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-rw-r--r--passes/opt/opt_dff.cc210
1 files changed, 112 insertions, 98 deletions
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<RTLIL::SigBit, bool> ctrl_t;
typedef std::set<ctrl_t> ctrls_t;
- ModWalker modwalker;
- QuickConeSat qcsat;
-
// Used as a queue.
std::vector<Cell *> 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<int> 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<int> 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<int> 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<int> 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)
generated by cgit v1.2.3 (git 2.25.1) at 2025-11-04 08:38:58 +0000