From: Marcelina Kościelnicka Date: Thu, 27 Jan 2022 16:06:57 +0000 (+0100) Subject: opt_dff: Don't mutate muxes while ModWalker is active. X-Git-Tag: yosys-0.14~16 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=db33b1e535f5ee93dba9ee1cc181b91c482a4dee;p=yosys.git opt_dff: Don't mutate muxes while ModWalker is active. --- diff --git a/passes/opt/opt_dff.cc b/passes/opt/opt_dff.cc index 98b66dee3..73d674c8d 100644 --- a/passes/opt/opt_dff.cc +++ b/passes/opt/opt_dff.cc @@ -58,13 +58,10 @@ struct OptDffWorker typedef std::pair ctrl_t; typedef std::set ctrls_t; - ModWalker modwalker; - QuickConeSat qcsat; - // Used as a queue. std::vector dff_cells; - OptDffWorker(const OptDffOptions &opt, Module *mod) : opt(opt), module(mod), sigmap(mod), initvals(&sigmap, mod), modwalker(module->design, module), qcsat(modwalker) { + OptDffWorker(const OptDffOptions &opt, Module *mod) : opt(opt), module(mod), sigmap(mod), initvals(&sigmap, mod) { // Gathering two kinds of information here for every sigmapped SigBit: // // - bitusers: how many users it has (muxes will only be merged into FFs if this is 1, making the FF the only user) @@ -569,100 +566,6 @@ struct OptDffWorker changed = true; } - // Now check if any bit can be replaced by a constant. - pool removed_sigbits; - for (int i = 0; i < ff.width; i++) { - State val = ff.val_init[i]; - if (ff.has_arst) - val = combine_const(val, ff.val_arst[i]); - if (ff.has_srst) - val = combine_const(val, ff.val_srst[i]); - if (ff.has_sr) { - if (ff.sig_clr[i] != (ff.pol_clr ? State::S0 : State::S1)) - val = combine_const(val, State::S0); - if (ff.sig_set[i] != (ff.pol_set ? State::S0 : State::S1)) - val = combine_const(val, State::S1); - } - if (val == State::Sm) - continue; - if (ff.has_clk || ff.has_gclk) { - if (!ff.sig_d[i].wire) { - val = combine_const(val, ff.sig_d[i].data); - if (val == State::Sm) - continue; - } else { - if (!opt.sat) - continue; - // For each register bit, try to prove that it cannot change from the initial value. If so, remove it - if (!modwalker.has_drivers(ff.sig_d.extract(i))) - continue; - if (val != State::S0 && val != State::S1) - continue; - - int init_sat_pi = qcsat.importSigBit(val); - int q_sat_pi = qcsat.importSigBit(ff.sig_q[i]); - int d_sat_pi = qcsat.importSigBit(ff.sig_d[i]); - - qcsat.prepare(); - - // Try to find out whether the register bit can change under some circumstances - bool counter_example_found = qcsat.ez->solve(qcsat.ez->IFF(q_sat_pi, init_sat_pi), qcsat.ez->NOT(qcsat.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) - continue; - } - } - if (ff.has_aload) { - if (!ff.sig_ad[i].wire) { - val = combine_const(val, ff.sig_ad[i].data); - if (val == State::Sm) - continue; - } else { - if (!opt.sat) - continue; - // For each register bit, try to prove that it cannot change from the initial value. If so, remove it - if (!modwalker.has_drivers(ff.sig_ad.extract(i))) - continue; - if (val != State::S0 && val != State::S1) - continue; - - int init_sat_pi = qcsat.importSigBit(val); - int q_sat_pi = qcsat.importSigBit(ff.sig_q[i]); - int d_sat_pi = qcsat.importSigBit(ff.sig_ad[i]); - - qcsat.prepare(); - - // Try to find out whether the register bit can change under some circumstances - bool counter_example_found = qcsat.ez->solve(qcsat.ez->IFF(q_sat_pi, init_sat_pi), qcsat.ez->NOT(qcsat.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) - continue; - } - } - log("Setting constant %d-bit at position %d on %s (%s) from module %s.\n", val ? 