[CP-SAT] speed up no_overlap_2d (presolve, propagation); tweak shared tree workers; improve hint preservation during presolve; remove memory contention

Author: lperron

ortools/sat/BUILD.bazel

@@ -196,6 +196,7 @@ cc_library(
         "//ortools/port:proto_utils",
         "//ortools/util:saturated_arithmetic",
         "//ortools/util:sorted_interval_list",
+        "@com_google_absl//absl/algorithm:container",
         "@com_google_absl//absl/container:btree",
         "@com_google_absl//absl/container:flat_hash_map",
         "@com_google_absl//absl/container:flat_hash_set",
@@ -2926,9 +2927,7 @@ cc_library(
         "//ortools/base",
         "//ortools/base:stl_util",
         "//ortools/base:strong_vector",
-        "//ortools/graph",
         "//ortools/graph:connected_components",
-        "//ortools/graph:minimum_spanning_tree",
         "//ortools/graph:strongly_connected_components",
         "//ortools/util:fixed_shape_binary_tree",
         "//ortools/util:integer_pq",
@@ -3110,9 +3109,11 @@ cc_test(
         ":integer_base",
         ":util",
         "//ortools/base",
-        "//ortools/base:gmock_main",
+        "//ortools/base:fuzztest",
+        "//ortools/base:gmock",
         "//ortools/graph:connected_components",
         "//ortools/graph:strongly_connected_components",
+        "//ortools/util:saturated_arithmetic",
         "//ortools/util:strong_integers",
         "@com_google_absl//absl/algorithm:container",
         "@com_google_absl//absl/container:flat_hash_map",
@@ -3123,6 +3124,7 @@ cc_test(
         "@com_google_absl//absl/strings",
         "@com_google_absl//absl/types:span",
         "@com_google_benchmark//:benchmark",
+        "@com_google_fuzztest//fuzztest:fuzztest_gtest_main",
     ],
 )
 

ortools/sat/cp_model_checker.cc

@@ -17,11 +17,13 @@
 #include <cmath>
 #include <cstdint>
 #include <limits>
+#include <optional>
 #include <string>
 #include <tuple>
 #include <utility>
 #include <vector>
 
+#include "absl/algorithm/container.h"
 #include "absl/container/btree_map.h"
 #include "absl/container/flat_hash_map.h"
 #include "absl/container/flat_hash_set.h"
@@ -1420,6 +1422,7 @@ class ConstraintChecker {
     const auto& arg = ct.no_overlap_2d();
     // Those intervals from arg.x_intervals and arg.y_intervals where both
     // the x and y intervals are enforced.
+    bool has_zero_sizes = false;
     std::vector<Rectangle> enforced_rectangles;
     {
       const int num_intervals = arg.x_intervals_size();
@@ -1432,16 +1435,34 @@ class ConstraintChecker {
                                          .x_max = IntervalEnd(x.interval()),
                                          .y_min = IntervalStart(y.interval()),
                                          .y_max = IntervalEnd(y.interval())});
+          const auto& rect = enforced_rectangles.back();
+          if (rect.x_min == rect.x_max || rect.y_min == rect.y_max) {
+            has_zero_sizes = true;
+          }
         }
       }
     }
-    const std::vector<std::pair<int, int>> intersections =
-        FindPartialRectangleIntersectionsAlsoEmpty(enforced_rectangles);
-    if (!intersections.empty()) {
-      VLOG(1) << "Rectangles " << intersections[0].first << "("
-              << enforced_rectangles[intersections[0].first] << ") and "
-              << intersections[0].second << "("
-              << enforced_rectangles[intersections[0].second]
+
+    std::optional<std::pair<int, int>> one_intersection;
+    if (!has_zero_sizes) {
+      absl::c_stable_sort(enforced_rectangles,
+                          [](const Rectangle& a, const Rectangle& b) {
+                            return a.x_min < b.x_min;
+                          });
+      one_intersection = FindOneIntersectionIfPresent(enforced_rectangles);
+    } else {
+      const std::vector<std::pair<int, int>> intersections =
+          FindPartialRectangleIntersections(enforced_rectangles);
+      if (!intersections.empty()) {
+        one_intersection = intersections[0];
+      }
+    }
+
+    if (one_intersection != std::nullopt) {
+      VLOG(1) << "Rectangles " << one_intersection->first << "("
+              << enforced_rectangles[one_intersection->first] << ") and "
+              << one_intersection->second << "("
+              << enforced_rectangles[one_intersection->second]
               << ") are not disjoint.";
       return false;
     }

ortools/sat/cp_model_lns.cc

@@ -471,6 +471,7 @@ NeighborhoodGeneratorHelper::GetActiveRectangles(
   }
 
   std::vector<ActiveRectangle> results;
+  results.reserve(active_rectangles.size());
   for (const auto& [rectangle, no_overlap_2d_constraints] : active_rectangles) {
     ActiveRectangle& result = results.emplace_back();
     result.x_interval = rectangle.first;
@@ -532,7 +533,9 @@ void RestrictAffineExpression(const LinearExpressionProto& expr,
   const Domain domain =
       ReadDomainFromProto(mutable_proto->variables(expr.vars(0)))
           .IntersectionWith(implied_domain);
-  FillDomainInProto(domain, mutable_proto->mutable_variables(expr.vars(0)));
+  if (!domain.IsEmpty()) {
+    FillDomainInProto(domain, mutable_proto->mutable_variables(expr.vars(0)));
+  }
 }
 
 struct StartEndIndex {
@@ -1034,7 +1037,14 @@ std::vector<std::vector<int>> NeighborhoodGeneratorHelper::GetRoutingPaths(
 Neighborhood NeighborhoodGeneratorHelper::FixGivenVariables(
     const CpSolverResponse& base_solution,
     const absl::flat_hash_set<int>& variables_to_fix) const {
-  Neighborhood neighborhood;
+  int initial_num_variables = 0;
+  {
+    absl::ReaderMutexLock domain_lock(&domain_mutex_);
+
+    initial_num_variables =
+        model_proto_with_only_variables_->variables().size();
+  }
+  Neighborhood neighborhood(initial_num_variables);
 
   // TODO(user): Maybe relax all variables in the objective when the number
   // is small or negligible compared to the number of variables.

ortools/sat/cp_model_lns.h

@@ -44,6 +44,14 @@ namespace sat {
 
 // Neighborhood returned by Neighborhood generators.
 struct Neighborhood {
+  static constexpr int kDefaultArenaSizePerVariable = 128;
+
+  explicit Neighborhood(int num_variables_hint = 10)
+      : arena_buffer(kDefaultArenaSizePerVariable * num_variables_hint),
+        arena(std::make_unique<google::protobuf::Arena>(arena_buffer.data(),
+                                                        arena_buffer.size())),
+        delta(*google::protobuf::Arena::Create<CpModelProto>(arena.get())) {}
+
   // True if neighborhood generator was able to generate a neighborhood.
   bool is_generated = false;
 
@@ -58,7 +66,9 @@ struct Neighborhood {
   // The delta will contains all variables from the initial model, potentially
   // with updated domains.
   // It can contains new variables and new constraints, and solution hinting.
-  CpModelProto delta;
+  std::vector<char> arena_buffer;
+  std::unique_ptr<google::protobuf::Arena> arena;
+  CpModelProto& delta;
 
   // Neighborhood Id. Used to identify the neighborhood by a generator.
   // Currently only used by WeightedRandomRelaxationNeighborhoodGenerator.