phetdp: new placer

common/place/placer_phetdp.cc

@@ -0,0 +1,344 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2023  Hannah Ravensloft <[email protected]>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "placer_phetdp.h"
+#include <algorithm>
+#include <chrono>
+#include <vector>
+#include "hashlib.h"
+#include "nextpnr.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+struct GridSpace {
+    GridSpace(int x, int y) : x(x), y(y) {}
+    GridSpace(Loc loc) : x(loc.x), y(loc.y) {}
+    int x, y;
+};
+
+struct BinSpace {
+    BinSpace(int x, int y) : x(x), y(y) {
+        NPNR_ASSERT(x >= 0 && x < 12);
+        NPNR_ASSERT(y >= 0 && y < 12);
+    }
+    BinSpace(Context *ctx, GridSpace grid) {
+        x = grid.x * 12 / ctx->getGridDimX();
+        y = grid.y * 12 / ctx->getGridDimY();
+    }
+    int x, y;
+};
+
+class GlobalBin {
+public:
+    GlobalBin(size_t capacity = 1250) : capacity{capacity}, conns{}, nets{} {}
+
+    // The amount of available space in this bin.
+    int whitespace() const {
+        return int(capacity) - int(nets.size());
+    }
+
+    // The number of edges 
+    // Confusingly, this term is e_uv in Formula (2), but also `c_x <- (n_i ∩ n_j)` in Formula (3).
+    int edge_count(const NetInfo *candidate) const {
+        auto edges = 0;
+        auto result = conns.find(candidate->name);
+        if (result != conns.end())
+            edges += result->second;
+        for (const auto port : candidate->users) {
+            result = conns.find(port.cell->name);
+            if (result != conns.end())
+                edges += result->second;
+        }
+        return edges;
+    }
+
+    // Add a net to this bin.
+    void insert_net(NetInfo* net) {
+        nets.push_back(net);
+        build_connectivity_for_net(net);
+    }
+
+    // Formula (2), which scores a net for this bin based on its connectivity or free space.
+    // `(1 + edge_count(net))` is used to work around `edge_count(net) == 0` leading to whitespace
+    // being ignored.
+    // TODO: this is more or less `gamma(net) * whitespace()`.
+    int connectivity(const NetInfo *net) const {
+        return (1 + edge_count(net)) * whitespace() / (1 + net->users.entries());
+    }
+
+    // Formula (3), which scores how connected this net is to the other nets in this bin.
+    int gamma(const NetInfo* net) const {
+        return edge_count(net) / (1 + net->users.entries());
+    }
+
+    // Sort nets by their gamma score.
+    void sort() {
+        std::sort(nets.begin(), nets.end(), [&](const NetInfo* a, const NetInfo* b) {
+            return gamma(a) > gamma(b);
+        });
+    }
+
+    // Pop the lowest-gamma net from this bin.
+    NetInfo* pop_least_connected(int *net_gamma) {
+        if (nets.empty())
+            return nullptr;
+        auto net = nets.back();
+        *net_gamma = gamma(net);
+        nets.pop_back();
+        auto cell_name = net->driver.cell->name;
+        auto result1 = conns.find(cell_name);
+        if (result1 != conns.end())
+            result1->second--;
+        for (const auto port : net->users) {
+            auto result2 = conns.find(port.cell->name);
+            if (result2 != conns.end())
+                result2->second--;
+        }
+        return net;
+    }
+
+private:
+    // Incrementally update conn when a new net is added.
+    void build_connectivity_for_net(const NetInfo *net) {
+        auto cell_name = net->driver.cell->name;
+        auto result1 = conns.insert({cell_name, 1});
+        if (!result1.second)
+            result1.first->second++;
+        for (const auto port : net->users) {
+            auto result2 = conns.insert({port.cell->name, 1});
+            if (!result2.second)
+                result2.first->second++;
+        }
+    }
+
+    size_t capacity;
+    dict<IdString, int> conns;
+    std::vector<NetInfo*> nets;
+};
+
+
+class GlobalBins {
+public:
+    GlobalBins(Context *ctx) : ctx{ctx}, bins{12, std::vector<GlobalBin>(12)} {}
+
+    // Return the net with the highest connectivity score.
+    // TODO: can I turn this into a std::max_element call?
