[clang] 460ff58 - [clang] Reapply Handle templated operators with reversed arguments (#72213)
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Fri Jan 12 06:03:05 PST 2024
Author: Utkarsh Saxena
Date: 2024-01-12T15:03:01+01:00
New Revision: 460ff58f62456a1f3ccf61ec9cf9d10781bd41bb
URL: https://github.com/llvm/llvm-project/commit/460ff58f62456a1f3ccf61ec9cf9d10781bd41bb
DIFF: https://github.com/llvm/llvm-project/commit/460ff58f62456a1f3ccf61ec9cf9d10781bd41bb.diff
LOG: [clang] Reapply Handle templated operators with reversed arguments (#72213)
Re-applies https://github.com/llvm/llvm-project/pull/69595 with extra
[diff](https://github.com/llvm/llvm-project/pull/72213/commits/79181efd0d7aef1b8396d44cdf40c0dfa4054984)
### New changes
Further relax ambiguities with a warning for member operators of a
template class (primary templates of such ops do not match). Eg:
```cpp
template <class T>
struct S {
template <typename OtherT>
bool operator==(const OtherT &rhs);
};
struct A : S<int> {};
struct B : S<bool> {};
bool x = A{} == B{}; // accepted with a warning.
```
This is important for making llvm build using previous clang versions in
C++20 mode (eg: this makes the commit
e558be51bab051d1471d92e967f8a2aecc13567a keep working with a warning
instead of an error).
### Description from https://github.com/llvm/llvm-project/pull/69595
https://github.com/llvm/llvm-project/pull/68999 correctly computed
conversion sequence for reversed args to a template operator. 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
Added:
Modified:
clang/docs/ReleaseNotes.rst
clang/lib/Sema/SemaOverload.cpp
clang/test/CXX/over/over.match/over.match.funcs/over.match.oper/p3-2a.cpp
Removed:
################################################################################
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 10e426a30d98f9..3cbce1be159437 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -37,6 +37,29 @@ 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.
+ Clang did not properly diagnose such casese in C++20 before this change. 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>`_.
+
- The CMake variable ``GCC_INSTALL_PREFIX`` (which sets the default
``--gcc-toolchain=``) is deprecated and will be removed. Specify
``--gcc-install-dir=`` or ``--gcc-triple=`` in a `configuration file
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 64bc3851980272..23b9bc0fe2d6e2 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -7723,9 +7723,19 @@ bool Sema::CheckNonDependentConversions(
++I) {
QualType ParamType = ParamTypes[I + Offset];
if (!ParamType->isDependentType()) {
- unsigned ConvIdx = PO == OverloadCandidateParamOrder::Reversed
- ? 0
- : (ThisConversions + I);
+ unsigned ConvIdx;
+ if (PO == OverloadCandidateParamOrder::Reversed) {
+ ConvIdx = Args.size() - 1 - I;
+ assert(Args.size() + ThisConversions == 2 &&
+ "number of args (including 'this') must be exactly 2 for "
+ "reversed order");
+ // For members, there would be only one arg 'Args[0]' whose ConvIdx
+ // would also be 0. 'this' got ConvIdx = 1 previously.
+ assert(!HasThisConversion || (ConvIdx == 0 && I == 0));
+ } else {
+ // For members, 'this' got ConvIdx = 0 previously.
+ ConvIdx = ThisConversions + I;
+ }
Conversions[ConvIdx]
= TryCopyInitialization(*this, Args[I], ParamType,
SuppressUserConversions,
@@ -10121,11 +10131,23 @@ 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;
-
+ auto PT1 = F1->getPrimaryTemplate();
+ auto PT2 = F2->getPrimaryTemplate();
+ if (PT1 && PT2) {
+ if (declaresSameEntity(PT1, PT2) ||
+ declaresSameEntity(PT1->getInstantiatedFromMemberTemplate(),
+ PT2->getInstantiatedFromMemberTemplate()))
+ return true;
+ }
+ // TODO: It is not clear whether comparing parameters is necessary (i.e.
+ //
diff erent 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))
@@ -10329,14 +10351,14 @@ 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.
@@ -14526,7 +14548,7 @@ 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 d83a176ec07eec..d757d28860a40e 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 +324,124 @@ 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&) { return true; } // 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&) { return true; } // 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_class_template {
+template<class S>
+struct P {
+ template <class T>
+ friend bool operator==(const T&, const P&) { // expected-note 2 {{candidate}}
+ return true;
+ }
+};
+struct A : public P<int> {};
+struct B : public P<bool> {};
+bool check(A a, B b) { return a == b; } // expected-warning {{ambiguous}}
+}
+
+namespace friend_template_fixme {
+// FIXME(GH70210): This should not rewrite operator== and definitely not a hard error.
+struct P {
+ template <class T>
+ friend bool operator==(const T &, const P &) { return true; } // expected-note 2 {{candidate}}
+ template <class T>
+ friend bool operator!=(const T &, const P &) { return true; } // expected-note {{candidate}}
+};
+struct A : public P {};
+struct B : public P {};
+bool check(A a, B b) { return a != b; } // expected-error{{ambiguous}}
+}
+
+namespace member_template_1 {
+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 member_template
+
+namespace member_template_2{
+template <typename T>
+class Foo {
+ public:
+ template <typename U = T>
+ bool operator==(const Foo& other) const;
+};
+bool x = Foo<int>{} == Foo<int>{};
+} // namespace template_member_opeqeq
+
+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_1
+
+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 non_member_template_2
+
+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 class_and_member_template
+
+namespace ambiguous_case {
+template <class T>
+struct Foo {};
+template <class T, class U> bool operator==(Foo<U>, Foo<T*>); // expected-note{{candidate}}
+template <class T, class U> bool operator==(Foo<T*>, Foo<U>); // expected-note{{candidate}}
+
+void test() {
+ Foo<int*>() == Foo<int*>(); // expected-error{{ambiguous}}
+}
+} // namespace ambiguous_case
+} // namespace
namespace ADL_GH68901{
namespace test1 {
namespace A {
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