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/*
* yosys -- Yosys Open SYnthesis Suite
*
* Copyright (C) 2012 Clifford Wolf <clifford@clifford.at>
*
* 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/satgen.h"
#include "kernel/sigtools.h"
USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN
struct EquivInductWorker
{
Module *module;
SigMap sigmap;
vector<Cell*> cells;
pool<Cell*> workset;
ezDefaultSAT ez;
SatGen satgen;
int max_seq;
int success_counter;
dict<int, int> ez_step_is_consistent;
pool<Cell*> cell_warn_cache;
SigPool undriven_signals;
EquivInductWorker(Module *module, const pool<Cell*> &unproven_equiv_cells, bool model_undef, int max_seq) : module(module), sigmap(module),
cells(module->selected_cells()), workset(unproven_equiv_cells), satgen(&ez, &sigmap), max_seq(max_seq), success_counter(0)
{
satgen.model_undef = model_undef;
}
void create_timestep(int step)
{
vector<int> ez_equal_terms;
for (auto cell : cells) {
if (!satgen.importCell(cell, step) && !cell_warn_cache.count(cell)) {
log_warning("No SAT model available for cell %s (%s).\n", log_id(cell), log_id(cell->type));
cell_warn_cache.insert(cell);
}
if (cell->type == "$equiv") {
SigBit bit_a = sigmap(cell->getPort("\\A")).to_single_sigbit();
SigBit bit_b = sigmap(cell->getPort("\\B")).to_single_sigbit();
if (bit_a != bit_b) {
int ez_a = satgen.importSigBit(bit_a, step);
int ez_b = satgen.importSigBit(bit_b, step);
int cond = ez.IFF(ez_a, ez_b);
if (satgen.model_undef)
cond = ez.OR(cond, satgen.importUndefSigBit(bit_a, step));
ez_equal_terms.push_back(cond);
}
}
}
if (satgen.model_undef) {
for (auto bit : undriven_signals.export_all())
ez.assume(ez.NOT(satgen.importUndefSigBit(bit, step)));
}
log_assert(!ez_step_is_consistent.count(step));
ez_step_is_consistent[step] = ez.expression(ez.OpAnd, ez_equal_terms);
}
void run()
{
log("Found %d unproven $equiv cells in module %s:\n", GetSize(workset), log_id(module));
if (satgen.model_undef) {
for (auto cell : cells)
if (yosys_celltypes.cell_known(cell->type))
for (auto &conn : cell->connections())
if (yosys_celltypes.cell_input(cell->type, conn.first))
undriven_signals.add(sigmap(conn.second));
for (auto cell : cells)
if (yosys_celltypes.cell_known(cell->type))
for (auto &conn : cell->connections())
if (yosys_celltypes.cell_output(cell->type, conn.first))
undriven_signals.del(sigmap(conn.second));
}
create_timestep(1);
if (satgen.model_undef) {
for (auto bit : satgen.initial_state.export_all())
ez.assume(ez.NOT(satgen.importUndefSigBit(bit, 1)));
log(" Undef modelling: force def on %d initial reg values and %d inputs.\n",
GetSize(satgen.initial_state), GetSize(undriven_signals));
}
for (int step = 1; step <= max_seq; step++)
{
ez.assume(ez_step_is_consistent[step]);
log(" Proving existence of base case for step %d. (%d clauses over %d variables)\n", step, ez.numCnfClauses(), ez.numCnfVariables());
if (!ez.solve()) {
log(" Proof for base case failed. Circuit inherently diverges!\n");
return;
}
create_timestep(step+1);
int new_step_not_consistent = ez.NOT(ez_step_is_consistent[step+1]);
ez.bind(new_step_not_consistent);
log(" Proving induction step %d. (%d clauses over %d variables)\n", step, ez.numCnfClauses(), ez.numCnfVariables());
if (!ez.solve(new_step_not_consistent)) {
log(" Proof for induction step holds. Entire workset of %d cells proven!\n", GetSize(workset));
for (auto cell : workset)
cell->setPort("\\B", cell->getPort("\\A"));
success_counter += GetSize(workset);
return;
}
log(" Proof for induction step failed. %s\n", step != max_seq ? "Extending to next time step." : "Trying to prove individual $equiv from workset.");
}
workset.sort();
for (auto cell : workset)
{
SigBit bit_a = sigmap(cell->getPort("\\A")).to_single_sigbit();
SigBit bit_b = sigmap(cell->getPort("\\B")).to_single_sigbit();
log(" Trying to prove $equiv for %s:", log_signal(sigmap(cell->getPort("\\Y"))));
int ez_a = satgen.importSigBit(bit_a, max_seq+1);
int ez_b = satgen.importSigBit(bit_b, max_seq+1);
int cond = ez.XOR(ez_a, ez_b);
if (satgen.model_undef)
cond = ez.AND(cond, ez.NOT(satgen.importUndefSigBit(bit_a, max_seq+1)));
if (!ez.solve(cond)) {
log(" success!\n");
cell->setPort("\\B", cell->getPort("\\A"));
success_counter++;
} else {
log(" failed.\n");
}
}
}
};
struct EquivInductPass : public Pass {
EquivInductPass() : Pass("equiv_induct", "proving $equiv cells using temporal induction") { }
virtual void help()
{
// |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
log("\n");
log(" equiv_induct [options] [selection]\n");
log("\n");
log("Uses a version of temporal induction to prove $equiv cells.\n");
log("\n");
log("Only selected $equiv cells are proven and only selected cells are used to\n");
log("perform the proof.\n");
log("\n");
log(" -undef\n");
log(" enable modelling of undef states\n");
log("\n");
log(" -seq <N>\n");
log(" the max. number of time steps to be considered (default = 4)\n");
log("\n");
log("This command is very effective in proving complex sequential circuits, when\n");
log("the internal state of the circuit quickly propagates to $equiv cells.\n");
log("\n");
log("However, this command uses a weak definition of 'equivalence': This command\n");
log("proves that the two circuits will not diverge after they produce equal\n");
log("outputs (observable points via $equiv) for at least <N> cycles (the <N>\n");
log("specified via -seq).\n");
log("\n");
log("Combined with simulation this is very powerful because simulation can give\n");
log("you confidence that the circuits start out synced for at least <N> cycles\n");
log("after reset.\n");
log("\n");
}
virtual void execute(std::vector<std::string> args, Design *design)
{
int success_counter = 0;
bool model_undef = false;
int max_seq = 4;
log_header("Executing EQUIV_INDUCT pass.\n");
size_t argidx;
for (argidx = 1; argidx < args.size(); argidx++) {
if (args[argidx] == "-undef") {
model_undef = true;
continue;
}
if (args[argidx] == "-seq" && argidx+1 < args.size()) {
max_seq = atoi(args[++argidx].c_str());
continue;
}
break;
}
extra_args(args, argidx, design);
for (auto module : design->selected_modules())
{
pool<Cell*> unproven_equiv_cells;
for (auto cell : module->selected_cells())
if (cell->type == "$equiv") {
if (cell->getPort("\\A") != cell->getPort("\\B"))
unproven_equiv_cells.insert(cell);
}
if (unproven_equiv_cells.empty()) {
log("No selected unproven $equiv cells found in %s.\n", log_id(module));
continue;
}
EquivInductWorker worker(module, unproven_equiv_cells, model_undef, max_seq);
worker.run();
success_counter += worker.success_counter;
}
log("Proved %d previously unproven $equiv cells.\n", success_counter);
}
} EquivInductPass;
PRIVATE_NAMESPACE_END
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