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  18 <!--*************************************************************************-->
  19 <h1>Clang - Performance</h1>
  20 <!--*************************************************************************-->
  21
  22 <p>This page shows the compile time performance of Clang on two
  23 interesting benchmarks:
  24 <ul>
  25   <li><i>Sketch</i>: The Objective-C example application shipped on
  26     Mac OS X as part of Xcode. <i>Sketch</i> is indicative of a
  27     "typical" Objective-C app. The source itself has a relatively
  28     small amount of code (~7,500 lines of source code), but it relies
  29     on the extensive Cocoa APIs to build its functionality. Like many
  30     Objective-C applications, it includes <tt>Cocoa/Cocoa.h</tt> in
  31     all of its source files, which represents a significant stress
  32     test of the front-end's performance on lexing, preprocessing,
  33     parsing, and syntax analysis.</li>
  34   <li><i>176.gcc</i>: This is the gcc-2.7.2.2 code base as present in
  35     SPECINT 2000. In contrast to Sketch, <i>176.gcc</i> consists of a
  36     large amount of C source code (~200,000 lines) with few system
  37     dependencies. This stresses the back-end's performance on generating
  38     assembly code and debug information.</li>
  39 </ul>
  40 </p>
  41
  42 <p>
  43 For previous performance numbers, please
  44 go <a href="performance-2008-10-31.html">here</a>.
  45 </p>
  46
  47 <!--*************************************************************************-->
  48 <h2><a name="experiments">Experiments</a></h2>
  49 <!--*************************************************************************-->
  50
  51 <p>Measurements are done by running a full build (using xcodebuild or
  52 make for Sketch and 176.gcc respectively) using Clang and gcc 4.2 as
  53 compilers; gcc is run both with and without the new clang driver (ccc)
  54 in order to evaluate the overhead of the driver itself.</p>
  55
  56 <p>In order to track the performance of various subsystems the timings
  57 have been broken down into separate stages where possible. This is
  58 done by over-riding the CC environment variable used during the build
  59 to point to one of a few simple shell scripts which may skip part of
  60 the build.
  61
  62 <ul>
  63   <li><tt>non-compiler</tt>: The overhead of the build system itself;
  64     for Sketch this also includes the time to build/copy various
  65     non-source code resource files.</li>
  66   <li><tt>+ driver</tt>: Add execution of the driver, but do not execute any
  67     commands (by using the -### driver option).</li>
  68   <li><tt>+ pch gen</tt>: Add generation of PCH files.</li>
  69   <li><tt>+ cpp</tt>: Add preprocessing of source files (this time is
  70     include in syntax for gcc).</li>
  71   <li><tt>+ parse</tt>: Add parsing of source files (this time is
  72     include in syntax for gcc).</li>
  73   <li><tt>+ syntax</tt>: Add semantic checking of source files (for
  74     gcc, this includes preprocessing and parsing as well).</li>
  75   <li><tt>+ IRgen</tt>: Add generation of LLVM IR (gcc has no
  76     corresponding phase).</li>
  77   <li><tt>+ codegen</tt>: Add generation of assembler files.</li>
  78   <li><tt>+ assembler</tt>: Add assembler time to generate .o files.</li>
  79   <li><tt>+ linker</tt>: Add linker time.</li>
  80 </ul>
  81 </p>
  82
  83 <p>This set of stages is chosen to be approximately additive, that is
  84 each subsequent stage simply adds some additional processing. The
  85 timings measure the delta of the given stage from the previous
  86 one. For example, the timings for <tt>+ syntax</tt> below show the
  87 difference of running with <tt>+ syntax</tt> versus running with <tt>+
  88 parse</tt> (for clang) or <tt>+ driver</tt> with gcc. This amounts to
  89 a fairly accurate measure of only the time to perform semantic
  90 analysis (and preprocessing/parsing, in the case of gcc).</p>
  91
  92 <!--*************************************************************************-->
  93 <h2><a name="timings">Timing Results</a></h2>
  94 <!--*************************************************************************-->
  95
  96 <!--=======================================================================-->
  97 <h3><a name="2009-03-02">2009-03-02</a></h3>
  98 <!--=======================================================================-->
  99
 100 <a href="timing-data/2009-03-02/sketch.pdf">
 101 <img class="img_slide"
 102      src="timing-data/2009-03-02/sketch.png" alt="Sketch Timings"/>
 103 </a>
 104
 105 <a href="timing-data/2009-03-02/176.gcc.pdf">
 106 <img class="img_slide"
 107      src="timing-data/2009-03-02/176.gcc.png" alt="176.gcc Timings"/>
 108 </a>
 109
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