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Diffstat (limited to 'passes/techmap/flowmap.cc')
| -rw-r--r-- | passes/techmap/flowmap.cc | 729 |
1 files changed, 694 insertions, 35 deletions
diff --git a/passes/techmap/flowmap.cc b/passes/techmap/flowmap.cc index be70b579b..ddbd7bf5d 100644 --- a/passes/techmap/flowmap.cc +++ b/passes/techmap/flowmap.cc @@ -17,11 +17,16 @@ * */ -// [[CITE]] +// [[CITE]] FlowMap algorithm // Jason Cong; Yuzheng Ding, "An Optimal Technology Mapping Algorithm for Delay Optimization in Lookup-Table Based FPGA Designs," // Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions on, Vol. 13, pp. 1-12, Jan. 1994. // doi: 10.1109/43.273754 +// [[CITE]] FlowMap-r algorithm +// Jason Cong; Yuzheng Ding, "On Area/Depth Tradeoff in LUT-Based FPGA Technology Mapping," +// Very Large Scale Integration Systems, IEEE Transactions on, Vol. 2, June 1994. +// doi: 10.1109/92.28574 + // Required reading material: // // Min-cut max-flow theorem: @@ -29,11 +34,14 @@ // FlowMap paper: // http://cadlab.cs.ucla.edu/~cong/papers/iccad92.pdf (short version) // https://limsk.ece.gatech.edu/book/papers/flowmap.pdf (long version) +// FlowMap-r paper: +// http://cadlab.cs.ucla.edu/~cong/papers/dac93.pdf (short version) +// https://sci-hub.tw/10.1109/92.285741 (long version) -// Notes on implementation: +// Notes on correspondence between paper and implementation: // -// 1. In the paper, the nodes are logic elements (analogous to Yosys cells) and edges are wires. However, in our implementation, we use -// an inverted approach: the nodes are Yosys wire bits, and the edges are derived from (but aren't represented by) Yosys cells. +// 1. In the FlowMap paper, the nodes are logic elements (analogous to Yosys cells) and edges are wires. However, in our implementation, +// we use an inverted approach: the nodes are Yosys wire bits, and the edges are derived from (but aren't represented by) Yosys cells. // This may seem counterintuitive. Three observations may help understanding this. First, for a cell with a 1-bit Y output that is // the sole driver of its output net (which is the typical case), these representations are equivalent, because there is an exact // correspondence between cells and output wires. Second, in the paper, primary inputs (analogous to Yosys cell or module ports) are @@ -42,17 +50,50 @@ // such cells are supported without any additional effort; any Yosys cell with n output wire bits ends up being split into n flow graph // nodes. // -// 2. The paper introduces three networks: Nt, Nt', and Nt''. The network Nt is directly represented by a subgraph of RTLIL graph, +// 2. The FlowMap paper introduces three networks: Nt, Nt', and Nt''. The network Nt is directly represented by a subgraph of RTLIL graph, // which is parsed into an equivalent but easier to traverse representation in FlowmapWorker. The network Nt' is built explicitly // from a subgraph of Nt, and uses a similar representation in FlowGraph. The network Nt'' is implicit in FlowGraph, which is possible // because of the following observation: each Nt' node corresponds to an Nt'' edge of capacity 1, and each Nt' edge corresponds to // an Nt'' edge of capacity ∞. Therefore, we only need to explicitly record flow for Nt' edges and through Nt' nodes. // -// 3. The paper ambiguously states: "Moreover, we can find such a cut (X′′, X̅′′) by performing a depth first search starting at the source s, -// and including in X′′ all the nodes which are reachable from s." This actually refers to a specific kind of search, mincut computation. -// Mincut computation involves computing the set of nodes reachable from s by an undirected path with no full (i.e. zero capacity) forward -// edges or empty (i.e. no flow) backward edges. In addition, the depth first search is required to compute a max-volume max-flow min-cut -// specifically, because a max-flow min-cut is not, in general, unique. +// 3. The FlowMap paper ambiguously states: "Moreover, we can find such a cut (X′′, X̅′′) by