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Add more opt_dff documentation.

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This commit is contained in:
nella 2026-01-23 09:17:14 +01:00
parent f6eba53d1f
commit 0e4282d442
1 changed files with 10 additions and 6 deletions
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16
passes/opt/opt_dff.cc
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@ -55,10 +55,11 @@ struct OptDffWorker
dict<SigBit, int> bitusers; // Signal sink count
dict<SigBit, cell_int_t> bit2mux; // Signal bit to driving MUX
typedef std::map<RTLIL::SigBit, bool> pattern_t;
typedef std::set<pattern_t> patterns_t;
typedef std::pair<RTLIL::SigBit, bool> ctrl_t;
typedef std::set<ctrl_t> ctrls_t;
// Eattern matching for clock enable
typedef std::map<RTLIL::SigBit, bool> pattern_t; // Control signal -> required vals
typedef std::set<pattern_t> patterns_t; // Alternative patterns (OR)
typedef std::pair<RTLIL::SigBit, bool> ctrl_t; // Control signal
typedef std::set<ctrl_t> ctrls_t; // Control signals (AND)
std::vector<Cell *> dff_cells;
@ -794,7 +795,7 @@ struct OptDffWorker
continue;
}
// Control signal opt
// Async control signal opt
if (ff.has_sr && optimize_sr(ff, cell, changed)) {
did_something = true;
continue;
@ -810,6 +811,7 @@ struct OptDffWorker
continue;
}
// Sync control signal opt
if (ff.has_srst)
optimize_srst(ff, cell, changed);
@ -859,9 +861,9 @@ struct OptDffWorker
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;
@ -870,6 +872,7 @@ struct OptDffWorker
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)));
@ -892,6 +895,7 @@ struct OptDffWorker
bool run_constbits()
{
// Find FFs that are provably constant
ModWalker modwalker(module->design, module);
QuickConeSat qcsat(modwalker);