[llvm-dev] ilist/iplist are broken (maybe I'll fix them?)

Justin Bogner via llvm-dev llvm-dev at lists.llvm.org
Thu Oct 8 11:00:19 PDT 2015

"Duncan P. N. Exon Smith" <dexonsmith at apple.com> writes:
> I don't feel totally comfortable just going ahead and fixing this
> without buy-in, since it'll touch some things.  Here's my basic plan:
>   - Fix `getNextNode()` and `getPrevNode()` by taking in the parent list
>     and checking against `end()` instead of checking for `nullptr`.
>   - Change the lists to be normal circular linked lists (possibly I'll
>     stick an "is-sentinel" bit in the prev pointer in asserts builds so
>     we can have assertions instead of infinite loops).  I'll layer our
>     weird partial ownership semantics on top to keep this part NFC.
>   - Re-layer the external state hooks so that they're on top of the
>     basic list instead of inside of it (so that someone in the future
>     can understand the code with far less studying).
> Anyone want to back me on this before I dive in?  Even better, did I
> miss something fundamental?


Other than having to update pretty well the entire code base, I don't
see any drawbacks to replacing ilist/iplist with something sane. The
current thing is complicated, tries to do too many things (and not many
of them well), and broken in several ways. In addition to the UB and
re-capitation you mention, I've also heard of issues using the reverse

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