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<p class="MsoNormal"><span 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 style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">-Eli<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal" align="left" style="margin-left:.5in;text-align:left"><b><span style="font-size:11.0pt">From:</span></b><span style="font-size:11.0pt"> llvm-dev <llvm-dev-bounces@lists.llvm.org>
<b>On Behalf Of </b>chenmindong via llvm-dev<br>
<b>Sent:</b> Thursday, July 16, 2020 7:54 AM<br>
<b>To:</b> llvm-dev@lists.llvm.org<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:.5in;text-align:left"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">Hi guys,<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">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:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">When parseConstants() reads in a CST_CODE_CE_SELECT record, e.g.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">select <selty><cond>, <ty><val1>, <ty><val2><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">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:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"> Type *SelectorTy = Type::getInt1Ty(Context);<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"> // The selector might be an i1 or an <n x i1><o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"> // Get the type from the ValueList before getting a forward ref.<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"> if (VectorType *VTy = dyn_cast<VectorType>(CurTy))<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"> if (Value *V = ValueList[Record[0]])<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"> if (SelectorTy != V->getType())<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"> SelectorTy = VectorType::get(SelectorTy, VTy->getNumElements());
<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">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:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">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:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">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:.5in"><span style="mso-fareast-language:ZH-CN"><o:p> </o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">Regards,<o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="mso-fareast-language:ZH-CN">Mindong<o:p></o:p></span></p>
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