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Re: [PATCH 00/89] Compile-time gimple-checking


On Wed, 2014-04-23 at 16:19 +0200, Richard Biener wrote:
> On Tue, Apr 22, 2014 at 9:42 PM, Richard Biener
> <richard.guenther@gmail.com> wrote:
> > On April 22, 2014 8:56:56 PM CEST, Richard Sandiford <rdsandiford@googlemail.com> wrote:
> >>David Malcolm <dmalcolm@redhat.com> writes:
> >>> Alternatively we could change the is-a.h API to eliminate this
> >>> discrepancy, and keep the typedefs; giving something like the
> >>following:
> >>>
> >>>   static void
> >>>   dump_gimple_switch (pretty_printer *buffer, gimple_switch gs, int
> >>spc,
> >>>                       int flags)
> >>>   [...snip...]
> >>>
> >>>   [...later, within pp_gimple_stmt_1:]
> >>>
> >>>      case GIMPLE_SWITCH:
> >>>        dump_gimple_switch (buffer, as_a <gimple_switch> (gs), spc,
> >>flags);
> >>>        break;
> >>>
> >>> which is concise, readable, and avoid the change in pointerness
> >>compared
> >>> to the "gimple" typedef; the local decls above would look like this:
> >>>   gimple some_stmt;  /* note how this doesn't have a star... */
> >>>   gimple_assign assign_stmt; /* ...and neither do these */
> >>>   gimple_cond assign_stmt;
> >>>   gimple_phi phi;
> >>>
> >>> I think this last proposal is my preferred API, but it requires the
> >>> change to is-a.h
> >>>
> >>> Attached is a proposed change to the is-a.h API that elimintates the
> >>> discrepancy, allowing the use of typedefs with is-a.h (doesn't yet
> >>> compile, but hopefully illustrates the idea).  Note how it changes
> >>the
> >>> API to match C++'s  dynamic_cast<> operator i.e. you do
> >>>
> >>>   Q* q = dyn_cast<Q*> (p);
> >>>
> >>> not:
> >>>
> >>>   Q* q = dyn_cast<Q> (p);
> >>
> >>Thanks for being flexible. :-)  I like this version too FWIW, for the
> >>reason you said: it really does look like a proper C++ cast.
> >
> > Indeed. I even wasn't aware it is different Than a c++ cast...
> 
> It would be nice if you can change that with a separate patch posted
> in a separate thread to be more visible.

Done, as:
  http://gcc.gnu.org/ml/gcc-patches/2014-04/msg01439.html

I've experimentally ported patch 2 of the series (gimple_switch) to this
approach, dropping the unloved casting methods in favor of as_a and
dyn_cast, and it works.

> Also I see you introduce a const_FOO class with every FOO one.
> I wonder whether, now that we have C++, can address const-correctness
> in a less awkward way than with a typedef.  Can you try to go back
> in time and see why we did with that in the first place?  ISTR that
> it was "oh, if we were only using C++ we wouldn't need to jump through
> that hoop".
> 
> Thanks,
> Richard.
> 
> > Richard.
> >
> >>If we ever decide to get rid of the typedefs (maybe at the same time as
> >>using "auto") then the choice might be different, but that would be a
> >>much
> >>more systematic and easily-automated change than this one.
> >>
> >>Thanks,
> >>Richard
> >
> >



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