https://gcc.gnu.org/g:0ffbcec62de9419812ef0017d74ce20572586c6c
commit r17-4594-g0ffbcec62de9419812ef0017d74ce20572586c6c Author: Jakub Jelinek <[email protected]> Date: Wed Sep 23 09:22:07 2026 +0200 c++: Improve printing of null pointer to data member constants [PR126599] For null pointer to data member we use INTEGER_CST with OFFSET_TYPE and -1 value. When that is printed in diagnostics or in display_string_of, it is printed as -1, which is confusing to users and an implementation detail (well, part of ABI https://itanium-cxx-abi.github.io/cxx-abi/abi.html#data-member-pointers A null data member pointer is represented as an offset of -1. ). Now, as the first testcase shows, if we have a non-null pointer to data member constant, it is actually PTRMEM_CST and is printed in a user-friendly way, the following patch just arranges to print the OFFSET_TYPE -1 INTEGER_CST similarly. 2026-09-23 Jakub Jelinek <[email protected]> PR c++/126599 * error.cc (dump_expr): Print OFFSET_TYPE -1 differently. * g++.dg/diagnostic/ptrtomem5.C: New test. * g++.dg/diagnostic/ptrtomem6.C: New test. * g++.dg/reflect/display_string_of1.C: Add 2 new tests. * g++.dg/reflect/u8display_string_of1.C: Likewise. Reviewed-by: Jason Merrill <[email protected]> Diff: --- gcc/cp/error.cc | 17 ++++++++++++++++- gcc/testsuite/g++.dg/diagnostic/ptrtomem5.C | 15 +++++++++++++++ gcc/testsuite/g++.dg/diagnostic/ptrtomem6.C | 7 +++++++ gcc/testsuite/g++.dg/reflect/display_string_of1.C | 2 ++ gcc/testsuite/g++.dg/reflect/u8display_string_of1.C | 2 ++ 5 files changed, 42 insertions(+), 1 deletion(-) diff --git a/gcc/cp/error.cc b/gcc/cp/error.cc index 3d5a194b9bc4..47065b11e22a 100644 --- a/gcc/cp/error.cc +++ b/gcc/cp/error.cc @@ -2472,8 +2472,23 @@ dump_expr (cxx_pretty_printer *pp, tree t, int flags) pp_cxx_ws_string (pp, M_("<unknown>")); break; - case VOID_CST: case INTEGER_CST: + if (TYPE_PTRDATAMEM_P (TREE_TYPE (t)) && integer_all_onesp (t)) + { + /* OFFSET_TYPE -1 is a null pointer to member. */ + if (flags & TFF_EXPR_IN_PARENS) + pp_cxx_left_paren (pp); + pp_cxx_left_paren (pp); + dump_type (pp, TREE_TYPE (t), flags); + pp_cxx_right_paren (pp); + pp->constant (cxx_dialect < cxx11 ? null_pointer_node : nullptr_node); + if (flags & TFF_EXPR_IN_PARENS) + pp_cxx_right_paren (pp); + break; + } + /* FALLTHRU */ + + case VOID_CST: case REAL_CST: case STRING_CST: case COMPLEX_CST: diff --git a/gcc/testsuite/g++.dg/diagnostic/ptrtomem5.C b/gcc/testsuite/g++.dg/diagnostic/ptrtomem5.C new file mode 100644 index 000000000000..e1def87e7825 --- /dev/null +++ b/gcc/testsuite/g++.dg/diagnostic/ptrtomem5.C @@ -0,0 +1,15 @@ +// PR c++/126599 +// { dg-do compile { target c++17 } } + +struct S { int s, t, u[3][3]; }; +using A = int[3][3]; +template <auto M> +void foo (int); +void +bar () +{ + foo <(int S::*)nullptr> (); // { dg-error "no matching function for call to 'foo<\\\(\\\(int S::\\\*\\\)nullptr\\\)>\\\(\\\)'" } + foo <&S::s> (); // { dg-error "no matching function for call to 'foo<\\\&S::s>\\\(\\\)'" } + foo <&S::t> (); // { dg-error "no matching function for call to 'foo<\\\&S::t>\\\(\\\)'" } + foo <(A S::*)nullptr> (); // { dg-error "no matching function for call to 'foo<\\\(\\\(int \\\(S::\\\*\\\)\\\[3\\\]\\\[3\\\]\\\)nullptr\\\)>\\\(\\\)'" } +} diff --git a/gcc/testsuite/g++.dg/diagnostic/ptrtomem6.C b/gcc/testsuite/g++.dg/diagnostic/ptrtomem6.C new file mode 100644 index 000000000000..e5105ec065c5 --- /dev/null +++ b/gcc/testsuite/g++.dg/diagnostic/ptrtomem6.C @@ -0,0 +1,7 @@ +// PR c++/126599 +// { dg-do compile } + +struct A { int a; }; +__attribute__((assume_aligned ((int A::*) 0))) int *foo (); +// { dg-warning "'assume_aligned' attribute argument \\\(int A::\\\*\\\)0 is not positive" "" { target c++98_only } .-1 } +// { dg-warning "'assume_aligned' attribute argument \\\(int A::\\\*\\\)nullptr is not positive" "" { target c++11 } .-2 } diff --git a/gcc/testsuite/g++.dg/reflect/display_string_of1.C b/gcc/testsuite/g++.dg/reflect/display_string_of1.C index ae24aff1e9d2..1f1df4b978c6 100644 --- a/gcc/testsuite/g++.dg/reflect/display_string_of1.C +++ b/gcc/testsuite/g++.dg/reflect/display_string_of1.C @@ -135,6 +135,8 @@ foo (int a, const long b, T c, int d[4], T &e) static_assert (display_string_of (members_of (^^V4, ctx)[0]) == "V4& V4::operator+=(const V4&)"); static_assert (display_string_of (members_of (^^V5, ctx)[0]) == "V5::operator int()"); static_assert (display_string_of (^^operator""_a) == "int operator\"\"_a(const char*)"); + static_assert (display_string_of (reflect_constant ((int U::*)nullptr)) == "(int U::*)nullptr"); + static_assert (display_string_of (reflect_constant (&U::u)) == "&U::u"); } namespace NS5 { diff --git a/gcc/testsuite/g++.dg/reflect/u8display_string_of1.C b/gcc/testsuite/g++.dg/reflect/u8display_string_of1.C index 0ff9cc7c992d..e0fb2e3b0a4a 100644 --- a/gcc/testsuite/g++.dg/reflect/u8display_string_of1.C +++ b/gcc/testsuite/g++.dg/reflect/u8display_string_of1.C @@ -135,6 +135,8 @@ foo (int a, const long b, T c, int d[4], T &e) static_assert (u8display_string_of (members_of (^^V4, ctx)[0]) == u8"V4& V4::operator+=(const V4&)"); static_assert (u8display_string_of (members_of (^^V5, ctx)[0]) == u8"V5::operator int()"); static_assert (u8display_string_of (^^operator""_a) == u8"int operator\"\"_a(const char*)"); + static_assert (u8display_string_of (reflect_constant ((int U::*)nullptr)) == u8"(int U::*)nullptr"); + static_assert (u8display_string_of (reflect_constant (&U::u)) == u8"&U::u"); } namespace NS5 {
