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Add splitfanout pass #4741

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Add splitfanout pass #4741

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1 change: 1 addition & 0 deletions passes/cmds/Makefile.inc
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Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@ OBJS += passes/cmds/scatter.o
OBJS += passes/cmds/setundef.o
OBJS += passes/cmds/splitnets.o
OBJS += passes/cmds/splitcells.o
OBJS += passes/cmds/splitfanout.o
OBJS += passes/cmds/stat.o
OBJS += passes/cmds/internal_stats.o
OBJS += passes/cmds/setattr.o
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244 changes: 244 additions & 0 deletions passes/cmds/splitfanout.cc
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Original file line number Diff line number Diff line change
@@ -0,0 +1,244 @@
/*
* yosys -- Yosys Open SYnthesis Suite
*
* Copyright (C) 2012 Claire Xenia Wolf <[email protected]>
* 2024 Akash Levy <[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 "kernel/yosys.h"
#include "kernel/sigtools.h"
#include "kernel/utils.h"

USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN

struct SplitfanoutWorker
{
Module *module;
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
log("Making toposort nodes for module %s...\n", log_id(module));
for (auto cell : module->selected_cells())
toposort.node(cell->name);

// Build bit_drivers_db
log("Building bit_drivers_db...\n");
for (auto cell : module->cells()) {
for (auto conn : cell->connections()) {
if (!cell->output(conn.first)) continue;
for (int i = 0; i < GetSize(conn.second); i++) {
SigBit bit(sigmap(conn.second[i]));
bit_drivers_db[bit] = tuple<IdString,IdString,int>(cell->name, conn.first, i);
}
}
}

// Build bit_users_db and add edges to topological sorter
log("Building bit_users_db and adding edges to toposort...\n");
for (auto cell : module->cells()) {
for (auto conn : cell->connections()) {
if (!cell->input(conn.first)) continue;
for (int i = 0; i < GetSize(conn.second); i++) {
SigBit bit(sigmap(conn.second[i]));
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
log("Building bit_users_db for output ports...\n");
for (auto wire : module->wires()) {
if (!wire->port_output) continue;
SigSpec sig(sigmap(wire));
for (int i = 0; i < GetSize(sig); i++) {
SigBit bit(sig[i]);
if (!bit_drivers_db.count(bit)) continue;
bit_users_db[bit].insert(tuple<IdString,IdString,int>(wire->name,
IdString(), i-std::get<2>(bit_drivers_db[bit])));
}
}

// Sort using the topological sorter
log("Sorting using toposort...\n");
toposort.analyze_loops = false;
toposort.sort();
}

int split(Cell *cell, int limit)
{
// Get output signal/port
SigSpec outsig;
IdString outport;
int output_count = 0;
for (auto conn : cell->connections())
if (cell->output(conn.first)) {
output_count++;
outport = conn.first;
outsig = conn.second;
}
if (output_count != 1) {
log("Skipping %s cell %s/%s with %d output ports.\n", log_id(cell->type), log_id(module), log_id(cell), output_count);
return 0;
}

// Check if output signal is "bit-split", skip if so
auto bit_users = bit_users_db[outsig[0]];
for (int i = 0; i < GetSize(outsig); i++) {
if (bit_users_db[outsig[i]] != bit_users) {
log("Skipping %s cell %s/%s with bit-split output.\n", log_id(cell->type), log_id(module), log_id(cell));
return 0;
}
}

// Skip if output signal has only one user
if (GetSize(bit_users) <= 1)
return 0;

// Skip if fanout is above limit
if (limit != -1 && GetSize(bit_users) > limit) {
log("Skipping %s cell %s/%s with high fanout %d.\n", log_id(cell->type), log_id(module), log_id(cell), GetSize(bit_users)-1);
return 0;
}

