[libc++][math] Provide overloads for cv-unqualified floating point types for std::signbit

[robincaloudis]

Why

Following up on #105946, this patch provides the floating point overloads for std::signbit as defined by P0533R9.

What

• Test and add overloads for cv-unqualified floating point types
• Remove constrained overload as it is not needed anymore
• Make use of template<class = void> as the universal C runtime (UCRT) needed for Clang-Cl comes with overloads for all cv-unqualified floating point types (float, double, long double) for std::signbit() by itself in the WinSDK. In a certain way, this can be seen as a deviation from the C standard. We need to work around it as the compilation would otherwise error out due to duplicated definitions.

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[Zingam]

Nit: IMO it would be better to track the progress as subtasks in #105174
e.g. #105169
Have you also seen the description of this commit: #105581

[robincaloudis]

I was not aware that we have GitHub issues for each paper/issue that are fully synchronized with the CSV status files and that we can encode custom notes in the CSV files via Github issues. Amazing. I will track the progress as subtask. Thanks for the friendly reminder!

[Zingam]

@robincaloudis Please let me know if you need help with creating the subtasks while you wait for commit access. You can ping me on Discord too (same account name).

[robincaloudis]

Thanks. I will do so.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Robin Caloudis (robincaloudis)

Changes

Why

Following up on #105946, this patch provides the floating point overloads for std::signbit as defined by P0533R9.

What

• Test and add overloads for cv-unqualified floating point types
• Remove constrained overload as it is not needed anymore
• Make use of _LIBCPP_PREFERRED_OVERLOAD as the universal C runtime (UCRT) needed for Clang-Cl comes with overloads for all cv-unqualified floating point types (float, double, long double) for std::signbit() in the WinSDK. In a certain way, this can be seen as a deviation from the C standard. We need to work around it as the compilation would otherwise error out due to duplicated definitions.

---

Full diff: https://github.com/llvm/llvm-project/pull/106566.diff

2 Files Affected:

• (modified) libcxx/include/__math/traits.h (+24-2)
• (modified) libcxx/test/std/numerics/c.math/signbit.pass.cpp (+13)

diff --git a/libcxx/include/__math/traits.h b/libcxx/include/__math/traits.h
index 3d4f14fc9cd552..f3b1f03110ab71 100644
--- a/libcxx/include/__math/traits.h
+++ b/libcxx/include/__math/traits.h
@@ -34,8 +34,30 @@ namespace __math {
 #  define _LIBCPP_SIGNBIT_CONSTEXPR
 #endif
 
-template <class _A1, __enable_if_t<is_floating_point<_A1>::value, int> = 0>
-_LIBCPP_NODISCARD inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI bool signbit(_A1 __x) _NOEXCEPT {
+_LIBCPP_NODISCARD inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI
+#ifdef _LIBCPP_PREFERRED_OVERLOAD
+_LIBCPP_PREFERRED_OVERLOAD
+#endif
+    bool
+    signbit(float __x) _NOEXCEPT {
+  return __builtin_signbit(__x);
+}
+
+_LIBCPP_NODISCARD inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI
+#ifdef _LIBCPP_PREFERRED_OVERLOAD
+_LIBCPP_PREFERRED_OVERLOAD
+#endif
+    bool
+    signbit(double __x) _NOEXCEPT {
+  return __builtin_signbit(__x);
+}
+
+_LIBCPP_NODISCARD inline _LIBCPP_SIGNBIT_CONSTEXPR _LIBCPP_HIDE_FROM_ABI
+#ifdef _LIBCPP_PREFERRED_OVERLOAD
+_LIBCPP_PREFERRED_OVERLOAD
+#endif
+    bool
+    signbit(long double __x) _NOEXCEPT {
   return __builtin_signbit(__x);
 }
 
diff --git a/libcxx/test/std/numerics/c.math/signbit.pass.cpp b/libcxx/test/std/numerics/c.math/signbit.pass.cpp
index c85033e363ce55..a8a566f7de6434 100644
--- a/libcxx/test/std/numerics/c.math/signbit.pass.cpp
+++ b/libcxx/test/std/numerics/c.math/signbit.pass.cpp
@@ -70,9 +70,22 @@ struct TestInt {
   }
 };
 
+template <typename T>
+struct ConvertibleTo {
+  operator T() const { return T(); }
+};
+
 int main(int, char**) {
   types::for_each(types::floating_point_types(), TestFloat());
   types::for_each(types::integral_types(), TestInt());
 
+  // Make sure we can call `std::signbit` with convertible types. This checks
+  // whether overloads for all cv-unqualified floating-point types are working
+  // as expected.
+  {
+    assert(!std::signbit(ConvertibleTo<float>()));
+    assert(!std::signbit(ConvertibleTo<double>()));
+    assert(!std::signbit(ConvertibleTo<long double>()));
+  }
   return 0;
 }