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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">Thanks Peter! I think PS4 will have to follow what Darwin does here, at least for now.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">I assume the new API would consume old-format bitcode with no problem, if we decide to make that conversion and still want to read old-style bitcode files.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D">--paulr<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Peter Collingbourne [mailto:peter@pcc.me.uk]
<br>
<b>Sent:</b> Wednesday, July 12, 2017 2:55 PM<br>
<b>To:</b> Robinson, Paul; Mehdi AMINI<br>
<b>Cc:</b> llvm-dev@lists.llvm.org<br>
<b>Subject:</b> Re: [llvm-dev] ThinLTO and the C API<o:p></o:p></span></p>
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<p class="MsoNormal">Hi Paul,<o:p></o:p></p>
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<p class="MsoNormal">The current C LTO API wraps a legacy C++ implementation of the LTO API, which does not support multi-module bitcode files, and we do not intend to teach it to do so. We planned to replace the old API with a new C API that wraps the new
resolution-based C++ API, but that hasn't happened yet.<o:p></o:p></p>
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<p class="MsoNormal">Mehdi was working on the new C API here: <a href="https://reviews.llvm.org/D31898" target="_blank">https://reviews.llvm.org/D31898</a><o:p></o:p></p>
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<p class="MsoNormal">I'm not sure if he will have time to finish it, though.<o:p></o:p></p>
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<p class="MsoNormal">To deal with Apple's linker the clang driver passes a flag to the frontend on Darwin which prevents it from creating multi-module bitcode files.<o:p></o:p></p>
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<p class="MsoNormal"><a href="http://llvm-cs.pcc.me.uk/tools/clang/lib/Driver/ToolChains/Clang.cpp#2073" target="_blank">http://llvm-cs.pcc.me.uk/tools/clang/lib/Driver/ToolChains/Clang.cpp#2073</a><o:p></o:p></p>
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<p class="MsoNormal">Peter<o:p></o:p></p>
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<p class="MsoNormal">On Wed, Jul 12, 2017 at 2:29 PM, Robinson, Paul via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p>
<p class="MsoNormal">Our ThinLTO testing was inoperative for a while, and now that it's running<br>
again, we're seeing the linker step reporting "Expected a single module."<br>
Note that our linker is using the C API to read bitcode.<br>
<br>
It looks like the ThinLTO writer now emits two modules, but AFAICT most of<br>
the APIs in BitcodeReader.cpp expect to see only one. Is this just an<br>
oversight in supporting ThinLTO from the C API?<br>
<br>
I am a little bemused because I had thought Apple's "ld64" also used the<br>
C API and supported ThinLTO.<br>
<br>
Any help/guidance/tips welcome (other than "switch to the C++ API").<br>
Thanks,<br>
--paulr<br>
<br>
_______________________________________________<br>
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<p class="MsoNormal">Peter<o:p></o:p></p>
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