[Packer] Reorganized Iterative Packer Algorithm

The packer iteratively restarts itself with different options if the
packer fails to find a dense enough clustering. The way this was written
was very hard to follow and was error prone.

Rewrote the iterative packer code to be more like a state-machine. This
makes it easier to add new states in the future and maintain the current
states.

Author: AlexandreSinger

vpr/src/pack/pack.cpp

@@ -145,7 +145,40 @@ bool try_pack(const t_packer_opts& packer_opts,
 
     g_vpr_ctx.mutable_atom().mutable_lookup().set_atom_pb_bimap_lock(true);
 
-    while (true) {
+    /**
+     * @brief Enumeration for the state of the packer.
+     *
+     * If the packer fails to find a dense enough packing, depending on how the
+     * packer failed, the packer may iteratively retry packing with different
+     * setting to try and find a denser packing. These states represent a
+     * different type of iteration.
+     */
+    enum class e_packer_state {
+        /// @brief Default packer state.
+        DEFAULT,
+        /// @brief Succcess state for the packer.
+        SUCCESS,
+        /// @brief Standard fallback where there is not region constraints. Turns
+        ///        on unrelated clustering and balanced packing if it can.
+        UNRELATED_AND_BALANCED,
+        /// @brief Region constraints: Turns on attraction groups for overfilled regions.
+        ATTRACTION_GROUPS,
+        /// @brief Region constraints: Turns on more attraction groups for overfilled regions.
+        MORE_ATTRACTION_GROUPS,
+        /// @brief Region constraints: Turns on more attraction groups for all regions.
+        ATTRACTION_GROUPS_ALL_REGIONS,
+        /// @brief Region constraints: Turns on more attraction groups for all regions
+        ///        and increases the target density of clb blocks.
+        ATTRACTION_GROUPS_ALL_REGIONS_AND_INCREASED_TARGET_DENSITY,
+        /// @brief The failure state.
+        FAILURE
+    };
+
+    // The current state of the packer during iterative packing.
+    e_packer_state current_packer_state = e_packer_state::DEFAULT;
+
+    while (current_packer_state != e_packer_state::SUCCESS &&
+           current_packer_state != e_packer_state::FAILURE) {
         //Cluster the netlist
         //  num_used_type_instances: A map used to save the number of used
         //                           instances from each logical block type.
@@ -170,48 +203,98 @@ bool try_pack(const t_packer_opts& packer_opts,
 
         bool floorplan_not_fitting = (floorplan_regions_overfull || g_vpr_ctx.floorplanning().constraints.get_num_partitions() > 0);
 
