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<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Hi Eli,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Thanks for the advice! By delaying processing the “select” until we have resolved other records(like “aggregate ” in this case) as you did for “shuffle”, the test case passes now. But I wonder if
it’s an ultimate solution: what if the selector of a “select” is the output of another forward-reference “select” that hasn’t been resolved yet? We still cannot determine its type then. Is it possible?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D">Mindong<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal" align="left" style="text-align:left"><b><span lang="EN-US" style="font-size:11.0pt">From:</span></b><span lang="EN-US" style="font-size:11.0pt"> Eli Friedman [mailto:efriedma@quicinc.com]
<br>
<b>Sent:</b> Friday, July 17, 2020 3:06 AM<br>
<b>To:</b> chenmindong <chenmindong1@huawei.com>; llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Subject:</b> RE: [llvm-dev] BitcodeReader.cpp bug under LTO<o:p></o:p></span></p>
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<p class="MsoNormal" align="left" style="text-align:left"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt">The DelayedShuffles code in BitcodeReader::parseConstants is solving a sort of similar issue; you might be able to borrow the same approach.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt">-Eli<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal" align="left" style="margin-left:36.0pt;text-align:left"><b><span lang="EN-US" style="font-size:11.0pt">From:</span></b><span lang="EN-US" style="font-size:11.0pt"> llvm-dev <<a href="mailto:llvm-dev-bounces@lists.llvm.org">llvm-dev-bounces@lists.llvm.org</a>>
<b>On Behalf Of </b>chenmindong via llvm-dev<br>
<b>Sent:</b> Thursday, July 16, 2020 7:54 AM<br>
<b>To:</b> <a href="mailto:llvm-dev@lists.llvm.org">llvm-dev@lists.llvm.org</a><br>
<b>Subject:</b> [EXT] [llvm-dev] BitcodeReader.cpp bug under LTO<o:p></o:p></span></p>
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<p class="MsoNormal" align="left" style="margin-left:36.0pt;text-align:left"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">Hi guys,<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">We have found a bug of BitcodeReader.cpp in processing an LTO bitcode file. As LLVM doesn’t emit use-list for LTO bitcode files, many forward references will happen when BitcodeReader processes
the bitcode file, and LLVM uses placeholders for those forward references and resolve them later.
<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">When parseConstants() reads in a CST_CODE_CE_SELECT record, e.g.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">select <selty><cond>, <ty><val1>, <ty><val2><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">If “ty” here is a vector type and “cond” is a forward reference, LLVM uses i1 as the placeholder type of “cond” if it cannot find “cond” in ValueList, as the code follows:<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"> Type *SelectorTy = Type::getInt1Ty(Context);<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"> // The selector might be an i1 or an <n x i1><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"> // Get the type from the ValueList before getting a forward ref.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"> if (VectorType *VTy = dyn_cast<VectorType>(CurTy))<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"> if (Value *V = ValueList[Record[0]])<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"> if (SelectorTy != V->getType())<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"> SelectorTy = VectorType::get(SelectorTy, VTy->getNumElements());
<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">However, the program aborts in RAUW() if we find “selty” is a vector type later, because LLVM are trying to replace an i1 placeholder with an <n x i1> value.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">A rough idea is to create a BitcodeReader-specific RAUW which doesn’t check type legitimacy and any other suggestion is welcome.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">Bugzilla link:
<a href="https://bugs.llvm.org/show_bug.cgi?id=46750">https://bugs.llvm.org/show_bug.cgi?id=46750</a><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">Regards,<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:36.0pt"><span lang="EN-US">Mindong<o:p></o:p></span></p>
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