performing a depth first search starting at +// the source s, and including in X′′ all the nodes which are reachable from s." This actually refers to a specific kind of search, +// min-cut computation. Min-cut computation involves computing the set of nodes reachable from s by an undirected path with no full +// (i.e. zero capacity) forward edges or empty (i.e. no flow) backward edges. In addition, the depth first search is required to compute +// a max-volume max-flow min-cut specifically, because a max-flow min-cut is not, in general, unique. + +// Notes on implementation: +// +// 1. To compute depth optimal packing, an intermediate representation is used, where each cell with n output bits is split into n graph +// nodes. Each such graph node is represented directly with the wire bit (RTLIL::SigBit instance) that corresponds to the output bit +// it is created from. Fan-in and fan-out are represented explicitly by edge lists derived from the RTLIL graph. This IR never changes +// after it has been computed. +// +// In terms of data, this IR is comprised of `inputs`, `outputs`, `nodes`, `edges_fw` and `edges_bw` fields. +// +// We call this IR "gate IR". +// +// 2. To compute area optimal packing, another intermediate representation is used, which consists of some K-feasible cone for every node +// that exists in the gate IR. Immediately after depth optimal packing with FlowMap, each such cone occupies the lowest possible depth, +// but this is not true in general, and transformations of this IR may change the cones, although each transformation has to keep each +// cone K-feasible. In this IR, LUT fan-in and fan-out are represented explicitly by edge lists; if a K-feasible cone chosen for node A +// includes nodes B and C, there are edges between all predecessors of A, B and C in the gate IR and node A in this IR. Moreover, in +// this IR, cones may be *realized* or *derealized*. Only realized cones will end up mapped to actual LUTs in the output of this pass. +// +// Intuitively, this IR contains (some, ideally but not necessarily optimal) LUT representation for each input cell. By starting at outputs +// and traversing the graph of this IR backwards, each K-feasible cone is converted to an actual LUT at the end of the pass. This is +// the same as iterating through each realized LUT. +// +// The following are the invariants of this IR: +// a) Each gate IR node corresponds to a K-feasible cut. +// b) Each realized LUT is reachable through backward edges from some output. +// c) The LUT fan-in is exactly the fan-in of its constituent gates minus the fan-out of its constituent gates. +// The invariants are kept even for derealized LUTs, since the whole point of this IR is ease of packing, unpacking, and repacking LUTs. +// +// In terms of data, this IR is comprised of `lut_nodes` (the set of all realized LUTs), `lut_gates` (the map from a LUT to its +// constituent gates), `lut_edges_fw` and `lut_edges_bw` fields. The `inputs` and `outputs` fields are shared with the gate IR. +// +// We call this IR "LUT IR". #include "kernel/yosys.h" #include "kernel/sigtools.h" @@ -405,7 +446,8 @@ struct FlowGraph struct FlowmapWorker { int order; - bool debug; + int r_alpha, r_beta, r_gamma; + bool debug, debug_relax; RTLIL::Module *module; SigMap sigmap; @@ -413,13 +455,16 @@ struct FlowmapWorker dict<RTLIL::SigBit, ModIndex::PortInfo> node_origins; + // Gate IR pool<RTLIL::SigBit> nodes, inputs, outputs; dict<RTLIL::SigBit, pool<RTLIL::SigBit>> edges_fw, edges_bw; dict<RTLIL::SigBit, int> labels; + // LUT IR pool<RTLIL::SigBit> lut_nodes; dict<RTLIL::SigBit, pool<RTLIL::SigBit>> lut_gates; dict<RTLIL::SigBit, pool<RTLIL::SigBit>> lut_edges_fw, lut_edges_bw; + dict<RTLIL::SigBit, int> lut_depths, lut_altitudes, lut_slacks; int gate_count = 0, lut_count = 0, packed_count = 0; int gate_area = 0, lut_area = 0; @@ -427,6 +472,7 @@ struct FlowmapWorker enum class GraphMode { Label, Cut, + Slack, }; void dump_dot_graph(string filename, GraphMode mode, @@ -465,6 +511,10 @@ struct FlowmapWorker if (cut.second[node]) return GraphStyle{label, "red"}; return GraphStyle{label}; + + case GraphMode::Slack: + label += stringf("\nd=%d a=%d\ns=%d", lut_depths[node], lut_altitudes[node], lut_slacks[node]); + return GraphStyle{label, lut_slacks[node] == 0 ? "red" : "black"}; } return GraphStyle{label}; }; @@ -474,6 +524,14 @@ struct FlowmapWorker ::dump_dot_graph(filename, subgraph_nodes, subgraph_edges, inputs, outputs, node_style, edge_style, module->name.str()); } + void dump_dot_lut_graph(string filename, GraphMode mode) + { + pool<RTLIL::SigBit> lut_and_input_nodes; + lut_and_input_nodes.insert(lut_nodes.begin(), lut_nodes.end()); + lut_and_input_nodes.insert(inputs.begin(), inputs.end()); + dump_dot_graph(filename, mode, lut_and_input_nodes, lut_edges_fw, lut_gates); + } + pool<RTLIL::SigBit> find_subgraph(RTLIL::SigBit sink) { pool<RTLIL::SigBit> subgraph; @@ -711,7 +769,7 @@ struct FlowmapWorker } } - int pack_luts() + int map_luts() { pool<RTLIL::SigBit> worklist = outputs; while (!worklist.empty()) @@ -726,21 +784,563 @@ struct FlowmapWorker int depth = 0; for (auto label : labels) depth = max(depth, label.second); - log("Solved to %d LUTs in %d levels.\n", (int)lut_nodes.size(), depth); + log("Mapped to %zu LUTs with maximum depth %d.\n", lut_nodes.size(), depth); if (debug) { - pool<RTLIL::SigBit> lut_and_input_nodes; - lut_and_input_nodes.insert(lut_nodes.begin(), lut_nodes.end()); - lut_and_input_nodes.insert(inputs.begin(), inputs.end()); - dump_dot_graph("flowmap-packed.dot", GraphMode::Label, lut_and_input_nodes, lut_edges_fw, lut_gates); - log("Dumped packed graph to `flowmap-packed.dot`.\n"); + dump_dot_lut_graph("flowmap-mapped.dot", GraphMode::Label); + log("Dumped mapped graph to `flowmap-mapped.dot`.\n"); } return depth; } - void map_cells(int minlut) + void realize_derealize_lut(RTLIL::SigBit lut, pool<RTLIL::SigBit> *changed = nullptr) + { + pool<RTLIL::SigBit> worklist = {lut}; + while (!worklist.empty()) + { + auto lut = worklist.pop(); + if (inputs[lut]) + continue; + + bool realized_successors = false; + for (auto lut_succ : lut_edges_fw[lut]) + if (lut_nodes[lut_succ]) + realized_successors = true; + + if (realized_successors && !lut_nodes[lut]) + lut_nodes.insert(lut); + else if (!realized_successors && lut_nodes[lut]) + lut_nodes.erase(lut); + else + continue; + + for (auto lut_pred : lut_edges_bw[lut]) + worklist.insert(lut_pred); + + if (changed) + changed->insert(lut); + } + } + + void add_lut_edge(RTLIL::SigBit pred, RTLIL::SigBit succ, pool<RTLIL::SigBit> *changed = nullptr) + { + log_assert(!lut_edges_fw[pred][succ] && !lut_edges_bw[succ][pred]); + log_assert((int)lut_edges_bw[succ].size() < order); + + lut_edges_fw[pred].insert(succ); + lut_edges_bw[succ].insert(pred); + realize_derealize_lut(pred, changed); + + if (changed) + { + changed->insert(pred); + changed->insert(succ); + } + } + + void remove_lut_edge(RTLIL::SigBit pred, RTLIL::SigBit succ, pool<RTLIL::SigBit> *changed = nullptr) + { + log_assert(lut_edges_fw[pred][succ] && lut_edges_bw[succ][pred]); + + lut_edges_fw[pred].erase(succ); + lut_edges_bw[succ].erase(pred); + realize_derealize_lut(pred, changed); + + if (changed) + { + if (lut_nodes[pred]) + changed->insert(pred); + changed->insert(succ); + } + } + + pair<pool<RTLIL::SigBit>, pool<RTLIL::SigBit>> cut_lut_at_gate(RTLIL::SigBit lut, RTLIL::SigBit lut_gate) + { + pool<RTLIL::SigBit> gate_inputs = lut_edges_bw[lut]; + pool<RTLIL::SigBit> other_inputs; + pool<RTLIL::SigBit> worklist = {lut}; + while (!worklist.empty()) + { + auto node = worklist.pop(); + for (auto node_pred : edges_bw[node]) + { + if (node_pred == lut_gate) + continue; + if (lut_gates[lut][node_pred]) + worklist.insert(node_pred); + else + { + gate_inputs.erase(node_pred); + other_inputs.insert(node_pred); + } + } + } + return {gate_inputs, other_inputs}; + } + + void compute_lut_distances(dict<RTLIL::SigBit, int> &lut_distances, bool forward, + pool<RTLIL::SigBit> initial = {}, pool<RTLIL::SigBit> *changed = nullptr) + { + pool<RTLIL::SigBit> terminals = forward ? inputs : outputs; + auto &lut_edges_next = forward ? lut_edges_fw : lut_edges_bw; + auto &lut_edges_prev = forward ? lut_edges_bw : lut_edges_fw; + + if (initial.empty()) + initial = terminals; + for (auto node : initial) + lut_distances.erase(node); + + pool<RTLIL::SigBit> worklist = initial; + while (!worklist.empty()) + { + auto lut = worklist.pop(); + int lut_distance = 0; + if (forward && inputs[lut]) + lut_distance = labels[lut]; // to support (* $flowmap_level=n *) + for (auto lut_prev : lut_edges_prev[lut]) + if ((lut_nodes[lut_prev] || inputs[lut_prev]) && lut_distances.count(lut_prev)) + lut_distance = max(lut_distance, lut_distances[lut_prev] + 1); + if (!lut_distances.count(lut) || lut_distances[lut] != lut_distance) + { + lut_distances[lut] = lut_distance; + if (changed != nullptr && !inputs[lut]) + changed->insert(lut); + for (auto lut_next : lut_edges_next[lut]) + if (lut_nodes[lut_next] || inputs[lut_next]) + worklist.insert(lut_next); + } + } + } + + void check_lut_distances(const dict<RTLIL::SigBit, int> &lut_distances, bool forward) + { + dict<RTLIL::SigBit, int> gold_lut_distances; + compute_lut_distances(gold_lut_distances, forward); + for (auto lut_distance : lut_distances) + if (lut_nodes[lut_distance.first]) + log_assert(lut_distance.second == gold_lut_distances[lut_distance.first]); + } + + // LUT depth is the length of the longest path from any input in LUT fan-in to LUT. + // LUT altitude (for lack of a better term) is the length of the longest path from LUT to any output in LUT fan-out. + void update_lut_depths_altitudes(pool<RTLIL::SigBit> worklist = {}, pool<RTLIL::SigBit> *changed = nullptr) + { + compute_lut_distances(lut_depths, /*forward=*/true, worklist, changed); + compute_lut_distances(lut_altitudes, /*forward=*/false, worklist, changed); + if (debug_relax && !worklist.empty()) { + check_lut_distances(lut_depths, /*forward=*/true); + check_lut_distances(lut_altitudes, /*forward=*/false); + } + } + + // LUT critical output set is the set of outputs whose depth will increase (equivalently, slack will decrease) if the depth of + // the LUT increases. (This is referred to as RPOv for LUTv in the paper.) + void compute_lut_critical_outputs(dict<RTLIL::SigBit, pool<RTLIL::SigBit>> &lut_critical_outputs, + pool<RTLIL::SigBit> worklist = {}) + { + if (worklist.empty()) + worklist = lut_nodes; + + while (!worklist.empty()) + { + bool updated_some = false; + for (auto lut : worklist) + { + if (outputs[lut]) + lut_critical_outputs[lut] = {lut}; + else + { + bool all_succ_computed = true; + lut_critical_outputs[lut] = {}; + for (auto lut_succ : lut_edges_fw[lut]) + { + if (lut_nodes[lut_succ] && lut_depths[lut_succ] == lut_depths[lut] + 1) + { + if (lut_critical_outputs.count(lut_succ)) + lut_critical_outputs[lut].insert(lut_critical_outputs[lut_succ].begin(), lut_critical_outputs[lut_succ].end()); + else + { + all_succ_computed = false; + break; + } + } + } + if (!all_succ_computed) + { + lut_critical_outputs.erase(lut); + continue; + } + } + worklist.erase(lut); + updated_some = true; + } + log_assert(updated_some); + } + } + + // Invalidating LUT critical output sets is tricky, because increasing the depth of a LUT may take other, adjacent LUTs off the critical + // path to the output. Conservatively, if we increase depth of some LUT, every LUT in its input cone needs to have its critical output + // set invalidated, too. + pool<RTLIL::SigBit> invalidate_lut_critical_outputs(dict<RTLIL::SigBit, pool<RTLIL::SigBit>> &lut_critical_outputs, + pool<RTLIL::SigBit> worklist) + { + pool<RTLIL::SigBit> changed; + while (!worklist.empty()) + { + auto lut = worklist.pop(); + changed.insert(lut); + lut_critical_outputs.erase(lut); + for (auto lut_pred : lut_edges_bw[lut]) + { + if (lut_nodes[lut_pred] && !changed[lut_pred]) + { + changed.insert(lut_pred); + worklist.insert(lut_pred); + } + } + } + return changed; + } + + void