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Add help message + cleanup.

This commit is contained in:
nella 2026-07-11 13:06:42 +02:00
parent c6371c2da8
commit 3f8433b52d
1 changed files with 41 additions and 61 deletions
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104
passes/opt/opt_dff.cc
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@ -153,9 +153,8 @@ struct OptDffWorker
void sat_budget_exceeded()
{
if (!sat_budget_out)
log_warning("opt_dff -sat: solver effort budget of %lld exceeded in module %s, "
"skipping remaining sat proofs (scratchpad option 'opt_dff.sat_effort').\n",
(long long)(sat_effort / 1000), log_id(module));
log_warning("opt_dff -sat: effort limit exceeded in module %s, skipping remaining "
"sat proofs (scratchpad option 'opt_dff.sat_effort').\n", log_id(module));
sat_budget_out = true;
}
@ -248,7 +247,7 @@ struct OptDffWorker
OptDffWorker(const OptDffOptions &opt, Module *mod)
: opt(opt), module(mod), sigmap(mod), initvals(&sigmap, mod)
{
sat_effort = (int64_t)module->design->scratchpad_get_int("opt_dff.sat_effort", 1000000) * 1000;
sat_effort = module->design->scratchpad_get_int("opt_dff.sat_effort", 1000000000);
sat_effort_left = sat_effort;
// Gathering two kinds of information here for every sigmapped SigBit:
@ -939,25 +938,6 @@ struct OptDffWorker
return did_something;
}
bool prove_const_with_sat(QuickConeSat &qcsat, ModWalker &modwalker, SigBit q, SigBit d, State val)
{
// Trivial non-const cases
if (!modwalker.has_drivers(d))
return false;
if (val != State::S0 && val != State::S1)
return false;
int init_sat_pi = qcsat.importSigBit(val);
int q_sat_pi = qcsat.importSigBit(q);
int d_sat_pi = qcsat.importSigBit(d);
qcsat.prepare();
// If no counterexample exists, FF is constant
return !qcsat.ez->solve(
qcsat.ez->IFF(q_sat_pi, init_sat_pi),
qcsat.ez->NOT(qcsat.ez->IFF(d_sat_pi, init_sat_pi)));
}
State check_constbit(FfData &ff, int i)
{
State val = ff.val_init[i];
@ -991,23 +971,30 @@ struct OptDffWorker
std::vector<ConstTarget> targets;
};
bool run_constbits()
void commit_const(dict<Cell *, pool<int>> &const_bits, Cell *cell, int i, SigBit q, State val)
{
// Find FFs that are provably constant
ModWalker modwalker(module->design, module);
QuickConeSat qcsat(modwalker);
dict<Cell *, pool<int>> const_bits;
bool did_something = false;
auto commit_const = [&](Cell *cell, int i, SigBit q, State val) {
log("Setting constant %d-bit at position %d on %s (%s) from module %s.\n",
val == State::S1 ? 1 : 0, i, cell, cell->type.unescape(), module);
initvals.remove_init(q);
module->connect(q, val);
const_bits[cell].insert(i);
did_something = true;
};
}
bool add_const_target(ModWalker &modwalker, ConstObligation &ob, SigBit sig)
{
if (!opt.sat || (ob.val != State::S0 && ob.val != State::S1) || !modwalker.has_drivers(sig))
return false;
ob.targets.push_back(ConstTarget{sig});
return true;
}
bool run_constbits()
{
// Find FFs that are provably constant
ModWalker modwalker(module->design, module);
dict<Cell *, pool<int>> const_bits;
bool did_something = false;
// Fold constant D/AD inputs into the tested value directly bits whose remaining inputs are
// wires become SAT proof obligations
@ -1018,7 +1005,6 @@ struct OptDffWorker
continue;
FfData ff(&initvals, cell);
pool<int> removed_sigbits;
for (int i = 0; i < ff.width; i++) {
State val = check_constbit(ff, i);
@ -1042,26 +1028,16 @@ struct OptDffWorker
ob.q = ff.sig_q[i];
bool feasible = true;
auto add_target = [&](SigBit sig) {
if (!opt.sat || (val != State::S0 && val != State::S1) ||
!modwalker.has_drivers(sig)) {
feasible = false;
return;
