[Bug target/99216] ICE in aarch64_sve::function_expander::expand() with LTO

["acoplan at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99216

--- Comment #4 from Alex Coplan <acoplan at gcc dot gnu.org> ---
Right, the problem appears to be to do with the way that overloaded functions
are implemented for the ACLE. Specifically the m_direct_overloads flag in
aarch64_sve::function_builder. If this flag is set, we register a separate
builtin (with a separate function code) for each overload as opposed to
registering the overloaded function once and resolving it later. The two
different schemes end up with each builtin having a different code.

We set m_direct_overloads to be true if the language is C++:

m_direct_overloads = lang_GNU_CXX ();

so in cc1plus, we use one numbering scheme, but in lto1, we use a different
numbering scheme, with predictably disastrous consequences (we try and expand
svaddv as an svbic).

So one options would be that for LTO we instantiate both sets of tree nodes.
Then, when expanding a tree node that came from LTO, we dispatch on a flag in
the tree node (essentially just whether it came from C++ or not) to determine
which set of functions to use. Seems a bit messy though.

@Richard: does that sound at all sane? Any ideas for a better approach?