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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Hello Teresa,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Thank you for your reply. I’m trying to create a small repro but find it hard to nail down because originally it is a big build. This happens with gold linker.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Taewook<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-family:Calibri;color:black">From: </span>
</b><span style="font-family:Calibri;color:black">Teresa Johnson <tejohnson@google.com><br>
<b>Date: </b>Thursday, July 28, 2016 at 5:08 PM<br>
<b>To: </b>Taewook Oh <twoh@fb.com><br>
<b>Cc: </b>via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject: </b>Re: [llvm-dev] [ThinLTO] assert(GS != DefinedGlobals.end()) failed in FunctionImport.cpp<o:p></o:p></span></p>
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<p class="MsoNormal">Hi Taewook, <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Thu, Jul 28, 2016 at 4:38 PM, Taewook Oh 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>
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<p class="gmail-msonormal"><span style="font-size:11.0pt">Encountered “assert(GS != DefinedGlobals.end())” failure while running ThinLTO. The assertion statement is in MustPreserveGV lambda function in llvm::thinLTOInternalizeModule (lib/Transforms/IPO/FunctionImport.cpp).</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">It seems that the assertion fails because it fails to recover the "original name" of the global value. ModuleSummaryIndex::getOriginalNameBeforePromote attempts to get the original name by stripping
.llvm.{HASH}, but what I observe is that ".1" is still appended to the expected original name.
</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">Then where this extra ".1" comes from? It is appended when the global value is materialized. IRLinker::materialize function calls IRLinker::linkGlobalValueProto function, and inside that function if
DGV is nullptr or ShouldLink is true then IRLinker::copyGlobalValueProto function is called to create a global variable in the destination module that corresponds to SGV. I found that newly created global variable has the extra ".1" added to the name of the
SGV. </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">When this happens? I don't have a complete understanding but I observed that the same global value is materialized twice during the single invocation of IRLinker::run, once with GlobalValueMaterializer
and once with LocalValueMaterializer. First, the global value</span><o:p></o:p></p>
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<p class="MsoNormal">Yes, the IRLinker will append an integer if it encounters a naming conflict. Normally this would happen in full LTO, but I guess is happening here since we are linking twice due to the alias.<o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">; Materializable</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">; Function Attrs: nounwind uwtable</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">define weak_odr void @foo(%1*) unnamed_addr #7 comdat($comdat1) align 2 personality i32 (...)* @__gxx_personality_v0 {}</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">(I renamed the function and comdat)</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">is materialized with GlobalValueMaterializer, (so the IRLinker::materialize function is called with ForAlias == false), and the materialized value is</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">; Function Attrs: nounwind uwtable</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">declare void @foo(%"type1"*) unnamed_addr #2 align 2</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">Then, later, the same value is materialized again with LocalValueMaterializer (so ForAlias == true for IRLinker::materialize), and the materialized value is</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">; Function Attrs: nounwind uwtable</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">define internal void @foo.1(%"type 0x7efb6ee89d80"*) unnamed_addr #2 comdat($comdat1) align 2 personality i32 (...)* @__gxx_personality_v0 !dbg !12345 {</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> // function definition</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">}</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">(here, “type 0x7efb6ee89d80” is not “type1” )</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">So for me it seems that we need a mechanism to retrieve the original name of the global value even when it is renamed during the materialization. I submitted the bug report as well (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D28760-29&d=CwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=kOsLCgQzH7N8ptZ7diJD9g&m=XtlNH01OW0mwOi0no2wur-HO6RY5szj-dgWaIcCki-k&s=9pGLGnxeOI3J3lvx9-ayiZJUImAefSzcGGJN5xo9_Kc&e=" target="_blank">https://llvm.org/bugs/show_bug.cgi?id=28760)</a>.</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Interestingly, we are already trying to handle a similar case in that lambda (see the comment about weak values linked in as a local copy due to an alias). However, we weren't anticipating the original weak value being linked in as well,
which is causing the rename.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Do you have a small reproducer? Is this with gold? I need to think about the best way to handle this case. One way of course is to conservatively return true if we can't find it in the map, but I don't love that since we may miss other
cases that need to be handled.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks,<o:p></o:p></p>
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<p class="MsoNormal">Teresa<o:p></o:p></p>
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<p class="gmail-msonormal"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">Thanks,</span><o:p></o:p></p>
<p class="gmail-msonormal"><span style="font-size:11.0pt">Taewook</span><o:p></o:p></p>
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<p class="MsoNormal">-- <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:Helvetica;color:#555555">Teresa Johnson |<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:Helvetica;color:#555555"> Software Engineer |<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:Helvetica;color:#555555"> <a href="mailto:tejohnson@google.com" target="_blank">tejohnson@google.com</a> |<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:Helvetica;color:#555555"> 408-460-2413<o:p></o:p></span></p>
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