[gcc r14-8630] c++: unifying integer parm with type-dep arg [PR113644]

[Patrick Palka]

https://gcc.gnu.org/g:af37bef86199e50368cbfbc97befe0622a07f12f

commit r14-8630-gaf37bef86199e50368cbfbc97befe0622a07f12f
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Jan 30 10:13:41 2024 -0500

    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.

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

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index fb2448a26e96..5871cb668d0c 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 000000000000..926a7726547d
--- /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" }
+}