C++ PATCH for c++/81102, wrong error with partial specialization

C++ PATCH for c++/81102, wrong error with partial specialization

[Jason Merrill]

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Two issues here: one, we were failing to look through references when
comparing types, so we decided that a function type in a template
non-type argument didn't match a reference-to-function type in the
type of the non-type parameter.

With that fixed, I also needed to move the C++17 non-type auto
handling down past that type comparison.

Tested x86_64-pc-linux-gnu, applying to trunk and 7.

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commit ecd071290cad1fcfb33eee3889f94dd1e9374b24
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Jun 16 13:10:53 2017 -0400

            PR c++/81102 - Wrong error with partial specialization.
    
            * pt.c (unify) [TEMPLATE_PARM_INDEX]: Strip reference when comparing
            types.  Do type deduction later.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index b055507..8c6499f 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -20632,18 +20632,6 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
 	  return x;
 	}
 
-      if (cxx_dialect >= cxx1z
-	  /* We deduce from array bounds in try_array_deduction.  */
-	  && !(strict & UNIFY_ALLOW_INTEGER)
-	  && uses_template_parms (TREE_TYPE (parm))
-	  && !type_uses_auto (TREE_TYPE (parm)))
-	{
-	  tree atype = TREE_TYPE (arg);
-	  RECUR_AND_CHECK_FAILURE (tparms, targs,
-				   TREE_TYPE (parm), atype,
-				   UNIFY_ALLOW_NONE, explain_p);
-	}
-
       /* [temp.deduct.type] If, in the declaration of a function template
 	 with a non-type template-parameter, the non-type
 	 template-parameter is used in an expression in the function
@@ -20664,7 +20652,8 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
 	/* Template-parameter dependent expression.  Just accept it for now.
 	   It will later be processed in convert_template_argument.  */
 	;
-      else if (same_type_p (TREE_TYPE (arg), tparm))
+      else if (same_type_p (non_reference (TREE_TYPE (arg)),
+			    non_reference (tparm)))
 	/* OK */;
       else if ((strict & UNIFY_ALLOW_INTEGER)
 	       && CP_INTEGRAL_TYPE_P (tparm))
@@ -20673,9 +20662,22 @@ unify (tree tparms, tree targs, tree parm, tree arg, int strict,
 	   corresponding parameter.  */
 	arg = fold (build_nop (tparm, arg));
       else if (uses_template_parms (tparm))
-	/* We haven't deduced the type of this parameter yet.  Try again
-	   later.  */
-	return unify_success (explain_p);
+	{
+	  /* We haven't deduced the type of this parameter yet.  */
+	  if (cxx_dialect >= cxx1z
+	      /* We deduce from array bounds in try_array_deduction.  */
+	      && !(strict & UNIFY_ALLOW_INTEGER))
+	    {
+	      /* Deduce it from the non-type argument.  */
+	      tree atype = TREE_TYPE (arg);
+	      RECUR_AND_CHECK_FAILURE (tparms, targs,
+				       tparm, atype,
+				       UNIFY_ALLOW_NONE, explain_p);
+	    }
+	  else
+	    /* Try again later.  */
+	    return unify_success (explain_p);
+	}
       else
 	return unify_type_mismatch (explain_p, tparm, TREE_TYPE (arg));
 
diff --git a/gcc/testsuite/g++.dg/template/partial-specialization7.C b/gcc/testsuite/g++.dg/template/partial-specialization7.C
new file mode 100644
index 0000000..aa42191
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/partial-specialization7.C
@@ -0,0 +1,40 @@
+// PR c++/81102
+
+template <typename FuncSig, FuncSig f>
+struct HelperWrapper;
+
+// [...]
+
+template <typename Ret, Ret (&Func)()>
+struct HelperWrapper<Ret (&)(), Func>
+{
+    static inline int WrapFuncT(const int)
+    {
+        return 0; // Changed
+    }
+};
+
+// Unary
+template <typename Ret, typename Arg1, Ret (&Func)(Arg1)>
+struct HelperWrapper<Ret (&)(Arg1), Func>
+{
+    static inline int WrapFuncT(const int)
+    {
+        return 1; // Changed
+    }
+};
+
+// Binary
+template <typename Ret, typename Arg1, typename Arg2, Ret (&Func)(Arg1, Arg2)>
+struct HelperWrapper<Ret (&)(Arg1, Arg2), Func>
+{
+    static inline int WrapFuncT(const int)
+    {
+        return 2; // Changed
+    }
+};
+
+int main()
+{
+  return 0;
+}
diff --git a/gcc/testsuite/g++.dg/template/partial5.C b/gcc/testsuite/g++.dg/template/partial5.C
index 1b56fb3..ee45a93 100644
--- a/gcc/testsuite/g++.dg/template/partial5.C
+++ b/gcc/testsuite/g++.dg/template/partial5.C
@@ -14,7 +14,7 @@ template<typename T, typename T::foo V>
 struct Y { };
 
 template<typename T, typename U, U v>
-struct Y<T, v> { }; // { dg-error "" }
+struct Y<T, v> { }; // { dg-error "" "" { target { ! c++1z } } }
 
 
 template<typename T, T V>