[Flang] Assignments for complex variables are slower than GFortran

[yus3710-fj]

The execution of the following codes is slower than GFortran.

• test.f90

subroutine dcsnnn003(lhs,rhs)
  complex :: rhs
  complex :: lhs
  lhs = rhs
end subroutine

• main.f90

implicit none

integer, parameter :: count = 40000
integer :: i,j,k
complex :: x,y
real :: start_t, end_t
interface
  subroutine dcsnnn003(lhs,rhs)
    complex :: rhs
    complex :: lhs
  end subroutine
end interface

call cpu_time(start_t)
do i=1,count
  do j=1,count
    call dcsnnn003(t1,t2)
  end do
end do
call cpu_time(end_t)

print *, end_t - start_t
end

• commands

$ flang -Ofast -mcpu=native test.f90 main.f90 && ./a.out # for A64FX/Grace
$ flang -Ofast -march=native test.f90 main.f90 && ./a.out # for Xeon

	Flang [s]	GFortran [s]
A64FX	15.507674	2.75310898
Grace	3.046927	0.975827038
Xeon	3.6818552	1.50089192