1 files changed, 177 insertions, 0 deletions
diff --git a/backend/unittests/CodeGen/PBQPTest.cpp b/backend/unittests/CodeGen/PBQPTest.cpp
new file mode 100644
index 0000000..073de16
--- /dev/null
+++ b/backend/unittests/CodeGen/PBQPTest.cpp
@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+#include "rcc/CodeGen/PBQP/Graph.h"
+#include "rcc/CodeGen/PBQP/Math.h"
+#include "rcc/CodeGen/PBQP/Solver.h"
+
+#include <algorithm>
+#include <cstddef>
+#include <cstdint>
+#include <iostream>
+#include <string_view>
+#include <vector>
+
+namespace {
+
+class TestContext final {
+public:
+  void expect(bool Condition, std::string_view Message) {
+    if (Condition)
+      return;
+    std::cerr << Message << '\n';
+    ++Failures;
+  }
+
+  [[nodiscard]] int result() const noexcept {
+    return Failures == 0 ? 0 : 1;
+  }
+
+private:
+  int Failures = 0;
+};
+
+void testMath(TestContext &Context) {
+  using namespace rcc::pbqp;
+  Context.expect(
+      addCosts(InfiniteCost, -4) == InfiniteCost && addCosts(InfiniteCost - 1, 2) == InfiniteCost &&
+          addCosts(NegativeInfiniteCost + 1, -2) == NegativeInfiniteCost && addCosts(7, -3) == 4,
+      "PBQP cost arithmetic must saturate deterministically");
+
+  CostVector Vector(std::vector<Cost>{8, -2, 4});
+  Context.expect(Vector.minimumIndex() == 1,
+                 "PBQP cost vectors must choose the first stable minimum");
+  CostMatrix Matrix(2, 3);
+  Matrix.at(0, 0) = 1;
+  Matrix.at(0, 1) = 2;
+  Matrix.at(0, 2) = 3;
+  Matrix.at(1, 0) = 4;
+  Matrix.at(1, 1) = 5;
+  Matrix.at(1, 2) = 6;
+  const CostMatrix Transposed = Matrix.transpose();
+  Context.expect(Transposed.rows() == 3 && Transposed.columns() == 2 && Transposed.at(2, 1) == 6 &&
+                     Transposed.at(1, 0) == 2,
+                 "PBQP matrix transposition must preserve orientation");
+}
+
+void testGraphValidation(TestContext &Context) {
+  using namespace rcc::pbqp;
+  Graph Problem;
+  auto Empty = Problem.addNode(CostVector(0));
+  auto First = Problem.addNode(CostVector(std::vector<Cost>{0, 1}), 20);
+  auto Second = Problem.addNode(CostVector(std::vector<Cost>{2, 0, 3}), 10);
+  Context.expect(!Empty && First && Second,
+                 "PBQP graphs must reject empty nodes and accept stable nonempty nodes");
+  if (!First || !Second)
+    return;
+  auto Self = Problem.addEdge(*First, *First, CostMatrix(2, 2));
+  auto WrongShape = Problem.addEdge(*First, *Second, CostMatrix(2, 2));
+  CostMatrix EdgeCosts(2, 3);
+  EdgeCosts.at(1, 2) = 7;
+  auto Edge = Problem.addEdge(*Second, *First, EdgeCosts.transpose(), 99);
+  auto Duplicate = Problem.addEdge(*First, *Second, CostMatrix(2, 3));
+  Context.expect(!Self && !WrongShape && Edge && !Duplicate && Problem.verify().has_value(),
+                 "PBQP graph edges must enforce identity, dimensions, orientation, and uniqueness");
+  if (!Edge)
+    return;
+  const rcc::pbqp::Edge *Stored = Problem.edge(*Edge);
+  Context.expect(Stored != nullptr && Stored->First == *First && Stored->Second == *Second &&
+                     Stored->Costs.rows() == 2 && Stored->Costs.columns() == 3 &&
+                     Stored->Costs.at(1, 2) == 7,
+                 "PBQP graph insertion must normalize reversed edge orientation");
+}
+
+void testReductions(TestContext &Context) {
+  using namespace rcc::pbqp;
+  DeterministicSolver Solver;
+
+  Graph DegreeZero;
+  auto Only = DegreeZero.addNode(CostVector(std::vector<Cost>{4, 1, 1}), 3);
+  auto ZeroSolution = Solver.solve(DegreeZero);
+  Context.expect(Only && ZeroSolution && ZeroSolution->selection(*Only) == 1 &&
+                     ZeroSolution->totalCost() == 1,
