diff --git a/stan/math/fwd/fun/mdivide_left_tri_low.hpp b/stan/math/fwd/fun/mdivide_left_tri_low.hpp
index 8dfd8f4cb2d..d17a4c385f2 100644
--- a/stan/math/fwd/fun/mdivide_left_tri_low.hpp
+++ b/stan/math/fwd/fun/mdivide_left_tri_low.hpp
@@ -20,9 +20,6 @@ template <typename T1, typename T2,
 inline Eigen::Matrix<value_type_t<T1>, std::decay_t<T1>::RowsAtCompileTime,
                      std::decay_t<T2>::ColsAtCompileTime>
 mdivide_left_tri_low(T1&& A, T2&& b) {
-  constexpr int S1 = std::decay_t<T1>::RowsAtCompileTime;
-  constexpr int C2 = std::decay_t<T2>::ColsAtCompileTime;
-
   check_square("mdivide_left_tri_low", "A", A);
   check_multiplicable("mdivide_left_tri_low", "A", A, "b", b);
   if (A.size() == 0) {
@@ -47,7 +44,6 @@ template <typename T1, typename T2, require_eigen_t<T1>* = nullptr,
 inline Eigen::Matrix<value_type_t<T2>, std::decay_t<T1>::RowsAtCompileTime,
                      std::decay_t<T2>::ColsAtCompileTime>
 mdivide_left_tri_low(T1&& A, T2&& b) {
-  constexpr int S1 = std::decay_t<T1>::RowsAtCompileTime;
   check_square("mdivide_left_tri_low", "A", A);
   check_multiplicable("mdivide_left_tri_low", "A", A, "b", b);
   if (A.size() == 0) {
@@ -64,8 +60,6 @@ template <typename T1, typename T2, require_eigen_vt<is_fvar, T1>* = nullptr,
 inline Eigen::Matrix<value_type_t<T1>, std::decay_t<T1>::RowsAtCompileTime,
                      std::decay_t<T2>::ColsAtCompileTime>
 mdivide_left_tri_low(T1&& A, T2&& b) {
-  constexpr int S1 = std::decay_t<T1>::RowsAtCompileTime;
-  constexpr int C2 = std::decay_t<T2>::ColsAtCompileTime;
   check_square("mdivide_left_tri_low", "A", A);
   check_multiplicable("mdivide_left_tri_low", "A", A, "b", b);
   if (A.size() == 0) {
diff --git a/stan/math/opencl/kernel_generator/colwise_reduction.hpp b/stan/math/opencl/kernel_generator/colwise_reduction.hpp
index e4520b154c6..088577f8a88 100644
--- a/stan/math/opencl/kernel_generator/colwise_reduction.hpp
+++ b/stan/math/opencl/kernel_generator/colwise_reduction.hpp
@@ -222,7 +222,6 @@ class colwise_sum_ : public colwise_reduction<colwise_sum_<T>, T, sum_op> {
  */
 template <typename T, require_all_kernel_expressions_t<T>* = nullptr>
 inline auto colwise_sum(T&& a) {
-  auto&& arg_copy = as_operation_cl(std::forward<T>(a)).deep_copy();
   return colwise_sum_<as_operation_cl_t<T>>(
       as_operation_cl(std::forward<T>(a)));
 }
@@ -266,7 +265,6 @@ class colwise_prod_ : public colwise_reduction<colwise_prod_<T>, T, prod_op> {
  */
 template <typename T, require_all_kernel_expressions_t<T>* = nullptr>
 inline auto colwise_prod(T&& a) {
-  auto&& arg_copy = as_operation_cl(std::forward<T>(a)).deep_copy();
   return colwise_prod_<as_operation_cl_t<T>>(
       as_operation_cl(std::forward<T>(a)));
 }
@@ -315,7 +313,6 @@ class colwise_max_ : public colwise_reduction<
  */
 template <typename T, require_all_kernel_expressions_t<T>* = nullptr>
 inline auto colwise_max(T&& a) {
-  auto&& arg_copy = as_operation_cl(std::forward<T>(a)).deep_copy();
   return colwise_max_<as_operation_cl_t<T>>(
       as_operation_cl(std::forward<T>(a)));
 }
diff --git a/stan/math/opencl/kernel_generator/reduction_2d.hpp b/stan/math/opencl/kernel_generator/reduction_2d.hpp
index 4d019f1012c..b028c50f60a 100644
--- a/stan/math/opencl/kernel_generator/reduction_2d.hpp
+++ b/stan/math/opencl/kernel_generator/reduction_2d.hpp
@@ -231,7 +231,6 @@ class sum_2d_ : public reduction_2d<sum_2d_<T>, T, sum_op> {
  */
 template <typename T, require_all_kernel_expressions_t<T>* = nullptr>
 inline auto sum_2d(T&& a) {
-  auto&& arg_copy = as_operation_cl(std::forward<T>(a)).deep_copy();
   return sum_2d_<as_operation_cl_t<T>>(as_operation_cl(std::forward<T>(a)));
 }
 
@@ -274,7 +273,6 @@ class prod_2d_ : public reduction_2d<prod_2d_<T>, T, prod_op> {
  */
 template <typename T, require_all_kernel_expressions_t<T>* = nullptr>
 inline auto prod_2d(T&& a) {
-  auto&& arg_copy = as_operation_cl(std::forward<T>(a)).deep_copy();
   return prod_2d_<as_operation_cl_t<T>>(as_operation_cl(std::forward<T>(a)));
 }
 
@@ -321,7 +319,6 @@ class max_2d_
  */
 template <typename T, require_all_kernel_expressions_t<T>* = nullptr>
 inline auto max_2d(T&& a) {
-  auto&& arg_copy = as_operation_cl(std::forward<T>(a)).deep_copy();
   return max_2d_<as_operation_cl_t<T>>(as_operation_cl(std::forward<T>(a)));
 }
 
diff --git a/stan/math/opencl/prim/binomial_logit_glm_lpmf.hpp b/stan/math/opencl/prim/binomial_logit_glm_lpmf.hpp
index a569498f5e1..340f9250b84 100644
--- a/stan/math/opencl/prim/binomial_logit_glm_lpmf.hpp
+++ b/stan/math/opencl/prim/binomial_logit_glm_lpmf.hpp
@@ -34,7 +34,6 @@ inline return_type_t<T_x_cl, T_alpha_cl, T_beta_cl> binomial_logit_glm_lpmf(
     const T_beta_cl& beta) {
   static const char* function = "binomial_logit_glm_lpmf(OpenCL)";
   using T_partials_return = partials_return_t<T_x_cl, T_alpha_cl, T_beta_cl>;
-  constexpr bool is_y_vector = !is_stan_scalar<T_n_cl>::value;
   constexpr bool is_alpha_vector = !is_stan_scalar<T_alpha_cl>::value;
 
   const size_t N_instances
diff --git a/stan/math/opencl/zeros_strict_tri.hpp b/stan/math/opencl/zeros_strict_tri.hpp
index 339f987cb59..8e4b9989328 100644
--- a/stan/math/opencl/zeros_strict_tri.hpp
+++ b/stan/math/opencl/zeros_strict_tri.hpp
@@ -44,7 +44,6 @@ inline void matrix_cl<T>::zeros_strict_tri() try {
     return;
   }
   this->view_ = both(this->view_, invert(matrix_view));
-  cl::CommandQueue& cmdQueue = opencl_context.queue();
   opencl_kernels::fill_strict_tri(cl::NDRange(this->rows(), this->cols()),
                                   *this, 0.0, this->rows(), this->cols(),
                                   matrix_view);
diff --git a/stan/math/prim/constraint/unit_vector_free.hpp b/stan/math/prim/constraint/unit_vector_free.hpp
index c69a7ac9421..01624e01a4e 100644
--- a/stan/math/prim/constraint/unit_vector_free.hpp
+++ b/stan/math/prim/constraint/unit_vector_free.hpp
@@ -25,7 +25,7 @@ inline auto unit_vector_free(EigVec&& x) {
   auto&& x_ref = to_ref(std::forward<EigVec>(x));
   check_unit_vector("stan::math::unit_vector_free", "Unit vector variable",
                     x_ref);
-  return x_ref;
+  return std::forward<decltype(x_ref)>(x_ref);
 }
 
