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opt_clean: Add commentary around wire cleaning, NFC

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This commit is contained in:
Martin Povišer 2024-01-09 11:52:41 +01:00
parent 4585d60b8a
commit ec065186d3
1 changed files with 33 additions and 13 deletions
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46
passes/opt/opt_clean.cc
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@ -240,6 +240,7 @@ int count_nontrivial_wire_attrs(RTLIL::Wire *w)
return count;
}
// Should we pick `s2` over `s1` to represent a signal?
bool compare_signals(RTLIL::SigBit &s1, RTLIL::SigBit &s2, SigPool &regs, SigPool &conns, pool<RTLIL::Wire*> &direct_wires)
{
RTLIL::Wire *w1 = s1.wire;
@ -292,9 +293,10 @@ bool check_public_name(RTLIL::IdString id)
bool rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbose)
{
// `register_signals` and `connected_signals` will help us decide later on
// on picking representatives out of groups of connected signals
SigPool register_signals;
SigPool connected_signals;
if (!purge_mode)
for (auto &it : module->cells_) {
RTLIL::Cell *cell = it.second;
@ -309,20 +311,27 @@ bool rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbos
}
SigMap assign_map(module);
pool<RTLIL::SigSpec> direct_sigs;
// construct a pool of wires which are directly driven by a known celltype,
// this will influence our choice of representatives
pool<RTLIL::Wire*> direct_wires;
for (auto &it : module->cells_) {
RTLIL::Cell *cell = it.second;
if (ct_all.cell_known(cell->type))
for (auto &it2 : cell->connections())
if (ct_all.cell_output(cell->type, it2.first))
direct_sigs.insert(assign_map(it2.second));
}
for (auto &it : module->wires_) {
if (direct_sigs.count(assign_map(it.second)) || it.second->port_input)
direct_wires.insert(it.second);
{
pool<RTLIL::SigSpec> direct_sigs;
for (auto &it : module->cells_) {
RTLIL::Cell *cell = it.second;
if (ct_all.cell_known(cell->type))
for (auto &it2 : cell->connections())
if (ct_all.cell_output(cell->type, it2.first))
direct_sigs.insert(assign_map(it2.second));
}
for (auto &it : module->wires_) {
if (direct_sigs.count(assign_map(it.second)) || it.second->port_input)
direct_wires.insert(it.second);
}
}
// weight all options for representatives with `compare_signals`,
// the one that wins will be what `assign_map` maps to
for (auto &it : module->wires_) {
RTLIL::Wire *wire = it.second;
for (int i = 0; i < wire->width; i++) {
@ -332,21 +341,30 @@ bool rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbos
}
}
// we are removing all connections
module->connections_.clear();
// used signals sigmapped
SigPool used_signals;
// used signals pre-sigmapped
SigPool raw_used_signals;
// used signals sigmapped, ignoring drivers (we keep track of this to set `unused_bits`)
SigPool used_signals_nodrivers;
// gather the usage information for cells
for (auto &it : module->cells_) {
RTLIL::Cell *cell = it.second;
for (auto &it2 : cell->connections_) {
assign_map.apply(it2.second);
assign_map.apply(it2.second); // modify the cell connection in place
raw_used_signals.add(it2.second);
used_signals.add(it2.second);
if (!ct_all.cell_output(cell->type, it2.first))
used_signals_nodrivers.add(it2.second);
}
}
// gather the usage information for ports, wires with `keep`,
// also gather init bits
dict<RTLIL::SigBit, RTLIL::State> init_bits;
for (auto &it : module->wires_) {
RTLIL::Wire *wire = it.second;
@ -374,6 +392,7 @@ bool rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbos
}
}
// set init attributes on all wires of a connected group
for (auto wire : module->wires()) {
bool found = false;
Const val(State::Sx, wire->width);
@ -388,6 +407,7 @@ bool rmunused_module_signals(RTLIL::Module *module, bool purge_mode, bool verbos
wire->attributes[ID::init] = val;
}
// now decide for each wire if we should be deleting it
pool<RTLIL::Wire*> del_wires_queue;
for (auto wire : module->wires())
{