates are encoded as 32 bits)
        assert isinstance(from_loc, ConstFloatLoc)
        assert isinstance(to_loc,   StackLoc)
        low_part  = rffi.cast(rffi.CArrayPtr(rffi.INT), from_loc.value)[0]
        high_part = rffi.cast(rffi.CArrayPtr(rffi.INT), from_loc.value)[1]
        low_part  = intmask(low_part)
        high_part = intmask(high_part)
        self.mc.MOV32_bi(to_loc.value,     low_part)
        self.mc.MOV32_bi(to_loc.value + 4, high_part)

    def regalloc_perform(self, op, arglocs, resloc):
        genop_list[op.getopnum()](self, op, arglocs, resloc)

    def regalloc_perform_discard(self, op, arglocs):
        genop_discard_list[op.getopnum()](self, op, arglocs)

    def regalloc_perform_llong(self, op, arglocs, resloc):
        effectinfo = op.getdescr().get_extra_info()
        oopspecindex = effectinfo.oopspecindex
        genop_llong_list[oopspecindex](self, op, arglocs, resloc)

    def regalloc_perform_math(self, op, arglocs, resloc):
        effectinfo = op.getdescr().get_extra_info()
        oopspecindex = effectinfo.oopspecindex
        genop_math_list[oopspecindex](self, op, arglocs, resloc)

    def regalloc_perform_with_guard(self, op, guard_op, faillocs,
                                    arglocs, resloc, current_depths):
        faildescr = guard_op.getdescr()
        assert isinstance(faildescr, AbstractFailDescr)
        faildescr._x86_current_depths = current_depths
        failargs = guard_op.getfailargs()
        guard_opnum = guard_op.getopnum()
        guard_token = self.implement_guard_recovery(guard_opnum,
                                                    faildescr, failargs,
                                                    faillocs)
        if op is None:
            dispatch_opnum = guard_opnum
        else:
            dispatch_opnum = op.getopnum()
        genop_guard_list[dispatch_opnum](self, op, guard_op, guard_token,
                                         arglocs, resloc)
        if not we_are_translated():
            # must be added by the genop_guard_list[]()
            assert guard_token is self.pending_guard_tokens[-1]

    def regalloc_perform_guard(self, guard_op, faillocs, arglocs, resloc,
                               current_depths):
        self.regalloc_perform_with_guard(None, guard_op, faillocs, arglocs,
                                         resloc, current_depths)

    def load_effective_addr(self, sizereg, baseofs, scale, result, frm=imm0):
        self.mc.LEA(result, addr_add(frm, sizereg, baseofs, scale))

    def _unaryop(asmop):
        def genop_unary(self, op, arglocs, resloc):
            getattr(self.mc, asmop)(arglocs[0])
        return genop_unary

    def _binaryop(asmop, can_swap=False):
        def genop_binary(self, op, arglocs, result_loc):
            getattr(self.mc, asmop)(arglocs[0], arglocs[1])
        return genop_binary

    def _cmpop(cond, rev_cond):
        def genop_cmp(self, op, arglocs, result_loc):
            rl = result_loc.lowest8bits()
            if isinstance(op.getarg(0), Const):
                self.mc.CMP(arglocs[1], arglocs[0])
                self.mc.SET_ir(rx86.Conditions[rev_cond], rl.value)
            else:
                self.mc.CMP(arglocs[0], arglocs[1])
                self.mc.SET_ir(rx86.Conditions[cond], rl.value)
            self.mc.MOVZX8_rr(result_loc.value, rl.value)
        return genop_cmp

    def _cmpop_float(cond, rev_cond, is_ne=False):
        def genop_cmp(self, op, arglocs, result_loc):
            if isinstance(arglocs[0], RegLoc):
                self.mc.UCOMISD(arglocs[0], arglocs[1])
                checkcond = cond
            else:
                self.mc.UCOMISD(arglocs[1], arglocs[0])
                checkcond = rev_cond

            tmp1 = result_loc.lowest8bits()
            if IS_X86_32:
                tmp2 = result_loc.higher8bits()
            elif IS_X86_64:
                tmp2 = X86_64_SCRATCH_REG.lowest8bits()

            self.mc.SET_ir(rx86.Conditions[checkcond], tmp1.value)
            if is_ne:
                self.mc.SET_ir(rx86.Conditions['P'], tmp2.value)
                self.mc.OR8_rr(tmp1.value, tmp2.value)
            else:
                self.mc.SET_ir(rx86.Conditions['NP'], tmp2.value)
                self.mc.AND8_rr(tmp1.value, tmp2.value)
            self.mc.MOVZX8_rr(result_loc.value, tmp1.value)
        return genop_cmp

    def _cmpop_guard(cond, rev_cond, false_cond, false_rev_cond):
        def genop_cmp_guard(self, op, guard_op, guard_token, arglocs, result_loc):
            guard_opnum = guard_op.getopnum()
            if isinstance(op.getarg(0), Const):
                self.mc.CMP(arglocs[1], arglocs[0])
                if guard_opnum == rop.GUARD_FALSE:
                    self.implement_guard(guard_token, rev_cond)
                else:
                    self.implement_guard(guard_token, false_rev_cond)
            else:
                self.mc.CMP(arglocs[0], arglocs[1])
                if guard_opnum == rop.GUARD_FALSE:
                    self.implement_guard(guard_token, cond)
                else:
                    self.implement_guard(guard_token, false_cond)
        return genop_cmp_guard

    def _cmpop_guard_float(cond, rev_cond, false_cond, false_rev_cond):
        need_direct_jp = 'A' not in cond
        need_rev_jp = 'A' not in rev_cond
        def genop_cmp_guard_float(self, op, guard_op, guard_token, arglocs,
                                  result_loc):
            guard_opnum = guard_op.getopnum()
            if isinstance(arglocs[0], RegLoc):
                self.mc.UCOMISD(arglocs[0], arglocs[1])
                checkcond = cond
                checkfalsecond = false_cond
                need_jp = need_direct_jp
            else:
                self.mc.UCOMISD(arglocs[1], arglocs[0])
                checkcond = rev_cond
                checkfalsecond = false_rev_cond
                need_jp = need_rev_jp
            if guard_opnum == rop.GUARD_FALSE:
                if need_jp:
                    self.mc.J_il8(rx86.Conditions['P'], 6)
                self.implement_guard(guard_token, checkcond)
            else:
                if need_jp:
                    self.mc.J_il8(rx86.Conditions['P'], 2)
                    self.mc.J_il8(rx86.Conditions[checkcond], 5)
                    self.implement_guard(guard_token)
                else:
                    self.implement_guard(guard_token, checkfalsecond)
        return genop_cmp_guard_float

    def _emit_call(self, force_index, x, arglocs, start=0, tmp=eax,
                   argtypes=None, callconv=FFI_DEFAULT_ABI):
        if IS_X86_64:
            return self._emit_call_64(force_index, x, arglocs, start, argtypes)

        p = 0
        n = len(arglocs)
        for i in range(start, n):
            loc = arglocs[i]
            if isinstance(loc, RegLoc):
                if loc.is_xmm:
                    self.mc.MOVSD_sx(p, loc.value)
                else:
                    self.mc.MOV_sr(p, loc.value)
            p += loc.get_width()
        p = 0
        for i in range(start, n):
            loc = arglocs[i]
            if not isinstance(loc, RegLoc):
                if loc.get_width() == 8:
                    self.mc.MOVSD(xmm0, loc)
                    self.mc.MOVSD_sx(p, xmm0.value)
                else:
                    self.mc.MOV(tmp, loc)
                    self.mc.MOV_sr(p, tmp.value)
            p += loc.get_width()
        self._regalloc.reserve_param(p//WORD)
        # x is a location
        self.mc.CALL(x)
        self.mark_gc_roots(force_index)
        #
        if callconv != FFI_DEFAULT_ABI:
            self._fix_stdcall(callconv, p)

    def _fix_stdcall(self, callconv, p):
        from pypy.rlib.clibffi import FFI_STDCALL
        assert callconv == FFI_STDCALL
        # it's a bit stupid, but we're just going to cancel the fact that
        # the called function just added 'p' to ESP, by subtracting it again.
        self.mc.SUB_ri(esp.value, p)

    def _emit_call_64(self, force_index, x, arglocs, start, argtypes):
        src_locs = []
        dst_locs = []
        xmm_src_locs = []
        xmm_dst_locs = []
        pass_on_stack = []
        singlefloats = None

        # In reverse order for use with pop()
        unused_gpr = [r9, r8, ecx, edx, esi, edi]
        unused_xmm = [xmm7, xmm6, xmm5, xmm4, xmm3, xmm2, xmm1, xmm0]

        for i in range(start, len(arglocs)):
            loc = arglocs[i]
            # XXX: Should be much simplier to tell whether a location is a
            # float! It's so ugly because we have to "guard" the access to
            # .type with isinstance, since not all AssemblerLocation classes
            # are "typed"
            if ((isinstance(loc, RegLoc) and loc.is_xmm) or
                (isinstance(loc, StackLoc) and loc.type == FLOAT) or
                (isinstance(loc, ConstFloatLoc))):
                if len(unused_xmm) > 0:
                    xmm_src_locs.append(loc)
                    xmm_dst_locs.append(unused_xmm.pop())
                else:
                    pass_on_stack.append(loc)
            elif (argtypes is not None and argtypes[i-start] == 'S' and
                  len(unused_xmm) > 0):
                # Singlefloat argument
                if singlefloats is None: singlefloats = []
                singlefloats.append((loc, unused_xmm.pop()))
            else:
                if len(unused_gpr) > 0:
                    src_locs.append(loc)
                    dst_locs.append(unused_gpr.pop())
                else:
                    pass_on_stack.append(loc)

