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Clang - Performance

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This page shows the compile time performance of Clang on two +interesting benchmarks:

Sketch: The Objective-C example application shipped on + Mac OS X as part of Xcode. Sketch 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 Cocoa/Cocoa.h 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.
176.gcc: This is the gcc-2.7.2.2 code base as present in + SPECINT 2000. In contrast to Sketch, 176.gcc 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.

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+For previous performance numbers, please +go here. +

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Experiments

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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.

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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.

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non-compiler: The overhead of the build system itself; + for Sketch this also includes the time to build/copy various + non-source code resource files.
+ driver: Add execution of the driver, but do not execute any + commands (by using the -### driver option).
+ pch gen: Add generation of PCH files.
+ cpp: Add preprocessing of source files (this time is + include in syntax for gcc).
+ parse: Add parsing of source files (this time is + include in syntax for gcc).
+ syntax: Add semantic checking of source files (for + gcc, this includes preprocessing and parsing as well).
+ IRgen: Add generation of LLVM IR (gcc has no + corresponding phase).
+ codegen: Add generation of assembler files.
+ assembler: Add assembler time to generate .o files.
+ linker: Add linker time.

+ +

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 + syntax below show the +difference of running with + syntax versus running with + +parse (for clang) or + driver 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).

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Timing Results

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2009-03-02

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