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drt: total-order priority queue comparators for stdlib-independent results #10816

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drt: total-order priority queue comparators for stdlib-independent results #10816

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drt: total-order priority queue comparators for stdlib-independent re…
oharboe Jul 5, 2026
a3e70f5
drt: rebaseline aes_sky130hd and jpeg_sky130hd flow metrics
oharboe Jul 5, 2026
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15 changes: 14 additions & 1 deletion src/drt/src/dr/FlexDR.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -955,7 +955,20 @@ struct Wavefront
int expansion_south;
bool operator<(const Wavefront& rhs) const
{
return expansions_done > rhs.expansions_done;
// Total order so that priority_queue pop order does not depend on the

@hzeller hzeller Jul 6, 2026

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if we order the field in the struct the way we are interested in them (exapansion_done, id, ..east, ...) we could also just have the compiler take care of implementing the whole spaceship operator to deal with all situations, since we're on c++20:

auto operator <=>(const Wavefront& rhs) const = default;

@oharboe oharboe Jul 6, 2026

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Sounds like followup to this PR? I'm not a domain expert here, I'm just running Claude and this surfaced as an instability in testing.

// standard library's heap implementation.
if (expansions_done != rhs.expansions_done) {
return expansions_done > rhs.expansions_done;
}
if (id != rhs.id) {
return id > rhs.id;
}
return std::tie(
expansion_east, expansion_west, expansion_north, expansion_south)
> std::tie(rhs.expansion_east,
rhs.expansion_west,
rhs.expansion_north,
rhs.expansion_south);
}
};

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10 changes: 8 additions & 2 deletions src/drt/src/dr/FlexDR_conn.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -364,10 +364,16 @@ bool FlexDRConnectivityChecker::astar(
int cost;
bool operator<(const wf& b) const
{
if (cost == b.cost) {
// Total order so that priority_queue pop order (and therefore the
// chosen predecessor on cost ties) does not depend on the standard
// library's heap implementation.
if (cost != b.cost) {
return cost > b.cost;
}
if (nodeIdx != b.nodeIdx) {
return nodeIdx > b.nodeIdx;
}
return cost > b.cost;
return prevIdx > b.prevIdx;
}
};
for (int findNode = nNetRouteObjs; findNode < nNetObjs - 1; findNode++) {
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10 changes: 8 additions & 2 deletions src/drt/src/io/GuideProcessor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -339,10 +339,16 @@ class GuidePathFinder
int cost;
bool operator<(const Wavefront& b) const
{
if (cost == b.cost) {
// Total order so that priority_queue pop order (and therefore the
// chosen predecessor on cost ties) does not depend on the standard
// library's heap implementation.
if (cost != b.cost) {
return cost > b.cost;
}
if (node_idx != b.node_idx) {
return node_idx > b.node_idx;
}
return cost > b.cost;
return prev_idx > b.prev_idx;
}
};
/**
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404 changes: 192 additions & 212 deletions test/aes_sky130hd.metrics
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24 changes: 12 additions & 12 deletions test/aes_sky130hd.metrics_limits
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Original file line number Diff line number Diff line change
@@ -1,23 +1,23 @@
{
"IFP::instance_count" : "20652.0"
,"DPL::design_area" : "241789.19999999998"
,"DPL::design_area" : "243057.59999999998"
,"DPL::utilization" : "8.04"
,"RSZ::repair_design_buffer_count" : "693"
,"RSZ::repair_design_buffer_count" : "706"
,"RSZ::max_slew_slack" : "0"
,"RSZ::max_capacitance_slack" : "0"
,"RSZ::max_fanout_slack" : "0"
,"RSZ::worst_slack_min" : "-0.3723263387430433"
,"RSZ::worst_slack_max" : "-1.326974615082891"
,"RSZ::tns_max" : "-748.1016605879365"
,"RSZ::hold_buffer_count" : "424"
,"RSZ::worst_slack_min" : "-0.3735384802756107"
,"RSZ::worst_slack_max" : "-1.283988998799738"
,"RSZ::tns_max" : "-734.9413784624944"
,"RSZ::hold_buffer_count" : "417"
,"GRT::ANT::errors" : "0"
,"DRT::drv" : "0"
,"DRT::worst_slack_min" : "-0.4733114507628843"
,"DRT::worst_slack_max" : "-1.9136417909718662"
,"DRT::tns_max" : "-836.9442390632205"
,"DRT::clock_skew" : "0.7405977374320253"
,"DRT::max_slew_slack" : "-15.618910789489746"
,"DRT::max_capacitance_slack" : "-16.15476931306629"
,"DRT::worst_slack_min" : "-0.4402497853106166"
,"DRT::worst_slack_max" : "-1.6663618097035495"
,"DRT::tns_max" : "-823.2593845374129"
,"DRT::clock_skew" : "0.4280845132876491"
,"DRT::max_slew_slack" : "-26.159040927886963"
,"DRT::max_capacitance_slack" : "-3.5806363388753915"
,"DRT::max_fanout_slack" : "0"
,"DRT::clock_period" : "3.74"
,"DRT::ANT::errors" : "0"
Expand Down
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