Add final benchmarked optimization for solver omp_parallel_for

adelie/src/include/adelie_core/solver/solver_base.hpp

@@ -24,6 +24,7 @@ inline void update_abs_grad(
 )
 {
     using state_t = std::decay_t<StateType>;
+    using value_t = typename state_t::value_t;
     using vec_value_t = typename state_t::vec_value_t;
     using rowmat_uint64_t = util::rowmat_type<uint64_t>;
 
@@ -94,7 +95,12 @@ inline void update_abs_grad(
             try_failed = true;
         }
     };
-    util::omp_parallel_for(routine, 0, groups.size(), n_threads);
+    const bool is_not_all_none = util::rowvec_type<bool>::NullaryExpr(
+        constraints.size(), 
+        [&](auto i) { return constraints[i] != nullptr; }
+    ).any();
+    const size_t n_bytes = sizeof(value_t) * abs_grad.size();
+    util::omp_parallel_for(routine, 0, groups.size(), n_threads * (is_not_all_none || (n_bytes > Configs::min_bytes)));
     if (try_failed) {
         throw util::adelie_core_solver_error(
             "exception raised in constraint->solve_zero(). "
@@ -157,6 +163,8 @@ inline auto sparsify_dual(
     VecValueType& values
 )
 {
+    using index_t = typename StateType::index_t;
+    using value_t = typename StateType::value_t;
     using vec_index_t = typename StateType::vec_index_t;
     using vec_value_t = typename StateType::vec_value_t;
     using sp_vec_value_t = typename StateType::sp_vec_value_t;
@@ -192,7 +200,12 @@ inline auto sparsify_dual(
             constraint->dual(indices_v, values_v);
             indices_v += dual_groups[i];
         };
-        util::omp_parallel_for(routine, 0, n_constraints, n_threads);
+        const bool is_not_all_none = util::rowvec_type<bool>::NullaryExpr(
+            constraints.size(), 
+            [&](auto i) { return constraints[i] != nullptr; }
+        ).any();
+        const size_t n_bytes = (sizeof(index_t) + sizeof(value_t)) * indices.size();
+        util::omp_parallel_for(routine, 0, n_constraints, n_threads * (is_not_all_none || (n_bytes > Configs::min_bytes)));
     }
 
     const auto last_constraint = constraints[n_constraints-1];