Index: flang/runtime/coarray.h
===================================================================
--- /dev/null
+++ flang/runtime/coarray.h
@@ -0,0 +1,27 @@
+//===-- runtime/coarray.h ---------------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef FORTRAN_RUNTIME_COARRAY_H_
+#define FORTRAN_RUNTIME_COARRAY_H_
+
+// Defines API between compiled code and the coarray
+// support functions in the runtime library.
+
+#include "entry-names.h"
+
+namespace Fortran::runtime {
+
+extern "C" {
+// 16.9.145 NUM_IMAGES
+int RTNAME(NumImages)(int team_number = 0,
+    const char *sourceFile = nullptr, int sourceLine = 0);
+
+}
+} // namespace Fortran::runtime
+
+#endif // FORTRAN_RUNTIME_COARRAY_H_