hphp/util/bisector.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 #ifndef incl_HPHP_UTIL_BISECTOR_H_
  17 #define incl_HPHP_UTIL_BISECTOR_H_
  18
  19 #include "hphp/util/compilation-flags.h"
  20 #include "hphp/util/trace.h"
  21
  22 namespace HPHP {
  23
  24 /*
  25   Use this class to help bisect issues with optimizations.
  26
  27   Declare a bisector via:
  28
  29     BISECTOR(name);
  30
  31   Then guard each optimization by
  32
  33     if (name.go(<optional msg>)) {
  34       // do the optimization
  35     }
  36
  37   Then run via eg
  38
  39     env TRACE=bisector:1 name2=1000000 <program>
  40
  41   and look in the trace output to see how many times the optimization happened.
  42   eg:
  43
  44    name : 0
  45    name : 1
  46    name : 2
  47
  48   Now you can bisect down to the optimization thats causing issues by setting
  49   name1 and name2 (name1 will default to 0 if not set). If name1 < name2 it
  50   will run the optimizations in the interval [name1, name2). If name1 > name2
  51   it will skip the optimizations in the interval [name2, name1).
  52
  53   Note that its usually best to at least start by bisecting with name2 only,
  54   since (for some optimizations) skipping earlier optimizations can change
  55   later results.
  56 */
  57
  58 struct BisectorHelper {
  59   TRACE_SET_MOD(bisector)
  60
  61   explicit BisectorHelper(const char* e) : env(e) {
  62     if (debug) {
  63       auto const p1 = getenv((env + std::string("1")).c_str());
  64       auto const p2 = getenv((env + std::string("2")).c_str());
  65       if (p2) {
  66         low = p1 ? atoi(p1) : 0;
  67         high = atoi(p2);
  68       }
  69     }
  70   }
  71   bool go(const char* msg = nullptr) {
  72     if (!debug || (!high && !low)) return true;
  73     if ((count++ - low) < (high - low)) {
  74       FTRACE(1, "{} : {} {}\n",
  75              env, count - 1, msg ? msg : "");
  76       return true;
  77     }
  78     return false;
  79   }
  80 private:
  81   const char *env;
  82   uint32_t low = 0u;
  83   uint32_t high = 0u;
  84   uint32_t count = 0u;
  85 };
  86
  87 #define BISECTOR(name) static BisectorHelper name(#name);
  88
  89 }
  90
  91 #endif