✨ Planar Post-Layout Optimization (#496)

* planar optimization

* 📝 Update pyfiction docstrings

Signed-off-by: GitHub Actions <actions@github.com>

* 🎨 Incorporated pre-commit fixes

* Update post_layout_optimization.hpp

* 📝 Update pyfiction docstrings

Signed-off-by: GitHub Actions <actions@github.com>

* extend cli docstring

* 📝 Update pyfiction docstrings

Signed-off-by: GitHub Actions <actions@github.com>

---------

Signed-off-by: GitHub Actions <actions@github.com>
Co-authored-by: GitHub Actions <actions@github.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

bindings/pyfiction/include/pyfiction/algorithms/physical_design/post_layout_optimization.hpp

@@ -30,6 +30,8 @@ inline void post_layout_optimization(pybind11::module& m)
                        DOC(fiction_post_layout_optimization_params_max_gate_relocations))
         .def_readwrite("optimize_pos_only", &fiction::post_layout_optimization_params::optimize_pos_only,
                        DOC(fiction_post_layout_optimization_params_optimize_pos_only))
+        .def_readwrite("planar_optimization", &fiction::post_layout_optimization_params::planar_optimization,
+                       DOC(fiction_post_layout_optimization_params_planar_optimization))
 
         ;
 

bindings/pyfiction/include/pyfiction/pybind11_mkdoc_docstrings.hpp

@@ -5442,6 +5442,10 @@ Parameter ``start``:
 Parameter ``end``:
     The ending coordinate of the path.
 
+Parameter ``planar_optimization``:
+    Only allow relocation if a crossing-free wiring can be found.
+    Defaults to false.
+
 Returns:
     The computed path as a sequence of coordinates in the layout.)doc";
 
@@ -5778,6 +5782,10 @@ Parameter ``lyt``:
 Parameter ``old_pos``:
     Old position of the gate to be moved.
 
+Parameter ``planar_optimization``:
+    Only allow relocation if a crossing-free wiring can be found.
+    Defaults to false.
+
 Returns:
     `true` if the gate was moved successfully, `false` otherwise.)doc";
 
@@ -13627,6 +13635,11 @@ number of tiles in the given layout if not specified.)doc";
 
 static const char *__doc_fiction_post_layout_optimization_params_optimize_pos_only = R"doc(Only optimize PO positions.)doc";
 
+static const char *__doc_fiction_post_layout_optimization_params_planar_optimization =
+R"doc(Disable the creation of crossings during optimization. If set to true,
+gates will only be relocated if a crossing-free wiring is found.
+Defaults to false.)doc";
+
 static const char *__doc_fiction_post_layout_optimization_stats =
 R"doc(This struct stores statistics about the post-layout optimization
 process.)doc";

cli/cmd/physical_design/optimize.hpp

@@ -44,6 +44,10 @@ class optimize_command : public command
         add_option("--max_gate_relocations,-m", max_gate_relocations,
                    "Specify the maximum number of relocations to try for each gate (defaults "
                    "to the number of tiles in the layout).");
+        add_flag("--planar_optimization,-p", ps.planar_optimization,
+                 "During optimization, only relocate gates if the new wiring contains no crossings. For planar "
+                 "layouts, the resulting layout will also be planar. If the layout already contains crossings, the "
+                 "optimized layout will have the same number of crossings or less.");
         add_flag("--verbose,-v", "Be verbose");
     }
 

include/fiction/algorithms/physical_design/post_layout_optimization.hpp

@@ -47,6 +47,11 @@ struct post_layout_optimization_params
      * Only optimize PO positions.
      */
     bool optimize_pos_only = false;
+    /**
+     * Disable the creation of crossings during optimization. If set to true, gates will only be relocated if a
+     * crossing-free wiring is found. Defaults to false.
+     */
+    bool planar_optimization = false;
 };
 