 /**
diff --git a/stan/math/prim/fun/log_softmax.hpp b/stan/math/prim/fun/log_softmax.hpp
index d6c9017edb6..8e34955c048 100644
--- a/stan/math/prim/fun/log_softmax.hpp
+++ b/stan/math/prim/fun/log_softmax.hpp
@@ -7,6 +7,7 @@
 #include <stan/math/prim/fun/log_sum_exp.hpp>
 #include <stan/math/prim/fun/to_ref.hpp>
 #include <stan/math/prim/functor/apply_vector_unary.hpp>
+#include <utility>
 
 namespace stan {
 namespace math {
@@ -53,7 +54,7 @@ inline auto log_softmax(Container&& x) {
             std::forward<decltype(a)>(a),
             [](auto&& v) -> plain_type_t<decltype(v)> {
               if (v.size() == 0) {
-                return v;
+                return std::forward<decltype(v)>(v);
               }
               return (v.array() - log_sum_exp(v)).matrix();
             });
diff --git a/stan/math/prim/fun/softmax.hpp b/stan/math/prim/fun/softmax.hpp
index 63a51876a60..a737a2e2d53 100644
--- a/stan/math/prim/fun/softmax.hpp
+++ b/stan/math/prim/fun/softmax.hpp
@@ -6,6 +6,7 @@
 #include <stan/math/prim/fun/Eigen.hpp>
 #include <stan/math/prim/fun/to_ref.hpp>
 #include <stan/math/prim/functor/apply_vector_unary.hpp>
+#include <utility>
 
 namespace stan {
 namespace math {
@@ -56,7 +57,7 @@ inline auto softmax(Container&& x) {
             std::forward<decltype(a)>(a),
             [](auto&& v) -> plain_type_t<decltype(v)> {
               if (v.size() == 0) {
-                return v;
+                return std::forward<decltype(v)>(v);
               }
               const auto theta = (v.array() - v.maxCoeff()).exp();
               return (theta / theta.sum()).matrix();
diff --git a/stan/math/prim/prob/normal_sufficient_lpdf.hpp b/stan/math/prim/prob/normal_sufficient_lpdf.hpp
index 996b5e2d052..83b8a061ffc 100644
--- a/stan/math/prim/prob/normal_sufficient_lpdf.hpp
+++ b/stan/math/prim/prob/normal_sufficient_lpdf.hpp
@@ -75,8 +75,6 @@ inline return_type_t<T_y, T_s, T_loc, T_scale> normal_sufficient_lpdf(
   decltype(auto) y_val = to_ref(as_value_column_array_or_scalar(y_ref));
   decltype(auto) s_squared_val
       = to_ref(as_value_column_array_or_scalar(s_squared_ref));
-  decltype(auto) n_obs_val_int
-      = to_ref(as_value_column_array_or_scalar(n_obs_ref));
   decltype(auto) n_obs_val = to_ref(
       promote_scalar<double>(as_value_column_array_or_scalar(n_obs_ref)));
   decltype(auto) mu_val = to_ref(as_value_column_array_or_scalar(mu_ref));
diff --git a/stan/math/prim/prob/student_t_qf.hpp b/stan/math/prim/prob/student_t_qf.hpp
index 5a4b9dbf920..c2c096de9a1 100644
--- a/stan/math/prim/prob/student_t_qf.hpp
+++ b/stan/math/prim/prob/student_t_qf.hpp
@@ -72,7 +72,6 @@ template <typename T_p, typename T_nu, typename T_mu, typename T_sigma,
 inline auto student_t_qf(const T_p& p, const T_nu& nu, const T_mu& mu,
                          const T_sigma& sigma) {
   using ret_scalar = return_type_t<T_p, T_nu, T_mu, T_sigma>;
-  static constexpr const char* function = "student_t_qf";
   const size_t max_size_all = max_size(p, nu, mu, sigma);
   Eigen::Matrix<ret_scalar, -1, 1> result(max_size_all);
 
diff --git a/stan/math/rev/prob/student_t_qf.hpp b/stan/math/rev/prob/student_t_qf.hpp
index e44d4cbbc9c..d9ff3e0314b 100644
--- a/stan/math/rev/prob/student_t_qf.hpp
+++ b/stan/math/rev/prob/student_t_qf.hpp
@@ -39,7 +39,6 @@ inline var student_t_qf(const T_p& p, const T_nu& nu, const T_mu& mu,
     const double p_val_flip = p_val < 0.5 ? p_val : 1.0 - p_val;
     const double p_sign = p_val < 0.5 ? -1.0 : 1.0;
     const double ibeta_arg = inv_inc_beta(0.5 * nu_val, 0.5, 2 * p_val_flip);
-    const double sqrt_inv_ibeta_m1 = sqrt(inv(ibeta_arg) - 1.0);
     double ret_val
         = mu_val
           + p_sign * sigma_val * sqrt(nu_val) * sqrt(-1.0 + 1.0 / ibeta_arg);
@@ -49,7 +48,6 @@ inline var student_t_qf(const T_p& p, const T_nu& nu, const T_mu& mu,
       const double mu_val = value_of(mu);
       const double sigma_val = value_of(sigma);
       const double nu_val = value_of(nu);
-      const double p_val_flip = p_val < 0.5 ? p_val : 1.0 - p_val;
       const double p_sign = p_val < 0.5 ? -1.0 : 1.0;
       const double sqrt_inv_ibeta_m1 = sqrt(inv(ibeta_arg) - 1.0);
       if constexpr (is_autodiff_v<T_p>) {
diff --git a/test/unit/math/opencl/kernel_generator/calc_if_test.cpp b/test/unit/math/opencl/kernel_generator/calc_if_test.cpp
index 0343ae0a350..89c233eb81d 100644
--- a/test/unit/math/opencl/kernel_generator/calc_if_test.cpp
+++ b/test/unit/math/opencl/kernel_generator/calc_if_test.cpp
@@ -50,7 +50,6 @@ TEST(KernelGenerator, calc_if_multi_result_pass_test) {
 }
 
 TEST(KernelGenerator, calc_if_multi_result_no_output_test) {
-  double eps = 0;
   MatrixXd m(2, 2);
   m << 1, 2, 3, 4;
   matrix_cl<double> m_cl(m);
diff --git a/test/unit/math/opencl/kernel_generator/colwise_reduction_test.cpp b/test/unit/math/opencl/kernel_generator/colwise_reduction_test.cpp
index 0ee89e52094..4982efa00e2 100644
--- a/test/unit/math/opencl/kernel_generator/colwise_reduction_test.cpp
+++ b/test/unit/math/opencl/kernel_generator/colwise_reduction_test.cpp
@@ -59,6 +59,26 @@ TEST(KernelGenerator, colwise_prod_test) {
   EXPECT_MATRIX_NEAR(correct, res, 1e-9);
 }
 
+TEST(KernelGenerator, colwise_reductions_rvalue_input) {
+  MatrixXd m(3, 2);
+  m << 1.1, 1.2, 1.3, 1.4, 1.5, 1.6;
+
+  matrix_cl<double> res_cl = stan::math::colwise_sum(matrix_cl<double>(m));
+  MatrixXd res = stan::math::from_matrix_cl(res_cl).colwise().sum();
+  MatrixXd correct = m.colwise().sum();
+  EXPECT_MATRIX_NEAR(correct, res, 1e-9);
+
+  matrix_cl<double> prod_cl = stan::math::colwise_prod(matrix_cl<double>(m));
+  MatrixXd prod = stan::math::from_matrix_cl(prod_cl).colwise().prod();
+  MatrixXd correct_prod = m.colwise().prod();
+  EXPECT_MATRIX_NEAR(correct_prod, prod, 1e-9);
+
+  matrix_cl<double> max_cl = stan::math::colwise_max(matrix_cl<double>(m));
+  MatrixXd max = stan::math::from_matrix_cl(max_cl).colwise().maxCoeff();
+  MatrixXd correct_max = m.colwise().maxCoeff();
+  EXPECT_MATRIX_NEAR(correct_max, max, 1e-9);
+}
+
 TEST(KernelGenerator, colwise_min_test) {
   MatrixXd m(3, 2);
   m << 1.1, 1.2, 1.3, 1.4, 1.5, 1.6;
diff --git a/test/unit/math/opencl/kernel_generator/reduction_2d_test.cpp b/test/unit/math/opencl/kernel_generator/reduction_2d_test.cpp
index 0569d901a1f..ca92f3a7ee6 100644
--- a/test/unit/math/opencl/kernel_generator/reduction_2d_test.cpp
+++ b/test/unit/math/opencl/kernel_generator/reduction_2d_test.cpp
@@ -57,6 +57,23 @@ TEST(KernelGenerator, prod_2d_test) {
   EXPECT_NEAR(correct, res, 1e-9);
 }
 