+    BinSpace highest_connectivity(NetInfo *const net) const {
+        auto best_score = -2147483648;
+        auto best_x = 0;
+        auto best_y = 0;
+        for (int x = 0; x < 12; x++) {
+            for (int y = 0; y < 12; y++) { 
+                auto score = bins.at(x).at(y).connectivity(net);
+                if (score > best_score) {
+                    best_score = score;
+                    best_x = x;
+                    best_y = y;
+                }
+            }
+        }
+        return BinSpace{best_x, best_y};
+    }
+
+    // Insert a net into a bin.
+    void insert_net(BinSpace bin, NetInfo* net) {
+        bins.at(bin.x).at(bin.y).insert_net(net);
+    }
+
+    // Reduce congestion by spreading cells with low connectivity into neighbouring cells.
+    void spread_whitespace() {
+        for (int x = 0; x < 12; x++) {
+            for (int y = 0; y < 12; y++) {
+                spread_bin(x, y);
+            }
+        }
+    }
+
+    // Display a heatmap of the whitespace in the bins.
+    void print_occupancy() const {
+        printf("\n");
+        for (int y = 11; y >= 0; y--) {
+            for (int x = 0; x < 12; x++) {
+                printf("%4d,", bins.at(x).at(y).whitespace());
+            }
+            printf("\n");
+        }
+    }
+
+private:
+
+    // Spread a bin's least-connected cells to its neighbours to reduce peak congestion.
+    bool spread_bin(int x, int y) {
+        bool updated_design = false;
+        bool did_something = true;
+        while (did_something) {
+            bins.at(x).at(y).sort();
+            did_something = false;
+            int gamma = 0;
+            auto net = bins.at(x).at(y).pop_least_connected(&gamma);
+            auto best_x = 0;
+            auto best_y = 0;
+            auto best_score = 100000;
+            for (int x_offset = -1; x_offset <= +1; x_offset++) {
+                for (int y_offset = -1; y_offset <= +1; y_offset++) {
+                    int new_x = x + x_offset;
+                    int new_y = y + y_offset;
+                    bool x_ok = new_x >= 0 && new_x < 12;
+                    bool y_ok = new_y >= 0 && new_y < 12;
+                    if (!x_ok || !y_ok || (new_x == x && new_y == y))
+                        continue;
+                    int score = (1250 - bins.at(new_x).at(new_y).whitespace()) + (1 - (std::abs(x_offset) + std::abs(y_offset)));
+                    if (score < best_score) {
+                        best_score = score;
+                        best_x = new_x;
+                        best_y = new_y;
+                    }
+                }
+            }
+            if (best_score < (1251 - bins.at(x).at(y).whitespace())) {
+                bins.at(best_x).at(best_y).insert_net(net);
+                did_something = true;
+                updated_design = true;
+            } else {
+                bins.at(x).at(y).insert_net(net);
+            }
+        }
+        return updated_design;
+    }
+
+    Context *ctx;
+    std::vector<std::vector<GlobalBin>> bins;
+};
+
+class Phetdp {
+public:
+    Phetdp(Context* ctx) : ctx(ctx), g{ctx} {}
+
+    void place() {
+        using std::chrono::high_resolution_clock;
+        using std::chrono::duration;
+        log_info("=== PHetDP START ===\n");
+        auto start_time = high_resolution_clock::now();
+        // Step 1: initial placement of fixed/constrained cells in global bins
+        initial_place_constraints();
+        auto post_initial_constraints = high_resolution_clock::now();
+        // Step 2: initial placement of unconstrained cells in global bins
+        initial_place_rest();
+        auto post_initial_rest = high_resolution_clock::now();
+        // Step 3: spreading of whitespace to reduce congestion
+        initial_spread_whitespace();
+        auto post_spread_whitespace = high_resolution_clock::now();
+        log_info("=== PHetDP FINISH ===\n");
+        log_info("initial placement:\n");
+        log_info("    initial_place_constraints(): %.02fs\n", duration<double>(post_initial_constraints - start_time).count());
+        log_info("    initial_place_rest():        %.02fs\n", duration<double>(post_initial_rest - post_initial_constraints).count());
+        log_info("    initial_spread_whitespace(): %.02fs\n", duration<double>(post_spread_whitespace - post_initial_rest).count()); 
+        NPNR_ASSERT_FALSE_STR("not yet implemented");
+    }
+
+    void initial_place_constraints() {
+        size_t placed_cells = 0;
+        for (auto &net_entry : ctx->nets) {
+            NetInfo *net = net_entry.second.get();
+            CellInfo *cell = net->driver.cell;
+            if (!cell)
+                continue; // maybe?
