From d69f32911ef5f1ecdb587c4c3f30488b09c0d26c Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 13 Dec 2019 00:10:02 -0500
Subject: [PATCH] PR c++/92446 - deduction of class NTTP.

Another place we need to look through the VIEW_CONVERT_EXPR we add to make a
use of a class NTTP have const type.

	* pt.c (deducible_expression): Look through VIEW_CONVERT_EXPR.

From-SVN: r279333
---
 gcc/cp/ChangeLog                             |  5 +++++
 gcc/cp/pt.c                                  |  2 +-
 gcc/testsuite/g++.dg/cpp2a/nontype-class26.C | 13 +++++++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/nontype-class26.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 19d70a329788..bda8304df575 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,8 @@
+2019-12-11  Jason Merrill  <jason@redhat.com>
+
+	PR c++/92446 - deduction of class NTTP.
+	* pt.c (deducible_expression): Look through VIEW_CONVERT_EXPR.
+
 2019-11-06  Jason Merrill  <jason@redhat.com>
 
 	PR c++/92150 - partial specialization with class NTTP.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index aa78ac980b3c..0ebac069984c 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -20575,7 +20575,7 @@ static bool
 deducible_expression (tree expr)
 {
   /* Strip implicit conversions.  */
-  while (CONVERT_EXPR_P (expr))
+  while (CONVERT_EXPR_P (expr) || TREE_CODE (expr) == VIEW_CONVERT_EXPR)
     expr = TREE_OPERAND (expr, 0);
   return (TREE_CODE (expr) == TEMPLATE_PARM_INDEX);
 }
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class26.C b/gcc/testsuite/g++.dg/cpp2a/nontype-class26.C
new file mode 100644
index 000000000000..315e0ac23098
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class26.C
@@ -0,0 +1,13 @@
+// { dg-do compile { target c++2a } }
+
+struct p { unsigned p_ {}; };
+
+template <p i> struct pp {};
+struct qq : public pp <p {}> {};
+
+template <p i> int f (pp <i> const &);
+
+int main ()
+{
+  return f (qq {});
+}
-- 
2.47.2