From 70ba76762c128e40d2488cf13b5e9b6a1745ce96 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Mon, 28 Apr 2014 18:30:50 -0700
Subject: [PATCH] Optimize item set transitions function further

---
 .../build_tables/item_set_transitions.cc      | 47 ++++++++++++-------
 src/compiler/build_tables/merge_transitions.h |  4 +-
 2 files changed, 33 insertions(+), 18 deletions(-)

diff --git a/src/compiler/build_tables/item_set_transitions.cc b/src/compiler/build_tables/item_set_transitions.cc
index add4619f..2e595a1d 100644
--- a/src/compiler/build_tables/item_set_transitions.cc
+++ b/src/compiler/build_tables/item_set_transitions.cc
@@ -1,5 +1,6 @@
 #include "compiler/build_tables/item_set_transitions.h"
 #include <unordered_set>
+#include <vector>
 #include "compiler/build_tables/item_set_closure.h"
 #include "compiler/build_tables/rule_transitions.h"
 #include "compiler/build_tables/merge_transitions.h"
@@ -7,26 +8,27 @@
 
 namespace tree_sitter {
     using std::map;
+    using std::vector;
     using std::unordered_set;
     using rules::CharacterSet;
     using rules::ISymbol;
 
     namespace build_tables {
         template<typename T>
-        static unordered_set<T> merge_sets(const unordered_set<T> &left, const unordered_set<T> &right) {
-            unordered_set<T> result = left;
-            result.insert(right.begin(), right.end());
-            return result;
+        static unordered_set<T> merge_sets(unordered_set<T> &left, const unordered_set<T> &right) {
+            left.insert(right.begin(), right.end());
+            return left;
         }
 
-        const ISymbol placeholder = ISymbol(-99);
+        const ISymbol placeholder_lookahead = ISymbol(-100);
+        const ISymbol placeholder_lhs = ISymbol(-101);
 
         static map<ISymbol, ParseItemSet> sym_transitions_for_rule(SymTransitions *self, const rules::rule_ptr &rule, const PreparedGrammar &grammar) {
             auto pair = self->transitions_cache.find(rule);
             if (pair != self->transitions_cache.end()) return pair->second;
             map<ISymbol, ParseItemSet> result;
             for (auto &transition : sym_transitions(rule)) {
-                ParseItem new_item(placeholder, transition.second, 10, placeholder);
+                ParseItem new_item(placeholder_lhs, transition.second, 1, placeholder_lookahead);
                 result.insert({
                     transition.first,
                     item_set_closure(new_item, grammar)
@@ -39,18 +41,31 @@ namespace tree_sitter {
         static map<ISymbol, ParseItemSet> sym_transitions_for_item(SymTransitions *self, const ParseItem &item, const PreparedGrammar &grammar) {
             auto result = sym_transitions_for_rule(self, item.rule, grammar);
             for (auto &pair : result) {
-                ParseItemSet new_items;
-                for (auto &i : pair.second) {
-                    ParseItem new_item(i);
-                    if (new_item.consumed_symbol_count > 0)
+                vector<ParseItem> new_items;
+                auto &items = pair.second;
+                for (auto iter = items.begin(), end = items.end(); iter != end;) {
+                    ParseItem new_item(*iter);
+                    bool changed = false;
+                    if (new_item.consumed_symbol_count > 0) {
                         new_item.consumed_symbol_count = item.consumed_symbol_count + 1;
-                    if (new_item.lookahead_sym == placeholder)
+                        changed = true;
+                    }
+                    if (new_item.lookahead_sym == placeholder_lookahead) {
                         new_item.lookahead_sym = item.lookahead_sym;
-                    if (new_item.lhs == placeholder)
+                        changed = true;
+                    }
+                    if (new_item.lhs == placeholder_lhs) {
                         new_item.lhs = item.lhs;
-                    new_items.insert(new_item);
+                        changed = true;
+                    }
+                    if (changed) {
+                        iter = pair.second.erase(iter);
+                        new_items.push_back(new_item);
+                    } else {
+                        ++iter;
+                    }
                 }
-                pair.second = new_items;
+                pair.second.insert(new_items.begin(), new_items.end());
             }
             return result;
         }
@@ -61,7 +76,7 @@ namespace tree_sitter {
             for (const ParseItem &item : item_set)
                 merge_sym_transitions<ParseItemSet>(result,
                                                     sym_transitions_for_item(this, item, grammar),
-                                                    [&](const ParseItemSet &l, const ParseItemSet &r) {
+                                                    [&](ParseItemSet &l, const ParseItemSet &r) {
                                                         return merge_sets(l, r);
                                                     });
             return result;
@@ -79,7 +94,7 @@ namespace tree_sitter {
                         LexItemSet({ next_item })
                     });
                 }
-                merge_char_transitions<LexItemSet>(result, item_transitions, [](const LexItemSet &l, const LexItemSet &r) {
+                merge_char_transitions<LexItemSet>(result, item_transitions, [](LexItemSet &l, const LexItemSet &r) {
                     return merge_sets(l, r);
                 });
             }
diff --git a/src/compiler/build_tables/merge_transitions.h b/src/compiler/build_tables/merge_transitions.h
index 7d3794b1..d0319c5b 100644
--- a/src/compiler/build_tables/merge_transitions.h
+++ b/src/compiler/build_tables/merge_transitions.h
@@ -17,7 +17,7 @@ namespace tree_sitter {
         template<typename T>
         void merge_sym_transitions(std::map<rules::ISymbol, T> &left,
                                    const std::map<rules::ISymbol, T> &right,
-                                   std::function<T(const T &, const T &)> merge_fn) {
+                                   std::function<T(T &, const T &)> merge_fn) {
             for (auto &pair : right) {
                 auto rule = pair.first;
                 bool merged = false;
@@ -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(const T &, const T &)> merge_fn) {
+                                    std::function<T(T &, const T &)> merge_fn) {
             for (auto &new_pair : right) {
                 rules::CharacterSet new_char_set = new_pair.first;
                 T new_value = new_pair.second;