hphp/runtime/vm/minstr-state.h

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-present Facebook, Inc. (http://www.facebook.com)  |
   6    +----------------------------------------------------------------------+
   7    | This source file is subject to version 3.01 of the PHP license,      |
   8    | that is bundled with this package in the file LICENSE, and is        |
   9    | available through the world-wide-web at the following url:           |
  10    | http://www.php.net/license/3_01.txt                                  |
  11    | If you did not receive a copy of the PHP license and are unable to   |
  12    | obtain it through the world-wide-web, please send a note to          |
  13    | license@php.net so we can mail you a copy immediately.               |
  14    +----------------------------------------------------------------------+
  15 */
  16
  17 #pragma once
  18
  19 #include "hphp/runtime/base/tv-val.h"
  20 #include "hphp/runtime/base/typed-value.h"
  21
  22 namespace HPHP {
  23
  24 /*
  25  * MInstrState contains VM registers used while executing member instructions.
  26  * It lives with the other VM registers in the RDS header, and is also saved and
  27  * restored with them when we reenter the VM.
  28  */
  29 struct MInstrState {
  30
  31   /*
  32    * This space is used for the return value of builtin functions that return by
  33    * reference, and for storing $this as the base for the BaseH bytecode,
  34    * without needing to acquire a reference to it.  Since we don't ever use the
  35    * two at the same time, it is okay to use a union.
  36    */
  37   union {
  38     TypedValue tvBuiltinReturn;
  39     TypedValue tvTempBase;
  40   };
  41
  42   // The JIT passes &tvBuiltinReturn::m_data to builtins returning
  43   // Array/Object/String, which perform RVO in C++, thus writing valid
  44   // pointers without updating m_type, preventing the GC from scanning
  45   // the pointer. But conservative scanning doesn't really hurt here
  46   // (given that the pointer is also passed into a C++ function), and
  47   // it allows us to keep rds::Header below 128 bytes.
  48   TYPE_SCAN_CONSERVATIVE_FIELD(tvBuiltinReturn);
  49
  50   tv_lval base;
  51
  52   // In order to support modifying readonly value type arrays, we need a bit to
  53   // determine whether the last prop access in a member chain is readonly and
  54   // COW.
  55   bool roProp;
  56
  57   // type-scan driven scanner
  58   TYPE_SCAN_IGNORE_FIELD(base);
  59 };
  60
  61 }