NVHPC newer than 23.11 appears to have an issue with cycle vs exit for named loops in GPU regions, causing a hang. It also was defaulting the z bounds to int max, forcing the periodic collision check loop to cycle for over 30 min.

Author: danieljvickers

src/simulation/m_collisions.fpp

@@ -350,8 +350,8 @@ contains
         do pid1 = 1, num_ibs - 1
             centroid_1 = [patch_ib(pid1)%x_centroid, patch_ib(pid1)%y_centroid, 0._wp]
             if (num_dims == 3) centroid_1(3) = patch_ib(pid1)%z_centroid
-            collision_partner_loop: do pid2 = pid1 + 1, num_ibs
-                do xp = xp_lower, xp_upper
+            do pid2 = pid1 + 1, num_ibs
+                periodic_search: do xp = xp_lower, xp_upper
                     do yp = yp_lower, yp_upper
                         do zp = zp_lower, zp_upper
                             centroid_2(1) = patch_ib(pid2)%x_centroid + real(xp, wp)*(x_domain%end - x_domain%beg)
@@ -372,12 +372,12 @@ contains
                                 collision_lookup(current_collisions, 2) = pid2
                                 collision_lookup(current_collisions, 3) = patch_ib(pid1)%gbl_patch_id
                                 collision_lookup(current_collisions, 4) = encoded_pid2
-                                cycle collision_partner_loop
+                                exit periodic_search
                             end if
                         end do
                     end do
-                end do
-            end do collision_partner_loop
+                end do periodic_search
+            end do
         end do
         $:END_GPU_PARALLEL_LOOP()
 

src/simulation/m_ib_patches.fpp

@@ -679,14 +679,17 @@ contains
         #:endfor
 
         ! z only if 3D
-        if (present(zp_lower) .and. p /= 0) then
+        if (present(zp_lower) .and. num_dims == 3) then
             if (ib_bc_z%beg == BC_PERIODIC) then
                 zp_lower = -1
                 zp_upper = 1
             else
                 zp_lower = 0
                 zp_upper = 0
             end if
+        else if (present(zp_lower)) then
+            zp_lower = 0
+            zp_upper = 0
         end if
 
     end subroutine s_get_periodicities