[PATCH] D140280: [llvm] Fix APInt to work in C++20 mode

[Joe Loser via Phabricator via llvm-commits]

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Currently, an `APSInt` test fails to compile in C++20 mode due to ambiguity in
the available set of `operator==` thanks to synthetic three-way rewrite rules.

Specifically, the error is:

  error: use of overloaded operator '==' is ambiguous
  (with operand types 'const llvm::APSInt' and 'const unsigned long long')

from llvm/unittests/ADT/APFixedPointTest.cpp:698:3:
note: in instantiation of function template specialization
'testing::internal::EqHelper::Compare<llvm::APSInt, unsigned long long, nullptr>' requested here

  ASSERT_EQ(Val.convert(getLFractSema()).getValue(), -(1ULL << 31));
  ^

The candidates are:
llvm/include/llvm/ADT/APInt.h:2032:13: note: candidate function (with reversed parameter order)
inline bool operator==(uint64_t V1, const APInt &V2) { return V2 == V1; }

  ^

llvm/include/llvm/ADT/APSInt.h:174:8: note: candidate function

  bool operator==(int64_t RHS) const {
       ^

llvm/include/llvm/ADT/APSInt.h:343:13: note: candidate function (with reversed parameter order)
inline bool operator==(int64_t V1, const APSInt &V2) { return V2 == V1; }

Make this case unambiguous by gating the extra `operator==` and `operator!=` on
the existence of three way comparison feature test macro.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D140280

Files:
  llvm/include/llvm/ADT/APInt.h


Index: llvm/include/llvm/ADT/APInt.h
===================================================================
--- llvm/include/llvm/ADT/APInt.h
+++ llvm/include/llvm/ADT/APInt.h
@@ -2027,9 +2027,11 @@
   /// @}
 };
 
+#if !(__cplusplus > 201703L && __cpp_impl_three_way_comparison >= 201907L)
 inline bool operator==(uint64_t V1, const APInt &V2) { return V2 == V1; }
 
 inline bool operator!=(uint64_t V1, const APInt &V2) { return V2 != V1; }
+#endif
 
 /// Unary bitwise complement operator.
 ///


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