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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal>Thanks, Richard. That works great!<o:p></o:p></p><p class=MsoNormal>Ok, I<span style='font-family:"Times New Roman",serif'>’</span>ll try to fix the remaining issues on my own <span style='font-family:"Segoe UI Emoji",sans-serif'>😊</span><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thanks,<o:p></o:p></p><p class=MsoNormal>Nuno<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><div style='border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm 0cm 0cm'><p class=MsoNormal><b>From:</b> Richard Smith <richard@metafoo.co.uk> <br><b>Sent:</b> 10 December 2020 21:39<br><b>To:</b> Nuno Lopes <nunoplopes@sapo.pt><br><b>Cc:</b> Clang Dev <cfe-dev@lists.llvm.org><br><b>Subject:</b> Re: [cfe-dev] -Wambiguous-reversed-operator with equal types<o:p></o:p></p></div><p class=MsoNormal><o:p> </o:p></p><div><div><p class=MsoNormal>On Thu, 10 Dec 2020 at 06:46, Nuno Lopes via cfe-dev <<a href="mailto:cfe-dev@lists.llvm.org">cfe-dev@lists.llvm.org</a>> wrote:<o:p></o:p></p></div><div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><p class=MsoNormal>Hi,<br><br>I've been trying to fix a bunch of LLVM headers so they are compatible with<br>C++20. (so I can include those from Alive2 source code)<br><br>I'm currently stuck with -Wambiguous-reversed-operator. I've fixed a couple,<br>but this one (a few similar) left me wondering if the warning is correct or<br>not:<br><br>In file included from llvm/include/llvm/Passes/PassBuilder.h:19:<br>In file included from llvm/include/llvm/Analysis/CGSCCPassManager.h:98:<br>llvm/include/llvm/Analysis/LazyCallGraph.h:1117:22: error: ISO C++20<br>considers use of overloaded operator '!=' (with operand types<br>'llvm::User::value_op_iterator' and 'llvm::User::value_op_iterator') to be<br>ambiguous despite there being a unique best viable function<br>[-Werror,-Wambiguous-reversed-operator]<br> for (Value *Op : C->operand_values())<br> ^<br>llvm/include/llvm/ADT/iterator.h:263:8: note: ambiguity is between a regular<br>call to this operator and a call with the argument order reversed<br> bool operator==(const DerivedT &RHS) const { return I == RHS.I; }<br> ^<br><br>Note that it's complaining about comparing 'llvm::User::value_op_iterator'<br>and 'llvm::User::value_op_iterator' (i.e., same type). Since both arguments<br>are of the same type and the comparison function has const on both LHS/RHS,<br>reversing them shouldn't have any impact, right?<br>Unless there's some type conversion going on that the error message is<br>hiding.<br><br>Could someone please confirm if the warning is correct and/or the code needs<br>fixing?<o:p></o:p></p></blockquote><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>The warning is correct. In C++20 there are four ways to perform this != comparison:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Using iterator_adaptor_base::operator==:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>1: !((iterator_adaptor_base&)a == b) [synthesized != from operator==]<o:p></o:p></p></div><div><p class=MsoNormal>2: !((iterator_adaptor_base&)b == a) [synthesized != from operator==, reversed]<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Using iterator_facade_base::operator!=:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>3: (iterator_facade_base&)a != b [regular operator!=]<o:p></o:p></p></div><div><p class=MsoNormal>4: (iterator_facade_base&)b != a [regular operator!=, reversed]<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Of these: 1 beats 3 (better conversion for a), 2 beats 4 (better conversion for b), and they're otherwise unordered, so the result is an ambiguity.<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>Probably the cleanest solution would be to replace:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>bool operator==(const DerivedT &RHS) const { return I == RHS.I; }<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>with:<o:p></o:p></p></div><div><p class=MsoNormal><o:p> </o:p></p></div><div><p class=MsoNormal>friend bool operator==(const DerivedT &LHS, const DerivedT &RHS) const { return LHS.I == RHS.I; }<o:p></o:p></p></div><div><p class=MsoNormal> <o:p></o:p></p></div><blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0cm 0cm 0cm 6.0pt;margin-left:4.8pt;margin-right:0cm'><p class=MsoNormal>Thanks,<br>Nuno<br><br>_______________________________________________<br>cfe-dev mailing list<br><a href="mailto:cfe-dev@lists.llvm.org" target="_blank">cfe-dev@lists.llvm.org</a><br><a href="https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev" target="_blank">https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-dev</a><o:p></o:p></p></blockquote></div></div></div></body></html>