[committed] libstdc++: Fix narrowing conversion in std::visit

[Jonathan Wakely via Gcc-patches]

Signed-off-by: Jonathan Wakely <jwak...@redhat.com>

libstdc++-v3/ChangeLog:

        * include/std/variant (__do_visit): Use variant_npos instead of
        literal -1 that requires a narrowing conversion.

Tested powerpc64le-linux. Committed to trunk.


commit dc1b29508d765b874372f4b1737ac6dc86962506
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Thu May 20 18:04:16 2021

    libstdc++: Fix narrowing conversion in std::visit
    
    Signed-off-by: Jonathan Wakely <jwak...@redhat.com>
    
    libstdc++-v3/ChangeLog:
    
            * include/std/variant (__do_visit): Use variant_npos instead of
            literal -1 that requires a narrowing conversion.

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index ddeefd9b35e..d50c6b7de1d 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -1830,7 +1830,8 @@ namespace __variant
                  if constexpr (is_same_v<_Result_type, __variant_idx_cookie>
                                || is_same_v<_Result_type, __variant_cookie>)
                    {
-                     return __gen_vtable_impl<_Ma, index_sequence<-1>>::
+                     using _Npos = index_sequence<variant_npos>;
+                     return __gen_vtable_impl<_Ma, _Npos>::
                        __visit_invoke(std::forward<_Visitor>(__visitor),
                                       std::forward<_V0>(__v0));
                    }