[PATCH] Add iterator for PHINode value/BB pair

[David Blaikie]

On Wed, Jul 22, 2015 at 12:11 PM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

>
> > On 2015-Jul-21, at 21:20, Pete Cooper <peter_cooper at apple.com> wrote:
> >
> > Thanks for all the feedback.  This is a patch which addresses all of it.
> >
> > <phinode.diff>
> >
>
> > +
> > +    const PHINodeEdge operator*() const {
>
> No reason for the const in `const PHINodeEdge` here.
>

to support operator-> you have to return a pointer, which means you need
the PHINodeEdge storage inside the iterator to point to (& then you can
just return a const ref from op*)


>
> > +      return { *Values, *Blocks };
> > +    }
> > +  };
> > +
>
> Otherwise LGTM.  Might want to pass it through clang-format; I noticed
> some minor whitespace oddities.
>
> > *snip*
> >> On Jul 21, 2015, at 8:21 PM, Duncan P. N. Exon Smith <
> dexonsmith at apple.com> wrote:
> >>
> >>
> >>
> >> If you drop the requirements from `forward_iterator` to
> >> `input_iterator`, then you're allowed to return a `PHINodeEdge` by-value
> >> here instead of by-reference (unfortunately this makes it illegal to use
> >> a bunch of STL algorithms; STL iterator traits are completely broken
> >> IMO).
> > I’m fine with this.  David, Chandler, please let me know how you feel
> about this.
> >
> > Also, i forgot to say that I considered doing a zip iterator and
> inheriting this from it.  This is something I think Chandler or David
> mentioned a few months ago.  If there’s been any progress in the C++
> committee on that then i’m happy to try implement something better.  If
> not, then i don’t think what I have here should be difficult to change in
> future.
>
> I guess a generalized version would return a
> `std::tuple<Value *const &, BasicBlock *const &>` or some such.  Not
> sure how to actually make zip iterators work well without something
> like N1550 though.


What's N1550 offer to make zip work?

I wouldn't mind a slightly half-hearted version that works for basic/common
cases...
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