+                 "PBQP R0 reduction must select the first minimum-cost option");
+
+  Graph DegreeOne;
+  auto Left = DegreeOne.addNode(CostVector(std::vector<Cost>{3, 0}), 1);
+  auto Right = DegreeOne.addNode(CostVector(std::vector<Cost>{0, 2}), 2);
+  CostMatrix Pair(2, 2);
+  Pair.at(1, 0) = InfiniteCost;
+  auto PairEdge = DegreeOne.addEdge(*Left, *Right, std::move(Pair));
+  auto OneSolution = Solver.solve(DegreeOne);
+  Context.expect(Left && Right && PairEdge && OneSolution && OneSolution->selection(*Left) == 1 &&
+                     OneSolution->selection(*Right) == 1 && OneSolution->totalCost() == 2,
+                 "PBQP R1 reduction must propagate unary costs to its neighbor");
+
+  Graph DegreeTwo;
+  auto A = DegreeTwo.addNode(CostVector(std::vector<Cost>{0, 2}), 1);
+  auto B = DegreeTwo.addNode(CostVector(std::vector<Cost>{0, 0}), 2);
+  auto C = DegreeTwo.addNode(CostVector(std::vector<Cost>{2, 0}), 3);
+  CostMatrix AB(2, 2);
+  CostMatrix BC(2, 2);
+  AB.at(0, 1) = 5;
+  AB.at(1, 0) = 5;
+  BC.at(0, 1) = 5;
+  BC.at(1, 0) = 5;
+  auto ABEdge = DegreeTwo.addEdge(*A, *B, std::move(AB));
+  auto BCEdge = DegreeTwo.addEdge(*B, *C, std::move(BC));
+  auto TwoSolution = Solver.solve(DegreeTwo);
+  Context.expect(A && B && C && ABEdge && BCEdge && TwoSolution &&
+                     TwoSolution->selection(*A) == 0 && TwoSolution->selection(*B) == 0 &&
+                     TwoSolution->selection(*C) == 0 && TwoSolution->totalCost() == 2,
+                 "PBQP R2 reduction must add the induced neighbor edge cost");
+}
+
+[[nodiscard]] rcc::Expected<rcc::pbqp::Solution> solveClique() {
+  using namespace rcc::pbqp;
+  Graph Problem;
+  std::vector<NodeID> Nodes;
+  for (std::uint64_t Index = 0; Index < 4; ++Index) {
+    auto Node = Problem.addNode(CostVector(std::vector<Cost>{9, 0, 0}), 100 - Index);
+    if (!Node)
+      return std::unexpected(Node.error());
+    Nodes.push_back(*Node);
+  }
+  for (std::size_t Left = 0; Left < Nodes.size(); ++Left) {
+    for (std::size_t Right = Left + 1; Right < Nodes.size(); ++Right) {
+      CostMatrix Costs(3, 3);
+      Costs.at(1, 1) = InfiniteCost;
+      Costs.at(2, 2) = InfiniteCost;
+      auto Edge = Problem.addEdge(Nodes[Left], Nodes[Right], std::move(Costs),
+                                  static_cast<std::uint64_t>(Left * Nodes.size() + Right));
+      if (!Edge)
+        return std::unexpected(Edge.error());
+    }
+  }
+  return DeterministicSolver{}.solve(Problem);
+}
+
+void testHeuristicAndDeterminism(TestContext &Context) {
+  auto First = solveClique();
+  auto Second = solveClique();
+  Context.expect(First && Second && std::ranges::equal(First->selections(), Second->selections()) &&
+                     First->totalCost() == Second->totalCost(),
+                 "PBQP higher-degree reduction must be deterministic");
+  if (First) {
+    Context.expect(First->totalCost() == 18,
+                   "a four-node two-register clique must spill exactly two nodes");
+  }
+
+  rcc::pbqp::Graph Impossible;
+  auto Node = Impossible.addNode(
+      rcc::pbqp::CostVector(std::vector<rcc::pbqp::Cost>{rcc::pbqp::InfiniteCost}));
+  auto Failure = rcc::pbqp::DeterministicSolver{}.solve(Impossible);
+  Context.expect(Node && !Failure &&
+                     Failure.error().code() == rcc::ErrorCode::RegisterAllocationFailed,
+                 "PBQP solver must diagnose a problem with no finite assignment");
+}
+
+} // namespace
+
+int main() {
+  TestContext Context;
+  testMath(Context);
+  testGraphValidation(Context);
+  testReductions(Context);
+  testHeuristicAndDeterminism(Context);
+  return Context.result();
+}