// Iterate over bit users and create a new cell for each one
log("Splitting %s cell %s/%s into %d copies based on fanout\n", log_id(cell->type), log_id(module), log_id(cell), GetSize(bit_users)-1);
int foi = 0;
cell->unsetPort(outport);
int num_new_cells = GetSize(bit_users)-1;
int bit_user_i = num_new_cells;
for (auto bit_user : bit_users)
{
// Configure the driver cell
IdString new_name;
Cell *new_cell;
if (bit_user_i-- != 0) { // create a new cell
new_name = module->uniquify(cell->name.str());
new_cell = module->addCell(new_name, cell);
// Add new cell to the bit_users_db
for (auto conn : new_cell->connections()) {
if (!new_cell->input(conn.first)) continue;
for (int i = 0; i < GetSize(conn.second); i++) {
SigBit bit(sigmap(conn.second[i]));
if (!bit_drivers_db.count(bit)) continue;
bit_users_db[bit].insert(tuple<IdString,IdString,int>(new_cell->name,
conn.first, i-std::get<2>(bit_drivers_db[bit])));
}
}
} else { // if last cell, reuse the original cell
new_name = cell->name;
new_cell = cell;
}

// Connect the new cell to the user
if (std::get<1>(bit_user) == IdString()) { // is wire
Wire *old_wire = module->wire(std::get<0>(bit_user));
Wire *new_wire = module->addWire(NEW_ID, old_wire);
module->swap_names(old_wire, new_wire);
old_wire->port_input = false;
old_wire->port_output = false;
SigSpec sig(new_wire, std::get<2>(bit_user), GetSize(outsig));
new_cell->setPort(outport, sig);
}
else {
Wire *new_wire = module->addWire(NEW_ID, GetSize(outsig));
Cell *target_cell = module->cell(std::get<0>(bit_user));
SigSpec sig = target_cell->getPort(std::get<1>(bit_user));
sig.replace(std::get<2>(bit_user), new_wire);
module->cell(std::get<0>(bit_user))->setPort(std::get<1>(bit_user), sig);
new_cell->setPort(outport, new_wire);
}

// Log the new cell
log_debug(" slice %d: %s => %s\n", foi++, log_id(new_name), log_signal(new_cell->getPort(outport)));
}

// Fix up ports
module->fixup_ports();

// Return the number of new cells created
return num_new_cells;
}
};

struct SplitfanoutPass : public Pass {
SplitfanoutPass() : Pass("splitfanout", "split up cells with >1 fanout into copies") { }
void help() override
{
// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
log("\n");
log(" splitfanout [selection]\n");
log("\n");
log("This command copies selected cells with >1 fanout into cells with fanout 1. It\n");
log("is effectively the opposite of the opt_merge pass.\n");
log("\n");
log("This command operates only on cells with 1 output and no 'bit split' on that\n");
log("output.\n");
log("\n");
log(" -limit n\n");
log(" max fanout to split.\n");
log("\n");
}
void execute(std::vector<std::string> args, RTLIL::Design *design) override
{
int limit = -1;
log_header(design, "Executing SPLITFANOUT pass (splitting up cells with >1 fanout into copies).\n");

size_t argidx;
for (argidx = 1; argidx < args.size(); argidx++)
{
// No options currently. When adding in the future make sure to update docstring with [options]
if (args[argidx] == "-limit" && argidx+1 < args.size()) {
limit = std::stoi(args[++argidx]);
continue;
}
break;
}
extra_args(args, argidx, design);

for (auto module : design->selected_modules())
{
int count_split_pre = 0;
int count_split_post = 0;

SplitfanoutWorker worker(module);
for (auto cell : worker.toposort.sorted) {
int n = worker.split(module->cell(cell), limit);
count_split_pre += (n != 0);
count_split_post += n;
}

if (count_split_pre)
log("Split %d cells in module '%s' into %d copies based on fanout.\n",
count_split_pre, log_id(module), count_split_post);
}

Pass::call(design, "clean *");
}
} SplitfanoutPass;

PRIVATE_NAMESPACE_END