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<p class="MsoNormal">My recollection is that type units can end up being used for types that actually don’t take up a lot of space, and so the overhead of the type units ends up costing extra. I put a task on our internal tracker to look into this properly,
but we wouldn’t mind if someone else had a run at it (if only to prove that my recollection is incorrect).<o:p></o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">--paulr<o:p></o:p></p>
<p class="MsoNormal">who is on vacation and really shouldn’t be looking at these emails<o:p></o:p></p>
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<p class="MsoNormal"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> <b>On Behalf Of
</b>Reid Kleckner via llvm-dev<br>
<b>Sent:</b> Friday, October 15, 2021 3:26 PM<br>
<b>To:</b> David Blaikie <dblaikie@gmail.com><br>
<b>Cc:</b> llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> Re: [llvm-dev] distinct DISubprograms hindering sharing inlined subprogram descriptions<o:p></o:p></p>
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<p class="MsoNormal">Sorry for derailing into your aside, but...<o:p></o:p></p>
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<p class="MsoNormal">On Fri, Oct 15, 2021 at 12:07 PM David Blaikie <<a href="mailto:dblaikie@gmail.com">dblaikie@gmail.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal">(side note: Anyone interested in making ThinLTO home type definitions? That'd be great to reduce type duplication - would mean ThinLTO could turn off type units and/or that .o/.dwo/etc files would just generally be smaller anyway)<o:p></o:p></p>
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<p class="MsoNormal">Hey, I think that is a great idea! ThinLTO tends to be used in release build configurations, which tend to have debug info enabled. The size of symbols in release build config matters a lot because it is typically archived for a long time.<o:p></o:p></p>
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<p class="MsoNormal">COFF & MachO platforms have other ways to deduplicate types (PDBs & dsymutil), but less duplicate stuff always makes things faster.<o:p></o:p></p>
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<p class="MsoNormal">For ELF users already using type units, this optimization will only allow us to recover the overhead of type units, which I recall is significant. In our evaluation of the feature for Chrome, we found it increased the final binary size
significantly: <a href="https://urldefense.com/v3/__http:/crbug.com/1031936*c4__;Iw!!JmoZiZGBv3RvKRSx!qg0PDEAWoBKjGth7hk524aPYTrQqB8FrCOws1hiil6XaLGH_lFZRG8n7oW4wMKqPkA$">
crbug.com/1031936#c4</a><o:p></o:p></p>
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