        # Emit instructions to pass the stack arguments
        # XXX: Would be nice to let remap_frame_layout take care of this, but
        # we'd need to create something like StackLoc, but relative to esp,
        # and I don't know if it's worth it.
        for i in range(len(pass_on_stack)):
            loc = pass_on_stack[i]
            if not isinstance(loc, RegLoc):
                if isinstance(loc, StackLoc) and loc.type == FLOAT:
                    self.mc.MOVSD(X86_64_XMM_SCRATCH_REG, loc)
                    self.mc.MOVSD_sx(i*WORD, X86_64_XMM_SCRATCH_REG.value)
                else:
                    self.mc.MOV(X86_64_SCRATCH_REG, loc)
                    self.mc.MOV_sr(i*WORD, X86_64_SCRATCH_REG.value)
            else:
                # It's a register
                if loc.is_xmm:
                    self.mc.MOVSD_sx(i*WORD, loc.value)
                else:
                    self.mc.MOV_sr(i*WORD, loc.value)

        # Handle register arguments: first remap the xmm arguments
        remap_frame_layout(self, xmm_src_locs, xmm_dst_locs,
                           X86_64_XMM_SCRATCH_REG)
        # Load the singlefloat arguments from main regs or stack to xmm regs
        if singlefloats is not None:
            for src, dst in singlefloats:
                self.mc.MOVD(dst, src)
        # Finally remap the arguments in the main regs
        # If x is a register and is in dst_locs, then oups, it needs to
        # be moved away:
        if x in dst_locs:
            src_locs.append(x)
            dst_locs.append(r10)
            x = r10
        remap_frame_layout(self, src_locs, dst_locs, X86_64_SCRATCH_REG)

        self._regalloc.reserve_param(len(pass_on_stack))
        self.mc.CALL(x)
        self.mark_gc_roots(force_index)

    def call(self, addr, args, res):
        force_index = self.write_new_force_index()
        self._emit_call(force_index, imm(addr), args)
        assert res is eax

    def write_new_force_index(self):
        # for shadowstack only: get a new, unused force_index number and
        # write it to FORCE_INDEX_OFS.  Used to record the call shape
        # (i.e. where the GC pointers are in the stack) around a CALL
        # instruction that doesn't already have a force_index.
        gcrootmap = self.cpu.gc_ll_descr.gcrootmap
        if gcrootmap and gcrootmap.is_shadow_stack:
            clt = self.current_clt
            force_index = clt.reserve_and_record_some_faildescr_index()
            self.mc.MOV_bi(FORCE_INDEX_OFS, force_index)
            return force_index
        else:
            # the return value is ignored, apart from the fact that it
            # is not negative.
            return 0

    genop_int_neg = _unaryop("NEG")
    genop_int_invert = _unaryop("NOT")
    genop_int_add = _binaryop("ADD", True)
    genop_int_sub = _binaryop("SUB")
    genop_int_mul = _binaryop("IMUL", True)
    genop_int_and = _binaryop("AND", True)
    genop_int_or  = _binaryop("OR", True)
    genop_int_xor = _binaryop("XOR", True)
    genop_int_lshift = _binaryop("SHL")
    genop_int_rshift = _binaryop("SAR")
    genop_uint_rshift = _binaryop("SHR")
    genop_float_add = _binaryop("ADDSD", True)
    genop_float_sub = _binaryop('SUBSD')
    genop_float_mul = _binaryop('MULSD', True)
    genop_float_truediv = _binaryop('DIVSD')

    genop_int_lt = _cmpop("L", "G")
    genop_int_le = _cmpop("LE", "GE")
    genop_int_eq = _cmpop("E", "E")
    genop_int_ne = _cmpop("NE", "NE")
    genop_int_gt = _cmpop("G", "L")
    genop_int_ge = _cmpop("GE", "LE")
    genop_ptr_eq = genop_instance_ptr_eq = genop_int_eq
    genop_ptr_ne = genop_instance_ptr_ne = genop_int_ne

    genop_float_lt = _cmpop_float('B', 'A')
    genop_float_le = _cmpop_float('BE', 'AE')
    genop_float_ne = _cmpop_float('NE', 'NE', is_ne=True)
    genop_float_eq = _cmpop_float('E', 'E')
    genop_float_gt = _cmpop_float('A', 'B')
    genop_float_ge = _cmpop_float('AE', 'BE')

    genop_uint_gt = _cmpop("A", "B")
    genop_uint_lt = _cmpop("B", "A")
    genop_uint_le = _cmpop("BE", "AE")
    genop_uint_ge = _cmpop("AE", "BE")

    genop_guard_int_lt = _cmpop_guard("L", "G", "GE", "LE")
    genop_guard_int_le = _cmpop_guard("LE", "GE", "G", "L")
    genop_guard_int_eq = _cmpop_guard("E", "E", "NE", "NE")
    genop_guard_int_ne = _cmpop_guard("NE", "NE", "E", "E")
    genop_guard_int_gt = _cmpop_guard("G", "L", "LE", "GE")
    genop_guard_int_ge = _cmpop_guard("GE", "LE", "L", "G")
    genop_guard_ptr_eq = genop_guard_instance_ptr_eq = genop_guard_int_eq
    genop_guard_ptr_ne = genop_guard_instance_ptr_ne = genop_guard_int_ne

    genop_guard_uint_gt = _cmpop_guard("A", "B", "BE", "AE")
    genop_guard_uint_lt = _cmpop_guard("B", "A", "AE", "BE")
    genop_guard_uint_le = _cmpop_guard("BE", "AE", "A", "B")
    genop_guard_uint_ge = _cmpop_guard("AE", "BE", "B", "A")

    genop_guard_float_lt = _cmpop_guard_float("B", "A", "AE","BE")
    genop_guard_float_le = _cmpop_guard_float("BE","AE", "A", "B")
    genop_guard_float_eq = _cmpop_guard_float("E", "E", "NE","NE")
    genop_guard_float_gt = _cmpop_guard_float("A", "B", "BE","AE")
    genop_guard_float_ge = _cmpop_guard_float("AE","BE", "B", "A")

    def genop_math_sqrt(self, op, arglocs, resloc):
        self.mc.SQRTSD(arglocs[0], resloc)

    def genop_guard_float_ne(self, op, guard_op, guard_token, arglocs, result_loc):
        guard_opnum = guard_op.getopnum()
        if isinstance(arglocs[0], RegLoc):
            self.mc.UCOMISD(arglocs[0], arglocs[1])
        else:
            self.mc.UCOMISD(arglocs[1], arglocs[0])
        if guard_opnum == rop.GUARD_TRUE:
            self.mc.J_il8(rx86.Conditions['P'], 6)
            self.implement_guard(guard_token, 'E')
        else:
            self.mc.J_il8(rx86.Conditions['P'], 2)
            self.mc.J_il8(rx86.Conditions['E'], 5)
            self.implement_guard(guard_token)

    def genop_float_neg(self, op, arglocs, resloc):
        # Following what gcc does: res = x ^ 0x8000000000000000
        self.mc.XORPD(arglocs[0], heap(self.float_const_neg_addr))

    def genop_float_abs(self, op, arglocs, resloc):
        # Following what gcc does: res = x & 0x7FFFFFFFFFFFFFFF
        self.mc.ANDPD(arglocs[0], heap(self.float_const_abs_addr))

    def genop_cast_float_to_int(self, op, arglocs, resloc):
        self.mc.CVTTSD2SI(resloc, arglocs[0])

    def genop_cast_int_to_float(self, op, arglocs, resloc):
        self.mc.CVTSI2SD(resloc, arglocs[0])

    def genop_cast_float_to_singlefloat(self, op, arglocs, resloc):
        loc0, loctmp = arglocs
        self.mc.CVTSD2SS(loctmp, loc0)
        assert isinstance(resloc, RegLoc)
        assert isinstance(loctmp, RegLoc)
        self.mc.MOVD_rx(resloc.value, loctmp.value)

    def genop_cast_singlefloat_to_float(self, op, arglocs, resloc):
        loc0, = arglocs
        assert isinstance(resloc, RegLoc)
        assert isinstance(loc0, RegLoc)
        self.mc.MOVD_xr(resloc.value, loc0.value)
        self.mc.CVTSS2SD_xx(resloc.value, resloc.value)

    def genop_guard_int_is_true(self, op, guard_op, guard_token, arglocs, resloc):
        guard_opnum = guard_op.getopnum()
        self.mc.CMP(arglocs[0], imm0)
        if guard_opnum == rop.GUARD_TRUE:
            self.implement_guard(guard_token, 'Z')
        else:
            self.implement_guard(guard_token, 'NZ')

    def genop_int_is_true(self, op, arglocs, resloc):
        self.mc.CMP(arglocs[0], imm0)
        rl = resloc.lowest8bits()
        self.mc.SET_ir(rx86.Conditions['NE'], rl.value)
        self.mc.MOVZX8(resloc, rl)

    def genop_guard_int_is_zero(self, op, guard_op, guard_token, arglocs, resloc):
        guard_opnum = guard_op.getopnum()
        self.mc.CMP(arglocs[0], imm0)
        if guard_opnum == rop.GUARD_TRUE:
            self.implement_guard(guard_token, 'NZ')
        else:
            self.implement_guard(guard_token, 'Z')