+TEST(KernelGenerator, reductions_2d_rvalue_input) {
+  MatrixXd m(3, 2);
+  m << 1.1, 1.2, 1.3, 1.4, 1.5, 1.6;
+
+  matrix_cl<double> res_cl = stan::math::sum_2d(matrix_cl<double>(m));
+  double res = stan::math::from_matrix_cl(res_cl).sum();
+  EXPECT_NEAR(m.sum(), res, 1e-9);
+
+  matrix_cl<double> prod_cl = stan::math::prod_2d(matrix_cl<double>(m));
+  double prod = stan::math::from_matrix_cl(prod_cl).prod();
+  EXPECT_NEAR(m.prod(), prod, 1e-9);
+
+  matrix_cl<double> max_cl = stan::math::max_2d(matrix_cl<double>(m));
+  double max = stan::math::from_matrix_cl(max_cl).maxCoeff();
+  EXPECT_NEAR(m.maxCoeff(), max, 1e-9);
+}
+
 TEST(KernelGenerator, min_2d_test) {
   MatrixXd m(3, 2);
   m << 1.1, 1.2, 1.3, 1.4, 1.5, 1.6;
diff --git a/test/unit/math/opencl/matrix_cl_test.cpp b/test/unit/math/opencl/matrix_cl_test.cpp
index 92a50033378..eb3f86678d8 100644
--- a/test/unit/math/opencl/matrix_cl_test.cpp
+++ b/test/unit/math/opencl/matrix_cl_test.cpp
@@ -50,7 +50,6 @@ TEST(MathMatrixCL, matrix_cl_value) {
 TEST(MathMatrixCL, assignment) {
   using stan::math::matrix_cl;
   Eigen::Matrix<double, 2, 2> mat_1;
-  Eigen::Matrix<double, 2, 2> mat_2;
   mat_1 << 1, 2, 3, 4;
   matrix_cl<double> mat1_cl(mat_1);
   matrix_cl<double> mat2_cl(2, 2);
diff --git a/test/unit/math/opencl/prim/mdivide_left_tri_low_test.cpp b/test/unit/math/opencl/prim/mdivide_left_tri_low_test.cpp
index c0151631ed1..93e5d029013 100644
--- a/test/unit/math/opencl/prim/mdivide_left_tri_low_test.cpp
+++ b/test/unit/math/opencl/prim/mdivide_left_tri_low_test.cpp
@@ -49,7 +49,6 @@ inline void mdivide_left_tri_low_Ab_test(int size) {
   stan::math::matrix_cl<double> m0_cl(m1, stan::math::matrix_cl_view::Lower);
   stan::math::matrix_d m1_cl = stan::math::from_matrix_cl(
       stan::math::mdivide_left_tri_low(m0_cl, m0_cl));
-  double max_error = 0;
   for (int i = 0; i < m1_cpu.size(); i++) {
     stan::test::expect_near_rel("mdivide_left_tri_low (OpenCL)", m1_cpu(i),
                                 m1_cl(i));
@@ -77,7 +76,6 @@ inline void mdivide_left_tri_low_A_test(int size) {
 
   stan::math::matrix_cl<double> m1_A_cl(m1, stan::math::matrix_cl_view::Lower);
   m1_cl = stan::math::from_matrix_cl(stan::math::mdivide_left_tri_low(m1_A_cl));
-  double max_error = 0;
   for (int i = 0; i < size; i++) {
     for (int j = 0; j <= i; j++) {
       stan::test::expect_near_rel("mdivide_left_tri_low (OpenCL)", m1_cpu(i, j),
diff --git a/test/unit/math/opencl/prim/mdivide_right_tri_low_test.cpp b/test/unit/math/opencl/prim/mdivide_right_tri_low_test.cpp
index a339cfbb107..d59099dc3cc 100644
--- a/test/unit/math/opencl/prim/mdivide_right_tri_low_test.cpp
+++ b/test/unit/math/opencl/prim/mdivide_right_tri_low_test.cpp
@@ -48,7 +48,6 @@ inline void mdivide_right_tri_low_Ab_test(int size) {
   stan::math::matrix_cl<double> m1_A_cl(m1, stan::math::matrix_cl_view::Lower);
   stan::math::matrix_d m1_cl = stan::math::from_matrix_cl(
       stan::math::mdivide_right_tri_low(m1_A_cl, m1_A_cl));
-  double max_error = 0;
   for (int i = 0; i < m1_cpu.size(); i++) {
     stan::test::expect_near_rel("mdivide_right_tri_low (OpenCL)", m1_cpu(i),
                                 m1_cl(i));
diff --git a/test/unit/math/opencl/rev/append_array_test.cpp b/test/unit/math/opencl/rev/append_array_test.cpp
index 3b2252a767c..4e9023f5e72 100644
--- a/test/unit/math/opencl/rev/append_array_test.cpp
+++ b/test/unit/math/opencl/rev/append_array_test.cpp
@@ -15,8 +15,6 @@ TEST(OpenCLAppendArray, prim_rev_values_small) {
 }
 
 TEST(OpenCLAppendArray, prim_rev_size_0) {
-  int N = 0;
-
   std::vector<double> a{};
   std::vector<double> b{};
   stan::math::test::compare_cpu_opencl_prim_rev(append_array_functor, a, b);
diff --git a/test/unit/math/opencl/rev/bernoulli_cdf_test.cpp b/test/unit/math/opencl/rev/bernoulli_cdf_test.cpp
index 107708c0d80..79975958028 100644
--- a/test/unit/math/opencl/rev/bernoulli_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/bernoulli_cdf_test.cpp
@@ -45,7 +45,6 @@ auto bernoulli_cdf_functor = [](const auto& n, const auto& theta) {
 
 TEST(ProbDistributionsBernoulliCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 1, 3};
   Eigen::VectorXd theta(N);
@@ -59,7 +58,6 @@ TEST(ProbDistributionsBernoulliCdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsBernoulliCdf, opencl_matches_cpu_small_n_negative) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 1, -5};
   Eigen::VectorXd theta(N);
@@ -83,8 +81,6 @@ TEST(ProbDistributionsBernoulliCdf, opencl_broadcast_n) {
 }
 
 TEST(ProbDistributionsBernoulliCdf, opencl_broadcast_theta) {
-  int N = 3;
-
   std::vector<int> n{0, 1, 0};
   double theta_scal = 0.4;
 
diff --git a/test/unit/math/opencl/rev/bernoulli_lccdf_test.cpp b/test/unit/math/opencl/rev/bernoulli_lccdf_test.cpp
index 732b1e62f2c..51a2e43a4a6 100644
--- a/test/unit/math/opencl/rev/bernoulli_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/bernoulli_lccdf_test.cpp
@@ -45,7 +45,6 @@ auto bernoulli_lccdf_functor = [](const auto& n, const auto& theta) {
 
 TEST(ProbDistributionsBernoulliLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 0, 0};
   Eigen::VectorXd theta(N);
@@ -59,7 +58,6 @@ TEST(ProbDistributionsBernoulliLccdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsBernoulliLccdf, opencl_matches_cpu_small_n_negative) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 0, -5};
   Eigen::VectorXd theta(N);
@@ -73,7 +71,6 @@ TEST(ProbDistributionsBernoulliLccdf, opencl_matches_cpu_small_n_negative) {
 
 TEST(ProbDistributionsBernoulliLccdf, opencl_matches_cpu_small_n_over_one) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 1, 5};
   Eigen::VectorXd theta(N);
@@ -97,8 +94,6 @@ TEST(ProbDistributionsBernoulliLccdf, opencl_broadcast_n) {
 }
 
 TEST(ProbDistributionsBernoulliLccdf, opencl_broadcast_theta) {
-  int N = 3;
-
   std::vector<int> n{0, 0, 0};
   double theta_scal = 0.4;
 
diff --git a/test/unit/math/opencl/rev/bernoulli_logit_lpmf_test.cpp b/test/unit/math/opencl/rev/bernoulli_logit_lpmf_test.cpp
index 401b88349f7..b6d86ae5e90 100644
--- a/test/unit/math/opencl/rev/bernoulli_logit_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/bernoulli_logit_lpmf_test.cpp
@@ -48,7 +48,6 @@ auto bernoulli_logit_lpmf_functor_propto
 
 TEST(ProbDistributionsBernoulliLogit, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 1, 1};
   Eigen::VectorXd theta(N);
@@ -78,8 +77,6 @@ TEST(ProbDistributionsBernoulliLogit, opencl_broadcast_n) {
 }
 
 TEST(ProbDistributionsBernoulliLogit, opencl_broadcast_theta) {
-  int N = 3;
-
   std::vector<int> n{0, 1, 0};
   double theta = 0.4;
 
diff --git a/test/unit/math/opencl/rev/bernoulli_lpmf_test.cpp b/test/unit/math/opencl/rev/bernoulli_lpmf_test.cpp
index 2dd8ae41530..7351e45d7a2 100644
--- a/test/unit/math/opencl/rev/bernoulli_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/bernoulli_lpmf_test.cpp
@@ -47,7 +47,6 @@ auto bernoulli_lpmf_functor_propto = [](const auto& n, const auto& theta) {
 
