mirror of https://github.com/YosysHQ/yosys.git
Improvements in muxcover
- Slightly under-estimate cost of decoder muxes - Prefer larger muxes at tree root at same cost - Don't double-count input cost for partial muxes - Add debug log output
This commit is contained in:
Clifford Wolf
Eddie Hung
parent
844c42cef8
commit
891ea6512e
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@ -178,7 +178,7 @@ struct MuxcoverWorker
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if (A == State::Sx || B == State::Sx)
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return 0;
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return cost_mux2 / GetSize(std::get<1>(entry));
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return std::max((cost_mux2 / GetSize(std::get<1>(entry))) - 1, 1);
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}
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void implement_decode_mux(SigBit ctrl_bit)
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@ -206,6 +206,23 @@ struct MuxcoverWorker
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std::get<2>(entry) = true;
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}
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void find_best_covers(tree_t &tree, const vector<SigBit> &bits)
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{
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for (auto bit : bits)
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find_best_cover(tree, bit);
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}
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int sum_best_covers(tree_t &tree, const vector<SigBit> &bits)
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{
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int sum = 0;
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for (auto bit : pool<SigBit>(bits.begin(), bits.end())) {
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int cost = tree.newmuxes.at(bit).cost;
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log_debug(" Best cost for %s: %d\n", log_signal(bit), cost);
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sum += cost;
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}
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return sum;
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}
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int find_best_cover(tree_t &tree, SigBit bit)
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{
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if (tree.newmuxes.count(bit)) {
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@ -236,9 +253,13 @@ struct MuxcoverWorker
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mux.inputs.push_back(B);
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mux.selects.push_back(S1);
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find_best_covers(tree, mux.inputs);
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log_debug(" Decode cost for mux2 at %s: %d\n", log_signal(bit), mux.cost);
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mux.cost += cost_mux2;
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mux.cost += find_best_cover(tree, A);
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mux.cost += find_best_cover(tree, B);
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mux.cost += sum_best_covers(tree, mux.inputs);
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log_debug(" Cost of mux2 at %s: %d\n", log_signal(bit), mux.cost);
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best_mux = mux;
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}
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@ -274,13 +295,15 @@ struct MuxcoverWorker
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mux.selects.push_back(S1);
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mux.selects.push_back(T1);
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mux.cost += cost_mux4;
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mux.cost += find_best_cover(tree, A);
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mux.cost += find_best_cover(tree, B);
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mux.cost += find_best_cover(tree, C);
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mux.cost += find_best_cover(tree, D);
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find_best_covers(tree, mux.inputs);
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log_debug(" Decode cost for mux4 at %s: %d\n", log_signal(bit), mux.cost);
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if (best_mux.cost > mux.cost)
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mux.cost += cost_mux4;
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mux.cost += sum_best_covers(tree, mux.inputs);
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log_debug(" Cost of mux4 at %s: %d\n", log_signal(bit), mux.cost);
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if (best_mux.cost >= mux.cost)
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best_mux = mux;
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}
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}
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@ -337,17 +360,15 @@ struct MuxcoverWorker
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mux.selects.push_back(T1);
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mux.selects.push_back(U1);
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mux.cost += cost_mux8;
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mux.cost += find_best_cover(tree, A);
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mux.cost += find_best_cover(tree, B);
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mux.cost += find_best_cover(tree, C);
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mux.cost += find_best_cover(tree, D);
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mux.cost += find_best_cover(tree, E);
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mux.cost += find_best_cover(tree, F);
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mux.cost += find_best_cover(tree, G);
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mux.cost += find_best_cover(tree, H);
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find_best_covers(tree, mux.inputs);
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log_debug(" Decode cost for mux8 at %s: %d\n", log_signal(bit), mux.cost);
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if (best_mux.cost > mux.cost)
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mux.cost += cost_mux8;
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mux.cost += sum_best_covers(tree, mux.inputs);
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log_debug(" Cost of mux8 at %s: %d\n", log_signal(bit), mux.cost);
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if (best_mux.cost >= mux.cost)
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best_mux = mux;
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}
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}
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@ -441,25 +462,15 @@ struct MuxcoverWorker
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mux.selects.push_back(U1);
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mux.selects.push_back(V1);
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mux.cost += cost_mux16;
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mux.cost += find_best_cover(tree, A);
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mux.cost += find_best_cover(tree, B);
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mux.cost += find_best_cover(tree, C);
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mux.cost += find_best_cover(tree, D);
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mux.cost += find_best_cover(tree, E);
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mux.cost += find_best_cover(tree, F);
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mux.cost += find_best_cover(tree, G);
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mux.cost += find_best_cover(tree, H);
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mux.cost += find_best_cover(tree, I);
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mux.cost += find_best_cover(tree, J);
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mux.cost += find_best_cover(tree, K);
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mux.cost += find_best_cover(tree, L);
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mux.cost += find_best_cover(tree, M);
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mux.cost += find_best_cover(tree, N);
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mux.cost += find_best_cover(tree, O);
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mux.cost += find_best_cover(tree, P);
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find_best_covers(tree, mux.inputs);
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log_debug(" Decode cost for mux16 at %s: %d\n", log_signal(bit), mux.cost);
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if (best_mux.cost > mux.cost)
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mux.cost += cost_mux16;
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mux.cost += sum_best_covers(tree, mux.inputs);
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log_debug(" Cost of mux16 at %s: %d\n", log_signal(bit), mux.cost);
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if (best_mux.cost >= mux.cost)
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best_mux = mux;
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}
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}
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@ -555,6 +566,7 @@ struct MuxcoverWorker
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void treecover(tree_t &tree)
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{
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int count_muxes_by_type[4] = {0, 0, 0, 0};
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log_debug(" Searching for best cover for tree at %s.\n", log_signal(tree.root));
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find_best_cover(tree, tree.root);
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implement_best_cover(tree, tree.root, count_muxes_by_type);
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log(" Replaced tree at %s: %d MUX2, %d MUX4, %d MUX8, %d MUX16\n", log_signal(tree.root),
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@ -571,12 +583,13 @@ struct MuxcoverWorker
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log(" Covering trees:\n");
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// pre-fill cache of decoder muxes
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if (!nodecode)
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if (!nodecode) {
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log_debug(" Populating cache of decoder muxes.\n");
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for (auto &tree : tree_list) {
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find_best_cover(tree, tree.root);
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tree.newmuxes.clear();
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}
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}
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for (auto &tree : tree_list)
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treecover(tree);
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@ -607,6 +620,10 @@ struct MuxcoverPass : public Pass {
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log(" substitutions, but guarantees that the resulting circuit is not\n");
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log(" less efficient than the original circuit.\n");
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log("\n");
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log(" -nopartial\n");
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log(" Do not consider mappings that use $_MUX<N>_ to select from less\n");
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log(" than <N> different signals.\n");
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log("\n");
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}
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void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
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{
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