From af37bef86199e50368cbfbc97befe0622a07f12f Mon Sep 17 00:00:00 2001
From: Patrick Palka <ppalka@redhat.com>
Date: Tue, 30 Jan 2024 10:13:41 -0500
Subject: [PATCH] c++: unifying integer parm with type-dep arg [PR113644]

Here when trying to unify P=42 A=T::value we ICE due to the latter's
empty type, which same_type_p dislikes.

	PR c++/113644

gcc/cp/ChangeLog:

	* pt.cc (unify) <case INTEGER_CST>: Handle NULL_TREE type.

gcc/testsuite/ChangeLog:

	* g++.dg/template/nontype30.C: New test.
---
 gcc/cp/pt.cc                              |  3 ++-
 gcc/testsuite/g++.dg/template/nontype30.C | 13 +++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/template/nontype30.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index fb2448a26e9..5871cb668d0 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24949,7 +24949,8 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
       /* Type INTEGER_CST can come from ordinary constant template args.  */
     case INTEGER_CST:
     case REAL_CST:
-      if (!same_type_p (TREE_TYPE (parm), TREE_TYPE (arg)))
+      if (TREE_TYPE (arg) == NULL_TREE
+	  || !same_type_p (TREE_TYPE (parm), TREE_TYPE (arg)))
 	return unify_template_argument_mismatch (explain_p, parm, arg);
       while (CONVERT_EXPR_P (arg))
 	arg = TREE_OPERAND (arg, 0);
diff --git a/gcc/testsuite/g++.dg/template/nontype30.C b/gcc/testsuite/g++.dg/template/nontype30.C
new file mode 100644
index 00000000000..926a7726547
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/nontype30.C
@@ -0,0 +1,13 @@
+// PR c++/113644
+
+template<int> struct A { };
+
+template<class T> void f(A<42>);
+template<class T> void f(A<T::value>);
+
+struct B { static const int value = 42; };
+
+int main() {
+  A<42> a;
+  f<B>(a); // { dg-error "ambiguous" }
+}
-- 
2.11.4.GIT