[gcc r11-10822] libstdc++: Fix SFINAE for __is_intrinsic_type on ARM

[Matthias Kretz]

https://gcc.gnu.org/g:ad27280442d7979cf9da03d59268919fecfd12f4

commit r11-10822-gad27280442d7979cf9da03d59268919fecfd12f4
Author: Matthias Kretz <m.kretz@gsi.de>
Date:   Wed May 24 12:50:46 2023 +0200

    libstdc++: Fix SFINAE for __is_intrinsic_type on ARM
    
    On ARM NEON doesn't support double, so __is_intrinsic_type_v<double,
    whatever> should say false (instead of being ill-formed).
    
    Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
    
    libstdc++-v3/ChangeLog:
    
            PR libstdc++/109261
            * include/experimental/bits/simd.h (__intrinsic_type):
            Specialize __intrinsic_type<double, 8> and
            __intrinsic_type<double, 16> in any case, but provide the member
            type only with __aarch64__.
    
    (cherry picked from commit aa8b363171a95b8f867a74f29c75f9577e9087e1)

Diff:
---
 libstdc++-v3/include/experimental/bits/simd.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/include/experimental/bits/simd.h b/libstdc++-v3/include/experimental/bits/simd.h
index f6e8f3b24c4..7e877e85f80 100644
--- a/libstdc++-v3/include/experimental/bits/simd.h
+++ b/libstdc++-v3/include/experimental/bits/simd.h
@@ -2240,15 +2240,21 @@ template <>
   struct __intrinsic_type<float, 16, void>
   { using type = float32x4_t; };
 
-#if _GLIBCXX_SIMD_HAVE_NEON_A64
 template <>
   struct __intrinsic_type<double, 8, void>
-  { using type = float64x1_t; };
+  {
+#if _GLIBCXX_SIMD_HAVE_NEON_A64
+   using type = float64x1_t;
+#endif
+  };
 
 template <>
   struct __intrinsic_type<double, 16, void>
-  { using type = float64x2_t; };
+  {
+#if _GLIBCXX_SIMD_HAVE_NEON_A64
+    using type = float64x2_t;
 #endif
+  };
 
 #define _GLIBCXX_SIMD_ARM_INTRIN(_Bits, _Np)                                   \
 template <>                                                                    \