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router2: Try harder on constants to prevent infinite loop (#1647) 

Signed-off-by: gatecat <gatecat@ds0.me>
This commit is contained in:
myrtle 2026-02-24 14:28:25 +01:00 committed by GitHub
parent 1f4d3fdc91
commit 2400a90e04
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1 changed files with 22 additions and 6 deletions
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28
common/route/router2.cc
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@ -707,6 +707,7 @@ struct Router2
// This records the point where forwards and backwards routing met
int midpoint_wire = -1;
float best_midpoint_cost = 0;
int explored = 1;
for (; mode < 2; mode++) {
@ -776,7 +777,7 @@ struct Router2
// Mode 0 required both queues to be live
while (((mode == 0) ? (!t.fwd_queue.empty() && !t.bwd_queue.empty())
: (!t.fwd_queue.empty() || !t.bwd_queue.empty())) &&
(!is_bb || iter < toexplore)) {
((!is_bb && midpoint_wire == -1) || iter < toexplore)) {
++iter;
if (!t.fwd_queue.empty() && !const_mode) {
// Explore forwards
@ -828,11 +829,26 @@ struct Router2
t.bwd_queue.pop();
++explored;
auto &curr_data = flat_wires.at(curr.wire);
if (was_visited_fwd(curr.wire, std::numeric_limits<float>::max()) ||
(const_mode && ctx->getWireConstantValue(curr_data.w) == net->constant_value)) {
// Meet in the middle; done
midpoint_wire = curr.wire;
break;
if (const_mode && ctx->getWireConstantValue(curr_data.w) == net->constant_value) {
if (midpoint_wire == -1) {
midpoint_wire = curr.wire;
best_midpoint_cost = curr.score.cost;
if (curr_cong_weight >= 10) {
// try harder at this point to prevent infinite iterations when constants conflict
toexplore = iter + std::min(200, int(curr.score.cost));
} else {
break;
}
} else if (curr.score.cost < best_midpoint_cost) {
midpoint_wire = curr.wire;
best_midpoint_cost = curr.score.cost;
}
} else {
if (was_visited_fwd(curr.wire, std::numeric_limits<float>::max())) {
// Meet in the middle; done
midpoint_wire = curr.wire;
break;
}
}
// Don't allow the same wire to be bound to the same net with a different driving pip
PipId bound_pip;