[PATCH] PR c++/80990 use cv-qualifiers in class template argument deduction

[Jonathan Wakely]

This fixes class template argument deduction so that cv-qualifiers are
not ignored.

Bootstrapped and tested powerpc64le-linux. OK for trunk?

        PR c++/80990
        * pt.c (do_class_deduction): Build qualified type.


commit 1a81d74fa9cf32cb33580cc4a5e9a7c5868ce32b
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Jun 6 18:38:30 2017 +0100

    PR c++/80990 use cv-qualifiers in class template argument deduction
    
    gcc/cp:
    
    	PR c++/80990
    	* pt.c (do_class_deduction): Build qualified type.
    
    gcc/testsuite:
    
    	PR c++/80990
    	* g++.dg/cpp1z/class-deduction39.C: New.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index a04f2e0..ada94bd 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -25367,7 +25367,7 @@ do_class_deduction (tree ptype, tree tmpl, tree init, int flags,
   --cp_unevaluated_operand;
   release_tree_vector (args);
 
-  return TREE_TYPE (t);
+  return cp_build_qualified_type (TREE_TYPE (t), cp_type_quals (ptype));
 }
 
 /* Replace occurrences of 'auto' in TYPE with the appropriate type deduced
diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction39.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction39.C
new file mode 100644
index 0000000..98a3664
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction39.C
@@ -0,0 +1,15 @@
+// { dg-options -std=c++1z }
+
+template <class T> struct A { };
+
+A<int> a;
+const A c = a;
+volatile A v = a;
+const volatile A cv = a;
+
+template <class,class> struct same;
+template <class T> struct same<T,T> {};
+
+same<decltype(c), const A<int>> s1;
+same<decltype(v), volatile A<int>> s2;
+same<decltype(cv), const volatile A<int>> s3;