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opt_dff: skip convertion to dffe for keep wires

This commit is contained in:
Philippe Sauter 2025-12-15 15:46:09 +01:00 committed by phsauter
parent e56c6a954c
commit fb40e019aa
1 changed files with 22 additions and 4 deletions
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26
passes/opt/opt_dff.cc
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@ -55,6 +55,7 @@ struct OptDffWorker
FfInitVals initvals;
dict<SigBit, int> bitusers; // Signal sink count
dict<SigBit, cell_int_t> bit2mux; // Signal bit to driving MUX
pool<SigBit> kept_bits;
std::vector<Cell *> dff_cells;
@ -117,15 +118,26 @@ struct OptDffWorker
// - bit2mux: the mux cell and bit index that drives it, if any
for (auto wire : module->wires())
{
if (wire->get_bool_attribute(ID::keep))
for (auto bit : sigmap(wire))
kept_bits.insert(bit);
if (wire->port_output)
for (auto bit : sigmap(wire))
bitusers[bit]++;
}
for (auto cell : module->cells()) {
if (cell->type.in(ID($mux), ID($pmux), ID($_MUX_))) {
RTLIL::SigSpec sig_y = sigmap(cell->getPort(ID::Y));
for (int i = 0; i < GetSize(sig_y); i++)
bit2mux[sig_y[i]] = cell_int_t(cell, i);
for (int i = 0; i < GetSize(sig_y); i++) {
SigBit bit = sig_y[i];
// skip kept wires, remove once yosys has optimization barriers
if (kept_bits.count(bit))
continue;
bit2mux[bit] = cell_int_t(cell, i);
}
}
for (auto conn : cell->connections()) {
@ -763,8 +775,14 @@ struct OptDffWorker
optimize_const_clk(ff, cell, changed);
// Feedback (D=Q) opt
if ((ff.has_clk || ff.has_gclk) && ff.sig_d == ff.sig_q)
optimize_d_equals_q(ff, cell, changed);
if ((ff.has_clk || ff.has_gclk) && ff.sig_d == ff.sig_q) {
// skip kept wires, remove once yosys has optimization barriers
bool d_has_kept_bit = false;
for (int i = 0; i < ff.width; i++)
if (kept_bits.count(ff.sig_d[i])) { d_has_kept_bit = true; break; }
if (!d_has_kept_bit)
optimize_d_equals_q(ff, cell, changed);
}
if (ff.has_aload && !ff.has_clk && ff.sig_ad == ff.sig_q) {
log("Handling AD = Q on %s (%s) from module %s (removing async load path).\n",