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Improvements in muxcover

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- 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 2019-06-20 11:30:27 +02:00 • committed by Eddie Hung
parent 844c42cef8
commit 891ea6512e
1 changed files with 56 additions and 39 deletions
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95
passes/techmap/muxcover.cc
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@ -178,7 +178,7 @@ struct MuxcoverWorker
if (A == State::Sx || B == State::Sx) if (A == State::Sx || B == State::Sx)
return 0; return 0;
return cost_mux2 / GetSize(std::get<1>(entry)); return std::max((cost_mux2 / GetSize(std::get<1>(entry))) - 1, 1);
} }
void implement_decode_mux(SigBit ctrl_bit) void implement_decode_mux(SigBit ctrl_bit)
@ -206,6 +206,23 @@ struct MuxcoverWorker
std::get<2>(entry) = true; std::get<2>(entry) = true;
} }
void find_best_covers(tree_t &tree, const vector<SigBit> &bits)
{
for (auto bit : bits)
find_best_cover(tree, bit);
}
int sum_best_covers(tree_t &tree, const vector<SigBit> &bits)
{
int sum = 0;
for (auto bit : pool<SigBit>(bits.begin(), bits.end())) {
int cost = tree.newmuxes.at(bit).cost;
log_debug(" Best cost for %s: %d\n", log_signal(bit), cost);
sum += cost;
}
return sum;
}
int find_best_cover(tree_t &tree, SigBit bit) int find_best_cover(tree_t &tree, SigBit bit)
{ {
if (tree.newmuxes.count(bit)) { if (tree.newmuxes.count(bit)) {
@ -236,9 +253,13 @@ struct MuxcoverWorker
mux.inputs.push_back(B); mux.inputs.push_back(B);
mux.selects.push_back(S1); mux.selects.push_back(S1);
find_best_covers(tree, mux.inputs);
log_debug(" Decode cost for mux2 at %s: %d\n", log_signal(bit), mux.cost);
mux.cost += cost_mux2; mux.cost += cost_mux2;
mux.cost += find_best_cover(tree, A); mux.cost += sum_best_covers(tree, mux.inputs);
mux.cost += find_best_cover(tree, B);
log_debug(" Cost of mux2 at %s: %d\n", log_signal(bit), mux.cost);
best_mux = mux; best_mux = mux;
} }
@ -274,13 +295,15 @@ struct MuxcoverWorker
mux.selects.push_back(S1); mux.selects.push_back(S1);
mux.selects.push_back(T1); mux.selects.push_back(T1);
mux.cost += cost_mux4; find_best_covers(tree, mux.inputs);
mux.cost += find_best_cover(tree, A); log_debug(" Decode cost for mux4 at %s: %d\n", log_signal(bit), mux.cost);
mux.cost += find_best_cover(tree, B);
mux.cost += find_best_cover(tree, C);
mux.cost += find_best_cover(tree, D);
if (best_mux.cost > mux.cost) mux.cost += cost_mux4;
mux.cost += sum_best_covers(tree, mux.inputs);
log_debug(" Cost of mux4 at %s: %d\n", log_signal(bit), mux.cost);
if (best_mux.cost >= mux.cost)
best_mux = mux; best_mux = mux;
} }
} }
@ -337,17 +360,15 @@ struct MuxcoverWorker
mux.selects.push_back(T1); mux.selects.push_back(T1);
mux.selects.push_back(U1); mux.selects.push_back(U1);
mux.cost += cost_mux8; find_best_covers(tree, mux.inputs);
mux.cost += find_best_cover(tree, A); log_debug(" Decode cost for mux8 at %s: %d\n", log_signal(bit), mux.cost);
mux.cost += find_best_cover(tree, B);
mux.cost += find_best_cover(tree, C);
mux.cost += find_best_cover(tree, D);
mux.cost += find_best_cover(tree, E);
