hphp/hhbbc/cfg-opts.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 #pragma once
  17
  18 #include "hphp/hhbbc/representation.h"
  19
  20 namespace HPHP::HHBBC {
  21
  22 struct Index;
  23 struct FuncAnalysis;
  24
  25 //////////////////////////////////////////////////////////////////////
  26
  27 /*
  28  * Assist in removing blocks that aren't reachable by removing
  29  * conditional jumps that are never taken.  Conditional jumps that are
  30  * always taken are turned into unconditional jumps in first_pass.
  31  *
  32  * If options.RemoveDeadBlocks is off, this function just replaces
  33  * blocks we believe are unreachable with fatal opcodes.
  34  */
  35 void remove_unreachable_blocks(const FuncAnalysis&, php::WideFunc& func);
  36
  37 /*
  38  * Simplify control flow, and create Switch and SSwitch bytecodes.
  39  */
  40 bool control_flow_opts(const FuncAnalysis&, php::WideFunc& func);
  41
  42 /*
  43  * Split critical edges.
  44  *
  45  * Some optimizations require or are better if we split critical edges in the
  46  * cfg.  One example of this is UnsetL insertion.  With the following cfg:
  47  *
  48  *  B1
  49  *  | \
  50  *  |  B2
  51  *  | /
  52  *  B3
  53  *
  54  * Suppose in B1 we have local l1 holding a counted value.  B2 may leave local
  55  * l1 uninit (after a move optisation is applied during a call).  Inserting an
  56  * UnsetL(l1) at the start of block B3 will require a decref of
  57  * Union(TCnt, TUninit), which is not great.  If we split critical edges, the
  58  * UnsetL(l1) (and its decref) could sit on the edge from B1 to B2 making it
  59  * a decref of TCnt.
  60  *
  61  * Critical edge blocks that remain a single nop will get folded away by
  62  * control_flow_opts.
  63  */
  64 void split_critical_edges(const Index&, FuncAnalysis&, php::WideFunc& func);
  65
  66 //////////////////////////////////////////////////////////////////////
  67
  68 }
  69