    def genop_int_is_zero(self, op, arglocs, resloc):
        self.mc.CMP(arglocs[0], imm0)
        rl = resloc.lowest8bits()
        self.mc.SET_ir(rx86.Conditions['E'], rl.value)
        self.mc.MOVZX8(resloc, rl)

    def genop_same_as(self, op, arglocs, resloc):
        self.mov(arglocs[0], resloc)
    genop_cast_ptr_to_int = genop_same_as
    genop_cast_int_to_ptr = genop_same_as

    def genop_int_mod(self, op, arglocs, resloc):
        if IS_X86_32:
            self.mc.CDQ()
        elif IS_X86_64:
            self.mc.CQO()

        self.mc.IDIV_r(ecx.value)

    genop_int_floordiv = genop_int_mod

    def genop_uint_floordiv(self, op, arglocs, resloc):
        self.mc.XOR_rr(edx.value, edx.value)
        self.mc.DIV_r(ecx.value)

    genop_llong_add = _binaryop("PADDQ", True)
    genop_llong_sub = _binaryop("PSUBQ")
    genop_llong_and = _binaryop("PAND",  True)
    genop_llong_or  = _binaryop("POR",   True)
    genop_llong_xor = _binaryop("PXOR",  True)

    def genop_llong_to_int(self, op, arglocs, resloc):
        loc = arglocs[0]
        assert isinstance(resloc, RegLoc)
        if isinstance(loc, RegLoc):
            self.mc.MOVD_rx(resloc.value, loc.value)
        elif isinstance(loc, StackLoc):
            self.mc.MOV_rb(resloc.value, loc.value)
        else:
            not_implemented("llong_to_int: %s" % (loc,))

    def genop_llong_from_int(self, op, arglocs, resloc):
        loc1, loc2 = arglocs
        if isinstance(loc1, ConstFloatLoc):
            assert loc2 is None
            self.mc.MOVSD(resloc, loc1)
        else:
            assert isinstance(loc1, RegLoc)
            assert isinstance(loc2, RegLoc)
            assert isinstance(resloc, RegLoc)
            self.mc.MOVD_xr(loc2.value, loc1.value)
            self.mc.PSRAD_xi(loc2.value, 31)    # -> 0 or -1
            self.mc.MOVD_xr(resloc.value, loc1.value)
            self.mc.PUNPCKLDQ_xx(resloc.value, loc2.value)

    def genop_llong_from_uint(self, op, arglocs, resloc):
        loc1, = arglocs
        assert isinstance(resloc, RegLoc)
        assert isinstance(loc1, RegLoc)
        self.mc.MOVD_xr(resloc.value, loc1.value)

    def genop_llong_eq(self, op, arglocs, resloc):
        loc1, loc2, locxtmp = arglocs
        self.mc.MOVSD(locxtmp, loc1)
        self.mc.PCMPEQD(locxtmp, loc2)
        self.mc.PMOVMSKB_rx(resloc.value, locxtmp.value)
        # Now the lower 8 bits of resloc contain 0x00, 0x0F, 0xF0 or 0xFF
        # depending on the result of the comparison of each of the two
        # double-words of loc1 and loc2.  The higher 8 bits contain random
        # results.  We want to map 0xFF to 1, and 0x00, 0x0F and 0xF0 to 0.
        self.mc.CMP8_ri(resloc.value | rx86.BYTE_REG_FLAG, -1)
        self.mc.SBB_rr(resloc.value, resloc.value)
        self.mc.ADD_ri(resloc.value, 1)

    def genop_llong_ne(self, op, arglocs, resloc):
        loc1, loc2, locxtmp = arglocs
        self.mc.MOVSD(locxtmp, loc1)
        self.mc.PCMPEQD(locxtmp, loc2)
        self.mc.PMOVMSKB_rx(resloc.value, locxtmp.value)
        # Now the lower 8 bits of resloc contain 0x00, 0x0F, 0xF0 or 0xFF
        # depending on the result of the comparison of each of the two
        # double-words of loc1 and loc2.  The higher 8 bits contain random
        # results.  We want to map 0xFF to 0, and 0x00, 0x0F and 0xF0 to 1.
        self.mc.CMP8_ri(resloc.value | rx86.BYTE_REG_FLAG, -1)
        self.mc.SBB_rr(resloc.value, resloc.value)
        self.mc.NEG_r(resloc.value)

    def genop_llong_lt(self, op, arglocs, resloc):
        # XXX just a special case for now: "x < 0"
        loc1, = arglocs
        self.mc.PMOVMSKB_rx(resloc.value, loc1.value)
        self.mc.SHR_ri(resloc.value, 7)
        self.mc.AND_ri(resloc.value, 1)

    # ----------

    def genop_call_malloc_gc(self, op, arglocs, result_loc):
        self.genop_call(op, arglocs, result_loc)
        self.propagate_memoryerror_if_eax_is_null()

    def propagate_memoryerror_if_eax_is_null(self):
        # if self.propagate_exception_path == 0 (tests), this may jump to 0
        # and segfaults.  too bad.  the alternative is to continue anyway
        # with eax==0, but that will segfault too.
        self.mc.TEST_rr(eax.value, eax.value)
        if WORD == 4:
            self.mc.J_il(rx86.Conditions['Z'], self.propagate_exception_path)
            self.mc.add_pending_relocation()
        elif WORD == 8:
            self.mc.J_il(rx86.Conditions['Z'], 0)
            pos = self.mc.get_relative_pos()
            self.pending_memoryerror_trampoline_from.append(pos)

    # ----------

    def load_from_mem(self, resloc, source_addr, size_loc, sign_loc):
        assert isinstance(resloc, RegLoc)
        size = size_loc.value
        sign = sign_loc.value
        if resloc.is_xmm:
            self.mc.MOVSD(resloc, source_addr)
        elif size == WORD:
            self.mc.MOV(resloc, source_addr)
        elif size == 1:
            if sign:
                self.mc.MOVSX8(resloc, source_addr)
            else:
                self.mc.MOVZX8(resloc, source_addr)
        elif size == 2:
            if sign:
                self.mc.MOVSX16(resloc, source_addr)
            else:
                self.mc.MOVZX16(resloc, source_addr)
        elif IS_X86_64 and size == 4:
            if sign:
                self.mc.MOVSX32(resloc, source_addr)
            else:
                self.mc.MOV32(resloc, source_addr)    # zero-extending
        else:
            not_implemented("load_from_mem size = %d" % size)

    def save_into_mem(self, dest_addr, value_loc, size_loc):
        size = size_loc.value
        if isinstance(value_loc, RegLoc) and value_loc.is_xmm:
            self.mc.MOVSD(dest_addr, value_loc)
        elif size == 1:
            self.mc.MOV8(dest_addr, value_loc.lowest8bits())
        elif size == 2:
            self.mc.MOV16(dest_addr, value_loc)
        elif size == 4:
            self.mc.MOV32(dest_addr, value_loc)
        elif size == 8:
            if IS_X86_64:
                self.mc.MOV(dest_addr, value_loc)
            else:
                assert isinstance(value_loc, FloatImmedLoc)
                self.mc.MOV(dest_addr, value_loc.low_part_loc())
                self.mc.MOV(dest_addr.add_offset(4), value_loc.high_part_loc())
        else:
            not_implemented("save_into_mem size = %d" % size)

    def genop_getfield_gc(self, op, arglocs, resloc):
        base_loc, ofs_loc, size_loc, sign_loc = arglocs
        assert isinstance(size_loc, ImmedLoc)
        source_addr = AddressLoc(base_loc, ofs_loc)
        self.load_from_mem(resloc, source_addr, size_loc, sign_loc)

    genop_getfield_raw = genop_getfield_gc
    genop_getfield_raw_pure = genop_getfield_gc
    genop_getfield_gc_pure = genop_getfield_gc

    def genop_getarrayitem_gc(self, op, arglocs, resloc):
        base_loc, ofs_loc, size_loc, ofs, sign_loc = arglocs
        assert isinstance(ofs, ImmedLoc)
        assert isinstance(size_loc, ImmedLoc)
        scale = _get_scale(size_loc.value)
        src_addr = addr_add(base_loc, ofs_loc, ofs.value, scale)
        self.load_from_mem(resloc, src_addr, size_loc, sign_loc)

    genop_getarrayitem_gc_pure = genop_getarrayitem_gc
    genop_getarrayitem_raw = genop_getarrayitem_gc

    def _get_interiorfield_addr(self, temp_loc, index_loc, itemsize_loc,
                                base_loc, ofs_loc):
        assert isinstance(itemsize_loc, ImmedLoc)
        if isinstance(index_loc, ImmedLoc):
            temp_loc = imm(index_loc.value * itemsize_loc.value)
        elif _valid_addressing_size(itemsize_loc.value):
            return AddressLoc(base_loc, index_loc, _get_scale(itemsize_loc.value), ofs_loc.value)
        else:
            # XXX should not use IMUL in more cases, it can use a clever LEA
            assert isinstance(temp_loc, RegLoc)
            assert isinstance(index_loc, RegLoc)
            assert not temp_loc.is_xmm
            self.mc.IMUL_rri(temp_loc.value, index_loc.value,
                             itemsize_loc.value)
        assert isinstance(ofs_loc, ImmedLoc)
        return AddressLoc(base_loc, temp_loc, 0, ofs_loc.value)

