[gcc r12-7589] libstdc++: Support VAX floats in std::strong_order

[gcc r12-7589] libstdc++: Support VAX floats in std::strong_order

[Jonathan Wakely]

https://gcc.gnu.org/g:cfaa2fac42f6f4bddb197dc1fc601f2ba136f9f0

commit r12-7589-gcfaa2fac42f6f4bddb197dc1fc601f2ba136f9f0
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Tue Mar 8 12:15:55 2022 +0000

    libstdc++: Support VAX floats in std::strong_order
    
    The VAX float and double format does not support NaN, so the
    std::partial_ordering returned by <=> will never be 'unordered'. We can
    just use the partial_ordering value as the strong_ordering.
    
    libstdc++-v3/ChangeLog:
    
            * libsupc++/compare (_Strong_ordering::_S_fp_cmp) [__vax__]: Use
            <=> comparison.

Diff:
---
 libstdc++-v3/libsupc++/compare | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libstdc++-v3/libsupc++/compare b/libstdc++-v3/libsupc++/compare
index 050cf7ed20d..3c22d9addf1 100644
--- a/libstdc++-v3/libsupc++/compare
+++ b/libstdc++-v3/libsupc++/compare
@@ -843,6 +843,11 @@ namespace std
 	static constexpr strong_ordering
 	_S_fp_cmp(_Tp __x, _Tp __y) noexcept
 	{
+#ifdef __vax__
+	  // VAX format has no NaN, only "excess" for Inf, so totally ordered.
+	  return __builtin_bit_cast(strong_ordering, __x <=> __y);
+#endif
+
 	  auto __ix = _S_fp_bits(__x);
 	  auto __iy = _S_fp_bits(__y);