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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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+<html>
+<head>
+  <META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
+  <title>Clang - Performance</title>
+  <link type="text/css" rel="stylesheet" href="menu.css" />
+  <link type="text/css" rel="stylesheet" href="content.css" />
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+<body>
+
+<!--#include virtual="menu.html.incl"-->
+
+<div id="content">
+
+<!--*************************************************************************-->
+<h1>Clang - Performance</h1>
+<!--*************************************************************************-->
+
+<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-2008-10-31.html">here</a>.
+</p>
+
+<!--*************************************************************************-->
+<h2><a name="experiments">Experiments</a></h2>
+<!--*************************************************************************-->
+
+<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; gcc is run both with and without the new clang driver (ccc)
+in order to evaluate the overhead of the driver itself.</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.</li>
+  <li><tt>+ cpp</tt>: Add preprocessing of source files (this time is
+    include in syntax for gcc).</li>
+  <li><tt>+ parse</tt>: Add parsing of source files (this time is
+    include in syntax for gcc).</li>
+  <li><tt>+ syntax</tt>: Add semantic checking of source files (for
+    gcc, this includes preprocessing and parsing as well).</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 running with <tt>+
+parse</tt> (for clang) or <tt>+ driver</tt> with gcc. This amounts to
+a fairly accurate measure of only the time to perform semantic
+analysis (and preprocessing/parsing, in the case of gcc).</p>
+
+<!--*************************************************************************-->
+<h2><a name="timings">Timing Results</a></h2>
+<!--*************************************************************************-->
+
+<!--=======================================================================-->
+<h3><a name="2009-03-02">2009-03-02</a></h3>
+<!--=======================================================================-->
+
+<a href="timing-data/2009-03-02/sketch.pdf">
+<img class="img_slide" 
+     src="timing-data/2009-03-02/sketch.png" alt="Sketch Timings"/>
+</a>
+
+<a href="timing-data/2009-03-02/176.gcc.pdf">
+<img class="img_slide" 
+     src="timing-data/2009-03-02/176.gcc.png" alt="176.gcc Timings"/>
+</a>
+
+</div>
+</body>
+</html>