+        // Next packer state logic
+        e_packer_state next_packer_state = e_packer_state::FAILURE;
         if (fits_on_device && !floorplan_regions_overfull) {
-            break; //Done
-        } else if (pack_iteration == 1 && !floorplan_not_fitting) {
-            //1st pack attempt was unsuccessful (i.e. not dense enough) and we have control of unrelated clustering
-            //
-            //Turn it on to increase packing density
-            if (packer_opts.allow_unrelated_clustering == e_unrelated_clustering::AUTO) {
-                VTR_ASSERT(allow_unrelated_clustering == false);
-                allow_unrelated_clustering = true;
+            // If everything fits on the device and the floorplan regions are
+            // not overfilled, the next state is success.
+            next_packer_state = e_packer_state::SUCCESS;
+        } else {
+            if (floorplan_not_fitting) {
+                // If there are overfilled region constraints.
+                /*
+                 * When running with tight floorplan constraints, some regions may become overfull with clusters (i.e.
+                 * the number of blocks assigned to the region exceeds the number of blocks available). When this occurs, we
+                 * cluster more densely to be able to adhere to the floorplan constraints. However, we do not want to cluster more
+                 * densely unnecessarily, as this can negatively impact wirelength. So, we have iterative approach. We check at the end
+                 * of every iteration if any floorplan regions are overfull. In the first iteration, we run
+                 * with no attraction groups (not packing more densely). If regions are overfull at the end of the first iteration,
+                 * we create attraction groups for partitions with overfull regions (pack those atoms more densely). We continue this way
+                 * until the last iteration, when we create attraction groups for every partition, if needed.
+                 */
+                switch (current_packer_state) {
+                    case e_packer_state::DEFAULT:
+                        next_packer_state = e_packer_state::ATTRACTION_GROUPS;
+                        break;
+                    case e_packer_state::UNRELATED_AND_BALANCED:
+                    case e_packer_state::ATTRACTION_GROUPS:
+                        next_packer_state = e_packer_state::MORE_ATTRACTION_GROUPS;
+                        break;
+                    case e_packer_state::MORE_ATTRACTION_GROUPS:
+                        next_packer_state = e_packer_state::ATTRACTION_GROUPS_ALL_REGIONS;
+                        break;
+                    case e_packer_state::ATTRACTION_GROUPS_ALL_REGIONS:
+                        next_packer_state = e_packer_state::ATTRACTION_GROUPS_ALL_REGIONS_AND_INCREASED_TARGET_DENSITY;
+                        break;
+                    case e_packer_state::ATTRACTION_GROUPS_ALL_REGIONS_AND_INCREASED_TARGET_DENSITY:
+                    default:
+                        next_packer_state = e_packer_state::FAILURE;
+                        break;
+                }
+            } else {
+                // If there are no overfilled region constraints.
+                switch (current_packer_state) {
+                    case e_packer_state::DEFAULT:
+                        next_packer_state = e_packer_state::UNRELATED_AND_BALANCED;
+                        break;
+                    default:
+                        next_packer_state = e_packer_state::FAILURE;
+                        break;
+                }
             }
-            if (packer_opts.balance_block_type_utilization == e_balance_block_type_util::AUTO) {
-                VTR_ASSERT(balance_block_type_util == false);
-                balance_block_type_util = true;
+        }
+
+        // Set up for the next packer state.
+        switch (next_packer_state) {
+            case e_packer_state::UNRELATED_AND_BALANCED: {
+                //1st pack attempt was unsuccessful (i.e. not dense enough) and we have control of unrelated clustering
+                //
+                //Turn it on to increase packing density
+                // TODO: This will have no affect if unrelated clustering and
+                //       balance block type utilization is not auto. Should update
+                //       the next state logic.
+                if (packer_opts.allow_unrelated_clustering == e_unrelated_clustering::AUTO) {
+                    VTR_ASSERT(allow_unrelated_clustering == false);
+                    allow_unrelated_clustering = true;
+                }
+                if (packer_opts.balance_block_type_utilization == e_balance_block_type_util::AUTO) {
+                    VTR_ASSERT(balance_block_type_util == false);
+                    balance_block_type_util = true;
+                }
+                VTR_LOG("Packing failed to fit on device. Re-packing with: unrelated_logic_clustering=%s balance_block_type_util=%s\n",
+                        (allow_unrelated_clustering ? "true" : "false"),
+                        (balance_block_type_util ? "true" : "false"));
+                break;
             }
-            VTR_LOG("Packing failed to fit on device. Re-packing with: unrelated_logic_clustering=%s balance_block_type_util=%s\n",
-                    (allow_unrelated_clustering ? "true" : "false"),
-                    (balance_block_type_util ? "true" : "false"));
-            /*
-             * When running with tight floorplan constraints, some regions may become overfull with clusters (i.e.
-             * the number of blocks assigned to the region exceeds the number of blocks available). When this occurs, we
-             * cluster more densely to be able to adhere to the floorplan constraints. However, we do not want to cluster more
-             * densely unnecessarily, as this can negatively impact wirelength. So, we have iterative approach. We check at the end
-             * of every iteration if any floorplan regions are overfull. In the first iteration, we run
-             * with no attraction groups (not packing more densely). If regions are overfull at the end of the first iteration,
-             * we create attraction groups for partitions with overfull regions (pack those atoms more densely). We continue this way
-             * until the last iteration, when we create attraction groups for every partition, if needed.
-             */
-        } else if (pack_iteration == 1 && floorplan_not_fitting) {
-            VTR_LOG("Floorplan regions are overfull: trying to pack again using cluster attraction groups. \n");
-            attraction_groups.create_att_groups_for_overfull_regions(overfull_partition_regions);
-            attraction_groups.set_att_group_pulls(1);
-
-        } else if (pack_iteration >= 2 && pack_iteration < 5 && floorplan_not_fitting) {
-            if (pack_iteration == 2) {
+            case e_packer_state::ATTRACTION_GROUPS: {
+                VTR_LOG("Floorplan regions are overfull: trying to pack again using cluster attraction groups. \n");
+                attraction_groups.create_att_groups_for_overfull_regions(overfull_partition_regions);
+                attraction_groups.set_att_group_pulls(1);
+                break;
+            }
+            case e_packer_state::MORE_ATTRACTION_GROUPS: {
                 VTR_LOG("Floorplan regions are overfull: trying to pack again with more attraction groups exploration. \n");
                 attraction_groups.create_att_groups_for_overfull_regions(overfull_partition_regions);
                 VTR_LOG("Pack iteration is %d\n", pack_iteration);
-            } else if (pack_iteration == 3) {
+                break;
+            }
+            case e_packer_state::ATTRACTION_GROUPS_ALL_REGIONS: {
                 attraction_groups.create_att_groups_for_all_regions();
                 VTR_LOG("Floorplan regions are overfull: trying to pack again with more attraction groups exploration. \n");
                 VTR_LOG("Pack iteration is %d\n", pack_iteration);
-            } else if (pack_iteration == 4) {
+                break;
+            }
+            case e_packer_state::ATTRACTION_GROUPS_ALL_REGIONS_AND_INCREASED_TARGET_DENSITY: {
                 attraction_groups.create_att_groups_for_all_regions();
                 VTR_LOG("Floorplan regions are overfull: trying to pack again with more attraction groups exploration and higher target pin utilization. \n");
                 VTR_LOG("Pack iteration is %d\n", pack_iteration);
@@ -224,9 +307,18 @@ bool try_pack(const t_packer_opts& packer_opts,
                 //       do it for all block types. Doing it only for a clb
                 //       string is dangerous -VB.
                 cluster_legalizer.get_target_external_pin_util().set_block_pin_util("clb", pin_util);
+                break;
             }
+            case e_packer_state::DEFAULT:
+            case e_packer_state::SUCCESS:
+            case e_packer_state::FAILURE:
+            default:
+                // Nothing to set up.
+                break;
+        }
 