    def genop_getinteriorfield_gc(self, op, arglocs, resloc):
        (base_loc, ofs_loc, itemsize_loc, fieldsize_loc,
            index_loc, temp_loc, sign_loc) = arglocs
        src_addr = self._get_interiorfield_addr(temp_loc, index_loc,
                                                itemsize_loc, base_loc,
                                                ofs_loc)
        self.load_from_mem(resloc, src_addr, fieldsize_loc, sign_loc)

    genop_getinteriorfield_raw = genop_getinteriorfield_gc


    def genop_discard_setfield_gc(self, op, arglocs):
        base_loc, ofs_loc, size_loc, value_loc = arglocs
        assert isinstance(size_loc, ImmedLoc)
        dest_addr = AddressLoc(base_loc, ofs_loc)
        self.save_into_mem(dest_addr, value_loc, size_loc)

    def genop_discard_setinteriorfield_gc(self, op, arglocs):
        (base_loc, ofs_loc, itemsize_loc, fieldsize_loc,
            index_loc, temp_loc, value_loc) = arglocs
        dest_addr = self._get_interiorfield_addr(temp_loc, index_loc,
                                                 itemsize_loc, base_loc,
                                                 ofs_loc)
        self.save_into_mem(dest_addr, value_loc, fieldsize_loc)

    genop_discard_setinteriorfield_raw = genop_discard_setinteriorfield_gc

    def genop_discard_setarrayitem_gc(self, op, arglocs):
        base_loc, ofs_loc, value_loc, size_loc, baseofs = arglocs
        assert isinstance(baseofs, ImmedLoc)
        assert isinstance(size_loc, ImmedLoc)
        scale = _get_scale(size_loc.value)
        dest_addr = AddressLoc(base_loc, ofs_loc, scale, baseofs.value)
        self.save_into_mem(dest_addr, value_loc, size_loc)

    def genop_discard_strsetitem(self, op, arglocs):
        base_loc, ofs_loc, val_loc = arglocs
        basesize, itemsize, ofs_length = symbolic.get_array_token(rstr.STR,
                                              self.cpu.translate_support_code)
        assert itemsize == 1
        dest_addr = AddressLoc(base_loc, ofs_loc, 0, basesize)
        self.mc.MOV8(dest_addr, val_loc.lowest8bits())

    def genop_discard_unicodesetitem(self, op, arglocs):
        base_loc, ofs_loc, val_loc = arglocs
        basesize, itemsize, ofs_length = symbolic.get_array_token(rstr.UNICODE,
                                              self.cpu.translate_support_code)
        if itemsize == 4:
            self.mc.MOV32(AddressLoc(base_loc, ofs_loc, 2, basesize), val_loc)
        elif itemsize == 2:
            self.mc.MOV16(AddressLoc(base_loc, ofs_loc, 1, basesize), val_loc)
        else:
            assert 0, itemsize

    genop_discard_setfield_raw = genop_discard_setfield_gc
    genop_discard_setarrayitem_raw = genop_discard_setarrayitem_gc

    def genop_strlen(self, op, arglocs, resloc):
        base_loc = arglocs[0]
        basesize, itemsize, ofs_length = symbolic.get_array_token(rstr.STR,
                                             self.cpu.translate_support_code)
        self.mc.MOV(resloc, addr_add_const(base_loc, ofs_length))

    def genop_unicodelen(self, op, arglocs, resloc):
        base_loc = arglocs[0]
        basesize, itemsize, ofs_length = symbolic.get_array_token(rstr.UNICODE,
                                             self.cpu.translate_support_code)
        self.mc.MOV(resloc, addr_add_const(base_loc, ofs_length))

    def genop_arraylen_gc(self, op, arglocs, resloc):
        base_loc, ofs_loc = arglocs
        assert isinstance(ofs_loc, ImmedLoc)
        self.mc.MOV(resloc, addr_add_const(base_loc, ofs_loc.value))

    def genop_strgetitem(self, op, arglocs, resloc):
        base_loc, ofs_loc = arglocs
        basesize, itemsize, ofs_length = symbolic.get_array_token(rstr.STR,
                                             self.cpu.translate_support_code)
        assert itemsize == 1
        self.mc.MOVZX8(resloc, AddressLoc(base_loc, ofs_loc, 0, basesize))

    def genop_unicodegetitem(self, op, arglocs, resloc):
        base_loc, ofs_loc = arglocs
        basesize, itemsize, ofs_length = symbolic.get_array_token(rstr.UNICODE,
                                             self.cpu.translate_support_code)
        if itemsize == 4:
            self.mc.MOV32(resloc, AddressLoc(base_loc, ofs_loc, 2, basesize))
        elif itemsize == 2:
            self.mc.MOVZX16(resloc, AddressLoc(base_loc, ofs_loc, 1, basesize))
        else:
            assert 0, itemsize

    def genop_read_timestamp(self, op, arglocs, resloc):
        self.mc.RDTSC()
        if longlong.is_64_bit:
            self.mc.SHL_ri(edx.value, 32)
            self.mc.OR_rr(edx.value, eax.value)
        else:
            loc1, = arglocs
            self.mc.MOVD_xr(loc1.value, edx.value)
            self.mc.MOVD_xr(resloc.value, eax.value)
            self.mc.PUNPCKLDQ_xx(resloc.value, loc1.value)

    def genop_guard_guard_true(self, ign_1, guard_op, guard_token, locs, ign_2):
        loc = locs[0]
        self.mc.TEST(loc, loc)
        self.implement_guard(guard_token, 'Z')
    genop_guard_guard_nonnull = genop_guard_guard_true

    def genop_guard_guard_no_exception(self, ign_1, guard_op, guard_token,
                                       locs, ign_2):
        self.mc.CMP(heap(self.cpu.pos_exception()), imm0)
        self.implement_guard(guard_token, 'NZ')

    def genop_guard_guard_not_invalidated(self, ign_1, guard_op, guard_token,
                                     locs, ign_2):
        pos = self.mc.get_relative_pos() + 1 # after potential jmp
        guard_token.pos_jump_offset = pos
        self.pending_guard_tokens.append(guard_token)

    def genop_guard_guard_exception(self, ign_1, guard_op, guard_token,
                                    locs, resloc):
        loc = locs[0]
        loc1 = locs[1]
        self.mc.MOV(loc1, heap(self.cpu.pos_exception()))
        self.mc.CMP(loc1, loc)
        self.implement_guard(guard_token, 'NE')
        if resloc is not None:
            self.mc.MOV(resloc, heap(self.cpu.pos_exc_value()))
        self.mc.MOV(heap(self.cpu.pos_exception()), imm0)
        self.mc.MOV(heap(self.cpu.pos_exc_value()), imm0)

    def _gen_guard_overflow(self, guard_op, guard_token):
        guard_opnum = guard_op.getopnum()
        if guard_opnum == rop.GUARD_NO_OVERFLOW:
            self.implement_guard(guard_token, 'O')
        elif guard_opnum == rop.GUARD_OVERFLOW:
            self.implement_guard(guard_token, 'NO')
        else:
            not_implemented("int_xxx_ovf followed by %s" %
                            guard_op.getopname())

    def genop_guard_int_add_ovf(self, op, guard_op, guard_token, arglocs, result_loc):
        self.genop_int_add(op, arglocs, result_loc)
        return self._gen_guard_overflow(guard_op, guard_token)

    def genop_guard_int_sub_ovf(self, op, guard_op, guard_token, arglocs, result_loc):
        self.genop_int_sub(op, arglocs, result_loc)
        return self._gen_guard_overflow(guard_op, guard_token)

    def genop_guard_int_mul_ovf(self, op, guard_op, guard_token, arglocs, result_loc):
        self.genop_int_mul(op, arglocs, result_loc)
        return self._gen_guard_overflow(guard_op, guard_token)

    def genop_guard_guard_false(self, ign_1, guard_op, guard_token, locs, ign_2):
        loc = locs[0]
        self.mc.TEST(loc, loc)
        self.implement_guard(guard_token, 'NZ')
    genop_guard_guard_isnull = genop_guard_guard_false

    def genop_guard_guard_value(self, ign_1, guard_op, guard_token, locs, ign_2):
        if guard_op.getarg(0).type == FLOAT:
            assert guard_op.getarg(1).type == FLOAT
            self.mc.UCOMISD(locs[0], locs[1])
        else:
            self.mc.CMP(locs[0], locs[1])
        self.implement_guard(guard_token, 'NE')

    def _cmp_guard_class(self, locs):
        offset = self.cpu.vtable_offset
        if offset is not None:
            self.mc.CMP(mem(locs[0], offset), locs[1])
        else:
            # XXX hard-coded assumption: to go from an object to its class
            # we use the following algorithm:
            #   - read the typeid from mem(locs[0]), i.e. at offset 0
            #   - keep the lower 16 bits read there
            #   - multiply by 4 and use it as an offset in type_info_group
            #   - add 16 bytes, to go past the TYPE_INFO structure
            loc = locs[1]
            assert isinstance(loc, ImmedLoc)
            classptr = loc.value
            # here, we have to go back from 'classptr' to the value expected
            # from reading the 16 bits in the object header
            from pypy.rpython.memory.gctypelayout import GCData
            sizeof_ti = rffi.sizeof(GCData.TYPE_INFO)
            type_info_group = llop.gc_get_type_info_group(llmemory.Address)
            type_info_group = rffi.cast(lltype.Signed, type_info_group)
            expected_typeid = classptr - sizeof_ti - type_info_group
            if IS_X86_32:
                expected_typeid >>= 2
                self.mc.CMP16(mem(locs[0], 0), ImmedLoc(expected_typeid))
            elif IS_X86_64:
                self.mc.CMP32_mi((locs[0].value, 0), expected_typeid)

