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yosys/techlibs/xilinx/xilinx_dffopt.cc
Robert O'Callahan 09b493cfcd Update techlibs to avoid bits()
2025-09-16 03:17:23 +00:00

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/*
* yosys -- Yosys Open SYnthesis Suite
*
* Copyright (C) 2012 Claire Xenia Wolf <claire@yosyshq.com>
*
* 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"
USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN
typedef std::pair<Const, std::vector<SigBit>> LutData;
// Compute a LUT implementing (select ^ select_inv) ? alt_data : data. Returns true if successful.
bool merge_lut(LutData &result, const LutData &data, const LutData select, bool select_inv, SigBit alt_data, int max_lut_size) {
// First, gather input signals -- insert new signals at the beginning
// of the vector, so they don't disturb the likely-critical D LUT input
// timings.
result.second = data.second;
// D lut inputs initially start at 0.
int idx_data = 0;
// Now add the control input LUT inputs.
std::vector<int> idx_sel;
for (auto bit : select.second) {
int idx = -1;
for (int i = 0; i < GetSize(result.second); i++)
if (result.second[i] == bit)
idx = i;
if (idx == -1) {
idx = 0;
// Insert new signal at the beginning and bump all indices.
result.second.insert(result.second.begin(), bit);
idx_data++;
for (int &sidx : idx_sel)
sidx++;
}
idx_sel.push_back(idx);
}
// Insert the Q signal, if any, to the slowest input -- it will have
// no problem meeting timing.
int idx_alt = -1;
if (alt_data.wire) {
// Check if we already have it.
for (int i = 0; i < GetSize(result.second); i++)
if (result.second[i] == alt_data)
idx_alt = i;
// If not, add it.
if (idx_alt == -1) {
idx_alt = 0;
result.second.insert(result.second.begin(), alt_data);
idx_data++;
for (int &sidx : idx_sel)
sidx++;
}
}
// If LUT would be too large, bail.
if (GetSize(result.second) > max_lut_size)
return false;
// Okay, we're doing it — compute the LUT mask.
result.first = Const(0, 1 << GetSize(result.second));
for (int i = 0; i < GetSize(result.first); i++) {
int sel_lut_idx = 0;
for (int j = 0; j < GetSize(select.second); j++)
if (i & 1 << idx_sel[j])
sel_lut_idx |= 1 << j;
bool select_val = (select.first[sel_lut_idx] == State::S1);
bool new_bit;
if (select_val ^ select_inv) {
// Use alt_data.
if (alt_data.wire)
new_bit = (i & 1 << idx_alt) != 0;
else
new_bit = alt_data.data == State::S1;
} else {
// Use original LUT.
int lut_idx = i >> idx_data & ((1 << GetSize(data.second)) - 1);
new_bit = data.first[lut_idx] == State::S1;
}
result.first.set(i, new_bit ? State::S1 : State::S0);
}
return true;
}
struct XilinxDffOptPass : public Pass {
XilinxDffOptPass() : Pass("xilinx_dffopt", "Xilinx: optimize FF control signal usage") { }
void help() override
{
// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
log("\n");
log(" xilinx_dffopt [options] [selection]\n");
log("\n");
log("Converts hardware clock enable and set/reset signals on FFs to emulation\n");
log("using LUTs, if doing so would improve area. Operates on post-techmap Xilinx\n");
log("cells (LUT*, FD*).\n");
log("\n");
log(" -lut4\n");
log(" Assume a LUT4-based device (instead of a LUT6-based device).\n");
log("\n");
}
void execute(std::vector<std::string> args, RTLIL::Design *design) override
{
log_header(design, "Executing XILINX_DFFOPT pass (optimize FF control signal usage).\n");
size_t argidx;
int max_lut_size = 6;
for (argidx = 1; argidx < args.size(); argidx++)
{
if (args[argidx] == "-lut4") {
max_lut_size = 4;
continue;
}
break;
}
extra_args(args, argidx, design);
for (auto module : design->selected_modules())
{
log("Optimizing FFs in %s.\n", log_id(module));
SigMap sigmap(module);
dict<SigBit, pair<LutData, Cell *>> bit_to_lut;
dict<SigBit, int> bit_uses;
// Gather LUTs.
