On Thu, 25 Jan 2024, Patrick Palka wrote:
> On Thu, 25 Jan 2024, Jakub Jelinek wrote:
>
> > Hi!
> >
> > The following testcase reduced from GDB is miscompiled starting with
> > r14-5503 PR112427 change.
> > The problem is in the build_m_component_ref hunk, which changed
> > - datum = fold_build_pointer_plus (fold_convert (ptype, datum),
> > component);
> > + datum = cp_convert (ptype, datum, complain);
> > + if (!processing_template_decl)
> > + datum = build2 (POINTER_PLUS_EXPR, ptype,
> > + datum, convert_to_ptrofftype (component));
> > + datum = cp_fully_fold (datum);
> > Component is e, (sizetype) e is 16, offset of c inside of C.
> > ptype is A *, pointer to type of C::c and datum is &d.
> > Now, previously the above created ((A *) &d) p+ (sizetype) e which is
> > correct,
> > but in the new code cp_convert sees that C has A as base class and
> > instead of returning (A *) &d, it returns &d.D.2800 where D.2800 is
> > the FIELD_DECL for the A base at offset 8 into C.
> > So, instead of computing ((A *) &d) p+ (sizetype) e it computes
> > &d.D.2800 p+ (sizetype) e, which is ((A *) &d) p+ 24.
> >
> > The following patch fixes it by using convert instead of cp_convert which
> > eventually calls build_nop (ptype, datum).
>
> LGTM. IIUC using 'convert' would work here too thanks to its special
> case for indirect types, but I naively went with cp_convert since it has
> a complain parameter :/
D'oh, I completely overlooked this version of the patch already uses
convert instead of build_nop directly :) LGTM either way
>
> >
> > Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
> >
> > 2024-01-25 Jakub Jelinek <ja...@redhat.com>
> >
> > PR c++/113599
> > * typeck2.cc (build_m_component_ref): Use convert instead of
> > cp_convert for pointer conversion.
> >
> > * g++.dg/expr/ptrmem11.C: New test.
> >
> > --- gcc/cp/typeck2.cc.jj 2024-01-03 12:01:23.672476417 +0100
> > +++ gcc/cp/typeck2.cc 2024-01-25 14:11:40.656361310 +0100
> > @@ -2378,7 +2378,7 @@ build_m_component_ref (tree datum, tree
> > /* Build an expression for "object + offset" where offset is the
> > value stored in the pointer-to-data-member. */
> > ptype = build_pointer_type (type);
> > - datum = cp_convert (ptype, datum, complain);
> > + datum = convert (ptype, datum);
> > if (!processing_template_decl)
> > datum = build2 (POINTER_PLUS_EXPR, ptype,
> > datum, convert_to_ptrofftype (component));
> > --- gcc/testsuite/g++.dg/expr/ptrmem11.C.jj 2024-01-25 14:13:11.736089567
> > +0100
> > +++ gcc/testsuite/g++.dg/expr/ptrmem11.C 2024-01-25 14:18:47.720398222
> > +0100
> > @@ -0,0 +1,17 @@
> > +// PR c++/113599
> > +// { dg-do run }
> > +
> > +struct A { void *a; };
> > +struct B { void *b; };
> > +struct C : public B, public A { A c; };
> > +static C d;
> > +
> > +int
> > +main ()
> > +{
> > + A C::*e = &C::c;
> > + A *f = &(d.*e);
> > + A *g = &d.c;
> > + if (f != g)
> > + __builtin_abort ();
> > +}
> >
> > Jakub
> >
> >
>