    def genop_guard_guard_class(self, ign_1, guard_op, guard_token, locs, ign_2):
        self._cmp_guard_class(locs)
        self.implement_guard(guard_token, 'NE')

    def genop_guard_guard_nonnull_class(self, ign_1, guard_op,
                                        guard_token, locs, ign_2):
        self.mc.CMP(locs[0], imm1)
        # Patched below
        self.mc.J_il8(rx86.Conditions['B'], 0)
        jb_location = self.mc.get_relative_pos()
        self._cmp_guard_class(locs)
        # patch the JB above
        offset = self.mc.get_relative_pos() - jb_location
        assert 0 < offset <= 127
        self.mc.overwrite(jb_location-1, chr(offset))
        #
        self.implement_guard(guard_token, 'NE')

    def implement_guard_recovery(self, guard_opnum, faildescr, failargs,
                                                               fail_locs):
        exc = (guard_opnum == rop.GUARD_EXCEPTION or
               guard_opnum == rop.GUARD_NO_EXCEPTION or
               guard_opnum == rop.GUARD_NOT_FORCED)
        is_guard_not_invalidated = guard_opnum == rop.GUARD_NOT_INVALIDATED
        return GuardToken(faildescr, failargs, fail_locs, exc,
                          is_guard_not_invalidated)

    def generate_propagate_error_64(self):
        assert WORD == 8
        startpos = self.mc.get_relative_pos()
        self.mc.JMP(imm(self.propagate_exception_path))
        return startpos

    def generate_quick_failure(self, guardtok):
        """Generate the initial code for handling a failure.  We try to
        keep it as compact as possible.
        """
        fail_index = self.cpu.get_fail_descr_number(guardtok.faildescr)
        mc = self.mc
        startpos = mc.get_relative_pos()
        withfloats = False
        for box in guardtok.failargs:
            if box is not None and box.type == FLOAT:
                withfloats = True
                break
        exc = guardtok.exc
        target = self.failure_recovery_code[exc + 2 * withfloats]
        if WORD == 4:
            mc.CALL(imm(target))
        else:
            # Generate exactly 13 bytes:
            #        MOV r11, target-as-8-bytes
            #        CALL *r11
            # Keep the number 13 in sync with _find_failure_recovery_bytecode.
            start = mc.get_relative_pos()
            mc.MOV_ri64(X86_64_SCRATCH_REG.value, target)
            mc.CALL_r(X86_64_SCRATCH_REG.value)
            assert mc.get_relative_pos() == start + 13
        # write tight data that describes the failure recovery
        self.write_failure_recovery_description(mc, guardtok.failargs,
                                                guardtok.fail_locs)
        # write the fail_index too
        mc.writeimm32(fail_index)
        # for testing the decoding, write a final byte 0xCC
        if not we_are_translated():
            mc.writechar('\xCC')
            faillocs = [loc for loc in guardtok.fail_locs if loc is not None]
            guardtok.faildescr._x86_debug_faillocs = faillocs
        return startpos

    DESCR_REF       = 0x00
    DESCR_INT       = 0x01
    DESCR_FLOAT     = 0x02
    DESCR_SPECIAL   = 0x03
    CODE_FROMSTACK  = 4 * (8 + 8*IS_X86_64)
    CODE_STOP       = 0 | DESCR_SPECIAL
    CODE_HOLE       = 4 | DESCR_SPECIAL
    CODE_INPUTARG   = 8 | DESCR_SPECIAL

    def write_failure_recovery_description(self, mc, failargs, locs):
        for i in range(len(failargs)):
            arg = failargs[i]
            if arg is not None:
                if arg.type == REF:
                    kind = self.DESCR_REF
                elif arg.type == INT:
                    kind = self.DESCR_INT
                elif arg.type == FLOAT:
                    kind = self.DESCR_FLOAT
                else:
                    raise AssertionError("bogus kind")
                loc = locs[i]
                if isinstance(loc, StackLoc):
                    pos = loc.position
                    if pos < 0:
                        mc.writechar(chr(self.CODE_INPUTARG))
                        pos = ~pos
                    n = self.CODE_FROMSTACK//4 + pos
                else:
                    assert isinstance(loc, RegLoc)
                    n = loc.value
                n = kind + 4*n
                while n > 0x7F:
                    mc.writechar(chr((n & 0x7F) | 0x80))
                    n >>= 7
            else:
                n = self.CODE_HOLE
            mc.writechar(chr(n))
        mc.writechar(chr(self.CODE_STOP))
        # assert that the fail_boxes lists are big enough
        assert len(failargs) <= self.fail_boxes_int.SIZE

    def rebuild_faillocs_from_descr(self, bytecode):
        from pypy.jit.backend.x86.regalloc import X86FrameManager
        descr_to_box_type = [REF, INT, FLOAT]
        bytecode = rffi.cast(rffi.UCHARP, bytecode)
        arglocs = []
        code_inputarg = False
        while 1:
            # decode the next instruction from the bytecode
            code = rffi.cast(lltype.Signed, bytecode[0])
            bytecode = rffi.ptradd(bytecode, 1)
            if code >= self.CODE_FROMSTACK:
                # 'code' identifies a stack location
                if code > 0x7F:
                    shift = 7
                    code &= 0x7F
                    while True:
                        nextcode = rffi.cast(lltype.Signed, bytecode[0])
                        bytecode = rffi.ptradd(bytecode, 1)
                        code |= (nextcode & 0x7F) << shift
                        shift += 7
                        if nextcode <= 0x7F:
                            break
                kind = code & 3
                code = (code - self.CODE_FROMSTACK) >> 2
                if code_inputarg:
                    code = ~code
                    code_inputarg = False
                loc = X86FrameManager.frame_pos(code, descr_to_box_type[kind])
            elif code == self.CODE_STOP:
                break
            elif code == self.CODE_HOLE:
                continue
            elif code == self.CODE_INPUTARG:
                code_inputarg = True
                continue
            else:
                # 'code' identifies a register
                kind = code & 3
                code >>= 2
                if kind == self.DESCR_FLOAT:
                    loc = regloc.XMMREGLOCS[code]
                else:
                    loc = regloc.REGLOCS[code]
            arglocs.append(loc)
        return arglocs[:]

    @rgc.no_collect
    def grab_frame_values(self, bytecode, frame_addr, allregisters):
        # no malloc allowed here!!
        self.fail_ebp = allregisters[16 + ebp.value]
        code_inputarg = False
        num = 0
        value_hi = 0
        while 1:
            # decode the next instruction from the bytecode
            code = rffi.cast(lltype.Signed, bytecode[0])
            bytecode = rffi.ptradd(bytecode, 1)
            if code >= self.CODE_FROMSTACK:
                if code > 0x7F:
                    shift = 7
                    code &= 0x7F
                    while True:
                        nextcode = rffi.cast(lltype.Signed, bytecode[0])
                        bytecode = rffi.ptradd(bytecode, 1)
                        code |= (nextcode & 0x7F) << shift
                        shift += 7
                        if nextcode <= 0x7F:
                            break
                # load the value from the stack
                kind = code & 3
                code = (code - self.CODE_FROMSTACK) >> 2
                if code_inputarg:
                    code = ~code
                    code_inputarg = False
                stackloc = frame_addr + get_ebp_ofs(code)
                value = rffi.cast(rffi.LONGP, stackloc)[0]
                if kind == self.DESCR_FLOAT and WORD == 4:
                    value_hi = value
                    value = rffi.cast(rffi.LONGP, stackloc - 4)[0]
            else:
                # 'code' identifies a register: load its value
                kind = code & 3
                if kind == self.DESCR_SPECIAL:
                    if code == self.CODE_HOLE:
                        num += 1
                        continue
                    if code == self.CODE_INPUTARG:
                        code_inputarg = True
                        continue
                    assert code == self.CODE_STOP
                    break
                code >>= 2
                if kind == self.DESCR_FLOAT:
                    if WORD == 4:
                        value = allregisters[2*code]
                        value_hi = allregisters[2*code + 1]
                    else:
                        value = allregisters[code]
                else:
                    value = allregisters[16 + code]

            # store the loaded value into fail_boxes_<type>
            if kind == self.DESCR_INT:
                tgt = self.fail_boxes_int.get_addr_for_num(num)
            elif kind == self.DESCR_REF:
                tgt = self.fail_boxes_ptr.get_addr_for_num(num)
            elif kind == self.DESCR_FLOAT:
                tgt = self.fail_boxes_float.get_addr_for_num(num)
                if WORD == 4:
                    rffi.cast(rffi.LONGP, tgt)[1] = value_hi
            else:
                assert 0, "bogus kind"
            rffi.cast(rffi.LONGP, tgt)[0] = value
            num += 1
        #
        if not we_are_translated():
            assert bytecode[4] == 0xCC
        self.fail_boxes_count = num
        fail_index = rffi.cast(rffi.INTP, bytecode)[0]
        fail_index = rffi.cast(lltype.Signed, fail_index)
        return fail_index

    def setup_failure_recovery(self):