 TEST(ProbDistributionsBernoulli, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 1, 0};
   Eigen::VectorXd theta(N);
@@ -77,8 +76,6 @@ TEST(ProbDistributionsBernoulli, opencl_broadcast_n) {
 }
 
 TEST(ProbDistributionsBernoulli, opencl_broadcast_theta) {
-  int N = 3;
-
   std::vector<int> n{0, 1, 0};
   double theta_scal = 0.4;
 
diff --git a/test/unit/math/opencl/rev/beta_lpdf_test.cpp b/test/unit/math/opencl/rev/beta_lpdf_test.cpp
index dd0c3fce94e..a12ef5a5c80 100644
--- a/test/unit/math/opencl/rev/beta_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/beta_lpdf_test.cpp
@@ -85,7 +85,6 @@ auto beta_lpdf_functor_propto
 
 TEST(ProbDistributionsBeta, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0, 0.5, 1;
diff --git a/test/unit/math/opencl/rev/beta_proportion_lpdf_test.cpp b/test/unit/math/opencl/rev/beta_proportion_lpdf_test.cpp
index 6709ea03e42..157d598bc09 100644
--- a/test/unit/math/opencl/rev/beta_proportion_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/beta_proportion_lpdf_test.cpp
@@ -65,7 +65,6 @@ auto beta_proportion_lpdf_functor_propto
 
 TEST(ProbDistributionsBetaProportion, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/binomial_logit_lpmf_test.cpp b/test/unit/math/opencl/rev/binomial_logit_lpmf_test.cpp
index 92b85841292..4ee784145d0 100644
--- a/test/unit/math/opencl/rev/binomial_logit_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/binomial_logit_lpmf_test.cpp
@@ -114,8 +114,6 @@ TEST(ProbDistributionsBinomialLogit, opencl_broadcast_N) {
 }
 
 TEST(ProbDistributionsBinomialLogit, opencl_broadcast_alpha) {
-  int N = 3;
-
   std::vector<int> n{0, 1, 12};
   std::vector<int> m{0, 1, 123};
   double alpha_scal = 0.4;
diff --git a/test/unit/math/opencl/rev/binomial_lpmf_test.cpp b/test/unit/math/opencl/rev/binomial_lpmf_test.cpp
index 7be5166eb86..e84dc9c6eab 100644
--- a/test/unit/math/opencl/rev/binomial_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/binomial_lpmf_test.cpp
@@ -119,8 +119,6 @@ TEST(ProbDistributionsBinomial, opencl_broadcast_N) {
 }
 
 TEST(ProbDistributionsBinomial, opencl_broadcast_theta) {
-  int N = 3;
-
   std::vector<int> n{0, 1, 12};
   std::vector<int> m{0, 1, 123};
   double theta_scal = 0.4;
diff --git a/test/unit/math/opencl/rev/cauchy_lccdf_test.cpp b/test/unit/math/opencl/rev/cauchy_lccdf_test.cpp
index 342bf34c129..29fa178f33b 100644
--- a/test/unit/math/opencl/rev/cauchy_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/cauchy_lccdf_test.cpp
@@ -64,7 +64,6 @@ auto cauchy_lccdf_functor
 
 TEST(ProbDistributionsCauchyLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, -0.6, 1.0;
diff --git a/test/unit/math/opencl/rev/cauchy_lpdf_test.cpp b/test/unit/math/opencl/rev/cauchy_lpdf_test.cpp
index 7623819af84..a31ab65c0fe 100644
--- a/test/unit/math/opencl/rev/cauchy_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/cauchy_lpdf_test.cpp
@@ -67,7 +67,6 @@ auto cauchy_lpdf_functor_propto
 
 TEST(ProbDistributionsCauchy, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/double_exponential_cdf_test.cpp b/test/unit/math/opencl/rev/double_exponential_cdf_test.cpp
index fc441df05e9..91f9ed8afd6 100644
--- a/test/unit/math/opencl/rev/double_exponential_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/double_exponential_cdf_test.cpp
@@ -63,7 +63,6 @@ auto double_exponential_cdf_functor
 
 TEST(ProbDistributionsDoubleExponentialCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/double_exponential_lccdf_test.cpp b/test/unit/math/opencl/rev/double_exponential_lccdf_test.cpp
index eca87505ee9..3edb3b9bb21 100644
--- a/test/unit/math/opencl/rev/double_exponential_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/double_exponential_lccdf_test.cpp
@@ -66,7 +66,6 @@ auto double_exponential_lccdf_functor
 
 TEST(ProbDistributionsDoubleExponentialLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 2.8, 1.0;
diff --git a/test/unit/math/opencl/rev/double_exponential_lcdf_test.cpp b/test/unit/math/opencl/rev/double_exponential_lcdf_test.cpp
index 6e8f2f57f90..88a0d8e6aa1 100644
--- a/test/unit/math/opencl/rev/double_exponential_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/double_exponential_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto double_exponential_lcdf_functor
 
 TEST(ProbDistributionsDoubleExponentialLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.7;
diff --git a/test/unit/math/opencl/rev/exp_mod_normal_cdf_test.cpp b/test/unit/math/opencl/rev/exp_mod_normal_cdf_test.cpp
index 33c53bb16a7..711b9e38a3e 100644
--- a/test/unit/math/opencl/rev/exp_mod_normal_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/exp_mod_normal_cdf_test.cpp
@@ -88,7 +88,6 @@ auto exp_mod_normal_cdf_functor
 
 TEST(ProbDistributionsDoubleExpModNormalCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, 1.4;
@@ -109,7 +108,6 @@ TEST(ProbDistributionsDoubleExpModNormalCdf, opencl_matches_cpu_small) {
 TEST(ProbDistributionsDoubleExpModNormalCdf,
      opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -INFINITY, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/exp_mod_normal_lccdf_test.cpp b/test/unit/math/opencl/rev/exp_mod_normal_lccdf_test.cpp
index 677ce2a2f89..d03eae230b3 100644
--- a/test/unit/math/opencl/rev/exp_mod_normal_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/exp_mod_normal_lccdf_test.cpp
@@ -88,7 +88,6 @@ auto exp_mod_normal_lccdf_functor
 
 TEST(ProbDistributionsDoubleExpModNormalLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, 1.4;
@@ -109,7 +108,6 @@ TEST(ProbDistributionsDoubleExpModNormalLccdf, opencl_matches_cpu_small) {
 TEST(ProbDistributionsDoubleExpModNormalLccdf,
      opencl_matches_cpu_small_y_pos_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, INFINITY;
@@ -130,7 +128,6 @@ TEST(ProbDistributionsDoubleExpModNormalLccdf,
 TEST(ProbDistributionsDoubleExpModNormalLccdf,
      opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, -INFINITY;
diff --git a/test/unit/math/opencl/rev/exponential_cdf_test.cpp b/test/unit/math/opencl/rev/exponential_cdf_test.cpp
index 405ba03f6a5..8002466f000 100644
--- a/test/unit/math/opencl/rev/exponential_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/exponential_cdf_test.cpp
@@ -48,7 +48,6 @@ auto exponential_cdf_functor = [](const auto& y, const auto& beta) {
 
 TEST(ProbDistributionsExponentialCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/exponential_lccdf_test.cpp b/test/unit/math/opencl/rev/exponential_lccdf_test.cpp
index 99cea24f1d4..23386c90562 100644
--- a/test/unit/math/opencl/rev/exponential_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/exponential_lccdf_test.cpp
@@ -48,7 +48,6 @@ auto exponential_lccdf_functor = [](const auto& y, const auto& beta) {
 
 TEST(ProbDistributionsExponentialLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/exponential_lcdf_test.cpp b/test/unit/math/opencl/rev/exponential_lcdf_test.cpp
index 25d47a0248f..3a236b149a0 100644
--- a/test/unit/math/opencl/rev/exponential_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/exponential_lcdf_test.cpp
@@ -48,7 +48,6 @@ auto exponential_lcdf_functor = [](const auto& y, const auto& beta) {
 
 TEST(ProbDistributionsExponentialLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/exponential_lpdf_test.cpp b/test/unit/math/opencl/rev/exponential_lpdf_test.cpp
index 01e5671360a..cbf8018af98 100644
--- a/test/unit/math/opencl/rev/exponential_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/exponential_lpdf_test.cpp
@@ -57,7 +57,6 @@ auto exponential_lpdf_functor_propto = [](const auto& y, const auto& beta) {
 
 TEST(ProbDistributionsExponential, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0, 0.5, 12.3;
diff --git a/test/unit/math/opencl/rev/frechet_cdf_test.cpp b/test/unit/math/opencl/rev/frechet_cdf_test.cpp
index 0fbab3d7f5d..c5302fe7f4b 100644
--- a/test/unit/math/opencl/rev/frechet_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/frechet_cdf_test.cpp
@@ -63,7 +63,6 @@ auto frechet_cdf_functor
 
 TEST(ProbDistributionsFrechetCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/frechet_lccdf_test.cpp b/test/unit/math/opencl/rev/frechet_lccdf_test.cpp
index 36405481bac..918c6671cfc 100644
--- a/test/unit/math/opencl/rev/frechet_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/frechet_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto frechet_lccdf_functor
 
 TEST(ProbDistributionsFrechetLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/frechet_lcdf_test.cpp b/test/unit/math/opencl/rev/frechet_lcdf_test.cpp
index a9ab54e177c..905da61790b 100644
--- a/test/unit/math/opencl/rev/frechet_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/frechet_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto frechet_lcdf_functor
 
 TEST(ProbDistributionsFrechetLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/gumbel_cdf_test.cpp b/test/unit/math/opencl/rev/gumbel_cdf_test.cpp
index f65c838f4e6..572a06e0bd1 100644
--- a/test/unit/math/opencl/rev/gumbel_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/gumbel_cdf_test.cpp
@@ -62,7 +62,6 @@ auto gumbel_cdf_functor = [](const auto& y, const auto& mu, const auto& sigma) {
 
 TEST(ProbDistributionsGumbelCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/gumbel_lccdf_test.cpp b/test/unit/math/opencl/rev/gumbel_lccdf_test.cpp
index 859e48573c9..f6aa9a09500 100644
--- a/test/unit/math/opencl/rev/gumbel_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/gumbel_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto gumbel_lccdf_functor
 
 TEST(ProbDistributionsGumbelLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/gumbel_lcdf_test.cpp b/test/unit/math/opencl/rev/gumbel_lcdf_test.cpp
index 9340c0b4183..b40cc75cef0 100644
--- a/test/unit/math/opencl/rev/gumbel_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/gumbel_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto gumbel_lcdf_functor
 
 TEST(ProbDistributionsGumbelLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/inv_gamma_lpdf_test.cpp b/test/unit/math/opencl/rev/inv_gamma_lpdf_test.cpp
index d86600bd966..08bd621ff18 100644
--- a/test/unit/math/opencl/rev/inv_gamma_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/inv_gamma_lpdf_test.cpp
@@ -79,7 +79,6 @@ auto inv_gamma_lpdf_functor_propto
 
 TEST(ProbDistributionsInvGamma, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 10, 0.5, 1;
@@ -102,7 +101,6 @@ TEST(ProbDistributionsInvGamma, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsInvGamma, opencl_matches_cpu_small_zero_y) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0, 0.5, 1;
diff --git a/test/unit/math/opencl/rev/log_mix_test.cpp b/test/unit/math/opencl/rev/log_mix_test.cpp
index 68bccc12594..dc9eb721b83 100644
--- a/test/unit/math/opencl/rev/log_mix_test.cpp
+++ b/test/unit/math/opencl/rev/log_mix_test.cpp
@@ -59,7 +59,6 @@ auto log_mix_functor = [](const auto& theta, const auto& lambda) {
 
 TEST(OpenCLLogMix, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd theta1(N);
   theta1 << 0.5, 0.4, 0.1;
diff --git a/test/unit/math/opencl/rev/logistic_cdf_test.cpp b/test/unit/math/opencl/rev/logistic_cdf_test.cpp
index f279c45691e..385dab309b2 100644
--- a/test/unit/math/opencl/rev/logistic_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/logistic_cdf_test.cpp
@@ -63,7 +63,6 @@ auto logistic_cdf_functor
 
 TEST(ProbDistributionsLogisticCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsLogisticCdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsLogisticCdf, opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, -INFINITY, 1.0;
diff --git a/test/unit/math/opencl/rev/logistic_lccdf_test.cpp b/test/unit/math/opencl/rev/logistic_lccdf_test.cpp
index 50796ef91b6..00ff9dff489 100644
--- a/test/unit/math/opencl/rev/logistic_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/logistic_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto logistic_lccdf_functor
 
 TEST(ProbDistributionsLogisticLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsLogisticLccdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsLogisticLccdf, opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, -INFINITY, 1.0;
diff --git a/test/unit/math/opencl/rev/logistic_lcdf_test.cpp b/test/unit/math/opencl/rev/logistic_lcdf_test.cpp
index c3cb1cc9d4e..2a0e9ecd3a0 100644
--- a/test/unit/math/opencl/rev/logistic_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/logistic_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto logistic_lcdf_functor
 
 TEST(ProbDistributionsLogisticLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsLogisticLcdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsLogisticLcdf, opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, -INFINITY, 1.0;
diff --git a/test/unit/math/opencl/rev/logistic_lpdf_test.cpp b/test/unit/math/opencl/rev/logistic_lpdf_test.cpp
index 44cc923c6ea..9c3ba21f4b7 100644
--- a/test/unit/math/opencl/rev/logistic_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/logistic_lpdf_test.cpp
@@ -79,7 +79,6 @@ auto logistic_lpdf_functor_propto
 
 TEST(ProbDistributionsLogistic, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 10, -0.5, 1;
@@ -181,7 +180,6 @@ TEST(ProbDistributionsLogistic, opencl_matches_cpu_big) {
 
 TEST(ProbDistributionsLogistic, opencl_sigma_mu_scalar) {
   int N = 3;
-  int M = 2;
 
   double sigma = 0.3;
   double mu = 0.5;
diff --git a/test/unit/math/opencl/rev/lognormal_cdf_test.cpp b/test/unit/math/opencl/rev/lognormal_cdf_test.cpp
index bb45cc07d4a..4c80c21b39e 100644
--- a/test/unit/math/opencl/rev/lognormal_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/lognormal_cdf_test.cpp
@@ -63,7 +63,6 @@ auto lognormal_cdf_functor
 
 TEST(ProbDistributionsLognormalCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsLognormalCdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsLognormalCdf, opencl_matches_cpu_small_y_zero) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.0, 1.0;
diff --git a/test/unit/math/opencl/rev/lognormal_lccdf_test.cpp b/test/unit/math/opencl/rev/lognormal_lccdf_test.cpp
index 324864b55c3..a3619fcb1a3 100644
--- a/test/unit/math/opencl/rev/lognormal_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/lognormal_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto lognormal_lccdf_functor
 
 TEST(ProbDistributionsLognormalLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsLognormalLccdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsLognormalLccdf, opencl_matches_cpu_small_y_zero) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.0, 1.0;
diff --git a/test/unit/math/opencl/rev/lognormal_lcdf_test.cpp b/test/unit/math/opencl/rev/lognormal_lcdf_test.cpp
index b3c9163b015..9fdb5da9a8e 100644
--- a/test/unit/math/opencl/rev/lognormal_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/lognormal_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto lognormal_lcdf_functor
 
 TEST(ProbDistributionsLognormalLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsLognormalLcdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsLognormalLcdf, opencl_matches_cpu_small_y_zero) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.0, 1.0;
diff --git a/test/unit/math/opencl/rev/lognormal_lpdf_test.cpp b/test/unit/math/opencl/rev/lognormal_lpdf_test.cpp
index b3c0bdbd490..b984669aa5e 100644
--- a/test/unit/math/opencl/rev/lognormal_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/lognormal_lpdf_test.cpp
@@ -85,7 +85,6 @@ auto lognormal_lpdf_functor_propto
 
 TEST(ProbDistributionsLognormal, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.1, 0.5, 1;
@@ -107,7 +106,6 @@ TEST(ProbDistributionsLognormal, opencl_matches_cpu_small) {
 }
 TEST(ProbDistributionsLognormal, opencl_matches_cpu_small_zero_y) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0, 0.5, 1;
diff --git a/test/unit/math/opencl/rev/multi_normal_cholesky_lpdf_test.cpp b/test/unit/math/opencl/rev/multi_normal_cholesky_lpdf_test.cpp
index 221cec889d7..61443d022c4 100644
--- a/test/unit/math/opencl/rev/multi_normal_cholesky_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/multi_normal_cholesky_lpdf_test.cpp
@@ -90,7 +90,6 @@ auto multi_normal_cholesky_lpdf_functor_propto
 
 TEST(ProbDistributionsMultiNormalCholesky, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y1(N);
   y1 << 0.5, 0.4, 0.1;
diff --git a/test/unit/math/opencl/rev/neg_binomial_2_log_lpmf_test.cpp b/test/unit/math/opencl/rev/neg_binomial_2_log_lpmf_test.cpp
index d9e2e89b852..6aea791d8fe 100644
--- a/test/unit/math/opencl/rev/neg_binomial_2_log_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/neg_binomial_2_log_lpmf_test.cpp
@@ -69,7 +69,6 @@ auto neg_binomial_2_log_lpmf_functor_propto
 
