https://github.com/usx95 created https://github.com/llvm/llvm-project/pull/72213
None >From bc9e06ea87dca046227faf2996eb8de521863d57 Mon Sep 17 00:00:00 2001 From: Utkarsh Saxena <usaxen...@gmail.com> Date: Fri, 20 Oct 2023 14:40:25 +0200 Subject: [PATCH 1/2] [clang] Handle templated operators with reversed arguments (#69595) https://github.com/llvm/llvm-project/pull/68999 correctly computed conversion sequence for reversed args to a template operators. This was a breaking change as code, previously accepted in C++17, starts to break in C++20. Example: ```cpp struct P {}; template<class S> bool operator==(const P&, const S &); struct A : public P {}; struct B : public P {}; bool check(A a, B b) { return a == b; } // This is now ambiguous in C++20. ``` In order to minimise widespread breakages, as a clang extension, we had previously accepted such ambiguities with a warning (`-Wambiguous-reversed-operator`) for non-template operators. Due to the same reasons, we extend this relaxation for template operators. Fixes https://github.com/llvm/llvm-project/issues/53954 --- clang/docs/ReleaseNotes.rst | 21 +++++++ clang/lib/Sema/SemaOverload.cpp | 28 ++++++--- .../over.match.oper/p3-2a.cpp | 61 +++++++++++++++++++ 3 files changed, 100 insertions(+), 10 deletions(-) diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 7a131cb520aa600..5c974eec9ed67d1 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -37,6 +37,27 @@ These changes are ones which we think may surprise users when upgrading to Clang |release| because of the opportunity they pose for disruption to existing code bases. +- Fix a bug in reversed argument for templated operators. + This breaks code in C++20 which was previously accepted in C++17. Eg: + + .. code-block:: cpp + + struct P {}; + template<class S> bool operator==(const P&, const S&); + + struct A : public P {}; + struct B : public P {}; + + // This equality is now ambiguous in C++20. + bool ambiguous(A a, B b) { return a == b; } + + template<class S> bool operator!=(const P&, const S&); + // Ok. Found a matching operator!=. + bool fine(A a, B b) { return a == b; } + + To reduce such widespread breakages, as an extension, Clang accepts this code + with an existing warning ``-Wambiguous-reversed-operator`` warning. + Fixes `GH <https://github.com/llvm/llvm-project/issues/53954>`_. C/C++ Language Potentially Breaking Changes ------------------------------------------- diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp index f97e244120612e3..73f417cc8bd4024 100644 --- a/clang/lib/Sema/SemaOverload.cpp +++ b/clang/lib/Sema/SemaOverload.cpp @@ -7685,7 +7685,7 @@ bool Sema::CheckNonDependentConversions( QualType ParamType = ParamTypes[I + Offset]; if (!ParamType->isDependentType()) { unsigned ConvIdx = PO == OverloadCandidateParamOrder::Reversed - ? 0 + ? Args.size() - 1 - (ThisConversions + I) : (ThisConversions + I); Conversions[ConvIdx] = TryCopyInitialization(*this, Args[I], ParamType, @@ -10082,11 +10082,19 @@ getImplicitObjectParamType(ASTContext &Context, const FunctionDecl *F) { return M->getFunctionObjectParameterReferenceType(); } -static bool haveSameParameterTypes(ASTContext &Context, const FunctionDecl *F1, - const FunctionDecl *F2) { +// As a Clang extension, allow ambiguity among F1 and F2 if they represent +// represent the same entity. +static bool allowAmbiguity(ASTContext &Context, const FunctionDecl *F1, + const FunctionDecl *F2) { if (declaresSameEntity(F1, F2)) return true; - + if (F1->isTemplateInstantiation() && F2->isTemplateInstantiation() && + declaresSameEntity(F1->getPrimaryTemplate(), F2->getPrimaryTemplate())) { + return true; + } + // TODO: It is not clear whether comparing parameters is necessary (i.e. + // different functions with same params). Consider removing this (as no test + // fail w/o it). auto NextParam = [&](const FunctionDecl *F, unsigned &I, bool First) { if (First) { if (std::optional<QualType> T = getImplicitObjectParamType(Context, F)) @@ -10271,14 +10279,14 @@ bool clang::isBetterOverloadCandidate( case ImplicitConversionSequence::Worse: if (Cand1.Function && Cand2.Function && Cand1.isReversed() != Cand2.isReversed() && - haveSameParameterTypes(S.Context, Cand1.Function, Cand2.Function)) { + allowAmbiguity(S.Context, Cand1.Function, Cand2.Function)) { // Work around large-scale breakage caused by considering reversed // forms of operator== in C++20: // - // When comparing a function against a reversed function with the same - // parameter types, if we have a better conversion for one argument and - // a worse conversion for the other, the implicit conversion sequences - // are treated as being equally good. + // When comparing a function against a reversed function, if we have a + // better conversion for one argument and a worse conversion for the + // other, the implicit conversion sequences are treated as being equally + // good. // // This prevents a comparison function from being considered ambiguous // with a reversed form that is written in the same way. @@ -14449,7 +14457,7 @@ ExprResult Sema::CreateOverloadedBinOp(SourceLocation OpLoc, llvm::SmallVector<FunctionDecl*, 4> AmbiguousWith; for (OverloadCandidate &Cand : CandidateSet) { if (Cand.Viable && Cand.Function && Cand.isReversed() && - haveSameParameterTypes(Context, Cand.Function, FnDecl)) { + allowAmbiguity(Context, Cand.Function, FnDecl)) { for (unsigned ArgIdx = 0; ArgIdx < 2; ++ArgIdx) { if (CompareImplicitConversionSequences( *this, OpLoc, Cand.Conversions[ArgIdx], diff --git a/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp b/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp index d83a176ec07eec9..be391c26e1e8631 100644 --- a/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp +++ b/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp @@ -324,6 +324,67 @@ bool x = X() == X(); // expected-warning {{ambiguous}} } } // namespace P2468R2 +namespace GH53954{ +namespace friend_template_1 { +struct P { + template <class T> + friend bool operator==(const P&, const T&); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} +}; +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + +namespace friend_template_2 { +struct P { + template <class T> + friend bool operator==(const T&, const P&); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} +}; +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + +namespace member_template { +struct P { + template<class S> + bool operator==(const S &) const; // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} +}; +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + +namespace non_member_template_1 { +struct P {}; +template<class S> +bool operator==(const P&, const S &); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} + +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} + +template<class S> +bool operator!=(const P&, const S &); +bool fine(A a, B b) { return a == b; } // Ok. Found a matching operator!=. +} +} + +namespace non_member_template_2 { +struct P {}; +template<class S> +bool operator==(const S&, const P&); // expected-note {{candidate}} \ + // expected-note {{ambiguous candidate function with reversed arguments}} + +struct A : public P {}; +struct B : public P {}; +bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} +} + namespace ADL_GH68901{ namespace test1 { namespace A { >From 79181efd0d7aef1b8396d44cdf40c0dfa4054984 Mon Sep 17 00:00:00 2001 From: Utkarsh Saxena <u...@google.com> Date: Tue, 14 Nov 2023 07:32:44 +0100 Subject: [PATCH 2/2] accept member template ambiguities with a warning --- clang/lib/Sema/SemaOverload.cpp | 10 +++++++--- .../over.match.funcs/over.match.oper/p3-2a.cpp | 12 ++++++++++++ 2 files changed, 19 insertions(+), 3 deletions(-) diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp index 73f417cc8bd4024..9d50a5ec39f817a 100644 --- a/clang/lib/Sema/SemaOverload.cpp +++ b/clang/lib/Sema/SemaOverload.cpp @@ -10088,9 +10088,13 @@ static bool allowAmbiguity(ASTContext &Context, const FunctionDecl *F1, const FunctionDecl *F2) { if (declaresSameEntity(F1, F2)) return true; - if (F1->isTemplateInstantiation() && F2->isTemplateInstantiation() && - declaresSameEntity(F1->getPrimaryTemplate(), F2->getPrimaryTemplate())) { - return true; + if (F1->isTemplateInstantiation() && F2->isTemplateInstantiation()) { + auto PT1 = F1->getPrimaryTemplate(); + auto PT2 = F2->getPrimaryTemplate(); + if (declaresSameEntity(PT1, PT2) || + declaresSameEntity(PT1->getInstantiatedFromMemberTemplate(), + PT2->getInstantiatedFromMemberTemplate())) + return true; } // TODO: It is not clear whether comparing parameters is necessary (i.e. // different functions with same params). Consider removing this (as no test diff --git a/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp b/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp index be391c26e1e8631..486172e5d10232b 100644 --- a/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp +++ b/clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp @@ -385,6 +385,18 @@ struct B : public P {}; bool check(A a, B b) { return a == b; } // expected-warning {{use of overloaded operator '==' (with operand types 'A' and 'B') to be ambiguous}} } +namespace class_and_member_template { +template <class T> +struct S { + template <typename OtherT> + bool operator==(const OtherT &rhs); // expected-note {{candidate}} \ + // expected-note {{reversed arguments}} +}; +struct A : S<int> {}; +struct B : S<bool> {}; +bool x = A{} == B{}; // expected-warning {{ambiguous}} +} + namespace ADL_GH68901{ namespace test1 { namespace A { _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