        @rgc.no_collect
        def failure_recovery_func(registers):
            # 'registers' is a pointer to a structure containing the
            # original value of the registers, optionally the original
            # value of XMM registers, and finally a reference to the
            # recovery bytecode.  See _build_failure_recovery() for details.
            stack_at_ebp = registers[ebp.value]
            bytecode = rffi.cast(rffi.UCHARP, registers[self.cpu.NUM_REGS])
            allregisters = rffi.ptradd(registers, -16)
            return self.grab_frame_values(bytecode, stack_at_ebp, allregisters)

        self.failure_recovery_func = failure_recovery_func
        self.failure_recovery_code = [0, 0, 0, 0]

    _FAILURE_RECOVERY_FUNC = lltype.Ptr(lltype.FuncType([rffi.LONGP],
                                                        lltype.Signed))

    def _build_failure_recovery(self, exc, withfloats=False):
        failure_recovery_func = llhelper(self._FAILURE_RECOVERY_FUNC,
                                         self.failure_recovery_func)
        failure_recovery_func = rffi.cast(lltype.Signed,
                                          failure_recovery_func)
        mc = codebuf.MachineCodeBlockWrapper()
        self.mc = mc

        # Push all general purpose registers
        for gpr in range(self.cpu.NUM_REGS-1, -1, -1):
            mc.PUSH_r(gpr)

        # ebx/rbx is callee-save in both i386 and x86-64
        mc.MOV_rr(ebx.value, esp.value)

        if withfloats:
            # Push all float registers
            mc.SUB_ri(esp.value, self.cpu.NUM_REGS*8)
            for i in range(self.cpu.NUM_REGS):
                mc.MOVSD_sx(8*i, i)

        # we call a provided function that will
        # - call our on_leave_jitted_hook which will mark
        #   the fail_boxes_ptr array as pointing to young objects to
        #   avoid unwarranted freeing
        # - optionally save exception depending on the flag
        addr = self.cpu.get_on_leave_jitted_int(save_exception=exc)
        mc.CALL(imm(addr))

        # the following call saves all values from the stack and from
        # registers to the right 'fail_boxes_<type>' location.
        # Note that the registers are saved so far in esi[0] to esi[7],
        # as pushed above, plus optionally in esi[-16] to esi[-1] for
        # the XMM registers.  Moreover, esi[8] is a pointer to the recovery
        # bytecode, pushed just before by the CALL instruction written by
        # generate_quick_failure().  XXX misaligned stack in the call, but
        # it's ok because failure_recovery_func is not calling anything more

        # XXX
        if IS_X86_32:
            mc.PUSH_r(ebx.value)
        elif IS_X86_64:
            mc.MOV_rr(edi.value, ebx.value)
            # XXX: Correct to only align the stack on 64-bit?
            mc.AND_ri(esp.value, -16)
        else:
            raise AssertionError("Shouldn't happen")

        mc.CALL(imm(failure_recovery_func))
        # returns in eax the fail_index

        # now we return from the complete frame, which starts from
        # _call_header_with_stack_check().  The LEA in _call_footer below
        # throws away most of the frame, including all the PUSHes that we
        # did just above.

        self._call_footer()
        rawstart = mc.materialize(self.cpu.asmmemmgr, [])
        self.failure_recovery_code[exc + 2 * withfloats] = rawstart
        self.mc = None

    def generate_failure(self, fail_index, locs, exc, locs_are_ref):
        self.mc.begin_reuse_scratch_register()
        for i in range(len(locs)):
            loc = locs[i]
            if isinstance(loc, RegLoc):
                if loc.is_xmm:
                    adr = self.fail_boxes_float.get_addr_for_num(i)
                    self.mc.MOVSD(heap(adr), loc)
                else:
                    if locs_are_ref[i]:
                        adr = self.fail_boxes_ptr.get_addr_for_num(i)
                    else:
                        adr = self.fail_boxes_int.get_addr_for_num(i)
                    self.mc.MOV(heap(adr), loc)
        for i in range(len(locs)):
            loc = locs[i]
            if not isinstance(loc, RegLoc):
                if ((isinstance(loc, StackLoc) and loc.type == FLOAT) or
                        isinstance(loc, ConstFloatLoc)):
                    self.mc.MOVSD(xmm0, loc)
                    adr = self.fail_boxes_float.get_addr_for_num(i)
                    self.mc.MOVSD(heap(adr), xmm0)
                else:
                    if locs_are_ref[i]:
                        adr = self.fail_boxes_ptr.get_addr_for_num(i)
                    else:
                        adr = self.fail_boxes_int.get_addr_for_num(i)
                    self.mc.MOV(eax, loc)
                    self.mc.MOV(heap(adr), eax)
        self.mc.end_reuse_scratch_register()

        # we call a provided function that will
        # - call our on_leave_jitted_hook which will mark
        #   the fail_boxes_ptr array as pointing to young objects to
        #   avoid unwarranted freeing
        # - optionally save exception depending on the flag
        addr = self.cpu.get_on_leave_jitted_int(save_exception=exc)
        self.mc.CALL(imm(addr))

        self.mc.MOV_ri(eax.value, fail_index)

        # exit function
        self._call_footer()

    def implement_guard(self, guard_token, condition=None):
        # These jumps are patched later.
        if condition:
            self.mc.J_il(rx86.Conditions[condition], 0)
        else:
            self.mc.JMP_l(0)
        guard_token.pos_jump_offset = self.mc.get_relative_pos() - 4
        self.pending_guard_tokens.append(guard_token)

    def genop_call(self, op, arglocs, resloc):
        force_index = self.write_new_force_index()
        self._genop_call(op, arglocs, resloc, force_index)

    def _genop_call(self, op, arglocs, resloc, force_index):
        from pypy.jit.backend.llsupport.descr import CallDescr

        sizeloc = arglocs[0]
        assert isinstance(sizeloc, ImmedLoc)
        size = sizeloc.value
        signloc = arglocs[1]

        x = arglocs[2]     # the function address
        if x is eax:
            tmp = ecx
        else:
            tmp = eax

        descr = op.getdescr()
        assert isinstance(descr, CallDescr)

        self._emit_call(force_index, x, arglocs, 3, tmp=tmp,
                        argtypes=descr.get_arg_types(),
                        callconv=descr.get_call_conv())

        if IS_X86_32 and isinstance(resloc, StackLoc) and resloc.type == FLOAT:
            # a float or a long long return
            if descr.get_result_type() == 'L':
                self.mc.MOV_br(resloc.value, eax.value)      # long long
                self.mc.MOV_br(resloc.value + 4, edx.value)
                # XXX should ideally not move the result on the stack,
                #     but it's a mess to load eax/edx into a xmm register
                #     and this way is simpler also because the result loc
                #     can just be always a stack location
            else:
                self.mc.FSTPL_b(resloc.value)   # float return
        elif descr.get_result_type() == 'S':
            # singlefloat return
            assert resloc is eax
            if IS_X86_32:
                # must convert ST(0) to a 32-bit singlefloat and load it into EAX
                # mess mess mess
                self.mc.SUB_ri(esp.value, 4)
                self.mc.FSTPS_s(0)
                self.mc.POP_r(eax.value)
            elif IS_X86_64:
                # must copy from the lower 32 bits of XMM0 into eax
                self.mc.MOVD_rx(eax.value, xmm0.value)
        elif size == WORD:
            assert resloc is eax or resloc is xmm0    # a full word
        elif size == 0:
            pass    # void return
        else:
            # use the code in load_from_mem to do the zero- or sign-extension
            assert resloc is eax
            if size == 1:
                srcloc = eax.lowest8bits()
            else:
                srcloc = eax
            self.load_from_mem(eax, srcloc, sizeloc, signloc)

    def genop_guard_call_may_force(self, op, guard_op, guard_token,
                                   arglocs, result_loc):
        faildescr = guard_op.getdescr()
        fail_index = self.cpu.get_fail_descr_number(faildescr)
        self.mc.MOV_bi(FORCE_INDEX_OFS, fail_index)
        self._genop_call(op, arglocs, result_loc, fail_index)
        self.mc.CMP_bi(FORCE_INDEX_OFS, 0)
        self.implement_guard(guard_token, 'L')

    def genop_guard_call_release_gil(self, op, guard_op, guard_token,
                                     arglocs, result_loc):
        # first, close the stack in the sense of the asmgcc GC root tracker
        gcrootmap = self.cpu.gc_ll_descr.gcrootmap
        if gcrootmap:
            self.call_release_gil(gcrootmap, arglocs)
        # do the call
        faildescr = guard_op.getdescr()
        fail_index = self.cpu.get_fail_descr_number(faildescr)
        self.mc.MOV_bi(FORCE_INDEX_OFS, fail_index)
        self._genop_call(op, arglocs, result_loc, fail_index)
        # then reopen the stack
        if gcrootmap:
            self.call_reacquire_gil(gcrootmap, result_loc)
        # finally, the guard_not_forced
        self.mc.CMP_bi(FORCE_INDEX_OFS, 0)
        self.implement_guard(guard_token, 'L')

