direct_machine.cpp

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/*  GRAPHITE2 LICENSING

    Copyright 2010, SIL International

    All rights reserved.

    This library is free software; you can redistribute it and/or modify

    it under the terms of the GNU Lesser General Public License as published

    by the Free Software Foundation; either version 2.1 of License, or

    (at your option) any later version.

    This program is distributed in the hope that it will be useful,

    but WITHOUT ANY WARRANTY; without even the implied warranty of

    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

    Lesser General Public License for more details.

    You should also have received a copy of the GNU Lesser General Public

    License along with this library in the file named "LICENSE".

    If not, write to the Free Software Foundation, 51 Franklin Street,

    Suite 500, Boston, MA 02110-1335, USA or visit their web page on the

    internet at http://www.fsf.org/licenses/lgpl.html.

Alternatively, the contents of this file may be used under the terms of the

Mozilla Public License (http://mozilla.org/MPL) or the GNU General Public

License, as published by the Free Software Foundation, either version 2

of the License or (at your option) any later version.

*/

// This direct threaded interpreter implmentation for machine.h

// Author: Tim Eves

// Build either this interpreter or the call_machine implementation.

// The direct threaded interpreter is relies upon a gcc feature called

// labels-as-values so is only portable to compilers that support the

// extension (gcc only as far as I know) however it should build on any

// architecture gcc supports.

// This is twice as fast as the call threaded model and is likely faster on

// inorder processors with short pipelines and little branch prediction such

// as the ARM and possibly Atom chips.

#include <cassert>

#include <cstring>

#include "inc/Machine.h"

#include "inc/Segment.h"

#include "inc/Slot.h"

#include "inc/Rule.h"

#define STARTOP(name)           name: {

#define ENDOP                   }; goto *((sp - sb)/Machine::STACK_MAX ? &&end : *++ip);

#define EXIT(status)            { push(status); goto end; }

#define do_(name)               &&name

using namespace graphite2;

using namespace vm;

namespace {

// The GCC manual has this to say about labels as values:

//   The &&foo expressions for the same label might have different values

//   if the containing function is inlined or cloned. If a program relies

//   on them being always the same, __attribute__((__noinline__,__noclone__))

//   should be used to prevent inlining and cloning.

//

// is_return in Code.cpp relies on being able to do comparisons, so it needs

// them to be always the same.

//

// The GCC manual further adds:

//   If &&foo is used in a static variable initializer, inlining and

//   cloning is forbidden.

//

// In this file, &&foo *is* used in a static variable initializer, and it's not

// entirely clear whether this should prevent inlining of the function or not.

// In practice, though, clang 7 can end up inlining the function with ThinLTO,

// which breaks at least is_return. https://bugs.llvm.org/show_bug.cgi?id=39241

// So all in all, we need at least the __noinline__ attribute. __noclone__

// is not supported by clang.

__attribute__((__noinline__))

const void * direct_run(const bool          get_table_mode,

                        const instr       * program,

                        const byte        * data,

                        Machine::stack_t  * stack,

                        slotref         * & __map,

                        uint8                _dir,

                        Machine::status_t & status,

                        SlotMap           * __smap=0)

    // We need to define and return to opcode table from within this function

    // other inorder to take the addresses of the instruction bodies.

    #include "inc/opcode_table.h"

    if (get_table_mode)

        return opcode_table;

    // Declare virtual machine registers

    const instr           * ip = program;

    const byte            * dp = data;

    Machine::stack_t      * sp = stack + Machine::STACK_GUARD,

                    * const sb = sp;

    SlotMap             & smap = *__smap;

    Segment              & seg = smap.segment;

    slotref                 is = *__map,

                         * map = __map,

                  * const mapb = smap.begin()+smap.context();

    uint8                  dir = _dir;

    int8                 flags = 0;

    // start the program

    goto **ip;

    // Pull in the opcode definitions

    #include "inc/opcodes.h"

    end:

    __map  = map;

    *__map = is;

    return sp;

const opcode_t * Machine::getOpcodeTable() throw()

    slotref * dummy;

    Machine::status_t dumstat = Machine::finished;

    return static_cast<const opcode_t *>(direct_run(true, 0, 0, 0, dummy, 0, dumstat));

Machine::stack_t  Machine::run(const instr   * program,

                               const byte    * data,

                               slotref     * & is)

    assert(program != 0);

    const stack_t *sp = static_cast<const stack_t *>(

                direct_run(false, program, data, _stack, is, _map.dir(), _status, &_map));

    const stack_t ret = sp == _stack+STACK_GUARD+1 ? *sp-- : 0;

    check_final_stack(sp);

    return ret;