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 | <!--*************************************************************************--> | 
 | <h1>Clang - Performance</h1> | 
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 |  | 
 | <p>This page shows the compile time performance of Clang on two | 
 | interesting benchmarks: | 
 | <ul> | 
 |   <li><i>Sketch</i>: The Objective-C example application shipped on | 
 |     Mac OS X as part of Xcode. <i>Sketch</i> is indicative of a | 
 |     "typical" Objective-C app. The source itself has a relatively | 
 |     small amount of code (~7,500 lines of source code), but it relies | 
 |     on the extensive Cocoa APIs to build its functionality. Like many | 
 |     Objective-C applications, it includes <tt>Cocoa/Cocoa.h</tt> in | 
 |     all of its source files, which represents a significant stress | 
 |     test of the front-end's performance on lexing, preprocessing, | 
 |     parsing, and syntax analysis.</li> | 
 |   <li><i>176.gcc</i>: This is the gcc-2.7.2.2 code base as present in | 
 |     SPECINT 2000. In contrast to Sketch, <i>176.gcc</i> consists of a | 
 |     large amount of C source code (~200,000 lines) with few system | 
 |     dependencies. This stresses the back-end's performance on generating | 
 |     assembly code and debug information.</li> | 
 | </ul> | 
 | </p> | 
 |  | 
 | <p> | 
 | For previous performance numbers, please | 
 | go <a href="performance-2009-03-02.html">here</a>. | 
 | </p> | 
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 | <h2><a name="experiments">Experiments</a></h2> | 
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 |  | 
 | <p>Measurements are done by running a full build (using xcodebuild or | 
 | make for Sketch and 176.gcc respectively) using Clang and gcc 4.2 as | 
 | compilers.</p> | 
 |  | 
 | <p>In order to track the performance of various subsystems the timings | 
 | have been broken down into separate stages where possible. This is | 
 | done by over-riding the CC environment variable used during the build | 
 | to point to one of a few simple shell scripts which may skip part of | 
 | the build. | 
 |  | 
 | <ul> | 
 |   <li><tt>non-compiler</tt>: The overhead of the build system itself; | 
 |     for Sketch this also includes the time to build/copy various | 
 |     non-source code resource files.</li> | 
 |   <li><tt>+ driver</tt>: Add execution of the driver, but do not execute any | 
 |     commands (by using the -### driver option).</li> | 
 |   <li><tt>+ pch gen</tt>: Add generation of PCH files (if used).</li> | 
 |   <li><tt>+ syntax</tt>: Add preprocessing, parsing, and semantic checking of | 
 |     source files.</li> | 
 |   <li><tt>+ IRgen</tt>: Add generation of LLVM IR (gcc has no | 
 |     corresponding phase).</li> | 
 |   <li><tt>+ codegen</tt>: Add generation of assembler files.</li> | 
 |   <li><tt>+ assembler</tt>: Add assembler time to generate .o files.</li> | 
 |   <li><tt>+ linker</tt>: Add linker time.</li> | 
 | </ul> | 
 | </p> | 
 |  | 
 | <p>This set of stages is chosen to be approximately additive, that is each | 
 | subsequent stage simply adds some additional processing. The timings measure the | 
 | delta of the given stage from the previous one. For example, the timings | 
 | for <tt>+ syntax</tt> below show the difference of running with <tt>+ | 
 | syntax</tt> versus the times for <tt>+ pch gen</tt>. This amounts to a fairly | 
 | accurate measure of only the time to perform preprocessing, parsing, and | 
 | semantic analysis after PCH generation is done.</p> | 
 |  | 
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 | <h2><a name="timings">Timing Results</a></h2> | 
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 |  | 
 | <!--=======================================================================--> | 
 | <h3><a name="2009-06-26">2009-06-26</a></h3> | 
 | <!--=======================================================================--> | 
 |  | 
 | <a href="timing-data/2009-06-26/sketch.pdf"> | 
 | <img class="img_slide"  | 
 |      src="timing-data/2009-06-26/sketch.png" alt="Sketch Timings"/> | 
 | </a> | 
 |  | 
 | <a href="timing-data/2009-06-26/176.gcc.pdf"> | 
 | <img class="img_slide"  | 
 |      src="timing-data/2009-06-26/176.gcc.png" alt="176.gcc Timings"/> | 
 | </a> | 
 |  | 
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