[gcc r12-9180] libstdc++: Ensure __builtin_constant_p isn't lost on the way

[Matthias Kretz <mkretz@gcc.gnu.org>]

https://gcc.gnu.org/g:d1084be3151d447cffe2d36667e67939dcdf3e75

commit r12-9180-gd1084be3151d447cffe2d36667e67939dcdf3e75
Author: Matthias Kretz <m.kretz@gsi.de>
Date:   Fri Jan 13 16:20:36 2023 +0100

    libstdc++: Ensure __builtin_constant_p isn't lost on the way
    
    The more expensive code path should only be taken if it can be optimized
    away.
    
    Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
    
    libstdc++-v3/ChangeLog:
    
            * include/experimental/bits/simd.h
            (_SimdWrapper::_M_is_constprop_none_of)
            (_SimdWrapper::_M_is_constprop_all_of): Return false unless the
            computed result still satisfies __builtin_constant_p.
    
    (cherry picked from commit fea34ee491104f325682cc5fb75683b7d74a0a3b)

Diff:
---
 libstdc++-v3/include/experimental/bits/simd.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/experimental/bits/simd.h b/libstdc++-v3/include/experimental/bits/simd.h
index b0226fa4c53..2b1e5bcbe94 100644
--- a/libstdc++-v3/include/experimental/bits/simd.h
+++ b/libstdc++-v3/include/experimental/bits/simd.h
@@ -2673,7 +2673,8 @@ template <typename _Tp, size_t _Width>
 	  else
 	    __execute_n_times<_Width>(
 	      [&](auto __i) { __r &= _M_data[__i.value] == _Tp(); });
-	  return __r;
+	  if (__builtin_constant_p(__r))
+	    return __r;
 	}
       return false;
     }
@@ -2693,7 +2694,8 @@ template <typename _Tp, size_t _Width>
 	  else
 	    __execute_n_times<_Width>(
 	      [&](auto __i) { __r &= _M_data[__i.value] == ~_Tp(); });
-	  return __r;
+	  if (__builtin_constant_p(__r))
+	    return __r;
 	}
       return false;
     }