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

[Andrew MacLeod <amacleod at redhat dot com>]

On 11/01/2013 06:58 PM, David Malcolm wrote:
> On Fri, 2013-11-01 at 22:57 +0100, Jakub Jelinek wrote:
> > On Fri, Nov 01, 2013 at 05:47:14PM -0400, Andrew MacLeod wrote:
> > > On 11/01/2013 05:41 PM, Jakub Jelinek wrote:
> > > > On Fri, Nov 01, 2013 at 05:36:34PM -0400, Andrew MacLeod wrote:
> > > > >    static inline void
> > > > > ! gimple_call_set_lhs (gimple gs, tree lhs)
> > > > >    {
> > > > > -   GIMPLE_CHECK (gs, GIMPLE_CALL);
> > The checking you are removing here.
> >
> > > What checking?  There ought to be no checking at all in this
> > > example...  gimple_build_call_vec returns a gimple_call, and
> > > gimple_call_set_lhs()  doesn't have to check anything because it
> > > only accepts gimple_call's.. so there is no checking other than the
> > > usual "does my parameter match" that the compiler has to do...
> > and want to replace it by checking of the types at compile time.
> > The problem is that it uglifies the source too much, and, when you
> > actually don't have a gimple_call but supposedly a base class of it,
> > I expect you'd do as_a which is not only further uglification, but has
> > runtime cost also for --enable-checking=release.
> I can have a look next week at every call to gimple_call_set_lhs in the
> tree, and see to what extent we know at compile-time that the initial
> arg is indeed a call (of the ones I quickly grepped just now, most are
> from gimple_build_call and friends, but one was from a gimple_copy).
>
> FWIW I did some performance testing of the is_a/as_a code in the earlier
> version of the patch, and it didn't have a noticable runtime cost
> compared to the GIMPLE_CHECK in the existing code:
> Size of compiler executable:
> http://gcc.gnu.org/ml/gcc-patches/2013-08/msg01920.html
> Compile times:
> http://gcc.gnu.org/ml/gcc-patches/2013-09/msg00171.html
I actually really dislike as_a<> and is_a<>, and  think code needs to be 
restructured rather than use them, other than possibly at the very 
bottom level when we're allocating memory or something like that, or 
some kind of emergency :-)...   If we require frequent uses of those, 
I'd be against it, I find them quite ugly.

Like I said in the other reply, no rush, I don't think any of this 
follow up is appropriate this late in stage 1.  It would be more of an 
"interest" examination right now.. at least in my opinion...  I suspect 
thinks like gimple_assign are more complex cases, but without looking 
its hard to tell for sure.

Andrew