{"id":2223250,"url":"http://patchwork.ozlabs.org/api/patches/2223250/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/patch/20260414195412.221509-1-ppalka@redhat.com/","project":{"id":17,"url":"http://patchwork.ozlabs.org/api/projects/17/?format=json","name":"GNU Compiler Collection","link_name":"gcc","list_id":"gcc-patches.gcc.gnu.org","list_email":"gcc-patches@gcc.gnu.org","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260414195412.221509-1-ppalka@redhat.com>","list_archive_url":null,"date":"2026-04-14T19:54:12","name":"c++: identity of A<^^alias> [PR124544]","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"caf3c2d8acae2893db5d15fd30ba2a9aa5df0b12","submitter":{"id":78319,"url":"http://patchwork.ozlabs.org/api/people/78319/?format=json","name":"Patrick Palka","email":"ppalka@redhat.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/gcc/patch/20260414195412.221509-1-ppalka@redhat.com/mbox/","series":[{"id":499891,"url":"http://patchwork.ozlabs.org/api/series/499891/?format=json","web_url":"http://patchwork.ozlabs.org/project/gcc/list/?series=499891","date":"2026-04-14T19:54:12","name":"c++: identity of A<^^alias> [PR124544]","version":1,"mbox":"http://patchwork.ozlabs.org/series/499891/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2223250/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2223250/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=NbbzO5Au;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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charset=\"US-ASCII\"; x-default=true","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"},"content":"Tested on x86-64-pc-linux-gnu, does this look OK for trunk?\n\n-- >8 --\n\nSince a reflection of an alias represents the alias itself, not the\nunderlying type, equality of two such reflections needs to take that\ninto account. And don't strip such aliases when forming a\nspecialization A<^^alias>.\n\n\tPR c++/124544\n\ngcc/cp/ChangeLog:\n\n\t* tree.cc (strip_typedefs_expr) : Don't strip\n\ttypedefs within a type operand.\n\t(cp_tree_equal) : For a reflection of an\n\talias, also compare TYPE_NAMEs directly.\n\ngcc/testsuite/ChangeLog:\n\n\t* g++.dg/reflect/alias1.C: New test.\n\t* g++.dg/reflect/alias2.C: New test.\n---\n gcc/cp/tree.cc | 22 ++++++++++++++++++----\n gcc/testsuite/g++.dg/reflect/alias1.C | 26 ++++++++++++++++++++++++++\n gcc/testsuite/g++.dg/reflect/alias2.C | 17 +++++++++++++++++\n 3 files changed, 61 insertions(+), 4 deletions(-)\n create mode 100644 gcc/testsuite/g++.dg/reflect/alias1.C\n create mode 100644 gcc/testsuite/g++.dg/reflect/alias2.C","diff":"diff --git a/gcc/cp/tree.cc b/gcc/cp/tree.cc\nindex ff2e78cd89cf..d12ebc0f25e1 100644\n--- a/gcc/cp/tree.cc\n+++ b/gcc/cp/tree.cc\n@@ -2155,6 +2155,11 @@ strip_typedefs_expr (tree t, bool *remove_attributes, unsigned int flags)\n case STMT_EXPR:\n return t;\n \n+ case REFLECT_EXPR:\n+ /* ^^alias represents the alias itself, not the underlying type. */\n+ if (TYPE_P (TREE_OPERAND (t, 0)))\n+\treturn t;\n+\n default:\n break;\n }\n@@ -4510,10 +4515,19 @@ cp_tree_equal (tree t1, tree t2)\n return true;\n \n case REFLECT_EXPR:\n- if (!cp_tree_equal (REFLECT_EXPR_HANDLE (t1), REFLECT_EXPR_HANDLE (t2))\n-\t || REFLECT_EXPR_KIND (t1) != REFLECT_EXPR_KIND (t2))\n-\treturn false;\n- return true;\n+ {\n+\ttree h1 = REFLECT_EXPR_HANDLE (t1);\n+\ttree h2 = REFLECT_EXPR_HANDLE (t2);\n+\tif (!cp_tree_equal (h1, h2)\n+\t || REFLECT_EXPR_KIND (t1) != REFLECT_EXPR_KIND (t2))\n+\t return false;\n+\t/* ^^alias represents the alias itself, not the underlying type. */\n+\tif (TYPE_P (h1)\n+\t && (typedef_variant_p (h1) || typedef_variant_p (h2))\n+\t && TYPE_NAME (h1) != TYPE_NAME (h2))\n+\t return false;\n+\treturn true;\n+ }\n \n default:\n break;\ndiff --git a/gcc/testsuite/g++.dg/reflect/alias1.C b/gcc/testsuite/g++.dg/reflect/alias1.C\nnew file mode 100644\nindex 000000000000..d77fd9f2a978\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/reflect/alias1.C\n@@ -0,0 +1,26 @@\n+// PR c++/124544\n+// { dg-do compile { target c++26 } }\n+// { dg-additional-options \"-freflection\" }\n+\n+using alias = int;\n+template using alias_t = int;\n+\n+template struct A { };\n+static_assert( ! __is_same(A<^^int>, A<^^alias>) );\n+static_assert( ! __is_same(A<^^int>, A<^^alias_t>) );\n+static_assert( ! __is_same(A<^^alias>, A<^^alias_t>) );\n+static_assert( ! __is_same(A<^^alias_t>, A<^^alias_t>) );\n+static_assert( __is_same(A<^^alias_t>, A<^^alias_t>) );\n+\n+template struct B { };\n+static_assert( __is_same(A<^^B>, A<^^B>) );\n+\n+template int V;\n+static_assert( &V<^^int> != &V<^^alias_t> );\n+static_assert( &V<^^int> != &V<^^alias> );\n+static_assert( &V<^^alias_t> != &V<^^alias_t> );\n+\n+template void f();\n+static_assert( &f<^^int> != &f<^^alias_t> );\n+static_assert( &f<^^int> != &f<^^alias> );\n+static_assert( &f<^^alias_t> != &f<^^alias_t> );\ndiff --git a/gcc/testsuite/g++.dg/reflect/alias2.C b/gcc/testsuite/g++.dg/reflect/alias2.C\nnew file mode 100644\nindex 000000000000..c32a8724a9ba\n--- /dev/null\n+++ b/gcc/testsuite/g++.dg/reflect/alias2.C\n@@ -0,0 +1,17 @@\n+// PR c++/124544\n+// { dg-do compile { target c++26 } }\n+// { dg-additional-options \"-freflection\" }\n+\n+template struct A;\n+\n+template\n+struct A {\n+ static void f();\n+};\n+\n+template using alias_t = T;\n+\n+int main() {\n+ A<^^int, char>::f();\n+ A<^^alias_t, char>::f();\n+}\n","prefixes":[]}