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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-2009-03-02.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.</p>
  54
  55 <p>In order to track the performance of various subsystems the timings
  56 have been broken down into separate stages where possible. This is
  57 done by over-riding the CC environment variable used during the build
  58 to point to one of a few simple shell scripts which may skip part of
  59 the build.
  60
  61 <ul>
  62   <li><tt>non-compiler</tt>: The overhead of the build system itself;
  63     for Sketch this also includes the time to build/copy various
  64     non-source code resource files.</li>
  65   <li><tt>+ driver</tt>: Add execution of the driver, but do not execute any
  66     commands (by using the -### driver option).</li>
  67   <li><tt>+ pch gen</tt>: Add generation of PCH files (if used).</li>
  68   <li><tt>+ syntax</tt>: Add preprocessing, parsing, and semantic checking of
  69     source files.</li>
  70   <li><tt>+ IRgen</tt>: Add generation of LLVM IR (gcc has no
  71     corresponding phase).</li>
  72   <li><tt>+ codegen</tt>: Add generation of assembler files.</li>
  73   <li><tt>+ assembler</tt>: Add assembler time to generate .o files.</li>
  74   <li><tt>+ linker</tt>: Add linker time.</li>
  75 </ul>
  76 </p>
  77
  78 <p>This set of stages is chosen to be approximately additive, that is each
  79 subsequent stage simply adds some additional processing. The timings measure the
  80 delta of the given stage from the previous one. For example, the timings
  81 for <tt>+ syntax</tt> below show the difference of running with <tt>+
  82 syntax</tt> versus the times for <tt>+ pch gen</tt>. This amounts to a fairly
  83 accurate measure of only the time to perform preprocessing, parsing, and
  84 semantic analysis after PCH generation is done.</p>
  85
  86 <!--*************************************************************************-->
  87 <h2><a name="timings">Timing Results</a></h2>
  88 <!--*************************************************************************-->
  89
  90 <!--=======================================================================-->
  91 <h3><a name="2009-06-26">2009-06-26</a></h3>
  92 <!--=======================================================================-->
  93
  94 <a href="timing-data/2009-06-26/sketch.pdf">
  95 <img class="img_slide"
  96      src="timing-data/2009-06-26/sketch.png" alt="Sketch Timings"/>
  97 </a>
  98
  99 <a href="timing-data/2009-06-26/176.gcc.pdf">
 100 <img class="img_slide"
 101      src="timing-data/2009-06-26/176.gcc.png" alt="176.gcc Timings"/>
 102 </a>
 103
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