diff options
Diffstat (limited to 'www/performance-2008-10-31.html')
| -rw-r--r-- | www/performance-2008-10-31.html | 134 |
1 files changed, 134 insertions, 0 deletions
diff --git a/www/performance-2008-10-31.html b/www/performance-2008-10-31.html new file mode 100644 index 0000000..5246ac3 --- /dev/null +++ b/www/performance-2008-10-31.html @@ -0,0 +1,134 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<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" /> + <style type="text/css"> +</style> +</head> +<body> + +<!--#include virtual="menu.html.incl"--> + +<div id="content"> + +<!--*************************************************************************--> +<h1>Clang - Performance</h1> +<!--*************************************************************************--> + +<p>This page tracks 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 (~220,000 lines) with few system + dependencies. This stresses the back-end's performance on generating + assembly code and debug information.</li> +</ul> +</p> + +<!--*************************************************************************--> +<h2><a name="enduser">Experiments</a></h2> +<!--*************************************************************************--> + +<p>Measurements are done by serially processing each file in the +respective benchmark, using Clang, gcc, and llvm-gcc as compilers. In +order to track the performance of various subsystems the timings have +been broken down into separate stages where possible: + +<ul> + <li><tt>-Eonly</tt>: This option runs the preprocessor but does not + perform any output. For gcc and llvm-gcc, the -MM option is used + as a rough equivalent to this step.</li> + <li><tt>-parse-noop</tt>: This option runs the parser on the input, + but without semantic analysis or any output. gcc and llvm-gcc have + no equivalent for this option.</li> + <li><tt>-fsyntax-only</tt>: This option runs the parser with semantic + analysis.</li> + <li><tt>-emit-llvm -O0</tt>: For Clang and llvm-gcc, this option + converts to the LLVM intermediate representation but doesn't + generate native code.</li> + <li><tt>-S -O0</tt>: Perform actual code generation to produce a + native assembler file.</li> + <li><tt>-S -O0 -g</tt>: This adds emission of debug information to + the assembly output.</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>-fsyntax-only</tt> below show +the difference of running with <tt>-fsyntax-only</tt> versus running +with <tt>-parse-noop</tt> (for clang) or <tt>-MM</tt> with gcc and +llvm-gcc. This amounts to a fairly accurate measure of only the time +to perform semantic analysis (and parsing, in the case of gcc and llvm-gcc).</p> + +<p>These timings are chosen to break down the compilation process for +clang as much as possible. The graphs below show these numbers +combined so that it is easy to see how the time for a particular task +is divided among various components. For example, <tt>-S -O0</tt> +includes the time of <tt>-fsyntax-only</tt> and <tt>-emit-llvm -O0</tt>.</p> + +<p>Note that we already know that the LLVM optimizers are substantially (30-40%) +faster than the GCC optimizers at a given -O level, so we only focus on -O0 +compile time here.</p> + +<!--*************************************************************************--> +<h2><a name="enduser">Timing Results</a></h2> +<!--*************************************************************************--> + +<!--=======================================================================--> +<h3><a name="2008-10-31">2008-10-31</a></h3> +<!--=======================================================================--> + +<center><h4>Sketch</h4></center> +<img class="img_slide" + src="timing-data/2008-10-31/sketch.png" alt="Sketch Timings"/> + +<p>This shows Clang's substantial performance improvements in +preprocessing and semantic analysis; over 90% faster on +-fsyntax-only. As expected, time spent in code generation for this +benchmark is relatively small. One caveat, Clang's debug information +generation for Objective-C is very incomplete; this means the <tt>-S +-O0 -g</tt> numbers are unfair since Clang is generating substantially +less output.</p> + +<p>This chart also shows the effect of using precompiled headers (PCH) +on compiler time. gcc and llvm-gcc see a large performance improvement +with PCH; about 4x in wall time. Unfortunately, Clang does not yet +have an implementation of PCH-style optimizations, but we are actively +working to address this.</p> + +<center><h4>176.gcc</h4></center> +<img class="img_slide" + src="timing-data/2008-10-31/176.gcc.png" alt="176.gcc Timings"/> + +<p>Unlike the <i>Sketch</i> timings, compilation of <i>176.gcc</i> +involves a large amount of code generation. The time spent in Clang's +LLVM IR generation and code generation is on par with gcc's code +generation time but the improved parsing & semantic analysis +performance means Clang still comes in at ~29% faster versus gcc +on <tt>-S -O0 -g</tt> and ~20% faster versus llvm-gcc.</p> + +<p>These numbers indicate that Clang still has room for improvement in +several areas, notably our LLVM IR generation is significantly slower +than that of llvm-gcc, and both Clang and llvm-gcc incur a +significantly higher cost for adding debugging information compared to +gcc.</p> + +</div> +</body> +</html> |
