[webkit-dev] command line JSC vs. JSC in libQtWebKit

Maciej Stachowiak mjs at apple.com
Wed Feb 25 09:05:36 PST 2009

On Feb 25, 2009, at 3:55 AM, Osztrogonac Csaba wrote:

> Hi all,
> We are working on speedup jsc, and found a strange thing. Command
> line JSC and JSC in libQtWebkit build with different gcc options:
> - jsc.pro build command line jsc with: -O3
> - WebCore.pro build libQtWebKit with: -O2 -fPIC -fno-strict-aliasing
> (The latter is slower by 12%.)
> If you implement an optimization, you measure speedup with command
> line jsc on SunSpider. The results can be different if you measure
> with a web browser such as QtLauncher. User usually not run command
> line jsc, but a browser. Accordingly I suggest we should measure
> performance users' point of view. Is neccesary building faster, but
> different jsc? If no, possible solution can be: Build JavaScriptCore
> library with JavaScriptCore.pro and link it with jsc command line
> interface (jsc.o). Or make possibility in build system to build two
> different jsc. One of them is faster for using in real life. The other
> is slower, but same as running in browsers for testing and performance
> measuring.

On other platforms, we try to build the JavaScriptCore object files  
with -O3 and strict aliasing enabled, even if the rest of WebKit is  
not. For example, on Mac, JavaScriptCore.framework builds with "-O3 - 
fstrict-aliasing -fomit-frame-pointer" even though WebCore.framework  
builds with "-O2 -fno-strict-aliasing". So I suggest fixing this in  
the libQtWebKit build.


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