for (auto cell : module->selected_cells())
{
for (auto port : cell->connections())
for (auto bit : port.second)
bit_uses[sigmap(bit)]++;
if (cell->get_bool_attribute(ID::keep))
continue;
if (cell->type == ID(INV)) {
SigBit sigout = sigmap(cell->getPort(ID::O));
SigBit sigin = sigmap(cell->getPort(ID::I));
bit_to_lut[sigout] = make_pair(LutData(Const(1, 2), {sigin}), cell);
} else if (cell->type.in(ID(LUT1), ID(LUT2), ID(LUT3), ID(LUT4), ID(LUT5), ID(LUT6))) {
SigBit sigout = sigmap(cell->getPort(ID::O));
const Const &init = cell->getParam(ID::INIT);
std::vector<SigBit> sigin;
sigin.push_back(sigmap(cell->getPort(ID(I0))));
if (cell->type == ID(LUT1))
goto lut_sigin_done;
sigin.push_back(sigmap(cell->getPort(ID(I1))));
if (cell->type == ID(LUT2))
goto lut_sigin_done;
sigin.push_back(sigmap(cell->getPort(ID(I2))));
if (cell->type == ID(LUT3))
goto lut_sigin_done;
sigin.push_back(sigmap(cell->getPort(ID(I3))));
if (cell->type == ID(LUT4))
goto lut_sigin_done;
sigin.push_back(sigmap(cell->getPort(ID(I4))));
if (cell->type == ID(LUT5))
goto lut_sigin_done;
sigin.push_back(sigmap(cell->getPort(ID(I5))));
lut_sigin_done:
bit_to_lut[sigout] = make_pair(LutData(init, sigin), cell);
}
}
for (auto wire : module->wires())
if (wire->port_output || wire->port_input)
for (int i = 0; i < GetSize(wire); i++)
bit_uses[sigmap(SigBit(wire, i))]++;
// Iterate through FFs.
for (auto cell : module->selected_cells())
{
bool has_s = false, has_r = false;
if (cell->type.in(ID(FDCE), ID(FDPE), ID(FDCPE), ID(FDCE_1), ID(FDPE_1), ID(FDCPE_1))) {
// Async reset.
} else if (cell->type.in(ID(FDRE), ID(FDRE_1))) {
has_r = true;
} else if (cell->type.in(ID(FDSE), ID(FDSE_1))) {
has_s = true;
} else if (cell->type.in(ID(FDRSE), ID(FDRSE_1))) {
has_r = true;
has_s = true;
} else {
// Not a FF.
continue;
}
if (cell->get_bool_attribute(ID::keep))
continue;
// Don't bother if D has more than one use.
SigBit sig_D = sigmap(cell->getPort(ID::D));
if (bit_uses[sig_D] > 2)
continue;
// Find the D LUT.
auto it_D = bit_to_lut.find(sig_D);
if (it_D == bit_to_lut.end())
continue;
LutData lut_d = it_D->second.first;
Cell *cell_d = it_D->second.second;
if (cell->hasParam(ID(IS_D_INVERTED)) && cell->getParam(ID(IS_D_INVERTED)).as_bool()) {
// Flip all bits in the LUT.
for (auto bit : lut_d.first)
bit = (bit == State::S1) ? State::S0 : State::S1;
}
LutData lut_d_post_ce;
LutData lut_d_post_s;
LutData lut_d_post_r;
bool worthy_post_ce = false;
bool worthy_post_s = false;
bool worthy_post_r = false;
// First, unmap CE.
SigBit sig_Q = sigmap(cell->getPort(ID::Q));
SigBit sig_CE = sigmap(cell->getPort(ID(CE)));
LutData lut_ce = LutData(Const(2, 2), {sig_CE});
auto it_CE = bit_to_lut.find(sig_CE);
if (it_CE != bit_to_lut.end())
lut_ce = it_CE->second.first;
if (sig_CE.wire) {
// Merge CE LUT and D LUT into one. If it cannot be done, nothing to do about this FF.
if (!merge_lut(lut_d_post_ce, lut_d, lut_ce, true, sig_Q, max_lut_size))
continue;
// If this gets rid of a CE LUT, it's worth it. If not, it still may be worth it, if we can remove set/reset as well.
if (it_CE != bit_to_lut.end())
worthy_post_ce = true;
} else if (sig_CE.data != State::S1) {
// Strange. Should not happen in a reasonable flow, so bail.
continue;
} else {
lut_d_post_ce = lut_d;
}
// Second, unmap S, if any.
lut_d_post_s = lut_d_post_ce;
if (has_s) {
SigBit sig_S = sigmap(cell->getPort(ID::S));
LutData lut_s = LutData(Const(2, 2), {sig_S});
bool inv_s = cell->hasParam(ID(IS_S_INVERTED)) && cell->getParam(ID(IS_S_INVERTED)).as_bool();
auto it_S = bit_to_lut.find(sig_S);
if (it_S != bit_to_lut.end())
lut_s = it_S->second.first;
if (sig_S.wire) {
// Merge S LUT and D LUT into one. If it cannot be done, try to at least merge CE.
