Re: [PATCH 0/6] Conversion of gimple types to C++ inheritance (v3)

[Jeff Law <law at redhat dot com>]

On 11/06/13 04:02, Bernd Schmidt wrote:
> On 11/06/2013 10:31 AM, Richard Biener wrote:
> > We decided to move to C++.  As part of a later discussion we decided
> > to go with a single general dynamic-casting style, mimicing the "real"
> > C++ variant which is dynamic_cast < ... >.  Which resulted in
> > is-a.h.
> >
> > So yes, we've decided to go C++ so we have to live with certain
> > uglinesses of that decisions (and maybe over time those uglinesses
> > will fade away and we get used to it and like it).
> >
> > Thus, there isn't another option besides using the is-a.h machinery
> > and enabling and using RTTI.  Sticking to C for gimple doesn't seem
> > to be consistent with the decision to move to C++.
> >
> > Oh, I'm not saying I'm a big fan of as_a / is_a or C++ in general
> > as it plays out right now.  But well, we've had the discussion and
> > had a decision.
>
> Maybe we need to revisit it? As one of those who were not in favour of
> the C++ move, can I ask you guys to step back for a moment and think
> about - what do all of these changes buy us, exactly? Imagine the state
> at the end, where everything is converted and supposedly the temporary
> ugliness is gone, what have we gained over the code as it is now?
I think Andrew outlined much of this at the Cauldron.  I'd strongly 
recommend reviewing the talk/slides.  My personal favorite is the type 
checking and everything that implies.  For example, most/all of the tree 
checking crap just goes away as you'll almost always know what kind of 
tree you're working with.  Checking becomes limited to locations where 
we we have to do conversions.  It becomes a lot harder to mess something up.

> I still think all this effort is misdirected and distracts us from
> making changes that improve gcc for its users.
I disagree.  This effort is meant to restructure GCC so that we can 
continue to improve it without going insane.

In many respects it's similar to the tree-ssa work we undertook 10+ 
years ago and to some degree it's cleaning up things we decided not to 
deal with at that time -- namely reusing trees in gimple/ssa.


jeff