Add benchmarks for unsupported modules and extend supported benchmarks

libeigen/eigen!2179

Closes #3036

Co-authored-by: Rasmus Munk Larsen <rmlarsen@gmail.com>

unsupported/benchmarks/KroneckerProduct/bench_kronecker.cpp

@@ -0,0 +1,83 @@
+// Benchmarks for Kronecker product (dense and sparse).
+
+#include <benchmark/benchmark.h>
+#include <Eigen/Core>
+#include <Eigen/Sparse>
+#include <unsupported/Eigen/KroneckerProduct>
+
+using namespace Eigen;
+
+typedef double Scalar;
+typedef Matrix<Scalar, Dynamic, Dynamic> Mat;
+typedef SparseMatrix<Scalar> SpMat;
+
+// --- Dense Kronecker product ---
+static void BM_KroneckerDense(benchmark::State& state) {
+  int na = state.range(0);
+  int nb = state.range(1);
+
+  Mat A = Mat::Random(na, na);
+  Mat B = Mat::Random(nb, nb);
+
+  for (auto _ : state) {
+    Mat C = kroneckerProduct(A, B).eval();
+    benchmark::DoNotOptimize(C.data());
+    benchmark::ClobberMemory();
+  }
+  int outSize = na * nb;
+  state.counters["output_size"] = outSize;
+}
+
+// --- Sparse Kronecker product ---
+static void BM_KroneckerSparse(benchmark::State& state) {
+  int na = state.range(0);
+  int nb = state.range(1);
+
+  // Create sparse identity-like matrices with some fill.
+  SpMat A(na, na);
+  SpMat B(nb, nb);
+
+  std::vector<Triplet<Scalar>> tripsA, tripsB;
+  for (int i = 0; i < na; ++i) {
+    tripsA.emplace_back(i, i, 2.0);
+    if (i + 1 < na) {
+      tripsA.emplace_back(i, i + 1, -1.0);
+      tripsA.emplace_back(i + 1, i, -1.0);
+    }
+  }
+  for (int i = 0; i < nb; ++i) {
+    tripsB.emplace_back(i, i, 2.0);
+    if (i + 1 < nb) {
+      tripsB.emplace_back(i, i + 1, -1.0);
+      tripsB.emplace_back(i + 1, i, -1.0);
+    }
+  }
+  A.setFromTriplets(tripsA.begin(), tripsA.end());
+  B.setFromTriplets(tripsB.begin(), tripsB.end());
+
+  for (auto _ : state) {
+    SpMat C = kroneckerProduct(A, B).eval();
+    benchmark::DoNotOptimize(C.valuePtr());
+    benchmark::ClobberMemory();
+  }
+  state.counters["output_size"] = na * nb;
+}
+
+static void KroneckerSizes(::benchmark::Benchmark* b) {
+  for (int na : {4, 8, 16}) {
+    for (int nb : {4, 8, 16}) {
+      b->Args({na, nb});
+    }
+  }
+}
+
+static void KroneckerSparseSizes(::benchmark::Benchmark* b) {
+  for (int na : {16, 32, 64, 128}) {
+    for (int nb : {16, 32, 64, 128}) {
+      b->Args({na, nb});
+    }
+  }
+}
+
+BENCHMARK(BM_KroneckerDense)->Apply(KroneckerSizes);
+BENCHMARK(BM_KroneckerSparse)->Apply(KroneckerSparseSizes);