Refuses to thread OpenMP loop

Hi,

I have two OpenMP loops that ifort (Version 16.0.1.150 Build 20151021) refuses to parallelize.  I've added "-qopenmp -opt-report-file=stdout -opt-report-phase:openmp " to my compile/link commands and see this in the output:

Begin optimization report for: MODULE_VARSOLVER_QG::VAR_SOLVER

    Report from: OpenMP optimizations [openmp]

Optimization 'PRE' reduced: function size or variable count limit exceeded: use -override_limits / -Qoverride_limits to override
===========================================================================

 

I am not sure what that is telling me.  Is it saying that the function/subroutine calls inside the loop are too big for the compiler to generate threaded code?  If I add the " -override_limits" option, which does not appear to be documented in the man page or anywhere online, the error goes away, but I also do not get an OpenMP optimization report for those loops.  I have previously never encountered any limits to the "stuff" one can put inside a threaded region before that would cause this, and have seen functioning OpenMP loops with huge amounts of stuff in them.

I have included one of the the loops for reference even though it's probably too complicated because I haven't yet reduced it to a small "reproducer".

!$OMP PARALLEL DO SHARED (bkg_len,bht_ino,bkg_cov,brh_cov,bkg_vec,anl_vec,tlm_vec,new_vec,tim_len,alph,mthd,B,Q,bkg_config) DEFAULT(PRIVATE)
       do t=tim_len,1,-1
          tim_bkc(:,:)=bkg_cov(t,:,:)
          tim_hrh(:,:)=brh_cov(t,:,:)
          tim_htr(:)=bht_ino(t,:,1)
          tim_bkv(:)=bkg_vec(t,:)
          if(t.eq.tim_len) then
             mdl_vec(:)=tlm_vec(t,:)
             if(mthd > 3) mdl_vec(:)=0.5*(tlm_vec(t,:)+anl_vec(t,:))
          else
             if (mthd.eq.3) mdl_vec(:)=tlm_vec(t+1,:)
             if (mthd > 3) mdl_vec(:)=anl_vec(t+1,:)
             model = qg_model_type(bkg_config, state_vector=mdl_vec(:), step=t)
             call model%adv_nsteps(1)
             model_ADJ = qg_adj_type(bkg_config, state_vector=model%get_state_vector(), trajectory_vector=model%get_state_vector() - mdl_vec(:), step = t + 1)
             call model_ADJ%adv_nsteps(4)
             mdl_vec(:) = model_ADJ%get_state_vector()
          end if
          if(mthd < 4) ges_vec(:)=mdl_vec(:)
          if(mthd > 3) ges_vec(:)=0.5*(tlm_vec(t,:)+mdl_vec(:))
          tmp_vec(:)=(ges_vec(:)-tim_bkv(:))*(B+Q)
          dif_vec(:)=(ges_vec(:)-tim_bkv(:))*(B+Q)

          call pre_con_dif(tim_bkc,tmp_vec)
          pre_dif(:)=tmp_vec(:)

          call dgemv("N", bkg_len, bkg_len, 1.d0, tim_hrh, bkg_len, dif_vec, 1, 0.d0, tmp_vec, 1)

          tmp_vec(:)=pre_dif(:)+tmp_vec(:)-tim_htr(:)

          call dgemv("N", bkg_len, bkg_len, 1.d0, tim_bkc, bkg_len, tmp_vec, 1, 0.d0, grd_jvc, 1)
          new_vec(t,:)=ges_vec(:)-grd_jvc(:)*alph

          if(mthd < 4) tlm_vec(t,:)=new_vec(t,:)
       end do
!$OMP END PARALLEL DO