c++: ICE in is_really_empty_class [PR95497]

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.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 1939166e90792219a2564ddb26913de06a9388d8..ff78ebda2dc9fb83e9ff36d62aa8621d3aa32c67 100644 (file)
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -7443,7 +7443,7 @@ potential_constant_expression_1 (tree t, bool want_rval, bool strict, bool now,
       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;

diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C b/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
new file mode 100644 (file)
index 0000000..4d7718a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-pr95497.C
@@ -0,0 +1,12 @@
+// 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 };
+    };