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Merge pull request #1046 from bogdanvuk/master

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Optimizing DFFs whose initial value prevents their value from changing
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Clifford Wolf 2019-06-28 08:30:18 +02:00 • committed by GitHub
commit 1c7ce251f3
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5 changed files with 128 additions and 17 deletions
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8
passes/opt/opt.cc
View file

@ -44,7 +44,7 @@ struct OptPass : public Pass {
log(" opt_muxtree\n");
log(" opt_reduce [-fine] [-full]\n");
log(" opt_merge [-share_all]\n");
log(" opt_rmdff [-keepdc]\n");
log(" opt_rmdff [-keepdc] [-sat]\n");
log(" opt_clean [-purge]\n");
log(" opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
log(" while <changed design>\n");
@ -54,7 +54,7 @@ struct OptPass : public Pass {
log(" do\n");
log(" opt_expr [-mux_undef] [-mux_bool] [-undriven] [-clkinv] [-fine] [-full] [-keepdc]\n");
log(" opt_merge [-share_all]\n");
log(" opt_rmdff [-keepdc]\n");
log(" opt_rmdff [-keepdc] [-sat]\n");
log(" opt_clean [-purge]\n");
log(" while <changed design in opt_rmdff>\n");
log("\n");
@ -112,6 +112,10 @@ struct OptPass : public Pass {
opt_rmdff_args += " -keepdc";
continue;
}
if (args[argidx] == "-sat") {
opt_rmdff_args += " -sat";
continue;
}
if (args[argidx] == "-share_all") {
opt_merge_args += " -share_all";
continue;

111
passes/opt/opt_rmdff.cc
View file

@ -17,19 +17,24 @@
*
*/
#include "kernel/register.h"
#include "kernel/sigtools.h"
#include "kernel/log.h"
#include <stdlib.h>
#include "kernel/register.h"
#include "kernel/rtlil.h"
#include "kernel/satgen.h"
#include "kernel/sigtools.h"
#include <stdio.h>
#include <stdlib.h>
USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN
SigMap assign_map, dff_init_map;
SigSet<RTLIL::Cell*> mux_drivers;
dict<SigBit, RTLIL::Cell*> bit2driver;
dict<SigBit, pool<SigBit>> init_attributes;
bool keepdc;
bool sat;
void remove_init_attr(SigSpec sig)
{
@ -452,12 +457,84 @@ bool handle_dff(RTLIL::Module *mod, RTLIL::Cell *dff)
dff->unsetPort("\\E");
}
if (sat && has_init && (!sig_r.size() || val_init == val_rv))
{
bool removed_sigbits = false;
ezSatPtr ez;
SatGen satgen(ez.get(), &assign_map);
pool<Cell*> sat_cells;
std::function<void(Cell*)> sat_import_cell = [&](Cell *c) {
if (!sat_cells.insert(c).second)
return;
if (!satgen.importCell(c))
return;
for (auto &conn : c->connections()) {
if (!c->input(conn.first))
continue;
for (auto bit : assign_map(conn.second))
if (bit2driver.count(bit))
sat_import_cell(bit2driver.at(bit));
}
};
// For each register bit, try to prove that it cannot change from the initial value. If so, remove it
for (int position = 0; position < GetSize(sig_d); position += 1) {
RTLIL::SigBit q_sigbit = sig_q[position];
RTLIL::SigBit d_sigbit = sig_d[position];
if ((!q_sigbit.wire) || (!d_sigbit.wire))
continue;
if (!bit2driver.count(d_sigbit))
continue;
sat_import_cell(bit2driver.at(d_sigbit));
RTLIL::State sigbit_init_val = val_init[position];
if (sigbit_init_val != State::S0 && sigbit_init_val != State::S1)
continue;
int init_sat_pi = satgen.importSigSpec(sigbit_init_val).front();
int q_sat_pi = satgen.importSigBit(q_sigbit);
int d_sat_pi = satgen.importSigBit(d_sigbit);
// Try to find out whether the register bit can change under some circumstances
bool counter_example_found = ez->solve(ez->IFF(q_sat_pi, init_sat_pi), ez->NOT(ez->IFF(d_sat_pi, init_sat_pi)));
// If the register bit cannot change, we can replace it with a constant
if (!counter_example_found)
{
log("Setting constant %d-bit at position %d on %s (%s) from module %s.\n", sigbit_init_val ? 1 : 0,
position, log_id(dff), log_id(dff->type), log_id(mod));
SigSpec tmp = dff->getPort("\\D");
tmp[position] = sigbit_init_val;
dff->setPort("\\D", tmp);
removed_sigbits = true;
}
}
if (removed_sigbits) {
handle_dff(mod, dff);
return true;
}
}
return false;
delete_dff:
log("Removing %s (%s) from module %s.\n", log_id(dff), log_id(dff->type), log_id(mod));
remove_init_attr(dff->getPort("\\Q"));
mod->remove(dff);
for (auto &entry : bit2driver)
if (entry.second == dff)
bit2driver.erase(entry.first);
return true;
}
@ -467,11 +544,15 @@ struct OptRmdffPass : public Pass {
{
// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
log("\n");
log(" opt_rmdff [-keepdc] [selection]\n");
log(" opt_rmdff [-keepdc] [-sat] [selection]\n");
log("\n");
log("This pass identifies flip-flops with constant inputs and replaces them with\n");
log("a constant driver.\n");
log("\n");
log(" -sat\n");
log(" additionally invoke SAT solver to detect and remove flip-flops (with \n");
log(" non-constant inputs) that can also be replaced with a constant driver\n");
log("\n");
}
void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
{
@ -479,6 +560,7 @@ struct OptRmdffPass : public Pass {
log_header(design, "Executing OPT_RMDFF pass (remove dff with constant values).\n");
keepdc = false;
sat = false;
size_t argidx;
for (argidx = 1; argidx < args.size(); argidx++) {
@ -486,18 +568,22 @@ struct OptRmdffPass : public Pass {
keepdc = true;
continue;
}
if (args[argidx] == "-sat") {
sat = true;
continue;
}
break;
}
extra_args(args, argidx, design);
for (auto module : design->selected_modules())
{
for (auto module : design->selected_modules()) {
pool<SigBit> driven_bits;
dict<SigBit, State> init_bits;
assign_map.set(module);
dff_init_map.set(module);
mux_drivers.clear();
bit2driver.clear();
init_attributes.clear();
for (auto wire : module->wires())
@ -522,17 +608,21 @@ struct OptRmdffPass : public Pass {
driven_bits.insert(bit);
}
}
mux_drivers.clear();
std::vector<RTLIL::IdString> dff_list;
std::vector<RTLIL::IdString> dffsr_list;
std::vector<RTLIL::IdString> dlatch_list;
for (auto cell : module->cells())
{
for (auto &conn : cell->connections())
if (cell->output(conn.first) || !cell->known())
for (auto bit : assign_map(conn.second))
for (auto &conn : cell->connections()) {
bool is_output = cell->output(conn.first);
if (is_output || !cell->known())
for (auto bit : assign_map(conn.second)) {
if (is_output)
bit2driver[bit] = cell;
driven_bits.insert(bit);
}
}
if (cell->type == "$mux" || cell->type == "$pmux") {
if (cell->getPort("\\A").size() == cell->getPort("\\B").size())
@ -604,6 +694,7 @@ struct OptRmdffPass : public Pass {
assign_map.clear();
mux_drivers.clear();
bit2driver.clear();
init_attributes.clear();
if (total_count || total_initdrv)