On 8/19/26 3:25 AM, Jakub Jelinek wrote:
Hi!We ICE during mangling on the following testcase. There are two problems on it. One is the use of build_zero_cst for skipped members when using designated initializers. build_zero_cst is a gcc/tree.cc function, so it doesn't know about META_TYPE and how to create a zero constant for it. We could call probably build_zero_init instead, but it does significantly more work and apparently (from what I've been playing with e.g. using pointer-to-data-member types etc.) it isn't needed except for the reflection case, so this patch just calls get_null_reflection () for reflections and keeps using build_zero_cst for everything else. Another problem is that we mangle A { .a = {}, .b = {} } vs. A { .a = {} } differently, although both have the same value. If a and b fields have pointer-to-data-member type instead (or int), the zero initialized members are skipped from the tl value list, and this patch changes zero_init_expr_p so that it handles null reflections the same way (before P4101 mangling is probably the only way to observe whether null reflection is all zeros or not). Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
2026-08-19 Jakub Jelinek <[email protected]> PR c++/126922 * mangle.cc (write_expression): For CONSTRUCTOR skipped member of std::meta::info type, call write_expression on get_null_reflection rather than build_zero_cst. * tree.cc (zero_init_expr_p): If type is std::meta::info, return true iff t is null reflection. * g++.dg/reflect/mangle10.C: New test. --- gcc/cp/mangle.cc.jj 2026-08-18 17:49:06.122775263 +0200 +++ gcc/cp/mangle.cc 2026-08-18 20:34:38.984625917 +0200 @@ -3888,8 +3888,14 @@ write_expression (tree expr) if (field == ce->index) break; if (abi_check (21)) - write_expression (build_zero_cst - (TREE_TYPE (field))); + { + tree type = TREE_TYPE (field), expr; + if (REFLECTION_TYPE_P (type)) + expr = get_null_reflection (); + else + expr = build_zero_cst (type); + write_expression (expr); + } field = DECL_CHAIN (field); } } --- gcc/cp/tree.cc.jj 2026-08-18 20:15:37.371873189 +0200 +++ gcc/cp/tree.cc 2026-08-18 20:39:28.758837710 +0200 @@ -5328,6 +5328,8 @@ zero_init_expr_p (tree t) return false; if (TYPE_PTRMEM_P (type)) return null_member_pointer_value_p (t); + if (REFLECTION_TYPE_P (type)) + return null_reflection_p (t); if (TREE_CODE (t) == CONSTRUCTOR) { if (COMPOUND_LITERAL_P (t) --- gcc/testsuite/g++.dg/reflect/mangle10.C.jj 2026-08-18 20:42:48.583226296 +0200 +++ gcc/testsuite/g++.dg/reflect/mangle10.C 2026-08-18 20:42:31.088454926 +0200 @@ -0,0 +1,26 @@ +// PR c++/126922 +// { dg-do compile { target c++26 } } +// { dg-additional-options "-freflection -O0 -fno-short-enums" } + +struct A { decltype (^^::) a, b; }; +struct B { A c; }; + +template <int N, auto C> +[[gnu::noipa]] void +foo () +{ +} + +int +main () +{ + foo <1, A { .a = {}, .b = {} }> (); + foo <2, A { .a = {} }> (); + foo <3, A { .b = {} }> (); + foo <4, B { .c = {} }> (); +} + +// { dg-final { scan-assembler "_Z3fooILi1ETnDaXtl1AEEEvv" } } +// { dg-final { scan-assembler "_Z3fooILi2ETnDaXtl1AEEEvv" } } +// { dg-final { scan-assembler "_Z3fooILi3ETnDaXtl1AEEEvv" } } +// { dg-final { scan-assembler "_Z3fooILi4ETnDaXtl1BEEEvv" } } Jakub