    def call_release_gil(self, gcrootmap, save_registers):
        # First, we need to save away the registers listed in
        # 'save_registers' that are not callee-save.  XXX We assume that
        # the XMM registers won't be modified.  We store them in
        # [ESP+4], [ESP+8], etc., leaving enough room in [ESP] for the
        # single argument to closestack_addr below.
        p = WORD
        for reg in self._regalloc.rm.save_around_call_regs:
            if reg in save_registers:
                self.mc.MOV_sr(p, reg.value)
                p += WORD
        self._regalloc.reserve_param(p//WORD)
        #
        if gcrootmap.is_shadow_stack:
            args = []
        else:
            # note that regalloc.py used save_all_regs=True to save all
            # registers, so we don't have to care about saving them (other
            # than ebp) in the close_stack_struct.  But if they are registers
            # like %eax that would be destroyed by this call, *and* they are
            # used by arglocs for the *next* call, then trouble; for now we
            # will just push/pop them.
            from pypy.rpython.memory.gctransform import asmgcroot
            css = self._regalloc.close_stack_struct
            if css == 0:
                use_words = (2 + max(asmgcroot.INDEX_OF_EBP,
                                     asmgcroot.FRAME_PTR) + 1)
                pos = self._regalloc.fm.reserve_location_in_frame(use_words)
                css = get_ebp_ofs(pos + use_words - 1)
                self._regalloc.close_stack_struct = css
            # The location where the future CALL will put its return address
            # will be [ESP-WORD].  But we can't use that as the next frame's
            # top address!  As the code after releasegil() runs without the
            # GIL, it might not be set yet by the time we need it (very
            # unlikely), or it might be overwritten by the following call
            # to reaquiregil() (much more likely).  So we hack even more
            # and use a dummy location containing a dummy value (a pointer
            # to itself) which we pretend is the return address :-/ :-/ :-/
            # It prevents us to store any %esp-based stack locations but we
            # don't so far.
            adr = self.datablockwrapper.malloc_aligned(WORD, WORD)
            rffi.cast(rffi.CArrayPtr(lltype.Signed), adr)[0] = adr
            self.gcrootmap_retaddr_forced = adr
            frame_ptr = css + WORD * (2+asmgcroot.FRAME_PTR)
            if rx86.fits_in_32bits(adr):
                self.mc.MOV_bi(frame_ptr, adr)          # MOV [css.frame], adr
            else:
                self.mc.MOV_ri(eax.value, adr)          # MOV EAX, adr
                self.mc.MOV_br(frame_ptr, eax.value)    # MOV [css.frame], EAX
            # Save ebp
            index_of_ebp = css + WORD * (2+asmgcroot.INDEX_OF_EBP)
            self.mc.MOV_br(index_of_ebp, ebp.value)     # MOV [css.ebp], EBP
            # Call the closestack() function (also releasing the GIL)
            if IS_X86_32:
                reg = eax
            elif IS_X86_64:
                reg = edi
            self.mc.LEA_rb(reg.value, css)
            args = [reg]
        #
        self._emit_call(-1, imm(self.releasegil_addr), args)
        # Finally, restore the registers saved above.
        p = WORD
        for reg in self._regalloc.rm.save_around_call_regs:
            if reg in save_registers:
                self.mc.MOV_rs(reg.value, p)
                p += WORD

    def call_reacquire_gil(self, gcrootmap, save_loc):
        # save the previous result (eax/xmm0) into the stack temporarily.
        # XXX like with call_release_gil(), we assume that we don't need
        # to save xmm0 in this case.
        if isinstance(save_loc, RegLoc) and not save_loc.is_xmm:
            self.mc.MOV_sr(WORD, save_loc.value)
            self._regalloc.reserve_param(2)
        # call the reopenstack() function (also reacquiring the GIL)
        if gcrootmap.is_shadow_stack:
            args = []
        else:
            assert self.gcrootmap_retaddr_forced == -1, (
                      "missing mark_gc_roots() in CALL_RELEASE_GIL")
            self.gcrootmap_retaddr_forced = 0
            css = self._regalloc.close_stack_struct
            assert css != 0
            if IS_X86_32:
                reg = eax
            elif IS_X86_64:
                reg = edi
            self.mc.LEA_rb(reg.value, css)
            args = [reg]
        self._emit_call(-1, imm(self.reacqgil_addr), args)
        # restore the result from the stack
        if isinstance(save_loc, RegLoc) and not save_loc.is_xmm:
            self.mc.MOV_rs(save_loc.value, WORD)

    def genop_guard_call_assembler(self, op, guard_op, guard_token,
                                   arglocs, result_loc):
        faildescr = guard_op.getdescr()
        fail_index = self.cpu.get_fail_descr_number(faildescr)
        self.mc.MOV_bi(FORCE_INDEX_OFS, fail_index)
        descr = op.getdescr()
        assert isinstance(descr, JitCellToken)
        assert len(arglocs) - 2 == descr.compiled_loop_token._debug_nbargs
        #
        # Write a call to the target assembler
        self._emit_call(fail_index, imm(descr._x86_function_addr),
                        arglocs, 2, tmp=eax)
        if op.result is None:
            assert result_loc is None
            value = self.cpu.done_with_this_frame_void_v
        else:
            kind = op.result.type
            if kind == INT:
                assert result_loc is eax
                value = self.cpu.done_with_this_frame_int_v
            elif kind == REF:
                assert result_loc is eax
                value = self.cpu.done_with_this_frame_ref_v
            elif kind == FLOAT:
                value = self.cpu.done_with_this_frame_float_v
            else:
                raise AssertionError(kind)
        self.mc.CMP_ri(eax.value, value)
        # patched later
        self.mc.J_il8(rx86.Conditions['E'], 0) # goto B if we get 'done_with_this_frame'
        je_location = self.mc.get_relative_pos()
        #
        # Path A: use assembler_helper_adr
        jd = descr.outermost_jitdriver_sd
        assert jd is not None
        asm_helper_adr = self.cpu.cast_adr_to_int(jd.assembler_helper_adr)
        self._emit_call(fail_index, imm(asm_helper_adr), [eax, arglocs[1]], 0,
                        tmp=ecx)
        if IS_X86_32 and isinstance(result_loc, StackLoc) and result_loc.type == FLOAT:
            self.mc.FSTPL_b(result_loc.value)
        #else: result_loc is already either eax or None, checked below
        self.mc.JMP_l8(0) # jump to done, patched later
        jmp_location = self.mc.get_relative_pos()
        #
        # Path B: fast path.  Must load the return value, and reset the token
        offset = jmp_location - je_location
        assert 0 < offset <= 127
        self.mc.overwrite(je_location - 1, chr(offset))
        #
        # Reset the vable token --- XXX really too much special logic here:-(
        if jd.index_of_virtualizable >= 0:
            from pypy.jit.backend.llsupport.descr import FieldDescr
            fielddescr = jd.vable_token_descr
            assert isinstance(fielddescr, FieldDescr)
            ofs = fielddescr.offset
            self.mc.MOV(eax, arglocs[1])
            self.mc.MOV_mi((eax.value, ofs), 0)
            # in the line above, TOKEN_NONE = 0
        #
        if op.result is not None:
            # load the return value from fail_boxes_xxx[0]
            kind = op.result.type
            if kind == FLOAT:
                xmmtmp = xmm0
                adr = self.fail_boxes_float.get_addr_for_num(0)
                self.mc.MOVSD(xmmtmp, heap(adr))
                self.mc.MOVSD(result_loc, xmmtmp)
            else:
                assert result_loc is eax
                if kind == INT:
                    adr = self.fail_boxes_int.get_addr_for_num(0)
                    self.mc.MOV(eax, heap(adr))
                elif kind == REF:
                    adr = self.fail_boxes_ptr.get_addr_for_num(0)
                    self.mc.MOV(eax, heap(adr))
                    self.mc.MOV(heap(adr), imm0)
                else:
                    raise AssertionError(kind)
        #
        # Here we join Path A and Path B again
        offset = self.mc.get_relative_pos() - jmp_location
        assert 0 <= offset <= 127
        self.mc.overwrite(jmp_location - 1, chr(offset))
        self.mc.CMP_bi(FORCE_INDEX_OFS, 0)
        self.implement_guard(guard_token, 'L')

    def genop_discard_cond_call_gc_wb(self, op, arglocs):
        # Write code equivalent to write_barrier() in the GC: it checks
        # a flag in the object at arglocs[0], and if set, it calls the
        # function remember_young_pointer() from the GC.  The arguments
        # to the call are in arglocs[:N].  The rest, arglocs[N:], contains
        # registers that need to be saved and restored across the call.
        # N is either 2 (regular write barrier) or 3 (array write barrier).
        descr = op.getdescr()
        if we_are_translated():
            cls = self.cpu.gc_ll_descr.has_write_barrier_class()
            assert cls is not None and isinstance(descr, cls)
        #
        opnum = op.getopnum()
        if opnum == rop.COND_CALL_GC_WB:
            N = 2
            func = descr.get_write_barrier_fn(self.cpu)
            card_marking = False
        elif opnum == rop.COND_CALL_GC_WB_ARRAY:
            N = 3
            func = descr.get_write_barrier_from_array_fn(self.cpu)
            assert func != 0
            card_marking = descr.jit_wb_cards_set != 0
        else:
            raise AssertionError(opnum)
        #
        loc_base = arglocs[0]
        self.mc.TEST8(addr_add_const(loc_base, descr.jit_wb_if_flag_byteofs),
                      imm(descr.jit_wb_if_flag_singlebyte))
        self.mc.J_il8(rx86.Conditions['Z'], 0) # patched later
        jz_location = self.mc.get_relative_pos()

        # for cond_call_gc_wb_array, also add another fast path:
        # if GCFLAG_CARDS_SET, then we can just set one bit and be done
        if card_marking:
            self.mc.TEST8(addr_add_const(loc_base,
                                         descr.jit_wb_cards_set_byteofs),
                          imm(descr.jit_wb_cards_set_singlebyte))
            self.mc.J_il8(rx86.Conditions['NZ'], 0) # patched later
            jnz_location = self.mc.get_relative_pos()
        else:
            jnz_location = 0

