3 files changed, 30 insertions, 5 deletions
diff --git a/gcc/cp/cxx-pretty-print.cc b/gcc/cp/cxx-pretty-print.cc
index 950295e..4b547c7 100644
--- a/gcc/cp/cxx-pretty-print.cc
+++ b/gcc/cp/cxx-pretty-print.cc
@@ -844,7 +844,12 @@ cxx_pretty_printer::unary_expression (tree t)
       /* Fall through  */
 
     case ALIGNOF_EXPR:
-      pp_cxx_ws_string (this, code == SIZEOF_EXPR ? "sizeof" : "__alignof__");
+      if (code == SIZEOF_EXPR)
+	pp_cxx_ws_string (this, "sizeof");
+      else if (ALIGNOF_EXPR_STD_P (t))
+	pp_cxx_ws_string (this, "alignof");
+      else
+	pp_cxx_ws_string (this, "__alignof__");
       pp_cxx_whitespace (this);
       if (TREE_CODE (t) == SIZEOF_EXPR && SIZEOF_EXPR_TYPE_P (t))
 	{
diff --git a/gcc/cp/error.cc b/gcc/cp/error.cc
index 1cfa4f1..9b967ce 100644
--- a/gcc/cp/error.cc
+++ b/gcc/cp/error.cc
@@ -2840,11 +2840,10 @@ dump_expr (cxx_pretty_printer *pp, tree t, int flags)
     case ALIGNOF_EXPR:
       if (TREE_CODE (t) == SIZEOF_EXPR)
 	pp_cxx_ws_string (pp, "sizeof");
+      else if (ALIGNOF_EXPR_STD_P (t))
+	pp_cxx_ws_string (pp, "alignof");
       else
-	{
-	  gcc_assert (TREE_CODE (t) == ALIGNOF_EXPR);
-	  pp_cxx_ws_string (pp, "__alignof__");
-	}
+	pp_cxx_ws_string (pp, "__alignof__");
       op = TREE_OPERAND (t, 0);
       if (PACK_EXPANSION_P (op))
 	{
diff --git a/gcc/testsuite/g++.dg/diagnostic/alignof4.C b/gcc/testsuite/g++.dg/diagnostic/alignof4.C
new file mode 100644
index 0000000..f6fc5c3
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/alignof4.C
@@ -0,0 +1,21 @@
+// PR c++/85979
+// { dg-do compile { target c++11 } }
+
+template<int N> struct A { };
+
+template<class T>
+void f(A<alignof(T)>) { }
+
+#if __cpp_concepts
+template<class T>
+void g() requires (alignof(T) == 0);
+#endif
+
+int main() {
+  f<int>(); // { dg-error "no match" }
+#if __cpp_concepts
+  g<int>(); // { dg-error "no match" "" { target c++20 } }
+#endif
+}
+
+// { dg-bogus "__alignof__" "" { target *-*-* } 0 }