On Wed, 25 Sep 2024, Jason Merrill wrote: > On 7/30/24 6:49 PM, Giuseppe D'Angelo wrote: > > On 29/07/2024 22:53, Giuseppe D'Angelo wrote: > > > Hi, > > > > > > The attached patch is a stab at adding the necessary compiler builtin to > > > support std::is_virtual_base_of (P2985R0, approved for C++26). The name > > > of the builtin matches the one just merged into clang: > > > > > > https://github.com/llvm/llvm-project/issues/98310 > > > > > > The next patch will add the libstdc++ bits. > > > > Hello, > > > > This is a new revision of the same patch, this time with a DCO. > > > + ba_require_virtual = 1 << 3 /* Require a virtual base */ > > Why change lookup rather than just call lookup_base and then binfo_from_vbase > in trait_expr_value?
IIUC it's because of the ambiguous case: std::is_virtual_base_of needs to be true if there's an ambiguous virtual base, one of which is virtual, but lookup_base by default prefers returning a non-virtual base in case of ambiguity. > > Jason > >