check_lut_critical_outputs(const dict<RTLIL::SigBit, pool<RTLIL::SigBit>> &lut_critical_outputs) + { + dict<RTLIL::SigBit, pool<RTLIL::SigBit>> gold_lut_critical_outputs; + compute_lut_critical_outputs(gold_lut_critical_outputs); + for (auto lut_critical_output : lut_critical_outputs) + if (lut_nodes[lut_critical_output.first]) + log_assert(lut_critical_output.second == gold_lut_critical_outputs[lut_critical_output.first]); + } + + void update_lut_critical_outputs(dict<RTLIL::SigBit, pool<RTLIL::SigBit>> &lut_critical_outputs, + pool<RTLIL::SigBit> worklist = {}) + { + if (!worklist.empty()) + { + pool<RTLIL::SigBit> invalidated = invalidate_lut_critical_outputs(lut_critical_outputs, worklist); + compute_lut_critical_outputs(lut_critical_outputs, invalidated); + check_lut_critical_outputs(lut_critical_outputs); + } + else + compute_lut_critical_outputs(lut_critical_outputs); + } + + void update_breaking_node_potentials(dict<RTLIL::SigBit, dict<RTLIL::SigBit, int>> &potentials, + const dict<RTLIL::SigBit, pool<RTLIL::SigBit>> &lut_critical_outputs) + { + for (auto lut : lut_nodes) + { + if (potentials.count(lut)) + continue; + if (lut_gates[lut].size() == 1 || lut_slacks[lut] == 0) + continue; + + if (debug_relax) + log(" Computing potentials for LUT %s.\n", log_signal(lut)); + + for (auto lut_gate : lut_gates[lut]) + { + if (lut == lut_gate) + continue; + + if (debug_relax) + log(" Considering breaking node %s.\n", log_signal(lut_gate)); + + int r_ex, r_im, r_slk; + + auto cut_inputs = cut_lut_at_gate(lut, lut_gate); + pool<RTLIL::SigBit> gate_inputs = cut_inputs.first, other_inputs = cut_inputs.second; + if (gate_inputs.empty() && (int)other_inputs.size() == order) + { + if (debug_relax) + log(" Breaking would result in a (k+1)-LUT.\n"); + continue; + } + + pool<RTLIL::SigBit> elim_fanin_luts; + for (auto gate_input : gate_inputs) + { + if (lut_edges_fw[gate_input].size() == 1) + { + log_assert(lut_edges_fw[gate_input][lut]); + elim_fanin_luts.insert(gate_input); + } + } + if (debug_relax) + { + if (!lut_nodes[lut_gate]) + log(" Breaking requires a new LUT.\n"); + if (!gate_inputs.empty()) + { + log(" Breaking eliminates LUT inputs"); + for (auto gate_input : gate_inputs) + log(" %s", log_signal(gate_input)); + log(".\n"); + } + if (!elim_fanin_luts.empty()) + { + log(" Breaking eliminates fan-in LUTs"); + for (auto elim_fanin_lut : elim_fanin_luts) + log(" %s", log_signal(elim_fanin_lut)); + log(".\n"); + } + } + r_ex = (lut_nodes[lut_gate] ? 0 : -1) + elim_fanin_luts.size(); + + pool<pair<RTLIL::SigBit, RTLIL::SigBit>> maybe_mergeable_luts; + + // Try to merge LUTv with one of its successors. + RTLIL::SigBit last_lut_succ; + int fanout = 0; + for (auto lut_succ : lut_edges_fw[lut]) + { + if (lut_nodes[lut_succ]) + { + fanout++; + last_lut_succ = lut_succ; + } + } + if (fanout == 1) + maybe_mergeable_luts.insert({lut, last_lut_succ}); + + // Try to merge LUTv with one of its predecessors. + for (auto lut_pred : other_inputs) + { + int fanout = 0; + for (auto lut_pred_succ : lut_edges_fw[lut_pred]) + if (lut_nodes[lut_pred_succ] || lut_pred_succ == lut_gate) + fanout++; + if (fanout == 1) + maybe_mergeable_luts.insert({lut_pred, lut}); + } + + // Try to merge LUTw with one of its predecessors. + for (auto lut_gate_pred : lut_edges_bw[lut_gate]) + { + int fanout = 0; + for (auto lut_gate_pred_succ : lut_edges_fw[lut_gate_pred]) + if (lut_nodes[lut_gate_pred_succ] || lut_gate_pred_succ == lut_gate) + fanout++; + if (fanout == 1) + maybe_mergeable_luts.insert({lut_gate_pred, lut_gate}); + } + + r_im = 0; + for (auto maybe_mergeable_pair : maybe_mergeable_luts) + { + log_assert(lut_edges_fw[maybe_mergeable_pair.first][maybe_mergeable_pair.second]); + pool<RTLIL::SigBit> unique_inputs; + for (auto fst_lut_pred : lut_edges_bw[maybe_mergeable_pair.first]) + if (lut_nodes[fst_lut_pred]) + unique_inputs.insert(fst_lut_pred); + for (auto snd_lut_pred : lut_edges_bw[maybe_mergeable_pair.second]) + if (lut_nodes[snd_lut_pred]) + unique_inputs.insert(snd_lut_pred); + unique_inputs.erase(maybe_mergeable_pair.first); + if ((int)unique_inputs.size() <= order) + { + if (debug_relax) + log(" Breaking may allow merging %s and %s.