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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:</p>
     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 
     41 <p>
     42 For previous performance numbers, please
     43 go <a href="performance-2008-10-31.html">here</a>.
     44 </p>
     45 
     46 <!--*************************************************************************-->
     47 <h2><a name="experiments">Experiments</a></h2>
     48 <!--*************************************************************************-->
     49 
     50 <p>Measurements are done by running a full build (using xcodebuild or
     51 make for Sketch and 176.gcc respectively) using Clang and gcc 4.2 as
     52 compilers; gcc is run both with and without the new clang driver (ccc)
     53 in order to evaluate the overhead of the driver itself.</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.</p>
     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.</li>
     68   <li><tt>+ cpp</tt>: Add preprocessing of source files (this time is
     69     include in syntax for gcc).</li>
     70   <li><tt>+ parse</tt>: Add parsing of source files (this time is
     71     include in syntax for gcc).</li>
     72   <li><tt>+ syntax</tt>: Add semantic checking of source files (for
     73     gcc, this includes preprocessing and parsing as well).</li>
     74   <li><tt>+ IRgen</tt>: Add generation of LLVM IR (gcc has no
     75     corresponding phase).</li>
     76   <li><tt>+ codegen</tt>: Add generation of assembler files.</li>
     77   <li><tt>+ assembler</tt>: Add assembler time to generate .o files.</li>
     78   <li><tt>+ linker</tt>: Add linker time.</li>
     79 </ul>
     80 
     81 <p>This set of stages is chosen to be approximately additive, that is
     82 each subsequent stage simply adds some additional processing. The
     83 timings measure the delta of the given stage from the previous
     84 one. For example, the timings for <tt>+ syntax</tt> below show the
     85 difference of running with <tt>+ syntax</tt> versus running with <tt>+
     86 parse</tt> (for clang) or <tt>+ driver</tt> with gcc. This amounts to
     87 a fairly accurate measure of only the time to perform semantic
     88 analysis (and preprocessing/parsing, in the case of gcc).</p>
     89 
     90 <!--*************************************************************************-->
     91 <h2><a name="timings">Timing Results</a></h2>
     92 <!--*************************************************************************-->
     93 
     94 <!--=======================================================================-->
     95 <h3><a name="2009-03-02">2009-03-02</a></h3>
     96 <!--=======================================================================-->
     97 
     98 <a href="timing-data/2009-03-02/sketch.pdf">
     99 <img class="img_slide" 
    100      src="timing-data/2009-03-02/sketch.png" alt="Sketch Timings">
    101 </a>
    102 
    103 <a href="timing-data/2009-03-02/176.gcc.pdf">
    104 <img class="img_slide" 
    105      src="timing-data/2009-03-02/176.gcc.png" alt="176.gcc Timings">
    106 </a>
    107 
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