        # the following is supposed to be the slow path, so whenever possible
        # we choose the most compact encoding over the most efficient one.
        if IS_X86_32:
            limit = -1      # push all arglocs on the stack
        elif IS_X86_64:
            limit = N - 1   # push only arglocs[N:] on the stack
        for i in range(len(arglocs)-1, limit, -1):
            loc = arglocs[i]
            if isinstance(loc, RegLoc):
                self.mc.PUSH_r(loc.value)
            else:
                assert not IS_X86_64 # there should only be regs in arglocs[N:]
                self.mc.PUSH_i32(loc.getint())
        if IS_X86_64:
            # We clobber these registers to pass the arguments, but that's
            # okay, because consider_cond_call_gc_wb makes sure that any
            # caller-save registers with values in them are present in
            # arglocs[N:] too, so they are saved on the stack above and
            # restored below.
            if N == 2:
                callargs = [edi, esi]
            else:
                callargs = [edi, esi, edx]
            remap_frame_layout(self, arglocs[:N], callargs,
                               X86_64_SCRATCH_REG)
        #
        # misaligned stack in the call, but it's ok because the write barrier
        # is not going to call anything more.  Also, this assumes that the
        # write barrier does not touch the xmm registers.  (Slightly delicate
        # assumption, given that the write barrier can end up calling the
        # platform's malloc() from AddressStack.append().  XXX may need to
        # be done properly)
        self.mc.CALL(imm(func))
        if IS_X86_32:
            self.mc.ADD_ri(esp.value, N*WORD)
        for i in range(N, len(arglocs)):
            loc = arglocs[i]
            assert isinstance(loc, RegLoc)
            self.mc.POP_r(loc.value)

        # if GCFLAG_CARDS_SET, then we can do the whole thing that would
        # be done in the CALL above with just four instructions, so here
        # is an inline copy of them
        if card_marking:
            self.mc.JMP_l8(0) # jump to the exit, patched later
            jmp_location = self.mc.get_relative_pos()
            # patch the JNZ above
            offset = self.mc.get_relative_pos() - jnz_location
            assert 0 < offset <= 127
            self.mc.overwrite(jnz_location-1, chr(offset))
            #
            loc_index = arglocs[1]
            if isinstance(loc_index, RegLoc):
                # choose a scratch register
                tmp1 = loc_index
                self.mc.PUSH_r(tmp1.value)
                # SHR tmp, card_page_shift
                self.mc.SHR_ri(tmp1.value, descr.jit_wb_card_page_shift)
                # XOR tmp, -8
                self.mc.XOR_ri(tmp1.value, -8)
                # BTS [loc_base], tmp
                self.mc.BTS(addr_add_const(loc_base, 0), tmp1)
                # done
                self.mc.POP_r(tmp1.value)
            elif isinstance(loc_index, ImmedLoc):
                byte_index = loc_index.value >> descr.jit_wb_card_page_shift
                byte_ofs = ~(byte_index >> 3)
                byte_val = 1 << (byte_index & 7)
                self.mc.OR8(addr_add_const(loc_base, byte_ofs), imm(byte_val))
            else:
                raise AssertionError("index is neither RegLoc nor ImmedLoc")
            # patch the JMP above
            offset = self.mc.get_relative_pos() - jmp_location
            assert 0 < offset <= 127
            self.mc.overwrite(jmp_location-1, chr(offset))
        #
        # patch the JZ above
        offset = self.mc.get_relative_pos() - jz_location
        assert 0 < offset <= 127
        self.mc.overwrite(jz_location-1, chr(offset))

    genop_discard_cond_call_gc_wb_array = genop_discard_cond_call_gc_wb

    def not_implemented_op_discard(self, op, arglocs):
        not_implemented("not implemented operation: %s" % op.getopname())

    def not_implemented_op(self, op, arglocs, resloc):
        not_implemented("not implemented operation with res: %s" %
                        op.getopname())

    def not_implemented_op_guard(self, op, guard_op,
                                 failaddr, arglocs, resloc):
        not_implemented("not implemented operation (guard): %s" %
                        op.getopname())

    def mark_gc_roots(self, force_index, use_copy_area=False):
        if force_index < 0:
            return     # not needed
        gcrootmap = self.cpu.gc_ll_descr.gcrootmap
        if gcrootmap:
            mark = self._regalloc.get_mark_gc_roots(gcrootmap, use_copy_area)
            if gcrootmap.is_shadow_stack:
                gcrootmap.write_callshape(mark, force_index)
            else:
                if self.gcrootmap_retaddr_forced == 0:
                    self.mc.insert_gcroot_marker(mark)   # common case
                else:
                    assert self.gcrootmap_retaddr_forced != -1, (
                              "two mark_gc_roots() in a CALL_RELEASE_GIL")
                    gcrootmap.put(self.gcrootmap_retaddr_forced, mark)
                    self.gcrootmap_retaddr_forced = -1

    def closing_jump(self, target_token):
        # The backend's logic assumes that the target code is in a piece of
        # assembler that was also called with the same number of arguments,
        # so that the locations [ebp+8..] of the input arguments are valid
        # stack locations both before and after the jump.
        my_nbargs = self.current_clt._debug_nbargs
        target_nbargs = target_token._x86_clt._debug_nbargs
        assert my_nbargs == target_nbargs
        #
        target = target_token._x86_loop_code
        if target_token in self.target_tokens_currently_compiling:
            curpos = self.mc.get_relative_pos() + 5
            self.mc.JMP_l(target - curpos)
        else:
            self.mc.JMP(imm(target))

    def malloc_cond(self, nursery_free_adr, nursery_top_adr, size):
        assert size & (WORD-1) == 0     # must be correctly aligned
        self.mc.MOV(eax, heap(nursery_free_adr))
        self.mc.LEA_rm(edx.value, (eax.value, size))
        self.mc.CMP(edx, heap(nursery_top_adr))
        self.mc.J_il8(rx86.Conditions['NA'], 0) # patched later
        jmp_adr = self.mc.get_relative_pos()

        # See comments in _build_malloc_slowpath for the
        # details of the two helper functions that we are calling below.
        # First, we need to call two of them and not just one because we
        # need to have a mark_gc_roots() in between.  Then the calling
        # convention of slowpath_addr{1,2} are tweaked a lot to allow
        # the code here to be just two CALLs: slowpath_addr1 gets the
        # size of the object to allocate from (EDX-EAX) and returns the
        # result in EAX; slowpath_addr2 additionally returns in EDX a
        # copy of heap(nursery_free_adr), so that the final MOV below is
        # a no-op.

        # reserve room for the argument to the real malloc and the
        # saved XMM regs (on 32 bit: 8 * 2 words; on 64 bit: 16 * 1
        # word)
        self._regalloc.reserve_param(1+16)

        gcrootmap = self.cpu.gc_ll_descr.gcrootmap
        shadow_stack = (gcrootmap is not None and gcrootmap.is_shadow_stack)
        if not shadow_stack:
            # there are two helpers to call only with asmgcc
            slowpath_addr1 = self.malloc_slowpath1
            self.mc.CALL(imm(slowpath_addr1))
        self.mark_gc_roots(self.write_new_force_index(), use_copy_area=True)
        slowpath_addr2 = self.malloc_slowpath2
        self.mc.CALL(imm(slowpath_addr2))

        offset = self.mc.get_relative_pos() - jmp_adr
        assert 0 < offset <= 127
        self.mc.overwrite(jmp_adr-1, chr(offset))
        self.mc.MOV(heap(nursery_free_adr), edx)

genop_discard_list = [Assembler386.not_implemented_op_discard] * rop._LAST
genop_list = [Assembler386.not_implemented_op] * rop._LAST
genop_llong_list = {}
genop_math_list = {}
genop_guard_list = [Assembler386.not_implemented_op_guard] * rop._LAST

for name, value in Assembler386.__dict__.iteritems():
    if name.startswith('genop_discard_'):
        opname = name[len('genop_discard_'):]
        num = getattr(rop, opname.upper())
        genop_discard_list[num] = value
    elif name.startswith('genop_guard_') and name != 'genop_guard_exception':
        opname = name[len('genop_guard_'):]
        num = getattr(rop, opname.upper())
        genop_guard_list[num] = value
    elif name.startswith('genop_llong_'):
        opname = name[len('genop_llong_'):]
        num = getattr(EffectInfo, 'OS_LLONG_' + opname.upper())
        genop_llong_list[num] = value
    elif name.startswith('genop_math_'):
        opname = name[len('genop_math_'):]
        num = getattr(EffectInfo, 'OS_MATH_' + opname.upper())
        genop_math_list[num] = value
    elif name.startswith('genop_'):
        opname = name[len('genop_'):]
        num = getattr(rop, opname.upper())
        genop_list[num] = value

# XXX: ri386 migration shims:
def addr_add(reg_or_imm1, reg_or_imm2, offset=0, scale=0):
    return AddressLoc(reg_or_imm1, reg_or_imm2, scale, offset)

def addr_add_const(reg_or_imm1, offset):
    return AddressLoc(reg_or_imm1, ImmedLoc(0), 0, offset)

def mem(loc, offset):
    return AddressLoc(loc, ImmedLoc(0), 0, offset)

def heap(addr):
    return AddressLoc(ImmedLoc(addr), ImmedLoc(0), 0, 0)

def not_implemented(msg):
    os.write(2, '[x86/asm] %s\n' % msg)
    raise NotImplementedError(msg)

class BridgeAlreadyCompiled(Exception):
    pass