We are ICEing in the testcase below because we pass the
yet-uninstantiated class type A<int> of the PARM_DECL b to
is_really_empty_class from is_rvalue_constant_expression when parsing
the requirement t += b.
This patch fixes the ICE by guarding the problematic call to
is_really_empty_class with a COMPLETE_TYPE_P check, which should also
subsume the existing dependent_type_p check.
gcc/cp/ChangeLog:
PR c++/95497
* constexpr.c (potential_constant_expression_1) <case PARM_DECL>:
When processing_template_decl, check COMPLETE_TYPE_P before
calling is_really_empty_class. Don't check dependent_type_p.
gcc/testsuite/ChangeLog:
PR c++/95497
* g++.dg/cpp2a/concepts-pr95497.C: New test.
if (now && want_rval)
{
tree type = TREE_TYPE (t);
- if (dependent_type_p (type)
+ if ((processing_template_decl && !COMPLETE_TYPE_P (type))
|| is_really_empty_class (type, /*ignore_vptr*/false))
/* An empty class has no data to read. */
return true;
--- /dev/null
+// PR c++/95497
+// { dg-do compile { target c++20 } }
+
+template <typename T>
+struct A{};
+
+template <typename T>
+concept c =
+ requires(T t, A<int> b) // note that A<int> is independent of T
+ {
+ { t += b };
+ };