}
ConstTarget t;
t.sig = sig;
ob.targets.push_back(t);
};
if ((ff.has_clk || ff.has_gclk) && ff.sig_d[i].wire)
add_target(ff.sig_d[i]);
feasible = add_const_target(modwalker, ob, ff.sig_d[i]);
if (feasible && ff.has_aload && ff.sig_ad[i].wire)
add_target(ff.sig_ad[i]);
feasible = add_const_target(modwalker, ob, ff.sig_ad[i]);
if (!feasible)
continue;
if (ob.targets.empty()) {
commit_const(cell, i, ff.sig_q[i], val);
commit_const(const_bits, cell, i, ff.sig_q[i], val);
did_something = true;
continue;
}
obligations.push_back(ob);
@ -1178,8 +1154,10 @@ struct OptDffWorker
bool all_proven = true;
for (auto &t : ob.targets)
all_proven &= t.proven;
if (all_proven)
commit_const(ob.cell, ob.idx, ob.q, ob.val);
if (all_proven) {
commit_const(const_bits, ob.cell, ob.idx, ob.q, ob.val);
did_something = true;
}
}
// Reconstruct FF with constant bits removed
@ -1403,6 +1381,13 @@ struct OptDffWorker
return refined_classes;
}
std::vector<std::vector<int>> drop_all_classes()
{
// Verified merges can depend on the equality of classes that are still unproven, so an incomplete run cannot keep any of them
log("Dropping all equivalent-FF merge candidates in module %s (sat effort budget exceeded before all classes were proven).\n", log_id(module));
return {};
}
std::vector<std::vector<int>> filter_classes_sat(
std::vector<std::vector<int>> classes,
const std::vector<EqBit> &bits,
@ -1415,19 +1400,13 @@ struct OptDffWorker
// Build the next-state function n_lit[idx] of every candidate bit by
// folding the FF's control logic on top of the D input (-> next value)
// Verified merges can depend on the equality of classes that are still unproven, so an incomplete run cannot keep any of them
auto drop_all = [&]() -> std::vector<std::vector<int>> {
log("Dropping all equivalent-FF merge candidates in module %s (sat effort budget exceeded before all classes were proven).\n", log_id(module));
return {};
};
int64_t cells_charged = 0;
// Two bits are equivalent if their next states always agree whenever their
// current states (and those of every other candidate pair) agree
for (auto &cls : classes) {
if (sat_budget_spent())
return drop_all();
return drop_all_classes();
for (int idx : cls) {
const EqBit &eb = bits[idx];
const FfData &ff = ff_for_cell.at(eb.cell);
@ -1463,8 +1442,6 @@ struct OptDffWorker
charge_import(qcsat, cells_charged);
}
qcsat.prepare();
// Assume the induction hypo (that every current class is internally equal in the present cycle), and try
// to prove that the members of each class therefore also agree in the next cycle
@ -1502,7 +1479,7 @@ struct OptDffWorker
continue;
if (sat_budget_spent())
return drop_all();
return drop_all_classes();
// Can the next state of the rep and this member ever differ?
int query = qcsat.ez->XOR(n_lit[rep], n_lit[cls[i]]);
@ -1519,7 +1496,7 @@ struct OptDffWorker
if (res < 0) {
sat_budget_exceeded();
return drop_all();
return drop_all_classes();
}
if (res > 0) {
@ -1655,6 +1632,9 @@ struct OptDffPass : public Pass {
log(" non-constant inputs) that can also be replaced with a constant driver,\n");
log(" or merged with equivalent flip-flops. this reasons in 2-valued logic\n");
log(" and may resolve don't-care bits, so it is incompatible with -keepdc.\n");
log(" the scratchpad option 'opt_dff.sat_effort' (solver propagation steps,\n");
log(" default 1000000000, 0 = unlimited) deterministically bounds the total\n");
log(" sat effort spent per module, remaining proofs are skipped once exceeded.\n");
log("\n");
log(" -keepdc\n");
log(" some optimizations change the behavior of the circuit with respect to\n");