-        } else { //Unable to pack densely enough: Give Up
+        // Raise an error if the packer failed to pack.
+        if (next_packer_state == e_packer_state::FAILURE) {
             if (floorplan_regions_overfull) {
                 VPR_FATAL_ERROR(VPR_ERROR_OTHER,
                                 "Failed to find pack clusters densely enough to fit in the designated floorplan regions.\n"
@@ -255,14 +347,23 @@ bool try_pack(const t_packer_opts& packer_opts,
             VPR_FATAL_ERROR(VPR_ERROR_OTHER, "Failed to find device which satisfies resource requirements required: %s (available %s)", resource_reqs.c_str(), resource_avail.c_str());
         }
 
-        //Reset floorplanning constraints for re-packing
-        g_vpr_ctx.mutable_floorplanning().cluster_constraints.clear();
+        // If the packer was unsuccessful, reset the packed solution and try again.
+        if (next_packer_state != e_packer_state::SUCCESS) {
+            //Reset floorplanning constraints for re-packing
+            g_vpr_ctx.mutable_floorplanning().cluster_constraints.clear();
+
+            // Reset the cluster legalizer for re-clustering.
+            cluster_legalizer.reset();
+        }
+
+        // Set the current state to the next state.
+        current_packer_state = next_packer_state;
 
-        // Reset the cluster legalizer for re-clustering.
-        cluster_legalizer.reset();
         ++pack_iteration;
     }
 
+    VTR_ASSERT(current_packer_state == e_packer_state::SUCCESS);
+
     /* Packing iterative improvement can be done here */
     /*       Use the re-cluster API to edit it        */
     /******************* Start *************************/