From a42f498c5970f215a68e94c83cd248ce31291b0e Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Tue, 10 Jun 2014 13:50:51 -0700
Subject: [PATCH] Optimize merge_sym_transitions and merge_char_transitions

---
 spec/compiler/build_tables/merge_transitions_spec.cc |  4 ++--
 src/compiler/build_tables/item_set_transitions.cc    | 11 +++++------
 src/compiler/build_tables/merge_transitions.h        |  9 +++++----
 src/compiler/build_tables/rule_transitions.cc        |  4 ++--
 4 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/spec/compiler/build_tables/merge_transitions_spec.cc b/spec/compiler/build_tables/merge_transitions_spec.cc
index 43e1d744..a5af3857 100644
--- a/spec/compiler/build_tables/merge_transitions_spec.cc
+++ b/spec/compiler/build_tables/merge_transitions_spec.cc
@@ -10,8 +10,8 @@ describe("merging character set transitions", []() {
     typedef map<CharacterSet, int> int_map;
 
     auto merge_result = [&](int_map left, int_map right) -> int_map {
-        merge_char_transitions<int>(&left, right, [](const int *l, const int *r) -> int {
-            return *l | *r;
+        merge_char_transitions<int>(&left, right, [](int *l, const int *r) {
+            *l = *l | *r;
         });
         return left;
     };
diff --git a/src/compiler/build_tables/item_set_transitions.cc b/src/compiler/build_tables/item_set_transitions.cc
index a275c0e2..215ee9d7 100644
--- a/src/compiler/build_tables/item_set_transitions.cc
+++ b/src/compiler/build_tables/item_set_transitions.cc
@@ -15,9 +15,8 @@ namespace tree_sitter {
 
     namespace build_tables {
         template<typename T>
-        static unordered_set<T> merge_sets(unordered_set<T> *left, const unordered_set<T> *right) {
+        static void merge_sets(unordered_set<T> *left, const unordered_set<T> *right) {
             left->insert(right->begin(), right->end());
-            return *left;
         }
 
         const Symbol placeholder_lookahead = Symbol(-100);
@@ -76,8 +75,8 @@ namespace tree_sitter {
             for (const ParseItem &item : item_set)
                 merge_sym_transitions<ParseItemSet>(&result,
                                                     sym_transitions_for_item(this, item, grammar),
-                                                    [&](ParseItemSet *l, const ParseItemSet *r) {
-                                                        return merge_sets(l, r);
+                                                    [](ParseItemSet *l, const ParseItemSet *r) {
+                                                        merge_sets(l, r);
                                                     });
             return result;
         }
@@ -94,8 +93,8 @@ namespace tree_sitter {
                         LexItemSet({ next_item })
                     });
                 }
-                merge_char_transitions<LexItemSet>(&result, item_transitions, [](LexItemSet *l, const LexItemSet *r) -> LexItemSet {
-                    return merge_sets(l, r);
+                merge_char_transitions<LexItemSet>(&result, item_transitions, [](LexItemSet *l, const LexItemSet *r) {
+                    merge_sets(l, r);
                 });
             }
             return result;
diff --git a/src/compiler/build_tables/merge_transitions.h b/src/compiler/build_tables/merge_transitions.h
index 0bbe82bc..3a5ffbca 100644
--- a/src/compiler/build_tables/merge_transitions.h
+++ b/src/compiler/build_tables/merge_transitions.h
@@ -17,14 +17,14 @@ namespace tree_sitter {
         template<typename T>
         void merge_sym_transitions(std::map<rules::Symbol, T> *left,
                                    const std::map<rules::Symbol, T> &right,
-                                   std::function<T(T *, const T *)> merge_fn) {
+                                   std::function<void(T *, const T *)> merge_fn) {
             for (auto &pair : right) {
                 auto rule = pair.first;
                 bool merged = false;
                 for (auto &existing_pair : *left) {
                     auto existing_rule = existing_pair.first;
                     if (existing_rule == rule) {
-                        existing_pair.second = merge_fn(&existing_pair.second, &pair.second);
+                        merge_fn(&existing_pair.second, &pair.second);
                         merged = true;
                         break;
                     } else if (rule < existing_rule) {
@@ -45,7 +45,7 @@ namespace tree_sitter {
         template<typename T>
         void merge_char_transitions(std::map<rules::CharacterSet, T> *left,
                                     const std::map<rules::CharacterSet, T> &right,
-                                    std::function<T(T *, const T *)> merge_fn) {
+                                    std::function<void(T *, const T *)> merge_fn) {
             for (auto &new_pair : right) {
                 rules::CharacterSet new_char_set = new_pair.first;
                 T new_value = new_pair.second;
@@ -62,7 +62,8 @@ namespace tree_sitter {
                         new_char_set.remove_set(intersection);
                         if (!char_set.is_empty())
                             pairs_to_insert.insert({ char_set, value });
-                        pairs_to_insert.insert({ intersection, merge_fn(&value, &new_value) });
+                        merge_fn(&value, &new_value);
+                        pairs_to_insert.insert({ intersection, value });
                         left->erase(iter++);
                     } else {
                         ++iter;
diff --git a/src/compiler/build_tables/rule_transitions.cc b/src/compiler/build_tables/rule_transitions.cc
index d29da169..33d532ca 100644
--- a/src/compiler/build_tables/rule_transitions.cc
+++ b/src/compiler/build_tables/rule_transitions.cc
@@ -26,14 +26,14 @@ namespace tree_sitter {
         template<>
         void merge_transitions(map<CharacterSet, rule_ptr> *left, const map<CharacterSet, rule_ptr> &right) {
             merge_char_transitions<rule_ptr>(left, right, [](rule_ptr *left, const rule_ptr *right) {
-                return rules::Choice::Build({ *left, *right });
+                *left = rules::Choice::Build({ *left, *right });
             });
         }
 
         template<>
         void merge_transitions(map<Symbol, rule_ptr> *left, const map<Symbol, rule_ptr> &right) {
             merge_sym_transitions<rule_ptr>(left, right, [](rule_ptr *left, const rule_ptr *right) {
-                return rules::Choice::Build({ *left, *right });
+                *left = rules::Choice::Build({ *left, *right });
             });
         }