\n", + log_signal(maybe_mergeable_pair.first), log_signal(maybe_mergeable_pair.second)); + r_im++; + } + } + + int lut_gate_depth; + if (lut_nodes[lut_gate]) + lut_gate_depth = lut_depths[lut_gate]; + else + { + lut_gate_depth = 0; + for (auto lut_gate_pred : lut_edges_bw[lut_gate]) + lut_gate_depth = max(lut_gate_depth, lut_depths[lut_gate_pred] + 1); + } + if (lut_depths[lut] >= lut_gate_depth + 1) + r_slk = 0; + else + { + int depth_delta = lut_gate_depth + 1 - lut_depths[lut]; + if (depth_delta > lut_slacks[lut]) + { + if (debug_relax) + log(" Breaking would increase depth by %d, which is more than available slack.\n", depth_delta); + continue; + } + + if (debug_relax) + { + log(" Breaking increases depth of LUT by %d.\n", depth_delta); + if (lut_critical_outputs.at(lut).size()) + { + log(" Breaking decreases slack of outputs"); + for (auto lut_critical_output : lut_critical_outputs.at(lut)) + { + log(" %s", log_signal(lut_critical_output)); + log_assert(lut_slacks[lut_critical_output] > 0); + } + log(".\n"); + } + } + r_slk = lut_critical_outputs.at(lut).size() * depth_delta; + } + + int p = 100 * (r_alpha * r_ex + r_beta * r_im + r_gamma) / (r_slk + 1); + if (debug_relax) + log(" Potential for breaking node %s: %d (Rex=%d, Rim=%d, Rslk=%d).\n", + log_signal(lut_gate), p, r_ex, r_im, r_slk); + potentials[lut][lut_gate] = p; + } + } + } + + bool relax_depth_for_bound(bool first, int depth_bound, dict<RTLIL::SigBit, pool<RTLIL::SigBit>> &lut_critical_outputs) + { + size_t initial_count = lut_nodes.size(); + + for (auto node : lut_nodes) + { + lut_slacks[node] = depth_bound - (lut_depths[node] + lut_altitudes[node]); + log_assert(lut_slacks[node] >= 0); + } + if (debug) + { + dump_dot_lut_graph(stringf("flowmap-relax-%d-initial.dot", depth_bound), GraphMode::Slack); + log(" Dumped initial slack graph to `flowmap-relax-%d-initial.dot`.\n", depth_bound); + } + + dict<RTLIL::SigBit, dict<RTLIL::SigBit, int>> potentials; + for (int break_num = 1; ; break_num++) + { + update_breaking_node_potentials(potentials, lut_critical_outputs); + + if (potentials.empty()) + { + log(" Relaxed to %zu (+%zu) LUTs.\n", lut_nodes.size(), lut_nodes.size() - initial_count); + if (!first && break_num == 1) + { + log(" Design fully relaxed.\n"); + return true; + } + else + { + log(" Slack exhausted.\n"); + break; + } + } + + RTLIL::SigBit breaking_lut, breaking_gate; + int best_potential = INT_MIN; + for (auto lut_gate_potentials : potentials) + { + for (auto gate_potential : lut_gate_potentials.second) + { + if (gate_potential.second > best_potential) + { + breaking_lut = lut_gate_potentials.first; + breaking_gate = gate_potential.first; + best_potential = gate_potential.second; + } + } + } + log(" Breaking LUT %s to %s LUT %s (potential %d).\n", + log_signal(breaking_lut), lut_nodes[breaking_gate] ? "reuse" : "extract", log_signal(breaking_gate), best_potential); + + if (debug_relax) + log(" Removing breaking gate %s from LUT.\n", log_signal(breaking_gate)); + lut_gates[breaking_lut].erase(breaking_gate); + + auto cut_inputs = cut_lut_at_gate(breaking_lut, breaking_gate); + pool<RTLIL::SigBit> gate_inputs = cut_inputs.first, other_inputs = cut_inputs.second; + + pool<RTLIL::SigBit> worklist = lut_gates[breaking_lut]; + pool<RTLIL::SigBit> elim_gates = gate_inputs; + while (!worklist.empty()) + { + auto lut_gate = worklist.pop(); + bool all_gate_preds_elim = true; + for (auto lut_gate_pred : edges_bw[lut_gate]) + if (!elim_gates[lut_gate_pred]) + all_gate_preds_elim = false; + if (all_gate_preds_elim) + { + if (debug_relax) + log(" Removing gate %s from LUT.\n", log_signal(lut_gate)); + lut_gates[breaking_lut].erase(lut_gate); + for (auto lut_gate_succ : edges_fw[lut_gate]) + worklist.insert(lut_gate_succ); + } + } + log_assert(!lut_gates[breaking_lut].empty()); + + pool<RTLIL::SigBit> directly_affected_nodes = {breaking_lut}; + for (auto gate_input : gate_inputs) + { + if (debug_relax) + log(" Removing LUT edge %s -> %s.