On 1/25/24 14:14, 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).
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK
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