 TEST(ProbDistributionsNegBinomial2Log, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{1, 0, 12};
   Eigen::VectorXd eta(N);
@@ -169,9 +168,6 @@ TEST(ProbDistributionsNegBinomial2Log, opencl_matches_cpu_big) {
 }
 
 TEST(ProbDistributionsNegBinomial2Log, opencl_matches_cpu_eta_phi_scalar) {
-  int N = 3;
-  int M = 2;
-
   std::vector<int> n{1, 0, 12};
   double eta = 0.3;
   double phi = 0.8;
diff --git a/test/unit/math/opencl/rev/neg_binomial_2_lpmf_test.cpp b/test/unit/math/opencl/rev/neg_binomial_2_lpmf_test.cpp
index e7e863610d9..591d1598a86 100644
--- a/test/unit/math/opencl/rev/neg_binomial_2_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/neg_binomial_2_lpmf_test.cpp
@@ -74,7 +74,6 @@ auto neg_binomial_2_lpmf_functor_propto
 
 TEST(muProbDistributionsNegBinomial2, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{1, 0, 12};
   Eigen::VectorXd mu(N);
@@ -175,7 +174,6 @@ TEST(muProbDistributionsNegBinomial2, opencl_matches_cpu_big) {
 
 TEST(ProbDistributionsNegBinomial2, opencl_scalar_n_mu) {
   int N = 3;
-  int M = 2;
 
   int n = 1;
   double mu = 0.3;
diff --git a/test/unit/math/opencl/rev/neg_binomial_lpmf_test.cpp b/test/unit/math/opencl/rev/neg_binomial_lpmf_test.cpp
index 28014935e8e..ce7613b75e4 100644
--- a/test/unit/math/opencl/rev/neg_binomial_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/neg_binomial_lpmf_test.cpp
@@ -74,7 +74,6 @@ auto neg_binomial_lpmf_functor_propto
 
 TEST(muProbDistributionsNegBinomial, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{1, 0, 12};
   Eigen::VectorXd alpha(N);
diff --git a/test/unit/math/opencl/rev/normal_lccdf_test.cpp b/test/unit/math/opencl/rev/normal_lccdf_test.cpp
index e03341403ed..190ff5589a3 100644
--- a/test/unit/math/opencl/rev/normal_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/normal_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto normal_lccdf_functor
 
 TEST(ProbDistributionsNormalLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/normal_lcdf_test.cpp b/test/unit/math/opencl/rev/normal_lcdf_test.cpp
index e264c5e1d9c..a062e1304d4 100644
--- a/test/unit/math/opencl/rev/normal_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/normal_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto normal_lcdf_functor
 
 TEST(ProbDistributionsNormalLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/pareto_cdf_test.cpp b/test/unit/math/opencl/rev/pareto_cdf_test.cpp
index 89e7fcd3f8b..556bcb4f687 100644
--- a/test/unit/math/opencl/rev/pareto_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/pareto_cdf_test.cpp
@@ -63,7 +63,6 @@ auto pareto_cdf_functor
 
 TEST(ProbDistributionsParetoCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.35, 0.9, 1.5;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsParetoCdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsParetoCdf, opencl_matches_cpu_small_y_lower_than_y_min) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.35, 0.7, 1.3;
diff --git a/test/unit/math/opencl/rev/pareto_lccdf_test.cpp b/test/unit/math/opencl/rev/pareto_lccdf_test.cpp
index 64efae248b9..ffd41b62f82 100644
--- a/test/unit/math/opencl/rev/pareto_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/pareto_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto pareto_lccdf_functor
 
 TEST(ProbDistributionsParetoLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.35, 0.9, 1.5;
@@ -82,7 +81,6 @@ TEST(ProbDistributionsParetoLccdf, opencl_matches_cpu_small) {
 TEST(ProbDistributionsParetoLccdf,
      opencl_matches_cpu_small_y_lower_than_y_min) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.35, 0.7, 1.3;
diff --git a/test/unit/math/opencl/rev/pareto_lcdf_test.cpp b/test/unit/math/opencl/rev/pareto_lcdf_test.cpp
index 24c158cea90..1f2e27bd91d 100644
--- a/test/unit/math/opencl/rev/pareto_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/pareto_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto pareto_lcdf_functor
 
 TEST(ProbDistributionsParetoLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.35, 0.9, 1.5;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsParetoLcdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsParetoLcdf, opencl_matches_cpu_small_y_lower_than_y_min) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.35, 0.7, 1.3;
diff --git a/test/unit/math/opencl/rev/pareto_lpdf_test.cpp b/test/unit/math/opencl/rev/pareto_lpdf_test.cpp
index 1ab39a71093..e6378bf2634 100644
--- a/test/unit/math/opencl/rev/pareto_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/pareto_lpdf_test.cpp
@@ -77,7 +77,6 @@ auto pareto_lpdf_functor_propto
 
 TEST(ProbDistributionsPareto, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/pareto_type_2_cdf_test.cpp b/test/unit/math/opencl/rev/pareto_type_2_cdf_test.cpp
index e3bc404da15..13677126159 100644
--- a/test/unit/math/opencl/rev/pareto_type_2_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/pareto_type_2_cdf_test.cpp
@@ -86,7 +86,6 @@ auto pareto_type_2_cdf_functor
 
 TEST(ProbDistributionsParetoType2Cdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.5, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/pareto_type_2_lccdf_test.cpp b/test/unit/math/opencl/rev/pareto_type_2_lccdf_test.cpp
index fa71fc0cc8f..2d936ba78a9 100644
--- a/test/unit/math/opencl/rev/pareto_type_2_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/pareto_type_2_lccdf_test.cpp
@@ -86,7 +86,6 @@ auto pareto_type_2_lccdf_functor
 
 TEST(ProbDistributionsParetoType2Lccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.5, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/pareto_type_2_lcdf_test.cpp b/test/unit/math/opencl/rev/pareto_type_2_lcdf_test.cpp
index 2242c01a8bc..a6ee89e5097 100644
--- a/test/unit/math/opencl/rev/pareto_type_2_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/pareto_type_2_lcdf_test.cpp
@@ -86,7 +86,6 @@ auto pareto_type_2_lcdf_functor
 
 TEST(ProbDistributionsParetoType2Lcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.5, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/poisson_log_lpmf_test.cpp b/test/unit/math/opencl/rev/poisson_log_lpmf_test.cpp
index bc7dcfc3171..98ba889142e 100644
--- a/test/unit/math/opencl/rev/poisson_log_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/poisson_log_lpmf_test.cpp
@@ -47,7 +47,6 @@ auto poisson_log_lpmf_functor_propto = [](const auto& n, const auto& alpha) {
 
 TEST(ProbDistributionsPoissonLog, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 1, 6};
   Eigen::VectorXd alpha(N);
@@ -77,8 +76,6 @@ TEST(ProbDistributionsPoissonLog, opencl_broadcast_n) {
 }
 
 TEST(ProbDistributionsPoissonLog, opencl_broadcast_alpha) {
-  int N = 3;
-
   std::vector<int> n{0, 1, 5};
   double alpha_scal = 0.4;
 
diff --git a/test/unit/math/opencl/rev/poisson_lpmf_test.cpp b/test/unit/math/opencl/rev/poisson_lpmf_test.cpp
index 0da588c6ab7..2176126def3 100644
--- a/test/unit/math/opencl/rev/poisson_lpmf_test.cpp
+++ b/test/unit/math/opencl/rev/poisson_lpmf_test.cpp
@@ -47,7 +47,6 @@ auto poisson_lpmf_functor_propto = [](const auto& n, const auto& alpha) {
 
 TEST(ProbDistributionsPoisson, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   std::vector<int> n{0, 1, 6};
   Eigen::VectorXd alpha(N);
@@ -75,8 +74,6 @@ TEST(ProbDistributionsPoisson, opencl_broadcast_n) {
 }
 
 TEST(ProbDistributionsPoisson, opencl_broadcast_alpha) {
-  int N = 3;
-
   std::vector<int> n{0, 1, 5};
   double alpha_scal = 0.4;
 
diff --git a/test/unit/math/opencl/rev/rayleigh_cdf_test.cpp b/test/unit/math/opencl/rev/rayleigh_cdf_test.cpp
index 7db4882d0b8..ea8619bf53e 100644
--- a/test/unit/math/opencl/rev/rayleigh_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/rayleigh_cdf_test.cpp
@@ -46,7 +46,6 @@ auto rayleigh_cdf_functor = [](const auto& y, const auto& mu) {
 
 TEST(ProbDistributionsRayleighCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/rayleigh_lccdf_test.cpp b/test/unit/math/opencl/rev/rayleigh_lccdf_test.cpp
index 4ab1ea7384d..b9c5eadea45 100644
--- a/test/unit/math/opencl/rev/rayleigh_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/rayleigh_lccdf_test.cpp
@@ -48,7 +48,6 @@ auto rayleigh_lccdf_functor = [](const auto& y, const auto& mu) {
 
 TEST(ProbDistributionsRayleighLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/rayleigh_lcdf_test.cpp b/test/unit/math/opencl/rev/rayleigh_lcdf_test.cpp
index 713b5639fb4..c89f97394f3 100644
--- a/test/unit/math/opencl/rev/rayleigh_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/rayleigh_lcdf_test.cpp
@@ -46,7 +46,6 @@ auto rayleigh_lcdf_functor = [](const auto& y, const auto& mu) {
 
 TEST(ProbDistributionsRayleighLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/rayleigh_lpdf_test.cpp b/test/unit/math/opencl/rev/rayleigh_lpdf_test.cpp
index 93460840c2f..1c81a0b1f84 100644
--- a/test/unit/math/opencl/rev/rayleigh_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/rayleigh_lpdf_test.cpp
@@ -52,7 +52,6 @@ auto rayleigh_lpdf_functor_propto = [](const auto& y, const auto& sigma) {
 
 TEST(ProbDistributionsRayleigh, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.1, 0.5, 12.3;
diff --git a/test/unit/math/opencl/rev/segment_test.cpp b/test/unit/math/opencl/rev/segment_test.cpp
index 8f78952a071..c87a7fb47a2 100644
--- a/test/unit/math/opencl/rev/segment_test.cpp
+++ b/test/unit/math/opencl/rev/segment_test.cpp
@@ -19,15 +19,15 @@ TEST(MathMatrixCL, segment_exception) {
   EXPECT_THROW(segment(m3_cl, 1, 5), std::invalid_argument);
 
   stan::math::var_value<stan::math::matrix_cl<double>> m4_cl = m1_cl;
-  EXPECT_THROW(segment(m1_cl, 1, 5), std::invalid_argument);
+  EXPECT_THROW(segment(m4_cl, 1, 5), std::invalid_argument);
 
   stan::math::var_value<stan::math::matrix_cl<double>> m5_cl = m2_cl;
-  EXPECT_THROW(segment(m2_cl, 0, 2), std::invalid_argument);
-  EXPECT_THROW(segment(m2_cl, 1, 5), std::invalid_argument);
+  EXPECT_THROW(segment(m5_cl, 0, 2), std::invalid_argument);
+  EXPECT_THROW(segment(m5_cl, 1, 5), std::invalid_argument);
 
   stan::math::var_value<stan::math::matrix_cl<double>> m6_cl = m3_cl;
-  EXPECT_THROW(segment(m3_cl, 0, 2), std::invalid_argument);
-  EXPECT_THROW(segment(m3_cl, 1, 5), std::invalid_argument);
+  EXPECT_THROW(segment(m6_cl, 0, 2), std::invalid_argument);
+  EXPECT_THROW(segment(m6_cl, 1, 5), std::invalid_argument);
 }
 
 auto segment_functor = [](const auto& a, size_t i, size_t n) {
diff --git a/test/unit/math/opencl/rev/skew_double_exponential_cdf_test.cpp b/test/unit/math/opencl/rev/skew_double_exponential_cdf_test.cpp
index 7d82bffb838..397f97673ba 100644
--- a/test/unit/math/opencl/rev/skew_double_exponential_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/skew_double_exponential_cdf_test.cpp
@@ -88,7 +88,6 @@ auto skew_double_exponential_cdf_functor
 
 TEST(ProbDistributionsSkewDoubleExponentialCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, 1.4;
@@ -109,7 +108,6 @@ TEST(ProbDistributionsSkewDoubleExponentialCdf, opencl_matches_cpu_small) {
 TEST(ProbDistributionsSkewDoubleExponentialCdf,
      opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -INFINITY, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/skew_double_exponential_lccdf_test.cpp b/test/unit/math/opencl/rev/skew_double_exponential_lccdf_test.cpp
index 0628af47960..79092f6a583 100644
--- a/test/unit/math/opencl/rev/skew_double_exponential_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/skew_double_exponential_lccdf_test.cpp
@@ -88,7 +88,6 @@ auto skew_double_exponential_lccdf_functor
 
 TEST(ProbDistributionsSkewDoubleExponentialLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, 1.4;
@@ -109,7 +108,6 @@ TEST(ProbDistributionsSkewDoubleExponentialLccdf, opencl_matches_cpu_small) {
 TEST(ProbDistributionsSkewDoubleExponentialLccdf,
      opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -INFINITY, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/skew_double_exponential_lcdf_test.cpp b/test/unit/math/opencl/rev/skew_double_exponential_lcdf_test.cpp
index c8b5a250856..03ad9cbf643 100644
--- a/test/unit/math/opencl/rev/skew_double_exponential_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/skew_double_exponential_lcdf_test.cpp
@@ -88,7 +88,6 @@ auto skew_double_exponential_lcdf_functor
 
 TEST(ProbDistributionsSkewDoubleExponentialLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -0.3, 1.8, 1.4;
@@ -109,7 +108,6 @@ TEST(ProbDistributionsSkewDoubleExponentialLcdf, opencl_matches_cpu_small) {
 TEST(ProbDistributionsSkewDoubleExponentialLcdf,
      opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << -INFINITY, 1.8, 1.4;
diff --git a/test/unit/math/opencl/rev/skew_normal_lpdf_test.cpp b/test/unit/math/opencl/rev/skew_normal_lpdf_test.cpp
index 4e60315ee71..ad5220e8557 100644
--- a/test/unit/math/opencl/rev/skew_normal_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/skew_normal_lpdf_test.cpp
@@ -90,7 +90,6 @@ auto skew_normal_lpdf_functor_propto
 
 TEST(ProbDistributionsSkewNormal, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/std_normal_cdf_test.cpp b/test/unit/math/opencl/rev/std_normal_cdf_test.cpp
index 1bf3edff524..dea8b16e9f4 100644
--- a/test/unit/math/opencl/rev/std_normal_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/std_normal_cdf_test.cpp
@@ -26,7 +26,6 @@ auto std_normal_cdf_functor
 
 TEST(ProbDistributionsStdNormalCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/std_normal_lccdf_test.cpp b/test/unit/math/opencl/rev/std_normal_lccdf_test.cpp
index b261a062258..6f4b1e1f866 100644
--- a/test/unit/math/opencl/rev/std_normal_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/std_normal_lccdf_test.cpp
@@ -26,7 +26,6 @@ auto std_normal_lccdf_functor
 
 TEST(ProbDistributionsStdNormalLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/std_normal_lcdf_test.cpp b/test/unit/math/opencl/rev/std_normal_lcdf_test.cpp
index 52f3562c6fe..97fdbb38225 100644
--- a/test/unit/math/opencl/rev/std_normal_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/std_normal_lcdf_test.cpp
@@ -26,7 +26,6 @@ auto std_normal_lcdf_functor
 
 TEST(ProbDistributionsStdNormalLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/std_normal_lpdf_test.cpp b/test/unit/math/opencl/rev/std_normal_lpdf_test.cpp
index 7f8fcea56bd..ed4556ba09c 100644
--- a/test/unit/math/opencl/rev/std_normal_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/std_normal_lpdf_test.cpp
@@ -27,7 +27,6 @@ auto std_normal_lpdf_functor_propto
 
 TEST(ProbDistributionsStdNormal, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/uniform_cdf_test.cpp b/test/unit/math/opencl/rev/uniform_cdf_test.cpp
index 262e6985897..5ed2189f1fe 100644
--- a/test/unit/math/opencl/rev/uniform_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/uniform_cdf_test.cpp
@@ -63,7 +63,6 @@ auto uniform_cdf_functor
 
 TEST(ProbDistributionsUniformCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsUniformCdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsUniformCdf, opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, -INFINITY, 1.0;
diff --git a/test/unit/math/opencl/rev/uniform_lccdf_test.cpp b/test/unit/math/opencl/rev/uniform_lccdf_test.cpp
index bed3d490b85..05b8d00a41e 100644
--- a/test/unit/math/opencl/rev/uniform_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/uniform_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto uniform_lccdf_functor
 
 TEST(ProbDistributionsUniformLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsUniformLccdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsUniformLccdf, opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, -INFINITY, 1.0;
diff --git a/test/unit/math/opencl/rev/uniform_lcdf_test.cpp b/test/unit/math/opencl/rev/uniform_lcdf_test.cpp
index 5e028cb777e..cec558ada3f 100644
--- a/test/unit/math/opencl/rev/uniform_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/uniform_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto uniform_lcdf_functor
 