\n", log_signal(gate_input), log_signal(breaking_lut)); + remove_lut_edge(gate_input, breaking_lut, &directly_affected_nodes); + } + if (debug_relax) + log(" Adding LUT edge %s -> %s.\n", log_signal(breaking_gate), log_signal(breaking_lut)); + add_lut_edge(breaking_gate, breaking_lut, &directly_affected_nodes); + + if (debug_relax) + log(" Updating slack and potentials.\n"); + + pool<RTLIL::SigBit> indirectly_affected_nodes = {}; + update_lut_depths_altitudes(directly_affected_nodes, &indirectly_affected_nodes); + update_lut_critical_outputs(lut_critical_outputs, indirectly_affected_nodes); + for (auto node : indirectly_affected_nodes) + { + lut_slacks[node] = depth_bound - (lut_depths[node] + lut_altitudes[node]); + log_assert(lut_slacks[node] >= 0); + if (debug_relax) + log(" LUT %s now has depth %d and slack %d.\n", log_signal(node), lut_depths[node], lut_slacks[node]); + } + + worklist = indirectly_affected_nodes; + pool<RTLIL::SigBit> visited; + while (!worklist.empty()) + { + auto node = worklist.pop(); + visited.insert(node); + potentials.erase(node); + // We are invalidating the entire output cone of the gate IR node, not just of the LUT IR node. This is done to also invalidate + // all LUTs that could contain one of the indirectly affected nodes as a *part* of them, as they may not be in the output cone + // of any of the LUT IR nodes, e.g. if we have a LUT IR node A and node B as predecessors of node C, where node B includes all + // gates from node A. + for (auto node_succ : edges_fw[node]) + if (!visited[node_succ]) + worklist.insert(node_succ); + } + + if (debug) + { + dump_dot_lut_graph(stringf("flowmap-relax-%d-break-%d.dot", depth_bound, break_num), GraphMode::Slack); + log(" Dumped slack graph after break %d to `flowmap-relax-%d-break-%d.dot`.\n", break_num, depth_bound, break_num); + } + } + + return false; + } + + void optimize_area(int depth, int optarea) + { + dict<RTLIL::SigBit, pool<RTLIL::SigBit>> lut_critical_outputs; + update_lut_depths_altitudes(); + update_lut_critical_outputs(lut_critical_outputs); + + for (int depth_bound = depth; depth_bound <= depth + optarea; depth_bound++) + { + log("Relaxing with depth bound %d.\n", depth_bound); + bool fully_relaxed = relax_depth_for_bound(depth_bound == depth, depth_bound, lut_critical_outputs); + + if (fully_relaxed) + break; + } + } + + void pack_cells(int minlut) { ConstEval ce(module); for (auto input_node : inputs) @@ -753,15 +1353,15 @@ struct FlowmapWorker { auto origin = node_origins[node]; if (origin.cell->getPort(origin.port).size() == 1) - log("Mapping %s.%s.%s (%s).\n", + log("Packing %s.%s.%s (%s).\n", log_id(module), log_id(origin.cell), origin.port.c_str(), log_signal(node)); else - log("Mapping %s.%s.%s [%d] (%s).\n", + log("Packing %s.%s.%s [%d] (%s).\n", log_id(module), log_id(origin.cell), origin.port.c_str(), origin.offset, log_signal(node)); } else { - log("Mapping %s.%s.\n", log_id(module), log_signal(node)); + log("Packing %s.%s.\n", log_id(module), log_signal(node)); } for (auto gate_node : lut_gates[node]) @@ -819,9 +1419,9 @@ struct FlowmapWorker lut_area += lut_table.size(); if ((int)input_nodes.size() >= minlut) - log(" Packed into a %d-LUT %s.%s.\n", (int)input_nodes.size(), log_id(module), log_id(lut)); + log(" Packed into a %zu-LUT %s.%s.\n", input_nodes.size(), log_id(module), log_id(lut)); else - log(" Packed into a %d-LUT %s.%s (implemented as %d-LUT).\n", (int)input_nodes.size(), log_id(module), log_id(lut), minlut); + log(" Packed into a %zu-LUT %s.%s (implemented as %d-LUT).\n", input_nodes.size(), log_id(module), log_id(lut), minlut); } for (auto node : mapped_nodes) @@ -833,17 +1433,27 @@ struct FlowmapWorker } } - FlowmapWorker(int order, int minlut, pool<IdString> cell_types, bool debug, RTLIL::Module *module) : - order(order), debug(debug), module(module), sigmap(module), index(module) + FlowmapWorker(int order, int minlut, pool<IdString> cell_types, int r_alpha, int r_beta, int r_gamma, + bool relax, int optarea, bool debug, bool debug_relax, + RTLIL::Module *module) : + order(order), r_alpha(r_alpha), r_beta(r_beta), r_gamma(r_gamma), debug(debug), debug_relax(debug_relax), + module(module), sigmap(module), index(module) { log("Labeling cells.