On 6/12/26 4:41 AM, Jakub Jelinek wrote:
Hi!
Non-static data members are currently mangled as
dm <prefix> <unqualified-name>
This works fine for NSDMs with a name, or even the unnamed anon union/struct
NSDMs iff they have any named members in them (in that case the
<unqualified-name> is using anon_aggr_naming_decl).
As the following testcases show, if the anon union/struct is empty,
we ICE, because there is nothing we can print as the name.
The following patch mangles it similarly to unnamed bitfields in that case,
simply counts the index of such problematic empty unnamed anon union/struct
within the class and emits _ for the first one, etc.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
2026-06-12 Jakub Jelinek <[email protected]>
PR c++/125541
* mangle.cc (write_reflection): Mangle empty anonymous union/struct
data members as "da" rather than "dm" and use index of such a data
member instead of name.
* g++.dg/reflect/mangle1.C: Add further 2 tests.
* g++.dg/reflect/mangle9.C: New test.
--- gcc/cp/mangle.cc.jj 2026-06-10 17:42:21.452938363 +0200
+++ gcc/cp/mangle.cc 2026-06-11 17:11:36.438221176 +0200
@@ -4186,6 +4186,8 @@ write_expression (tree expr)
[ <alias template-args> ] _ <type> # type alias
::= ty <type> # type
::= dm <prefix> <unqualified-name> # ns data member
+ ::= da <prefix> [ <nonnegative number> ] _ # empty anon union
+ # data member
::= un <prefix> [ <nonnegative number> ] _ # unnamed bitfld
::= ct [ <prefix> ] <unqualified-name> # class template
::= ft [ <prefix> ] <unqualified-name> # function template
@@ -4207,6 +4209,11 @@ write_reflection (tree refl)
{
char prefix[3];
tree arg = reflection_mangle_prefix (refl, prefix);
+ if (strcmp (prefix, "dm") == 0
+ && DECL_NAME (arg) == NULL_TREE
+ && ANON_AGGR_TYPE_P (TREE_TYPE (arg))
+ && anon_aggr_naming_decl (TREE_TYPE (arg)) == NULL_TREE)
+ strcpy (prefix, "da");
write_string (prefix);
/* If there is no argument, nothing further needs to be mangled. */
if (arg == NULL_TREE)
@@ -4257,6 +4264,21 @@ write_reflection (tree refl)
write_prefix (ctx);
write_unqualified_name (arg);
}
+ else if (strcmp (prefix, "da") == 0)
+ {
+ int idx = 0;
+ tree ctx = decl_mangling_context (arg);
+ for (tree f = TYPE_FIELDS (ctx); f; f = DECL_CHAIN (f))
+ if (f == arg)
+ break;
+ else if (TREE_CODE (f) == FIELD_DECL
+ && DECL_NAME (f) == NULL_TREE
+ && ANON_AGGR_TYPE_P (TREE_TYPE (f))
+ && anon_aggr_naming_decl (TREE_TYPE (f)) == NULL_TREE)
+ ++idx;
+ write_prefix (ctx);
+ write_compact_number (idx);
+ }
else if (strcmp (prefix, "un") == 0)
{
tree ctx = DECL_CONTEXT (arg);
--- gcc/testsuite/g++.dg/reflect/mangle1.C.jj 2026-04-15 08:59:38.142570630
+0200
+++ gcc/testsuite/g++.dg/reflect/mangle1.C 2026-06-11 17:18:09.754062005
+0200
@@ -15,6 +15,7 @@ struct S : B {
int : 0;
static int var;
};
+struct W { union {}; union {}; union {}; union {}; };
template <auto> struct TCls {};
template <auto> void TFn ();
template <auto> int TVar;
@@ -172,6 +173,8 @@ baz (int x)
std::meta::reflect_constant (43L),
std::meta::reflect_constant (NS2::AA { 1, 2 }) } })> (); // data member
description
bar <340, ^^NS2::X::~X> (); // function
+ bar <350, members_of (^^W, ctx)[1]> (); // empty anon union non-static data
member
+ bar <351, members_of (^^W, ctx)[7]> (); // empty anon union non-static data
member
}
// { dg-final { scan-assembler "_Z3fooILi1EDmEvv" } }
@@ -258,3 +261,5 @@ baz (int x)
// { dg-final { scan-assembler "_Z3barILi334ELDmdsi___0_EEvv" } }
// { dg-final { scan-assembler
"_Z3barILi335ELDmdsi_1____Li42ELl43EXtlN3NS22AAELi1ELi2EEEEEvv" } }
// { dg-final { scan-assembler "_Z3barILi340ELDmfnN3NS21XD4EvEEvv" } }
+// { dg-final { scan-assembler "_Z3barILi350ELDmda1W_EEvv" } }
+// { dg-final { scan-assembler "_Z3barILi351ELDmda1W2_EEvv" } }
--- gcc/testsuite/g++.dg/reflect/mangle9.C.jj 2026-06-11 17:27:55.199383148
+0200
+++ gcc/testsuite/g++.dg/reflect/mangle9.C 2026-06-11 17:38:10.949291458
+0200
@@ -0,0 +1,31 @@
+// { dg-do compile { target c++26 } }
+// { dg-options "-freflection -O0" }
+
+#include <meta>
+
+struct W { union { union {}; union {}; union {}; union {}; };
+ union { union {}; union {}; union {}; union {}; }; };
+
+constexpr auto ctx = std::meta::access_context::current ();
+
+template <int N, std::meta::info I>
+void
+bar ()
+{
+}
+
+void
+baz (int x)
+{
+ constexpr auto a = members_of (^^W, ctx)[0];
+ bar <10, members_of (a, ctx)[1]> (); // empty anon union non-static data
member
+ bar <11, members_of (a, ctx)[7]> (); // empty anon union non-static data
member
+ constexpr auto b = members_of (^^W, ctx)[2];
+ bar <12, members_of (b, ctx)[1]> (); // empty anon union non-static data
member
+ bar <13, members_of (b, ctx)[7]> (); // empty anon union non-static data
member
+}
+
+// { dg-final { scan-assembler "_Z3barILi10ELDmda1WUt__EEvv" } }
+// { dg-final { scan-assembler "_Z3barILi11ELDmda1WUt_2_EEvv" } }
+// { dg-final { scan-assembler "_Z3barILi12ELDmda1WUt0__EEvv" } }
+// { dg-final { scan-assembler "_Z3barILi13ELDmda1WUt0_2_EEvv" } }
Jakub
