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OpenSTA/search/CheckFanouts.cc

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// OpenSTA, Static Timing Analyzer
// Copyright (c) 2026, Parallax Software, Inc.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <https://www.gnu.org/licenses/>.
//
// The origin of this software must not be misrepresented; you must not
// claim that you wrote the original software.
//
// Altered source versions must be plainly marked as such, and must not be
// misrepresented as being the original software.
//
// This notice may not be removed or altered from any source distribution.
#include "CheckFanouts.hh"
#include "ContainerHelpers.hh"
#include "Fuzzy.hh"
#include "Liberty.hh"
#include "Network.hh"
#include "Sdc.hh"
#include "Mode.hh"
#include "InputDrive.hh"
#include "Sim.hh"
#include "PortDirection.hh"
#include "Graph.hh"
#include "Search.hh"
#include "ClkNetwork.hh"
namespace sta {
CheckFanouts::CheckFanouts(const Sta *sta) :
sta_(sta),
heap_(0, FanoutCheckSlackLess(sta))
{
}
void
CheckFanouts::clear()
{
checks_.clear();
heap_.clear();
}
FanoutCheck
CheckFanouts::check(const Pin *pin,
const Mode *mode,
const MinMax *min_max) const
{
FanoutCheck min_slack_check;
float fanout = fanoutLoad(pin);
if (checkPin(pin, mode)) {
float limit;
bool limit_exists;
findLimit(pin, mode->sdc(), min_max, limit, limit_exists);
if (limit_exists) {
float slack = (min_max == MinMax::max())
? limit - fanout
: fanout - limit;
return FanoutCheck(pin, fanout, limit, slack, mode);
}
}
return FanoutCheck();
}
// return the tightest limit.
void
CheckFanouts::findLimit(const Pin *pin,
const Sdc *sdc,
const MinMax *min_max,
// Return values.
float &limit,
bool &exists) const
{
const Network *network = sta_->network();
limit = min_max->initValue();
exists = false;
// Default to top ("design") limit.
// Applies to input ports as well as instance outputs.
Cell *top_cell = network->cell(network->topInstance());
sdc->fanoutLimit(top_cell, min_max,
limit, exists);
float limit1;
bool exists1;
if (network->isTopLevelPort(pin)) {
Port *port = network->port(pin);
sdc->fanoutLimit(port, min_max, limit1, exists1);
if (exists1
&& (!exists
|| min_max->compare(limit, limit1))) {
limit = limit1;
exists = true;
}
InputDrive *drive = sdc->findInputDrive(port);
if (drive) {
for (auto rf : RiseFall::range()) {
const LibertyCell *cell;
const LibertyPort *from_port;
float *from_slews;
const LibertyPort *to_port;
drive->driveCell(rf, min_max, cell, from_port, from_slews, to_port);
if (to_port) {
to_port->fanoutLimit(min_max, limit1, exists1);
if (!exists1
&& min_max == MinMax::max()
&& to_port->direction()->isAnyOutput())
to_port->libertyLibrary()->defaultMaxFanout(limit1, exists1);
if (exists1
&& (!exists
|| min_max->compare(limit, limit1))) {
limit = limit1;
exists = true;
}
}
}
}
}
else {
Cell *cell = network->cell(network->instance(pin));
sdc->fanoutLimit(cell, min_max,
limit1, exists1);
if (exists1
&& (!exists
|| min_max->compare(limit, limit1))) {
limit = limit1;
exists = true;
}
LibertyPort *port = network->libertyPort(pin);
if (port) {
port->fanoutLimit(min_max, limit1, exists1);
if (!exists1
&& min_max == MinMax::max()
&& port->direction()->isAnyOutput())
port->libertyLibrary()->defaultMaxFanout(limit1, exists1);
if (exists1
&& (!exists
|| min_max->compare(limit, limit1))) {
limit = limit1;
exists = true;
}
}
}
}
float
CheckFanouts::fanoutLoad(const Pin *pin) const
{
float fanout = 0;
const Network *network = sta_->network();
NetConnectedPinIterator *pin_iter = network->connectedPinIterator(pin);
