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 :/ > > 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 > >