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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.5pt">Background:<o:p></o:p></span></b></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt">Our business need to link many BC files together to generate a final big BC file; we noticed that the linking time increase significantly(more than linearly) with the increase of the BC file number,
our biggest case (with ~8000 BC files ) takes > 1 hour time on XEON server which is unbearable to users.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.5pt">Profiling and Analysis:<o:p></o:p></span></b></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l3 level1 lfo3">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">a.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">From profiling data, it was observed that TypeFinder() consumes 98% of total time; TypeFinder() is not a key activity in llvm-link, it is just used to filter out all “Named Structure Types” in a module<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l3 level1 lfo3">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">b.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">In current llvm-link, when linking all BC files, the BC file is linked one by one; for example, link bc1, bc2, bc3, bc4, bc5, bcN, the workflow is that, link bc1 & bc2 to bc12, then link with bc3 to bc123, then
link with bc4 to bc1234, …, finally bc12345…N.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:0cm"><span lang="EN-US">The “Named Structure Types” in destination module is calculated in each linking; with the size increase of destination module, TypeFinder() will consume more and more
time, this explains why the linking time increase is more than linearly<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.5pt">Solution & Fix & Result:<o:p></o:p></span></b></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo4">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">a.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">“Named Structure Types” can be maintained in an incremental way in destination module, when linking a new module, just need to add new “Named Structure Types” into destination module to keep it most up-to-date<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo4">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">b.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">The fix is very small, just add a collection in module to keep all “Named Structure Types” in destination module for link. See attachment for details.<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:-18.0pt;mso-list:l0 level1 lfo4">
<![if !supportLists]><span lang="EN-US"><span style="mso-list:Ignore">c.<span style="font:7.0pt "Times New Roman"">
</span></span></span><![endif]><span lang="EN-US">After this fix:<o:p></o:p></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:0cm"><span lang="EN-US">For our biggest case, the linking time
<b>decrease from 70 minutes to 35 seconds.<o:p></o:p></b></span></p>
<p class="MsoListParagraph" style="margin-left:18.0pt;text-indent:0cm"><span lang="EN-US">For<b>
</b></span><span lang="EN-US">Xalan in SPEC2006, the linking time <b>decrease from 30 seconds to 2 second</b><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt">Please review, thanks!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt">--<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt">Best Regards<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt">Wan Xiaofei (xiaofei.wan@intel.com)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt">Intel Corporation, Shanghai, China<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:10.5pt">MCG, Android Runtime & Compiler Team<o:p></o:p></span></p>
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