 /**
@@ -376,17 +381,20 @@ template <typename Lyt>
  * @param lyt Reference to the layout.
  * @param start The starting coordinate of the path.
  * @param end The ending coordinate of the path.
+ * @param planar_optimization Only allow relocation if a crossing-free wiring can be found. Defaults to false.
  * @return The computed path as a sequence of coordinates in the layout.
  */
 template <typename Lyt>
-layout_coordinate_path<Lyt> get_path_and_obstruct(Lyt& lyt, const tile<Lyt>& start, const tile<Lyt>& end)
+layout_coordinate_path<Lyt> get_path_and_obstruct(Lyt& lyt, const tile<Lyt>& start, const tile<Lyt>& end,
+                                                  const bool planar_optimization = false)
 {
     static_assert(is_gate_level_layout_v<Lyt>, "Lyt is not a gate-level layout");
     static_assert(is_cartesian_layout_v<Lyt>, "Lyt is not a Cartesian layout");
 
     using dist = twoddwave_distance_functor<Lyt, uint64_t>;
     using cost = unit_cost_functor<Lyt, uint8_t>;
-    static const a_star_params params{true};
+    static a_star_params params{};
+    params.crossings = !planar_optimization;
 
     layout_coordinate_path<Lyt> path = a_star<layout_coordinate_path<Lyt>>(lyt, {start, end}, dist(), cost(), params);
 
@@ -412,11 +420,12 @@ layout_coordinate_path<Lyt> get_path_and_obstruct(Lyt& lyt, const tile<Lyt>& sta
  * @tparam Lyt Cartesian obstruction gate-level layout type.
  * @param lyt 2DDWave-clocked cartesian obstruction gate-level layout.
  * @param old_pos Old position of the gate to be moved.
+ * @param planar_optimization Only allow relocation if a crossing-free wiring can be found. Defaults to false.
  * @return `true` if the gate was moved successfully, `false` otherwise.
  */
 template <typename Lyt>
 bool improve_gate_location(Lyt& lyt, const tile<Lyt>& old_pos, const tile<Lyt>& max_non_po,
-                           const uint64_t max_gate_relocations) noexcept
+                           const uint64_t max_gate_relocations, const bool planar_optimization = false) noexcept
 {
     static_assert(is_gate_level_layout_v<Lyt>, "Lyt is not a gate-level layout");
     static_assert(is_cartesian_layout_v<Lyt>, "Lyt is not a Cartesian layout");
@@ -546,22 +555,26 @@ bool improve_gate_location(Lyt& lyt, const tile<Lyt>& old_pos, const tile<Lyt>&
                     // get paths for fanins and fanouts
                     if (!fanins.empty())
                     {
-                        new_path_from_fanin_1_to_gate = get_path_and_obstruct(lyt, fanins[0], new_pos);
+                        new_path_from_fanin_1_to_gate =
+                            get_path_and_obstruct(lyt, fanins[0], new_pos, planar_optimization);
                     }
 
                     if (fanins.size() == 2)
                     {
-                        new_path_from_fanin_2_to_gate = get_path_and_obstruct(lyt, fanins[1], new_pos);
+                        new_path_from_fanin_2_to_gate =
+                            get_path_and_obstruct(lyt, fanins[1], new_pos, planar_optimization);
                     }
 
                     if (!fanouts.empty())
                     {
-                        new_path_from_gate_to_fanout_1 = get_path_and_obstruct(lyt, new_pos, fanouts[0]);
+                        new_path_from_gate_to_fanout_1 =
+                            get_path_and_obstruct(lyt, new_pos, fanouts[0], planar_optimization);
                     }
 
                     if (fanouts.size() == 2)
                     {
-                        new_path_from_gate_to_fanout_2 = get_path_and_obstruct(lyt, new_pos, fanouts[1]);
+                        new_path_from_gate_to_fanout_2 =
+                            get_path_and_obstruct(lyt, new_pos, fanouts[1], planar_optimization);
                     }
 
                     // if possible routing was found, it will be applied
@@ -955,7 +968,8 @@ class post_layout_optimization_impl
                 {
                     if (!ps.optimize_pos_only || (ps.optimize_pos_only && layout.is_po_tile(gate_tile)))
                     {
-                        if (detail::improve_gate_location(layout, gate_tile, max_non_po, max_gate_relocations))
+                        if (detail::improve_gate_location(layout, gate_tile, max_non_po, max_gate_relocations,
+                                                          ps.planar_optimization))
                         {
                             moved_at_least_one_gate = true;
                         }

test/algorithms/physical_design/post_layout_optimization.cpp

@@ -106,7 +106,7 @@ TEST_CASE("Layout equivalence", "[post_layout_optimization]")
         check_layout_equiv_all<gate_layout>();
     }
 