if (!merge_lut(lut_d_post_s, lut_d_post_ce, lut_s, inv_s, SigBit(State::S1), max_lut_size))
goto unmap;
// If this gets rid of an S LUT, it's worth it.
if (it_S != bit_to_lut.end())
worthy_post_s = true;
} else if (sig_S.data != (inv_s ? State::S1 : State::S0)) {
// Strange. Should not happen in a reasonable flow, so bail.
continue;
}
}
// Third, unmap R, if any.
lut_d_post_r = lut_d_post_s;
if (has_r) {
SigBit sig_R = sigmap(cell->getPort(ID::R));
LutData lut_r = LutData(Const(2, 2), {sig_R});
bool inv_r = cell->hasParam(ID(IS_R_INVERTED)) && cell->getParam(ID(IS_R_INVERTED)).as_bool();
auto it_R = bit_to_lut.find(sig_R);
if (it_R != bit_to_lut.end())
lut_r = it_R->second.first;
if (sig_R.wire) {
// Merge R LUT and D LUT into one. If it cannot be done, try to at least merge CE/S.
if (!merge_lut(lut_d_post_r, lut_d_post_s, lut_r, inv_r, SigBit(State::S0), max_lut_size))
goto unmap;
// If this gets rid of an S LUT, it's worth it.
if (it_R != bit_to_lut.end())
worthy_post_r = true;
} else if (sig_R.data != (inv_r ? State::S1 : State::S0)) {
// Strange. Should not happen in a reasonable flow, so bail.
continue;
}
}
unmap:
LutData final_lut;
if (worthy_post_r) {
final_lut = lut_d_post_r;
} else if (worthy_post_s) {
final_lut = lut_d_post_s;
} else if (worthy_post_ce) {
final_lut = lut_d_post_ce;
} else {
// Nothing to do here.
continue;
}
std::string ports;
if (worthy_post_r) ports += " + R";
if (worthy_post_s) ports += " + S";
if (worthy_post_ce) ports += " + CE";
log(" Merging D%s LUTs for %s/%s (%d -> %d)\n", ports, log_id(cell), log_id(sig_Q.wire), GetSize(lut_d.second), GetSize(final_lut.second));
// Okay, we're doing it. Unmap ports.
if (worthy_post_r) {
cell->unsetParam(ID(IS_R_INVERTED));
cell->setPort(ID::R, Const(0, 1));
}
if (has_s && (worthy_post_r || worthy_post_s)) {
cell->unsetParam(ID(IS_S_INVERTED));
cell->setPort(ID::S, Const(0, 1));
}
cell->setPort(ID(CE), Const(1, 1));
cell->unsetParam(ID(IS_D_INVERTED));
// Create the new LUT.
Cell *lut_cell = 0;
switch (GetSize(final_lut.second)) {
case 1:
lut_cell = module->addCell(NEW_ID, ID(LUT1));
break;
case 2:
lut_cell = module->addCell(NEW_ID, ID(LUT2));
break;
case 3:
lut_cell = module->addCell(NEW_ID, ID(LUT3));
break;
case 4:
lut_cell = module->addCell(NEW_ID, ID(LUT4));
break;
case 5:
lut_cell = module->addCell(NEW_ID, ID(LUT5));
break;
case 6:
lut_cell = module->addCell(NEW_ID, ID(LUT6));
break;
default:
log_assert(!"unknown lut size");
}
lut_cell->attributes = cell_d->attributes;
Wire *lut_out = module->addWire(NEW_ID);
lut_cell->setParam(ID::INIT, final_lut.first);
cell->setPort(ID::D, lut_out);
lut_cell->setPort(ID::O, lut_out);
lut_cell->setPort(ID(I0), final_lut.second[0]);
if (GetSize(final_lut.second) >= 2)
lut_cell->setPort(ID(I1), final_lut.second[1]);
if (GetSize(final_lut.second) >= 3)
lut_cell->setPort(ID(I2), final_lut.second[2]);
if (GetSize(final_lut.second) >= 4)
lut_cell->setPort(ID(I3), final_lut.second[3]);
if (GetSize(final_lut.second) >= 5)
lut_cell->setPort(ID(I4), final_lut.second[4]);
if (GetSize(final_lut.second) >= 6)
lut_cell->setPort(ID(I5), final_lut.second[5]);
}
}
}
} XilinxDffOptPass;
PRIVATE_NAMESPACE_END
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