\n"); discover_nodes(cell_types); label_nodes(); - pack_luts(); + int depth = map_luts(); + + if (relax) + { + log("\n"); + log("Optimizing area.\n"); + optimize_area(depth, optarea); + } log("\n"); - log("Mapping cells.\n"); - map_cells(minlut); + log("Packing cells.\n"); + pack_cells(minlut); } }; @@ -881,16 +1491,34 @@ struct FlowmapPass : public Pass { log(" map specified cells. if not specified, maps $_NOT_, $_AND_, $_OR_,\n"); log(" $_XOR_ and $_MUX_, which are the outputs of the `simplemap` pass.\n"); log("\n"); + log(" -relax\n"); + log(" perform depth relaxation and area minimization.\n"); + log("\n"); + log(" -r-alpha n, -r-beta n, -r-gamma n\n"); + log(" parameters of depth relaxation heuristic potential function.\n"); + log(" if not specified, alpha=8, beta=2, gamma=1.\n"); + log("\n"); + log(" -optarea n\n"); + log(" optimize for area by trading off at most n logic levels for fewer LUTs.\n"); + log(" n may be zero, to optimize for area without increasing depth.\n"); + log(" implies -relax.\n"); + log("\n"); log(" -debug\n"); log(" dump intermediate graphs.\n"); log("\n"); + log(" -debug-relax\n"); + log(" explain decisions performed during depth relaxation.\n"); + log("\n"); } void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE { int order = 3; int minlut = 1; vector<string> cells; - bool debug = false; + bool relax = false; + int r_alpha = 8, r_beta = 2, r_gamma = 1; + int optarea = 0; + bool debug = false, debug_relax = false; size_t argidx; for (argidx = 1; argidx < args.size(); argidx++) @@ -910,11 +1538,42 @@ struct FlowmapPass : public Pass { split(cells, args[++argidx], ','); continue; } + if (args[argidx] == "-relax") + { + relax = true; + continue; + } + if (args[argidx] == "-r-alpha" && argidx + 1 < args.size()) + { + r_alpha = atoi(args[++argidx].c_str()); + continue; + } + if (args[argidx] == "-r-beta" && argidx + 1 < args.size()) + { + r_beta = atoi(args[++argidx].c_str()); + continue; + } + if (args[argidx] == "-r-gamma" && argidx + 1 < args.size()) + { + r_gamma = atoi(args[++argidx].c_str()); + continue; + } + if (args[argidx] == "-optarea" && argidx + 1 < args.size()) + { + relax = true; + optarea = atoi(args[++argidx].c_str()); + continue; + } if (args[argidx] == "-debug") { debug = true; continue; } + if (args[argidx] == "-debug-relax") + { + debug = debug_relax = true; + continue; + } break; } extra_args(args, argidx, design); @@ -930,13 +1589,14 @@ struct FlowmapPass : public Pass { cell_types = {"$_NOT_", "$_AND_", "$_OR_", "$_XOR_", "$_MUX_"}; } - log_header(design, "Executing FLOWMAP pass (pack LUTs with FlowMap).\n"); + const char *algo_r = relax ? "-r" : ""; + log_header(design, "Executing FLOWMAP pass (pack LUTs with FlowMap%s).\n", algo_r); int gate_count = 0, lut_count = 0, packed_count = 0; int gate_area = 0, lut_area = 0; for (auto module : design->selected_modules()) { - FlowmapWorker worker(order, minlut, cell_types, debug, module); + FlowmapWorker worker(order, minlut, cell_types, r_alpha, r_beta, r_gamma, relax, optarea, debug, debug_relax, module); gate_count += worker.gate_count; lut_count += worker.lut_count; packed_count += worker.packed_count; @@ -945,9 +1605,8 @@ struct FlowmapPass : public Pass { } log("\n"); - log("Mapped %d LUTs.\n", lut_count); - log("Packed %d cells; duplicated %d cells.\n", packed_count, packed_count - gate_count); - log("Solution has %.1f%% area overhead.\n", (lut_area - gate_area) * 100.0 / gate_area); + log("Packed %d cells (%d of them duplicated) into %d LUTs.\n", packed_count, packed_count - gate_count, lut_count); + log("Solution takes %.1f%% of original gate area.\n", lut_area * 100.0 / gate_area); } } FlowmapPass; |