Re: [PATCH] c++: unifying INTEGER_CST parm with type-dep arg [PR113644]

[Jason Merrill]

On 1/29/24 15:53, Patrick Palka wrote:

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
OK for trunk?

OK.

-- >8 --

Here when trying to unify P=42 A=T::value we ICE due to the latter's
empty type, which same_type_p dislikes.  If the argument has empty type
then it can't be an INTEGER_CST, so unification should fail.

        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 74013533b0f..0d8dbc68962 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -24953,7 +24953,8 @@ 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" }
+}