Re: PR libstdc++/78420 Make std::less etc. yield total order for pointers

[Jonathan Wakely <jwakely dot gcc at gmail dot com>]

On 14 March 2018 at 23:01, Jonathan Wakely wrote:
> Here's a very different patch. This gets rid of the __ptr_rel_ops and
> just puts the special handling for pointers directly in the
> std::less<_Tp*> etc. specializations. Then std::less<void> uses
> std::less<P*> for some pointer type P*. I've also added a ton of ugly
> metaprogramming to detect the "if the call operator calls a built-in
> operator comparing pointers" condition. The idea is borrowed from
> Casey Carter and Eric Niebler's Ranges work, but basically it checks
> if operator<(T,U) or T.operator<(U) can be called, and if not the
> comparison must be using a built-in operator. If both T and U are
> convertible to pointers (specifically, to const volatile void* which
> is the most accepting of all pointers) then we assume we're using a
> built-in operator comparing pointers, and delegate to std::less<const
> volatile void*>, which ensures a total order.
>
> Tested powerpc64le-linux, committed to trunk. This fixes a regression,
> but I'm not sure about backporting it yet, I haven't even tried
> testing it on the branches.

After testing the traits for detecting overloaded operators I made a
"small tweak" to reorganize them, and didn't retest. This fixes the
bug I introduced by reorganizing.

Tested powerpc64le-linux, committed to trunk.

Attachment: patch.txt
Description: Text document