From 49b2dcb1f3db8ac8c7f9cfcf1abfcb64194ff700 Mon Sep 17 00:00:00 2001
From: Tomasz Sobczyk <tomasz.sobczyk1997@gmail.com>
Date: Wed, 25 Nov 2020 21:53:53 +0100
Subject: [PATCH] Preallocate memory for unique_features. Keep the
 training_features temporary buffer as a thread_local so we reuse the storage.

---
 src/nnue/evaluate_nnue_learner.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/nnue/evaluate_nnue_learner.cpp b/src/nnue/evaluate_nnue_learner.cpp
index 644ac9a4..2f0a2122 100644
--- a/src/nnue/evaluate_nnue_learner.cpp
+++ b/src/nnue/evaluate_nnue_learner.cpp
@@ -157,8 +157,12 @@ namespace Eval::NNUE {
             active_indices[0].swap(active_indices[1]);
         }
 
+        static thread_local std::vector<TrainingFeature> s_training_features;
+        auto& training_features = s_training_features;
+
         for (const auto color : Colors) {
-            std::vector<TrainingFeature> training_features;
+            training_features.clear();
+
             for (const auto base_index : active_indices[color]) {
                 static_assert(Features::Factorizer<RawFeatures>::get_dimensions() <
                               (1 << TrainingFeature::kIndexBits), "");
@@ -169,6 +173,7 @@ namespace Eval::NNUE {
             std::sort(training_features.begin(), training_features.end());
 
             auto& unique_features = example.training_features[color];
+            unique_features.reserve(training_features.size());
             for (const auto& feature : training_features) {
                 if (!unique_features.empty() &&
                     feature.get_index() == unique_features.back().get_index()) {