1 : 0, - i, log_id(cell), log_id(cell->type), log_id(module)); - - initvals.remove_init(ff.sig_q[i]); - module->connect(ff.sig_q[i], val); - removed_sigbits.insert(i); - } - if (!removed_sigbits.empty()) { - std::vector keep_bits; - for (int i = 0; i < ff.width; i++) - if (!removed_sigbits.count(i)) - keep_bits.push_back(i); - if (keep_bits.empty()) { - module->remove(cell); - did_something = true; - continue; - } - ff = ff.slice(keep_bits); - ff.cell = cell; - changed = true; - } - // The cell has been simplified as much as possible already. Now try to spice it up with enables / sync resets. if (ff.has_clk) { if (!ff.has_arst && !ff.has_sr && (!ff.has_srst || !ff.has_ce || ff.ce_over_srst) && !opt.nosdff) { @@ -818,6 +721,115 @@ struct OptDffWorker } return did_something; } + + bool run_constbits() { + ModWalker modwalker(module->design, module); + QuickConeSat qcsat(modwalker); + + // Run as a separate sub-pass, so that we don't mutate (non-FF) cells under ModWalker. + bool did_something = false; + for (auto cell : module->selected_cells()) { + if (!RTLIL::builtin_ff_cell_types().count(cell->type)) + continue; + FfData ff(&initvals, cell); + + // Now check if any bit can be replaced by a constant. + pool removed_sigbits; + for (int i = 0; i < ff.width; i++) { + State val = ff.val_init[i]; + if (ff.has_arst) + val = combine_const(val, ff.val_arst[i]); + if (ff.has_srst) + val = combine_const(val, ff.val_srst[i]); + if (ff.has_sr) { + if (ff.sig_clr[i] != (ff.pol_clr ? State::S0 : State::S1)) + val = combine_const(val, State::S0); + if (ff.sig_set[i] != (ff.pol_set ? State::S0 : State::S1)) + val = combine_const(val, State::S1); + } + if (val == State::Sm) + continue; + if (ff.has_clk || ff.has_gclk) { + if (!ff.sig_d[i].wire) { + val = combine_const(val, ff.sig_d[i].data); + if (val == State::Sm) + continue; + } else { + if (!opt.sat) + continue; + // For each register bit, try to prove that it cannot change from the initial value. If so, remove it + if (!modwalker.has_drivers(ff.sig_d.extract(i))) + continue; + if (val != State::S0 && val != State::S1) + continue; + + int init_sat_pi = qcsat.importSigBit(val); + int q_sat_pi = qcsat.importSigBit(ff.sig_q[i]); + int d_sat_pi = qcsat.importSigBit(ff.sig_d[i]); + + qcsat.prepare(); + + // Try to find out whether the register bit can change under some circumstances + bool counter_example_found = qcsat.ez->solve(qcsat.ez->IFF(q_sat_pi, init_sat_pi), qcsat.ez->NOT(qcsat.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) + continue; + } + } + if (ff.has_aload) { + if (!ff.sig_ad[i].wire) { + val = combine_const(val, ff.sig_ad[i].data); + if (val == State::Sm) + continue; + } else { + if (!opt.sat) + continue; + // For each register bit, try to prove that it cannot change from the initial value. If so, remove it + if (!modwalker.has_drivers(ff.sig_ad.extract(i))) + continue; + if (val != State::S0 && val != State::S1) + continue; + + int init_sat_pi = qcsat.importSigBit(val); + int q_sat_pi = qcsat.importSigBit(ff.sig_q[i]); + int d_sat_pi = qcsat.importSigBit(ff.sig_ad[i]); + + qcsat.prepare(); + + // Try to find out whether the register bit can change under some circumstances + bool counter_example_found = qcsat.ez->solve(qcsat.ez->IFF(q_sat_pi, init_sat_pi), qcsat.ez->NOT(qcsat.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) + continue; + } + } + log("Setting constant %d-bit at position %d on %s (%s) from module %s.\n", val ? 1 : 0, + i, log_id(cell), log_id(cell->type), log_id(module)); + + initvals.remove_init(ff.sig_q[i]); + module->connect(ff.sig_q[i], val); + removed_sigbits.insert(i); + } + if (!removed_sigbits.empty()) { + std::vector keep_bits; + for (int i = 0; i < ff.width; i++) + if (!removed_sigbits.count(i)) + keep_bits.push_back(i); + if (keep_bits.empty()) { + module->remove(cell); + did_something = true; + continue; + } + ff = ff.slice(keep_bits); + ff.cell = cell; + ff.emit(); + did_something = true; + } + } + return did_something; + } }; struct OptDffPass : public Pass { @@ -894,6 +906,8 @@ struct OptDffPass : public Pass { OptDffWorker worker(opt, mod); if (worker.run()) did_something = true; + if (worker.run_constbits()) + did_something = true; } if (did_something)