 TEST(ProbDistributionsUniformLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
@@ -81,7 +80,6 @@ TEST(ProbDistributionsUniformLcdf, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsUniformLcdf, opencl_matches_cpu_small_y_neg_inf) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, -INFINITY, 1.0;
diff --git a/test/unit/math/opencl/rev/uniform_lpdf_test.cpp b/test/unit/math/opencl/rev/uniform_lpdf_test.cpp
index 8f58bf84d32..6a1546d3bd1 100644
--- a/test/unit/math/opencl/rev/uniform_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/uniform_lpdf_test.cpp
@@ -94,7 +94,6 @@ TEST(ProbDistributionsUniform, opencl_matches_cpu_small) {
 
 TEST(ProbDistributionsUniform, opencl_matches_cpu_small_y_out_of_bounds) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 14.0;
diff --git a/test/unit/math/opencl/rev/weibull_cdf_test.cpp b/test/unit/math/opencl/rev/weibull_cdf_test.cpp
index c8c6fe620c4..3fac364865e 100644
--- a/test/unit/math/opencl/rev/weibull_cdf_test.cpp
+++ b/test/unit/math/opencl/rev/weibull_cdf_test.cpp
@@ -63,7 +63,6 @@ auto weibull_cdf_functor
 
 TEST(ProbDistributionsWeibullCdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/weibull_lccdf_test.cpp b/test/unit/math/opencl/rev/weibull_lccdf_test.cpp
index bf845190153..91b82eda794 100644
--- a/test/unit/math/opencl/rev/weibull_lccdf_test.cpp
+++ b/test/unit/math/opencl/rev/weibull_lccdf_test.cpp
@@ -63,7 +63,6 @@ auto weibull_lccdf_functor
 
 TEST(ProbDistributionsWeibullLccdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/weibull_lcdf_test.cpp b/test/unit/math/opencl/rev/weibull_lcdf_test.cpp
index 4f0b1b89b63..a81c190e45a 100644
--- a/test/unit/math/opencl/rev/weibull_lcdf_test.cpp
+++ b/test/unit/math/opencl/rev/weibull_lcdf_test.cpp
@@ -63,7 +63,6 @@ auto weibull_lcdf_functor
 
 TEST(ProbDistributionsWeibullLcdf, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/opencl/rev/weibull_lpdf_test.cpp b/test/unit/math/opencl/rev/weibull_lpdf_test.cpp
index c6c4e13ab69..dbea51cb619 100644
--- a/test/unit/math/opencl/rev/weibull_lpdf_test.cpp
+++ b/test/unit/math/opencl/rev/weibull_lpdf_test.cpp
@@ -77,7 +77,6 @@ auto weibull_lpdf_functor_propto
 
 TEST(ProbDistributionsWeibull, opencl_matches_cpu_small) {
   int N = 3;
-  int M = 2;
 
   Eigen::VectorXd y(N);
   y << 0.3, 0.8, 1.0;
diff --git a/test/unit/math/prim/constraint/unit_vector_transform_test.cpp b/test/unit/math/prim/constraint/unit_vector_transform_test.cpp
index 4bf5a3957bf..2622aaae874 100644
--- a/test/unit/math/prim/constraint/unit_vector_transform_test.cpp
+++ b/test/unit/math/prim/constraint/unit_vector_transform_test.cpp
@@ -3,6 +3,20 @@
 #include <gtest/gtest.h>
 #include <limits>
 
+TEST(prob_transform, unit_vector_free_owns_evaluated_result) {
+  Eigen::VectorXd x(2);
+  x << 0.6, 0.8;
+  const Eigen::VectorXd expected = x;
+
+  auto from_lvalue = stan::math::unit_vector_free(x);
+  EXPECT_MATRIX_EQ(expected, x);
+  auto from_expression
+      = stan::math::unit_vector_free(x + Eigen::VectorXd::Zero(2));
+  x.setZero();
+  EXPECT_MATRIX_EQ(expected, from_lvalue);
+  EXPECT_MATRIX_EQ(expected, from_expression);
+}
+
 TEST(prob_transform, unit_vector_rt0) {
   using Eigen::Dynamic;
   using Eigen::Matrix;
diff --git a/test/unit/math/prim/fun/eval_test.cpp b/test/unit/math/prim/fun/eval_test.cpp
index 148cc2f1e12..5b6605bd7f3 100644
--- a/test/unit/math/prim/fun/eval_test.cpp
+++ b/test/unit/math/prim/fun/eval_test.cpp
@@ -196,7 +196,7 @@ TEST(MathFunctions, eval_return_type_expression) {
 
 TEST(MathFunctions, eval_return_type_short_circuit_static_sized_matrix) {
   Eigen::Matrix<double, 5, 4> a;
-  const Eigen::Matrix<double, 5, 4> b;
+  const Eigen::Matrix<double, 5, 4> b{};
   EXPECT_TRUE((std::is_same<decltype(stan::math::eval(a)),
                             Eigen::Matrix<double, 5, 4>&>::value));
   EXPECT_TRUE((std::is_same<decltype(stan::math::eval(b)),
diff --git a/test/unit/math/prim/fun/value_of_rec_test.cpp b/test/unit/math/prim/fun/value_of_rec_test.cpp
index c5da58d4171..5ed378a30f6 100644
--- a/test/unit/math/prim/fun/value_of_rec_test.cpp
+++ b/test/unit/math/prim/fun/value_of_rec_test.cpp
@@ -134,7 +134,7 @@ TEST(MathFunctions, value_of_rec_return_type_short_circuit_expression) {
 TEST(MathFunctions,
      value_of_rec_return_type_short_circuit_static_sized_matrix) {
   Eigen::Matrix<double, 5, 4> a;
-  const Eigen::Matrix<double, 5, 4> b;
+  const Eigen::Matrix<double, 5, 4> b{};
   EXPECT_TRUE((std::is_same<decltype(stan::math::value_of_rec(a)),
                             Eigen::Matrix<double, 5, 4>&>::value));
   EXPECT_TRUE((std::is_same<decltype(stan::math::value_of_rec(b)),
diff --git a/test/unit/math/prim/fun/value_of_test.cpp b/test/unit/math/prim/fun/value_of_test.cpp
index 9cd4acc8ad2..fe0b274eb3c 100644
--- a/test/unit/math/prim/fun/value_of_test.cpp
+++ b/test/unit/math/prim/fun/value_of_test.cpp
@@ -198,7 +198,7 @@ TEST(MathFunctions, value_of_return_type_short_circuit_expression) {
 
 TEST(MathFunctions, value_of_return_type_short_circuit_static_sized_matrix) {
   Eigen::Matrix<double, 5, 4> a;
-  const Eigen::Matrix<double, 5, 4> b;
+  const Eigen::Matrix<double, 5, 4> b{};
   EXPECT_TRUE((std::is_same<decltype(stan::math::value_of(a)),
                             Eigen::Matrix<double, 5, 4>&>::value));
   EXPECT_TRUE((std::is_same<decltype(stan::math::value_of(b)),
diff --git a/test/unit/math/prim/prob/student_t_qf_test.cpp b/test/unit/math/prim/prob/student_t_qf_test.cpp
index 4694264870d..999ef198f91 100644
--- a/test/unit/math/prim/prob/student_t_qf_test.cpp
+++ b/test/unit/math/prim/prob/student_t_qf_test.cpp
@@ -39,7 +39,6 @@ TEST(MathFunctions, student_t_qf_vec) {
 
 TEST(MathFunctions, student_t_qf_inf) {
   using stan::math::student_t_qf;
-  long double log_p = std::numeric_limits<long double>::min();
   const double inf = std::numeric_limits<double>::infinity();
   EXPECT_EQ(student_t_qf(0, 2, 0, 1), -inf);
   EXPECT_EQ(student_t_qf(1, 2, 0, 1), inf);
diff --git a/test/unit/math/rev/core/profiling_threading_test.cpp b/test/unit/math/rev/core/profiling_threading_test.cpp
index b3c2c78fa2b..2e15bbf9779 100644
--- a/test/unit/math/rev/core/profiling_threading_test.cpp
+++ b/test/unit/math/rev/core/profiling_threading_test.cpp
@@ -30,7 +30,6 @@ struct grouped_count_lpdf {
 TEST_F(AgradRev, Profiling_profile_threading) {
   using stan::math::var;
   using stan::math::test::get_new_msg;
-  double lambda_d = 10.0;
   const std::size_t groups = 10;
   const std::size_t elems_per_group = 1000;
   const std::size_t elems = groups * elems_per_group;
@@ -47,7 +46,6 @@ TEST_F(AgradRev, Profiling_profile_threading) {
 
   for (std::size_t i = 0; i != groups; ++i)
     vlambda_v[i] = i + 0.2;
-  var lambda_v = vlambda_v[0];
 
   var poisson_lpdf
       = stan::math::reduce_sum<profiling_test::grouped_count_lpdf<var>>(