c++: Fix up handling of name independent decls in coroutine lowering [PR125376]

For variables which do have non-NULL DECL_NAME, register_local_var_uses
uses either that name or name_depth_idx (that itself is a bug as it
can clash with user variables named that way) for the fields.  In C++26
we can have multiple _ variables in the same scope, so the following
testcase is miscompiled by using the same FIELD_DECL multiple times
(once for the first _ variable, once for the second one).

The following patch fixes it by pretending such variables don't have
a name, so it uses a serial number then instead.

2026-05-21  Jakub Jelinek  <jakub@redhat.com>

	PR c++/125376
	* coroutines.cc (register_local_var_uses): Ignore DECL_NAME for
	name independent decls.

	* g++.dg/coroutines/pr125376.C: New test.

diff --git a/gcc/cp/coroutines.cc b/gcc/cp/coroutines.cc
index 6bc58a4f2e68e1afd5a1c72e588853ad9e6c2860..de0de7a83e049d510e69fc56d48b50f0d21a4350 100644 (file)
--- a/gcc/cp/coroutines.cc
+++ b/gcc/cp/coroutines.cc
@@ -4403,6 +4403,8 @@ register_local_var_uses (tree *stmt, int *do_subtree, void *d)
         identify them in the coroutine frame.  */
       tree lvname = DECL_NAME (lvar);
       char *buf = NULL;
+      if (name_independent_decl_p (lvar))
+       lvname = NULL_TREE;
 
       /* The outermost bind scope contains the artificial variables that
         we inject to implement the coro state machine.  We want to be able

diff --git a/gcc/testsuite/g++.dg/coroutines/pr125376.C b/gcc/testsuite/g++.dg/coroutines/pr125376.C
new file mode 100644 (file)
index 0000000..432bf04
--- /dev/null
+++ b/gcc/testsuite/g++.dg/coroutines/pr125376.C
@@ -0,0 +1,40 @@
+// PR c++/125376
+// { dg-do run { target c++26 } }
+
+#include <coroutine>
+
+struct task {
+  struct promise_type {
+    task get_return_object () noexcept { return {}; }
+    std::suspend_never initial_suspend () noexcept { return {}; }
+    std::suspend_never final_suspend ()   noexcept { return {}; }
+    void return_void () noexcept {}
+    void unhandled_exception () {}
+  };
+};
+
+struct A {
+  unsigned value = 42;
+  A () {}
+  ~A () { if (value != 42) __builtin_abort (); }
+};
+
+struct B {
+  unsigned value = 43;
+  B () {}
+  ~B () { if (value != 43) __builtin_abort (); }
+};
+
+task
+foo ()
+{
+  auto _ = A {};
+  auto _ = B {};
+  co_return;
+}
+
+int
+main ()
+{
+  foo ();
+}