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