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Collect chains via TopoSort.

This commit is contained in:
nella 2026-08-06 11:10:12 +02:00
parent c5d47334f4
commit e20909bb3b
1 changed files with 28 additions and 32 deletions
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60
passes/opt/opt_balance_tree.cc
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@ -22,7 +22,6 @@
#include "kernel/yosys.h"
#include "kernel/sigtools.h"
#include "kernel/utils.h"
#include <deque>
USING_YOSYS_NAMESPACE
PRIVATE_NAMESPACE_BEGIN
@ -82,26 +81,6 @@ struct OptBalanceTreeWorker {
return drv;
}
// Check if the driver graph reachable from head contains a cycle,
// following the same edges as the backward chain traversal
bool has_cycle(Cell *head, IdString cell_type) {
TopoSort<Cell*, IdString::compare_ptr_by_name<Cell>> toposort;
toposort.analyze_loops = false;
vector<Cell*> queue = {head};
while (!queue.empty())
{
Cell *c = queue.back();
queue.pop_back();
for (IdString port: {ID::A, ID::B})
if (Cell *drv = chain_driver(c, port, cell_type)) {
if (!toposort.has_node(drv))
queue.push_back(drv);
toposort.edge(drv, c);
}
}
return !toposort.sort();
}
// Create a balanced binary tree from a vector of source signals
SigSpec create_balanced_tree(vector<SigSpec> &sources, IdString cell_type, Cell* cell) {
// Base case: if we have no sources, return an empty signal
@ -288,28 +267,45 @@ struct OptBalanceTreeWorker {
if (consumed_cells.count(head_cell))
continue;
// Collect the chain cone into a topological sort
TopoSort<Cell*, IdString::compare_ptr_by_name<Cell>> toposort;
toposort.analyze_loops = false;
toposort.node(head_cell);
vector<Cell*> queue = {head_cell};
while (!queue.empty())
{
Cell *x = queue.back();
queue.pop_back();
for (IdString port: {ID::A, ID::B})
if (Cell *drv = chain_driver(x, port, cell_type)) {
if (!toposort.has_node(drv))
queue.push_back(drv);
toposort.edge(drv, x);
}
}
// Abandon chains containing combinational loops, since
// rebalancing them is not sound (and would not terminate)
if (has_cycle(head_cell, cell_type))
if (!toposort.sort())
continue;
// Get sources of the chain
// Get sources of the chain: process cells from head to
// drivers, counting the paths leading back to the head so
// reconvergent sources are counted with multiplicity
dict<SigSpec, int> sources;
dict<SigSpec, bool> signeds;
int inner_cells = 0;
std::deque<Cell*> bfs_queue = {head_cell};
while (bfs_queue.size())
int inner_cells = GetSize(toposort.sorted) - 1;
dict<Cell*, int> reach;
reach[head_cell] = 1;
for (int i = GetSize(toposort.sorted); i-- > 0; )
{
Cell* x = bfs_queue.front();
bfs_queue.pop_front();
Cell* x = toposort.sorted[i];
for (IdString port: {ID::A, ID::B}) {
if (Cell *drv = chain_driver(x, port, cell_type)) {
inner_cells++;
bfs_queue.push_back(drv);
reach[drv] += reach[x];
} else {
auto sig = sigmap(x->getPort(port));
sources[sig]++;
sources[sig] += reach[x];
signeds[sig] = x->getParam(port == ID::A ? ID::A_SIGNED : ID::B_SIGNED).as_bool();
}
}