-    SECTION("Corner Cases")
+    SECTION("Corner cases")
     {
         using gate_layout = gate_level_layout<clocked_layout<tile_based_layout<cartesian_layout<>>>>;
 
@@ -127,7 +127,7 @@ TEST_CASE("Layout equivalence", "[post_layout_optimization]")
         }
     }
 
-    SECTION("Maximum Gate Relocations")
+    SECTION("Maximum gate relocations")
     {
         using gate_layout = gate_level_layout<clocked_layout<tile_based_layout<cartesian_layout<>>>>;
 
@@ -157,6 +157,39 @@ TEST_CASE("Layout equivalence", "[post_layout_optimization]")
 
         check_eq(blueprints::mux21_network<technology_network>(), layout);
     }
+
+    SECTION("Planar optimization with planar layout")
+    {
+        using gate_layout = gate_level_layout<clocked_layout<tile_based_layout<cartesian_layout<>>>>;
+
+        const auto layout = blueprints::planar_unoptimized_layout<gate_layout>();
+
+        post_layout_optimization_stats  stats{};
+        post_layout_optimization_params params{};
+        params.planar_optimization = true;
+        post_layout_optimization<gate_layout>(layout, params, &stats);
+
+        check_eq(blueprints::planar_unoptimized_layout<gate_layout>(), layout);
+        CHECK(layout.z() == 0);
+    }
+
+    SECTION("Planar optimization with crossing layout")
+    {
+        using gate_layout = gate_level_layout<clocked_layout<tile_based_layout<cartesian_layout<>>>>;
+
+        const auto layout = blueprints::planar_optimization_layout<gate_layout>();
+
+        post_layout_optimization_stats  stats{};
+        post_layout_optimization_params params{};
+
+        params.planar_optimization = true;
+        post_layout_optimization<gate_layout>(layout, params, &stats);
+        CHECK(!layout.is_inv(layout.get_node({1, 0})));
+
+        params.planar_optimization = false;
+        post_layout_optimization<gate_layout>(layout, params, &stats);
+        CHECK(layout.is_inv(layout.get_node({1, 0})));
+    }
 }
 
 TEST_CASE("Optimization steps", "[post_layout_optimization]")

test/utils/blueprints/layout_blueprints.hpp

@@ -535,6 +535,47 @@ GateLyt optimization_layout_corner_case_outputs_2() noexcept
     return layout;
 }
 
+template <typename GateLyt>
+GateLyt planar_unoptimized_layout() noexcept
+{
+    GateLyt layout{{4, 4, 0}, fiction::twoddwave_clocking<GateLyt>()};
+
+    const auto x1 = layout.create_pi("x1", {2, 0});
+    const auto x2 = layout.create_pi("x2", {0, 2});
+
+    const auto w1   = layout.create_buf(x1, {2, 1});
+    const auto w2   = layout.create_buf(x2, {1, 2});
+    const auto and1 = layout.create_and(w1, w2, {2, 2});
+    const auto w3   = layout.create_buf(and1, {3, 2});
+    const auto not2 = layout.create_not(w3, {4, 2});
+    const auto w4   = layout.create_buf(not2, {4, 3});
+
+    layout.create_po(w4, "f1", {4, 4});
+
+    return layout;
+}
+
+template <typename GateLyt>
+GateLyt planar_optimization_layout() noexcept
+{
+    GateLyt layout{{2, 2, 1}, fiction::twoddwave_clocking<GateLyt>()};
+
+    const auto x1 = layout.create_pi("x1", {0, 0});
+    const auto x2 = layout.create_pi("x2", {0, 1});
+    layout.create_pi("x3", {0, 2});
+    layout.create_pi("x4", {2, 0});
+
+    const auto w1   = layout.create_buf(x1, {1, 0});
+    const auto w2   = layout.create_buf(x2, {1, 1});
+    const auto w3   = layout.create_buf(w1, {1, 1, 1});
+    const auto not1 = layout.create_not(w3, {1, 2});
+
+    layout.create_po(w2, "f1", {2, 1});
+    layout.create_po(not1, "f2", {2, 2});
+
+    return layout;
+}
+
 template <typename CellLyt>
 CellLyt single_layer_qca_and_gate() noexcept
 {