From: Jason Merrill <jason@redhat.com>
Date: Mon, 5 Aug 2024 15:21:05 +0000 (-0400)
Subject: c++: alias and non-type template parm [PR116223]
X-Git-Tag: basepoints/gcc-16~6793
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4add6cd341a779e980e41ed6fb49175fca37496e;p=thirdparty%2Fgcc.git

c++: alias and non-type template parm [PR116223]

My r14-8291 for PR112632 introduced IMPLICIT_CONV_EXPR_FORCED to express
conversions to the type of an alias template parameter.  In this example,
that broke deduction of X in the call to foo, so let's teach deduction to
look through it.

	PR c++/116223
	PR c++/112632

gcc/cp/ChangeLog:

	* pt.cc (deducible_expression): Also look through
	IMPLICIT_CONV_EXPR_FORCED.
	(unify): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1z/nontype-auto25.C: New test.
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 35a9c5619f9..cf65b347f6c 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -23031,6 +23031,8 @@ deducible_expression (tree expr)
   /* Strip implicit conversions and implicit INDIRECT_REFs.  */
   while (CONVERT_EXPR_P (expr)
 	 || TREE_CODE (expr) == VIEW_CONVERT_EXPR
+	 || (TREE_CODE (expr) == IMPLICIT_CONV_EXPR
+	     && IMPLICIT_CONV_EXPR_FORCED (expr))
 	 || REFERENCE_REF_P (expr))
     expr = TREE_OPERAND (expr, 0);
   return (TREE_CODE (expr) == TEMPLATE_PARM_INDEX);
@@ -24560,7 +24562,9 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
      signedness is the only information lost, and I think that will be
      okay.  VIEW_CONVERT_EXPR can appear with class NTTP, thanks to
      finish_id_expression_1, and are also OK.  */
-  while (CONVERT_EXPR_P (parm) || TREE_CODE (parm) == VIEW_CONVERT_EXPR)
+  while (CONVERT_EXPR_P (parm) || TREE_CODE (parm) == VIEW_CONVERT_EXPR
+	 || (TREE_CODE (parm) == IMPLICIT_CONV_EXPR
+	     && IMPLICIT_CONV_EXPR_FORCED (parm)))
     parm = TREE_OPERAND (parm, 0);
 
   if (arg == error_mark_node)
diff --git a/gcc/testsuite/g++.dg/cpp1z/nontype-auto25.C b/gcc/testsuite/g++.dg/cpp1z/nontype-auto25.C
new file mode 100644
index 00000000000..36b38b48ec2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/nontype-auto25.C
@@ -0,0 +1,18 @@
+// PR c++/116223
+// { dg-do compile { target c++17 } }
+
+template <int T> struct A { int value = T; };
+
+template <unsigned char X> using B = A<X>;
+
+template <auto X>
+void foo(B<X>& mat) noexcept
+{
+  //    std::cout << mat.value << "\n";
+}
+
+int main()
+{
+    A<2> mat;
+    foo(mat);
+}