mux.cost += find_best_cover(tree, F);
mux.cost += find_best_cover(tree, G);
mux.cost += find_best_cover(tree, H);
if (best_mux.cost > mux.cost) mux.cost += cost_mux8;
mux.cost += sum_best_covers(tree, mux.inputs);
log_debug(" Cost of mux8 at %s: %d\n", log_signal(bit), mux.cost);
if (best_mux.cost >= mux.cost)
best_mux = mux; best_mux = mux;
} }
} }
@ -441,25 +462,15 @@ struct MuxcoverWorker
mux.selects.push_back(U1); mux.selects.push_back(U1);
mux.selects.push_back(V1); mux.selects.push_back(V1);
mux.cost += cost_mux16; find_best_covers(tree, mux.inputs);
mux.cost += find_best_cover(tree, A); log_debug(" Decode cost for mux16 at %s: %d\n", log_signal(bit), mux.cost);
mux.cost += find_best_cover(tree, B);
mux.cost += find_best_cover(tree, C);
mux.cost += find_best_cover(tree, D);
mux.cost += find_best_cover(tree, E);
mux.cost += find_best_cover(tree, F);
mux.cost += find_best_cover(tree, G);
mux.cost += find_best_cover(tree, H);
mux.cost += find_best_cover(tree, I);
mux.cost += find_best_cover(tree, J);
mux.cost += find_best_cover(tree, K);
mux.cost += find_best_cover(tree, L);
mux.cost += find_best_cover(tree, M);
mux.cost += find_best_cover(tree, N);
mux.cost += find_best_cover(tree, O);
mux.cost += find_best_cover(tree, P);
if (best_mux.cost > mux.cost) mux.cost += cost_mux16;
mux.cost += sum_best_covers(tree, mux.inputs);
log_debug(" Cost of mux16 at %s: %d\n", log_signal(bit), mux.cost);
if (best_mux.cost >= mux.cost)
best_mux = mux; best_mux = mux;
} }
} }
@ -555,6 +566,7 @@ struct MuxcoverWorker
void treecover(tree_t &tree) void treecover(tree_t &tree)
{ {
int count_muxes_by_type[4] = {0, 0, 0, 0}; int count_muxes_by_type[4] = {0, 0, 0, 0};
log_debug(" Searching for best cover for tree at %s.\n", log_signal(tree.root));
find_best_cover(tree, tree.root); find_best_cover(tree, tree.root);
implement_best_cover(tree, tree.root, count_muxes_by_type); implement_best_cover(tree, tree.root, count_muxes_by_type);
log(" Replaced tree at %s: %d MUX2, %d MUX4, %d MUX8, %d MUX16\n", log_signal(tree.root), log(" Replaced tree at %s: %d MUX2, %d MUX4, %d MUX8, %d MUX16\n", log_signal(tree.root),
@ -571,12 +583,13 @@ struct MuxcoverWorker
log(" Covering trees:\n"); log(" Covering trees:\n");
// pre-fill cache of decoder muxes if (!nodecode) {
if (!nodecode) log_debug(" Populating cache of decoder muxes.\n");
for (auto &tree : tree_list) { for (auto &tree : tree_list) {
find_best_cover(tree, tree.root); find_best_cover(tree, tree.root);
tree.newmuxes.clear(); tree.newmuxes.clear();
} }
}
for (auto &tree : tree_list) for (auto &tree : tree_list)
treecover(tree); treecover(tree);
@ -607,6 +620,10 @@ struct MuxcoverPass : public Pass {
log(" substitutions, but guarantees that the resulting circuit is not\n"); log(" substitutions, but guarantees that the resulting circuit is not\n");
log(" less efficient than the original circuit.\n"); log(" less efficient than the original circuit.\n");
log("\n"); log("\n");
log(" -nopartial\n");
log(" Do not consider mappings that use $_MUX<N>_ to select from less\n");
log(" than <N> different signals.\n");
log("\n");
} }
void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
{ {