SIMD instructions with condition copy - fortran

Question

I have a hotspot which looks like this. Some kind of vector gather here would be nice... Any suggestion on how to get the compiler to like this?
do ii = 1, N
if (diff(ii) .le. M ) then
i = i0 + ii - 1
rbuf( irb ) = i
irb = irb + 1
end if
end do
Using ifort 16.0.2 my opt report looks like
LOOP BEGIN at code.f(197,13)
remark #25084: Preprocess Loopnests: Moving Out Store [ code.f(203,13) ]
remark #15344: loop was not vectorized: vector dependence prevents vectorization
remark #15346: vector dependence: assumed FLOW dependence between irb line 201 and irb line 200
remark #15346: vector dependence: assumed ANTI dependence between irb line 200 and irb line 201
remark #15346: vector dependence: assumed ANTI dependence between irb line 200 and irb line 201
remark #15346: vector dependence: assumed FLOW dependence between irb line 201 and irb line 200
remark #25439: unrolled with remainder by 2
remark #25015: Estimate of max trip count of loop=1600
LOOP END
Here is small test program
program vect
integer :: ii, i0, irb
integer, parameter :: N=32
integer, parameter :: M=8
integer, dimension(N) :: diff
integer, dimension(2*N) :: rbuf
rbuf = 0
!only some values of diff will meet condition
!could be random
do ii=1, N
diff(ii) = ii
end do
!from an outer loop
i0=1003
!this is code for filling up a buffer for an expensive vectorized
!subroutine with full vectors, irb < 2*N
irb=3
do ii = 1, N
if (diff(ii) .le. M ) then
i = i0 + ii - 1
rbuf( irb ) = i
irb = irb + 1
end if
end do
!check
do ii = 1, 2*N
write(*,*) ii, rbuf(ii)
end do
end

Answer 1

Depending on the target architecture I was able to get the compiler to vectorize with a directive.
!CDIR$ IVDEP
do ii = 1, N
if (diff(ii) .le. M ) then
i = i0 + ii - 1
rbuf( irb ) = i
irb = irb + 1
end if
end do
and -xMIC-AVX512 or -mmic will give vector instructions for those architectures. e.g.
vpcompressd %zmm0, -4+vect_$RBUF.0.1(,%rax,4){%k1} #29.15 c1
For AVX2, I think one has resort to intrinsics/ asm as #Peter Cordes suggests in his comment, but it is good to know that compiler can figure this out going forward.