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opt_merge: fix the many collisions case

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This commit is contained in:
Emil J. Tywoniak 2024-10-18 20:39:52 +02:00
parent cbb776c626
commit ffc057a89c
1 changed files with 36 additions and 9 deletions
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45
passes/opt/opt_merge.cc
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@ -254,6 +254,11 @@ struct OptMergeWorker
initvals.set(&assign_map, module);
bool did_something = true;
bool warned_collisions = false;
// A cell may have to go through a lot of collisions if the hash
// function is performing poorly, but it's a symptom of something bad
// beyond the user's control.
int threshold = 1000; // adjust to taste
while (did_something)
{
std::vector<RTLIL::Cell*> cells;
@ -273,7 +278,10 @@ struct OptMergeWorker
}
did_something = false;
dict<Hasher::hash_t, RTLIL::Cell*> sharemap;
// INVARIANT: All cells associated with the same hash in sharemap
// are distinct as far as compare_cell_parameters_and_connections
// can tell.
std::unordered_multimap<Hasher::hash_t, RTLIL::Cell*> sharemap;
for (auto cell : cells)
{
if ((!mode_share_all && !ct.cell_known(cell->type)) || !cell->known())
@ -283,21 +291,30 @@ struct OptMergeWorker
continue;
Hasher::hash_t hash = hash_cell_function(cell, Hasher()).yield();
auto r = sharemap.insert(std::make_pair(hash, cell));
if (!r.second) {
if (compare_cell_parameters_and_connections(cell, r.first->second)) {
// Get all cells with matching hashes
auto matching = sharemap.equal_range(hash);
int collisions = 0;
bool found = false;
for (auto it = matching.first; it != matching.second && !found; ++it) {
if (collisions > threshold && !warned_collisions) {
log_warning("High hash collision counts. opt_merge runtime may be excessive.\n" \
"Please report to maintainers.\n");
warned_collisions = true;
}
auto other_cell = it->second;
if (compare_cell_parameters_and_connections(cell, other_cell)) {
found = true;
if (cell->has_keep_attr()) {
if (r.first->second->has_keep_attr())
if (other_cell->has_keep_attr())
continue;
std::swap(r.first->second, cell);
std::swap(other_cell, cell);
}
did_something = true;
log_debug(" Cell `%s' is identical to cell `%s'.\n", cell->name.c_str(), r.first->second->name.c_str());
log_debug(" Cell `%s' is identical to cell `%s'.\n", cell->name.c_str(), other_cell->name.c_str());
for (auto &it : cell->connections()) {
if (cell->output(it.first)) {
RTLIL::SigSpec other_sig = r.first->second->getPort(it.first);
RTLIL::SigSpec other_sig = other_cell->getPort(it.first);
log_debug(" Redirecting output %s: %s = %s\n", it.first.c_str(),
log_signal(it.second), log_signal(other_sig));
Const init = initvals(other_sig);
@ -311,8 +328,18 @@ struct OptMergeWorker
log_debug(" Removing %s cell `%s' from module `%s'.\n", cell->type.c_str(), cell->name.c_str(), module->name.c_str());
module->remove(cell);
total_count++;
break;
} else {
collisions++;
log_debug(" False hash match: `%s' and `%s'.\n", cell->name.c_str(), other_cell->name.c_str());
}
}
if (!did_something) {
// This cell isn't represented yet in the sharemap.
// Either it's the first of its hash,
// or falsely matches all cells in sharemap sharing its hash.
sharemap.insert(std::make_pair(hash, cell));
}
}
}