Re: [PATCH] ipa-sra: Consider the first parameter of methods safe to dereference

[Jan Hubicka <hubicka@ucw.cz>]

> On Wed, Dec 14, 2022 at 4:20 PM Jan Hubicka via Gcc-patches
> <gcc-patches@gcc.gnu.org> wrote:
> >
> > > Hi,
> > >
> > > Honza requested this after reviewing the patch that taught IPA-SRA
> > > that REFERENCE_TYPEs are always non-NULL that the pass also handles
> > > the first parameters of methods, this pointers, in the same way.  So
> > > this patch does that.
> > >
> > > The patch is undergoing bootstrap and testing on an x86_64-linux right
> > > now.  OK if it passes?
> > >
> > > Thanks,
> > >
> > > Martin
> > >
> > >
> > > gcc/ChangeLog:
> > >
> > > 2022-12-14  Martin Jambor  <mjambor@suse.cz>
> > >
> > >       * ipa-sra.cc (create_parameter_descriptors): Consider the first
> > >       parameter of a method safe to dereference.
> > >
> > > gcc/testsuite/ChangeLog:
> > >
> > > 2022-12-14  Martin Jambor  <mjambor@suse.cz>
> > >
> > >       * g++.dg/ipa/ipa-sra-6.C: New test.
> >
> > OK,
> 
> Are you sure that's safe?  The docs for METHOD_TYPE doesn't say 'this'
> is the first parameter nor does it say methods cannot be invoked for a
> nullptr object.
> 
> Do frontends other than C++ create METHOD_TYPE functions?  Grep
> shows uses in ada and objective C at least.

I think for Objective-C++ calling method is also considerd a
dereference.  We make similar assumptions in devirtualization code for
some time.  We could also check that the type is METHOD_TYPE satisfies
odr_type_p if we want to look specifically for C++ methods.

Honza
> 
> > thanks a lot!
> > Honza