+            if (cell->isPseudo())
+                continue;
+            auto loc = cell->attrs.find(ctx->id("BEL"));
+            if (loc != cell->attrs.end()) {
+                std::string loc_name = loc->second.as_string();
+                BelId bel = ctx->getBelByNameStr(loc_name);
+                if (bel == BelId()) {
+                    log_error("No Bel named \'%s\' located for "
+                              "this chip (processing BEL attribute on \'%s\')\n",
+                              loc_name.c_str(), cell->name.c_str(ctx));
+                }
+
+                if (!ctx->isValidBelForCellType(cell->type, bel)) {
+                    IdString bel_type = ctx->getBelType(bel);
+                    log_error("Bel \'%s\' of type \'%s\' does not match cell "
+                              "\'%s\' of type \'%s\'\n",
+                              loc_name.c_str(), bel_type.c_str(ctx), cell->name.c_str(ctx), cell->type.c_str(ctx));
+                }
+                auto bound_cell = ctx->getBoundBelCell(bel);
+                if (bound_cell) {
+                    if (cell != bound_cell) {
+                        log_error("Cell \'%s\' cannot be bound to bel \'%s\' since it is already bound to cell \'%s\'\n",
+                                cell->name.c_str(ctx), loc_name.c_str(), bound_cell->name.c_str(ctx));
+                    }
+                    continue;
+                }
+
+                ctx->bindBel(bel, cell, STRENGTH_USER);
+                auto bel_loc = BinSpace{ctx, GridSpace{ctx->getBelLocation(bel)}};
+                g.insert_net(bel_loc, net);
+
+                if (!ctx->isBelLocationValid(bel, /* explain_invalid */ true)) {
+                    IdString bel_type = ctx->getBelType(bel);
+                    log_error("Bel \'%s\' of type \'%s\' is not valid for cell "
+                              "\'%s\' of type \'%s\'\n",
+                              loc_name.c_str(), bel_type.c_str(ctx), cell->name.c_str(ctx), cell->type.c_str(ctx));
+                }
+                placed_cells++;
+            }
+        }
+        log_info("Placed %d cells based on constraints.\n", int(placed_cells));
+        log_info("after fixed initial placement:\n");
+        g.print_occupancy();
+    }
+
+    void initial_place_rest() {
+        size_t placed_cells = 0;
+        for (auto &net_entry : ctx->nets) {
+            NetInfo *net = net_entry.second.get();
+            CellInfo *cell = net->driver.cell;
+            if (!cell)
+                continue; // maybe?
+            if (cell->isPseudo())
+                continue;
+
+            // Fixed constraints are handled in initial_place_constraints().
+            auto loc = cell->attrs.find(ctx->id("BEL"));
+            if (loc != cell->attrs.end())
+                continue;
+
+            g.insert_net(g.highest_connectivity(net), net);
+            placed_cells++;
+        }
+        log_info("Binned %d cells.\n", int(placed_cells));
+        log_info("after connectivity-based initial placement:\n");
+        g.print_occupancy();
+    }
+
+    void initial_spread_whitespace() {
+        g.spread_whitespace();
+        log_info("after whitespace spreading:\n");
+        g.print_occupancy();
+    }
+private:
+    Context* ctx;
+
+    GlobalBins g;
+};
+
+void placer_phetdp(Context* ctx) {
+    Phetdp{ctx}.place();
+}
+
+NEXTPNR_NAMESPACE_END

common/place/placer_phetdp.h

@@ -0,0 +1,30 @@
+/*
+ *  nextpnr -- Next Generation Place and Route
+ *
+ *  Copyright (C) 2023  Hannah Ravensloft <[email protected]>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#ifndef PLACER_PHETDP_H
+#define PLACER_PHETDP_H
+#include "log.h"
+#include "nextpnr.h"
+
+NEXTPNR_NAMESPACE_BEGIN
+
+extern void placer_phetdp(Context *ctx);
+
+NEXTPNR_NAMESPACE_END
+
+#endif