while (pin_iter->hasNext()) {
const Pin *fanout_pin = pin_iter->next();
if (network->isLoad(fanout_pin)
&& !network->isTopLevelPort(fanout_pin)) {
LibertyPort *port = network->libertyPort(fanout_pin);
if (port) {
float fanout_load;
bool exists;
port->fanoutLoad(fanout_load, exists);
if (!exists) {
LibertyLibrary *lib = port->libertyLibrary();
lib->defaultFanoutLoad(fanout_load, exists);
}
if (exists)
fanout += fanout_load;
}
else
fanout += 1;
}
}
delete pin_iter;
return fanout;
}
////////////////////////////////////////////////////////////////
FanoutCheckSeq &
CheckFanouts::check(const Net *net,
size_t max_count,
bool violators,
const ModeSeq &modes,
const MinMax *min_max)
{
clear();
if (!violators)
heap_.setMaxSize(max_count);
if (net)
checkNet(net, violators, modes, min_max);
else
checkAll(violators, modes, min_max);
if (violators)
sort(checks_, FanoutCheckSlackLess(sta_));
else
checks_ = heap_.extract();
return checks_;
}
void
CheckFanouts::checkNet(const Net *net,
bool violators,
const ModeSeq &modes,
const MinMax *min_max)
{
const Network *network = sta_->network();
if (net) {
NetPinIterator *pin_iter = network->pinIterator(net);
while (pin_iter->hasNext()) {
const Pin *pin = pin_iter->next();
checkPin(pin, violators, modes, min_max);
}
delete pin_iter;
}
}
void
CheckFanouts::checkAll(bool violators,
const ModeSeq &modes,
const MinMax *min_max)
{
const Network *network = sta_->network();
LeafInstanceIterator *inst_iter = network->leafInstanceIterator();
while (inst_iter->hasNext()) {
const Instance *inst = inst_iter->next();
checkInst(inst, violators, modes, min_max);
}
delete inst_iter;
// Check top level ports.
checkInst(network->topInstance(), violators, modes, min_max);
}
void
CheckFanouts::checkInst(const Instance *inst,
bool violators,
const ModeSeq &modes,
const MinMax *min_max)
{
const Network *network = sta_->network();
InstancePinIterator *pin_iter = network->pinIterator(inst);
while (pin_iter->hasNext()) {
const Pin *pin = pin_iter->next();
checkPin(pin, violators, modes, min_max);
}
delete pin_iter;
}
void
CheckFanouts::checkPin(const Pin *pin,
bool violators,
const ModeSeq &modes,
const MinMax *min_max)
{
for (const Mode *mode : modes) {
if (checkPin(pin, mode)) {
FanoutCheck fanout_check = check(pin, mode, min_max);
if (!fanout_check.isNull()) {
if (violators) {
if (fanout_check.slack() < 0.0)
checks_.push_back(fanout_check);
}
else
heap_.insert(fanout_check);
}
}
}
}
bool
CheckFanouts::checkPin(const Pin *pin,
const Mode *mode) const
{
const Network *network = sta_->network();
return network->isDriver(pin)
&& !mode->sim()->isConstant(pin)
&& !mode->sdc()->isDisabledConstraint(pin)
&& !mode->clkNetwork()->isIdealClock(pin);
}
////////////////////////////////////////////////////////////////
FanoutCheck::FanoutCheck() :
pin_(nullptr),
fanout_(0.0),
limit_(INF),
slack_(INF),
mode_(nullptr)
{
}
FanoutCheck::FanoutCheck(const Pin *pin,
float fanout,
float limit,
float slack,
const Mode *mode) :
pin_(pin),
fanout_(fanout),
limit_(limit),
slack_(slack),
mode_(mode)
{
}
////////////////////////////////////////////////////////////////
FanoutCheckSlackLess::FanoutCheckSlackLess(const StaState *sta) :
sta_(sta)
{
}
bool
FanoutCheckSlackLess::operator()(const FanoutCheck &check1,
const FanoutCheck &check2) const
{
return fuzzyLess(check1.slack(), check2.slack())
|| (fuzzyEqual(check1.slack(), check2.slack())
// Break ties for the sake of regression stability.
&& sta_->network()->pinLess(check1.pin(), check2.pin()));
}
} // namespace
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