<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br></div><div><br>On Sep 5, 2014, at 3:23 PM, "Vienneau, Christopher" <<a href="mailto:cvienneau@ea.com">cvienneau@ea.com</a>> wrote:<br><br></div><blockquote type="cite"><div>
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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m looking for some information about the Java script interpreter ASM backend, aka OfflineAsm. <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">First a bit of background information; the code I have been using is about a year old, on several platforms we don’t run with JIT and won’t be able to enable it. This means that we’ve been using the
<span style="font-size:9.0pt;font-family:Consolas;color:#1E1E1E;background:white;mso-highlight:white">
LLINT_C_LOOP</span><span style="font-size:9.0pt;font-family:Consolas;color:#1E1E1E">
</span>path in these cases. It was considered that the ASM backend may be able to improve performance in this case, currently I’m taking a look at how things are done in a more recent snapshot of the trunk to be sure this development effort will be going in
the right direction on what is done there. As a side note I see that <span style="font-size:9.0pt;font-family:Consolas;color:#1E1E1E;background:white;mso-highlight:white">
LLINT_C_LOOP</span><span style="font-size:9.0pt;font-family:Consolas;color:#1E1E1E">
</span>has been replaced with <span style="font-size:9.0pt;font-family:Consolas;color:#1E1E1E;background:white;mso-highlight:white">
#if !ENABLE(JIT)</span><span style="font-size:9.0pt;font-family:Consolas;color:#1E1E1E">
</span>which I guess is pretty much how it has always behaved.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So my questions are:<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span style="mso-list:Ignore">1)<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]-->How is the ASM backend intended to be used? </p></div></div></blockquote><div><br></div><div>As a bottom tier for a mixed mode execution VM. We compile to assembly to be able to get an ABI that is compatible with our JITs and to be able to do OSR. </div><br><blockquote type="cite"><div><div class="WordSection1"><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1">Is there a doc that covers this?</p></div></div></blockquote><div><br></div><div>No. </div><br><blockquote type="cite"><div><div class="WordSection1"><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span style="mso-list:Ignore">2)<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]-->Can I essentially move from the “C LOOP” to neither “C LOOP” nor “JIT”? or is the ASM backend dependent on JIT itself? </p></div></div></blockquote><div><br></div><div>You should be able to use the asm backend without the JIT. We do this if we compiled with the JIT but we failed to allocate writable+executable memory at run time. With some hacks you could probably compile webkit to always do this. </div><br><blockquote type="cite"><div><div class="WordSection1"><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1">It appears this would be handled by the defines in Source\JavaScriptCore\llint\LLIntOfflineAsmConfig.h<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span style="mso-list:Ignore">3)<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]-->If JIT is expected to use the ASM backend is there a way this can be worked around?</p></div></div></blockquote><div><br></div><div>The JIT doesn't use offlineasm.</div><br><blockquote type="cite"><div><div class="WordSection1"><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span style="mso-list:Ignore">4)<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]-->Should I actually expect a performance increase compared to the “C LOOP”?</p></div></div></blockquote><div><br></div><div>Not really, unless your C compiler sucks. </div><br><blockquote type="cite"><div><div class="WordSection1"><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span style="mso-list:Ignore">5)<span style="font:7.0pt "Times New Roman"">
</span></span><!--[endif]-->Are there any other suggestions on how to improve performance of Java script code in a non-JIT port?</p></div></div></blockquote><div><br></div><div>Not really but contributions are welcome. </div><br><blockquote type="cite"><div><div class="WordSection1"><p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo1"><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks for any feedback<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Chris Vienneau<o:p></o:p></p>
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