[libcxx-commits] [libcxx] [libc++][math] Provide overloads for cv-unqualified floating point types for `std::signbit` (PR #106566)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: Robin Caloudis (robincaloudis)

<details>
<summary>Changes</summary>

## Why
Following up on https://github.com/llvm/llvm-project/pull/105946, this patch provides the floating point overloads for `std::signbit` as defined by [P0533R9](https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p0533r9.pdf).

## 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](https://github.com/microsoft/win32metadata/blob/e012b29924c53aa941fc010850b68331b0c3ea80/generation/WinSDK/RecompiledIdlHeaders/ucrt/corecrt_math.h#L309-L322). 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
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;
 }

``````````

</details>


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