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Use topological sorting for split fanout to get maximal splitting

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This commit is contained in:
Akash Levy 2024-10-25 02:07:03 -07:00
parent 7864c6dd34
commit 5e0475fc89
1 changed files with 20 additions and 2 deletions
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22
passes/cmds/splitfanout.cc
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@ -20,6 +20,7 @@
#include "kernel/yosys.h"
#include "kernel/sigtools.h"
#include "kernel/utils.h"
USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN
@ -30,9 +31,15 @@ struct SplitfanoutWorker
SigMap sigmap;
dict<SigBit, tuple<IdString,IdString,int>> bit_drivers_db;
dict<SigBit, pool<tuple<IdString,IdString,int>>> bit_users_db;
TopoSort<IdString, RTLIL::sort_by_id_str> toposort;
SplitfanoutWorker(Module *module) : module(module), sigmap(module)
{
// Add nodes to topological sorter for all selected cells
for (auto cell : module->selected_cells())
toposort.node(cell->name);
// Build bit_drivers_db
for (auto cell : module->cells()) {
for (auto conn : cell->connections()) {
if (!cell->output(conn.first)) continue;
@ -43,6 +50,7 @@ struct SplitfanoutWorker
}
}
// Build bit_users_db and add edges to topological sorter
for (auto cell : module->cells()) {
for (auto conn : cell->connections()) {
if (!cell->input(conn.first)) continue;
@ -51,10 +59,15 @@ struct SplitfanoutWorker
if (!bit_drivers_db.count(bit)) continue;
bit_users_db[bit].insert(tuple<IdString,IdString,int>(cell->name,
conn.first, i-std::get<2>(bit_drivers_db[bit])));
IdString driver_cell = std::get<0>(bit_drivers_db[bit]);
if (toposort.has_node(driver_cell) && toposort.has_node(cell->name))
// toposort.edge(driver_cell, cell->name);
toposort.edge(cell->name, driver_cell);
}
}
}
// Build bit_users_db for output ports
for (auto wire : module->wires()) {
if (!wire->port_output) continue;
SigSpec sig(sigmap(wire));
@ -65,6 +78,10 @@ struct SplitfanoutWorker
IdString(), i-std::get<2>(bit_drivers_db[bit])));
}
}
// Sort using the topological sorter
toposort.analyze_loops = false;
toposort.sort();
}
int split(Cell *cell)
@ -89,6 +106,7 @@ struct SplitfanoutWorker
for (int i = 0; i < GetSize(outsig); i++) {
if (bit_users_db[outsig[i]] != bit_users) {
log_debug("Skipping %s cell %s/%s with bit-split output.\n", log_id(cell->type), log_id(module), log_id(cell));
cell->set_bool_attribute(IdString("\\bitsplit"));
return 0;
}
}
@ -192,8 +210,8 @@ struct SplitfanoutPass : public Pass {
while (1) {
SplitfanoutWorker worker(module);
bool did_something = false;
for (auto cell : module->selected_cells()) {
int n = worker.split(cell);
for (auto cell : worker.toposort.sorted) {
int n = worker.split(module->cell(cell));
did_something |= (n != 0);
count_split_pre += (n != 0);
count_split_post += n;