So don't use them!

sub sub_exists {
   my $name = shift;
   no strict qw( refs );
   return exists( &$name );
}
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Bonus: Not limited to subs in the current namespace.

To avoid the bug the OP identified, place the sub outside of scope of no autovivification;, or add use autovivification; to it.

sub sub_exists {
   my $name = shift;
   no strict qw( refs );
   use autovivification;  # Disable module to avoid bug.
   return exists( &$name );
}
[download]