[gcc r12-10428] libstdc++: Silence irrelevant warnings in <experimental/simd>

[Matthias Kretz]

https://gcc.gnu.org/g:79aa69663cfbac30b76c85a8e4856b0865749ef7

commit r12-10428-g79aa69663cfbac30b76c85a8e4856b0865749ef7
Author: Matthias Kretz <m.kretz@gsi.de>
Date:   Wed Apr 17 10:35:47 2024 +0200

    libstdc++: Silence irrelevant warnings in <experimental/simd>
    
    Avoid
    -Wnarrowing in C code;
    -Wtautological-compare in unconditional static_assert (necessary for
    faking a dependency on a template parameter)
    
    Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
    
    libstdc++-v3/ChangeLog:
    
            * include/experimental/bits/simd.h: Ignore -Wnarrowing for
            arm_neon.h.
            (__int_for_sizeof): Replace tautological compare with checking
            for invalid template parameter value.
            * include/experimental/bits/simd_builtin.h (__extract_part):
            Remove tautological compare by combining two static_assert.
    
    (cherry picked from commit e7a3ad29c9c832b6ae999cbfb0af89e121959030)

Diff:
---
 libstdc++-v3/include/experimental/bits/simd.h         | 8 +++++++-
 libstdc++-v3/include/experimental/bits/simd_builtin.h | 3 +--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/experimental/bits/simd.h b/libstdc++-v3/include/experimental/bits/simd.h
index 6f7418a840ea..439545869be8 100644
--- a/libstdc++-v3/include/experimental/bits/simd.h
+++ b/libstdc++-v3/include/experimental/bits/simd.h
@@ -43,7 +43,12 @@
 #if _GLIBCXX_SIMD_X86INTRIN
 #include <x86intrin.h>
 #elif _GLIBCXX_SIMD_HAVE_NEON
+#pragma GCC diagnostic push
+// narrowing conversion of '__a' from 'uint64_t' {aka 'long long unsigned int'} to
+//   'int64x1_t' {aka 'long long int'} [-Wnarrowing]
+#pragma GCC diagnostic ignored "-Wnarrowing"
 #include <arm_neon.h>
+#pragma GCC diagnostic pop
 #endif
 
 /** @ingroup ts_simd
@@ -576,6 +581,7 @@ template <size_t _Bytes>
   constexpr auto
   __int_for_sizeof()
   {
+    static_assert(_Bytes > 0);
     if constexpr (_Bytes == sizeof(int))
       return int();
   #ifdef __clang__
@@ -641,7 +647,7 @@ template <size_t _Bytes>
 	return _Ip{};
       }
     else
-      static_assert(_Bytes != _Bytes, "this should be unreachable");
+      static_assert(_Bytes == 0, "this should be unreachable");
   }
 #pragma GCC diagnostic pop
 
diff --git a/libstdc++-v3/include/experimental/bits/simd_builtin.h b/libstdc++-v3/include/experimental/bits/simd_builtin.h
index e060816c6eac..fc8937a6e024 100644
--- a/libstdc++-v3/include/experimental/bits/simd_builtin.h
+++ b/libstdc++-v3/include/experimental/bits/simd_builtin.h
@@ -278,8 +278,7 @@ template <int _Index, int _Total, int _Combine = 1, size_t _Np>
   __extract_part(const _SimdWrapper<bool, _Np> __x)
   {
     static_assert(_Combine == 1, "_Combine != 1 not implemented");
-    static_assert(__have_avx512f && _Np == _Np);
-    static_assert(_Total >= 2 && _Index + _Combine <= _Total && _Index >= 0);
+    static_assert(__have_avx512f && _Total >= 2 && _Index + _Combine <= _Total && _Index >= 0);
     return __x._M_data >> (_Index * _Np / _Total);
   }