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see: https://gcc.gnu.org/ml/gcc-patches/2014-10/msg00536.html
> Hi Honza,
>
>
> as you know, we have a wrong code bug, when a pure or const method is called
> via a virtual thunk.
> I had some more Ideas, how to fix that, but all of them had some serious
> draw-backs, so I leave the details out...
>
>
> But now I have a new insight, why the "obvious" fix for this serious code
> generation bug did not work
> in the first place.
>
>
> And the reason was, that if ipa-pure-const.c calls set_const_flag or
> set_pure_flag for a thunk, it calls the same
> function later for the called method, and this overwrites the flags of _all_
> associated thunks and aliases.
> However that should at least not be done for virtual thunks, as these need to
> be IPA_NEITHER, even if
> the method itself has different attributes, that is because the assembler
> thunk accesses the vtable, while
> other thunks do not.
>
>
> So I re-factored set_const_flag and set_pure_flag to exclude the virtual
> thunks, taking care that other
> users of call_for_symbol_thunks_and_aliases do not get a different behavior
> than before this patch.
>
>
> The attached patch was boot-strapped and
> regression-tested on x86_64-linux-gnu.
> Ok for trunk?
>
>
> PS: As a side-note, there are two identical functions, named
> "call_for_symbol_and_aliases", in
> class symtab_node and in class cgraph_node, which inherits from symtab_node.
> Both functions are
> not declared virtual. Is that what's intended? Usually this could lead to
> errors, or at least some serious
> compiler warnings.
>
>
> Thanks
> Bernd.
>
