[gcc r17-3411] libstdc++: Remove unnecessary code from reduce implementation

[Matthias Kretz]

https://gcc.gnu.org/g:f09bafa778caaeac1faaa16eacf4d0ad7adb6c92

commit r17-3411-gf09bafa778caaeac1faaa16eacf4d0ad7adb6c92
Author: Matthias Kretz <m.kretz@gsi.de>
Date:   Thu Jul 2 13:37:57 2026 +0200

    libstdc++: Remove unnecessary code from reduce implementation
    
    Previously, this was necessary for efficient reductions. When I tried to
    turn it into a missed-optimization PR, there was no issue (anymore). The
    generic _S_static_permute implementation optimizes just fine (or better)
    at this point.
    
    The traits_impl.cc change is a simple drive-by fix.
    
    libstdc++-v3/ChangeLog:
    
            * include/bits/simd_vec.h (_M_elements_shifted_to_front): Remove
            x86-specific implementation.
            * testsuite/std/simd/traits_impl.cc: Fix incorrect macro name.
    
    Signed-off-by: Matthias Kretz <m.kretz@gsi.de>

Diff:
---
 libstdc++-v3/include/bits/simd_vec.h           | 32 ++++----------------------
 libstdc++-v3/testsuite/std/simd/traits_impl.cc |  2 +-
 2 files changed, 6 insertions(+), 28 deletions(-)

diff --git a/libstdc++-v3/include/bits/simd_vec.h b/libstdc++-v3/include/bits/simd_vec.h
index bf6616df227d..9473c57b6cd4 100644
--- a/libstdc++-v3/include/bits/simd_vec.h
+++ b/libstdc++-v3/include/bits/simd_vec.h
@@ -449,33 +449,11 @@ namespace simd
 	  static_assert(_Shift < _S_size && -_Shift < _S_size);
 	  if constexpr (_Shift == 0)
 	    return *this;
-#ifdef __SSE2__
-	  else if (!__is_const_known(*this))
-	    {
-	      if constexpr (sizeof(_M_data) == 16 && _Shift > 0)
-		return reinterpret_cast<_DataType>(
-			 __builtin_ia32_psrldqi128(__vec_bit_cast<long long>(_M_data),
-						   _Shift * sizeof(value_type) * 8));
-	      else if constexpr (sizeof(_M_data) == 16 && _Shift < 0)
-		return reinterpret_cast<_DataType>(
-			 __builtin_ia32_pslldqi128(__vec_bit_cast<long long>(_M_data),
-						   -_Shift * sizeof(value_type) * 8));
-	      else if constexpr (sizeof(_M_data) < 16)
-		{
-		  auto __x = reinterpret_cast<__vec_builtin_type_bytes<long long, 16>>(
-			       __vec_zero_pad_to_16(_M_data));
-		  if constexpr (_Shift > 0)
-		    __x = __builtin_ia32_psrldqi128(__x, _Shift * sizeof(value_type) * 8);
-		  else
-		    __x = __builtin_ia32_pslldqi128(__x, -_Shift * sizeof(value_type) * 8);
-		  return _VecOps<_DataType>::_S_extract(__vec_bit_cast<__canon_value_type>(__x));
-		}
-	    }
-#endif
-	  return _S_static_permute(*this, [](int __i) consteval {
-		   int __off = __i + _Shift;
-		   return __off >= _S_size || __off < 0 ? zero_element : __off;
-		 });
+	  else
+	    return _S_static_permute(*this, [](int __i) consteval {
+		     int __off = __i + _Shift;
+		     return __off >= _S_size || __off < 0 ? zero_element : __off;
+		   });
 	}
 
       /** @internal
diff --git a/libstdc++-v3/testsuite/std/simd/traits_impl.cc b/libstdc++-v3/testsuite/std/simd/traits_impl.cc
index dde41c70aca3..9f6e9f42b6eb 100644
--- a/libstdc++-v3/testsuite/std/simd/traits_impl.cc
+++ b/libstdc++-v3/testsuite/std/simd/traits_impl.cc
@@ -49,7 +49,7 @@ void test()
       static_assert(__vectorizable<__integer_from<N>>);
     }
   template for (constexpr int N : {
-#ifdef __STDCPP_BFLOAT16_T__
+#ifdef __STDCPP_FLOAT16_T__
 				  2,
 #endif
 				  4, 8})