Index: flang/test/Semantics/co_reduce.f90
===================================================================
--- /dev/null
+++ flang/test/Semantics/co_reduce.f90
@@ -0,0 +1,76 @@
+! RUN: %S/test_errors.sh %s %t %flang_fc1
+! REQUIRES: shell
+! Check for semantic errors in co_reduce() function calls
+
+module test_co_reduce
+  implicit none
+
+contains
+
+  subroutine test
+
+    type foo_t
+    end type
+  
+    type(foo_t) foo
+    integer i, status
+    real vector(1)
+    real array(1,1,1, 1,1,1, 1,1,1, 1,1,1, 1,1,1)
+    character(len=1) string, message
+  
+    ! correct calls, should produce no errors
+    call co_reduce(i,      int_op)
+    call co_reduce(i,      int_op,                           status)
+    call co_reduce(i,      int_op,                           stat=status)
+    call co_reduce(i,      int_op,                                        errmsg=message)
+    call co_reduce(i,      int_op,                           stat=status, errmsg=message)
+    call co_reduce(i,      int_op,           result_image=1, stat=status, errmsg=message)
+    call co_reduce(i,      operation=int_op,  result_image=1, stat=status, errmsg=message)
+    call co_reduce(a=i,    operation=int_op,  result_image=1, stat=status, errmsg=message)
+
+    call co_reduce(array,  operation=real_op, result_image=1, stat=status, errmsg=message)
+    call co_reduce(vector, operation=real_op, result_image=1, stat=status, errmsg=message)
+    call co_reduce(string, operation=char_op, result_image=1, stat=status, errmsg=message)
+    call co_reduce(foo,    operation=left,    result_image=1, stat=status, errmsg=message)
+  
+    ! the error is seen as an incorrect type for the stat= argument
+    !ERROR: Actual argument for ‘stat=’ has bad type ‘CHARACTER(KIND=1,LEN=1_8)’
+    call co_reduce(i, int_op)
+
+    ! the error is seen as too many arguments to the co_reduce() call
+    !ERROR: too many actual arguments for collective subroutines 'co_reduce'
+    call co_reduce(i, int_op, result_image=1, stat=status, errmsg=message, 3.4)
+  
+    ! keyword argument with incorrect type
+    !ERROR: unknown keyword argument to intrinsic 'co_reduce'
+    call co_reduce(fake=3.4)
+  
+  contains
+
+    pure function left(lhs, rhs) result(lhs_op_rhs)
+      type(foo_t), intent(in)  :: lhs, rhs
+      type(foo_t) :: lhs_op_rhs
+      lhs_op_rhs = lhs
+    end function
+
+    pure function char_op(lhs, rhs) result(lhs_op_rhs)
+      character(len=1), intent(in)  :: lhs, rhs
+      character(len=1) :: lhs_op_rhs
+      lhs_op_rhs = min(lhs, rhs)
+    end function
+
+    pure function real_op(lhs, rhs) result(lhs_op_rhs)
+      real, intent(in) :: lhs, rhs
+      real :: lhs_op_rhs
+      lhs_op_rhs = lhs + rhs 
+    end function
+
+    pure function int_op(lhs, rhs) result(lhs_op_rhs)
+      integer, intent(in) :: lhs, rhs
+      integer :: lhs_op_rhs
+      lhs_op_rhs = lhs + rhs 
+    end function
+
+  end subroutine
+
+end module test_co_reduce