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muxpack: reject slicing of predecessor Y ports in mux chain

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This commit is contained in:
Emil J. Tywoniak 2026-05-13 10:27:05 +02:00
parent 376d129df9
commit 334dd7b80c
3 changed files with 51 additions and 0 deletions
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26
passes/opt/muxpack.cc
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@ -150,6 +150,7 @@ struct MuxpackWorker
}
}
std::vector<Cell*> mux_cells;
for (auto cell : module->cells())
{
if (cell->type.in(ID($mux), ID($pmux)) && !cell->get_bool_attribute(ID::keep))
@ -179,6 +180,7 @@ struct MuxpackWorker
}
sig_chain_prev[y_sig] = cell;
mux_cells.push_back(cell);
continue;
}
@ -187,6 +189,30 @@ struct MuxpackWorker
for (auto bit : sigmap(conn.second))
sigbit_with_non_chain_users.insert(bit);
}
// A port can serve as a chain link only if its full sigspec matches
// some chain producer's Y. Bits used by any other input port
// have non-chain users.
for (auto cell : mux_cells)
{
SigSpec a_sig = sigmap(cell->getPort(ID::A));
SigSpec b_sig;
if (cell->type == ID($mux))
b_sig = sigmap(cell->getPort(ID::B));
SigSpec s_sig = sigmap(cell->getPort(ID::S));
bool a_is_chain_link = sig_chain_prev.count(a_sig);
bool b_is_chain_link = !b_sig.empty() && sig_chain_prev.count(b_sig);
if (!a_is_chain_link)
for (auto bit : a_sig)
sigbit_with_non_chain_users.insert(bit);
if (!b_is_chain_link)
for (auto bit : b_sig)
sigbit_with_non_chain_users.insert(bit);
for (auto bit : s_sig)
sigbit_with_non_chain_users.insert(bit);
}
}
bool is_start_cell(Cell* cell)