c++: Add testcase for DR 2836

Seems we already handle it the way the DR clarifies, if double/long double
and std::float64_t have the same mode, foo has long double type (while
x + y would be _Float64 in C23), so this patch just adds a testcase which
verifies that.

2024-09-25  Jakub Jelinek  <jakub@redhat.com>

	* g++.dg/DRs/dr2836.C: New test.

diff --git a/gcc/testsuite/g++.dg/DRs/dr2836.C b/gcc/testsuite/g++.dg/DRs/dr2836.C
new file mode 100644 (file)
index 0000000..88e35a7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/DRs/dr2836.C
@@ -0,0 +1,30 @@
+// DR 2836 - Conversion rank of long double and extended floating-point types
+// { dg-do compile { target c++23 } }
+// { dg-additional-options "-mlong-double-64" { target powerpc*-*-* s390*-*-* } }
+
+#include <stdfloat>
+
+#if defined (__STDCPP_FLOAT64_T__) \
+    && __LDBL_MAX_EXP__ == __FLT64_MAX_EXP__ \
+    && __LDBL_MANT_DIG__ == __FLT64_MANT_DIG__ \
+    && __DBL_MAX_EXP__ == __FLT64_MAX_EXP__ \
+    && __DBL_MANT_DIG__ == __FLT64_MANT_DIG__
+auto
+foo (long double x, std::float64_t y)
+{
+  return x + y;
+}
+
+template<typename T, T v> struct integral_constant {
+  static constexpr T value = v;
+};
+typedef integral_constant<bool, false> false_type;
+typedef integral_constant<bool, true> true_type;
+template<class T, class U>
+struct is_same : false_type {};
+template <class T>
+struct is_same<T, T> : true_type {};
+
+static_assert (is_same <decltype (foo (1.0L, 1.0F64)), long double>::value);
+
+#endif