From be49f362059c641ea58807cde3571b14be2cabe7 Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Sun, 19 Feb 2023 12:15:33 +1100
Subject: [PATCH] Only decode current codepoint once per step

Instead of potentially decoding for each thread, always decode as
its only slightly slower than finding next codepoint (which will
be necessary anyway) and pass the codepoint to each thread.
---
 src/regex_impl.hh | 35 ++++++++++++++++++++---------------
 1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/src/regex_impl.hh b/src/regex_impl.hh
index d0c11c5d..9d1748bb 100644
--- a/src/regex_impl.hh
+++ b/src/regex_impl.hh
@@ -352,7 +352,7 @@ private:
 
     // Steps a thread until it consumes the current character, matches or fail
     [[gnu::always_inline]]
-    void step_thread(const Iterator& pos, uint16_t current_step, Thread thread, const ExecConfig& config)
+    void step_thread(const Iterator& pos, Codepoint cp, uint16_t current_step, Thread thread, const ExecConfig& config)
     {
         auto failed = [this, &thread]() {
             release_saves(thread.saves);
@@ -388,14 +388,13 @@ private:
                     return;
                 case CompiledRegex::Literal:
                     if (pos != config.end and
-                        inst.param.literal.codepoint == (inst.param.literal.ignore_case ? to_lower(codepoint(pos, config))
-                                                                                        : codepoint(pos, config)))
+                        inst.param.literal.codepoint == (inst.param.literal.ignore_case ? to_lower(cp) : cp))
                         return consumed();
                     return failed();
                 case CompiledRegex::AnyChar:
                     return consumed();
                 case CompiledRegex::AnyCharExceptNewLine:
-                    if (pos != config.end and codepoint(pos, config) != '\n')
+                    if (pos != config.end and cp != '\n')
                         return consumed();
                     return failed();
                 case CompiledRegex::Jump:
@@ -428,13 +427,11 @@ private:
                 case CompiledRegex::CharClass:
                     if (pos == config.end)
                         return failed();
-                    return m_program.character_classes[inst.param.character_class_index].matches(codepoint(pos, config)) ?
-                        consumed() : failed();
+                    return m_program.character_classes[inst.param.character_class_index].matches(cp) ? consumed() : failed();
                 case CompiledRegex::CharType:
                     if (pos == config.end)
                         return failed();
-                    return is_ctype(inst.param.character_type, codepoint(pos, config)) ?
-                        consumed() : failed();
+                    return is_ctype(inst.param.character_type, cp) ? consumed() : failed();
                 case CompiledRegex::LineAssertion:
                     if (not (inst.param.line_start ? is_line_start(pos, config) : is_line_end(pos, config)))
                         return failed();
@@ -486,8 +483,11 @@ private:
                 current_step = 1; // step 0 is never valid
             }
 
+            auto next = pos;
+            Codepoint cp = pos != config.end ? codepoint(next, config) : -1;
+
             while (not m_threads.current_is_empty())
-                step_thread(pos, current_step, m_threads.pop_current(), config);
+                step_thread(pos, cp, current_step, m_threads.pop_current(), config);
 
             if (pos == config.end or
                 (m_threads.next_is_empty() and (not search or m_found_match)) or
@@ -498,9 +498,7 @@ private:
                 return m_found_match;
             }
 
-            forward ? utf8::to_next(pos, config.end)
-                    : utf8::to_previous(pos, config.end);
-
+            pos = next;
             if (search and not m_found_match)
             {
                 if (start_desc and m_threads.next_is_empty())
@@ -611,10 +609,17 @@ private:
                is_word(utf8::codepoint(pos, config.subject_end));
     }
 
-    static Codepoint codepoint(const Iterator& it, const ExecConfig& config)
+    static Codepoint codepoint(Iterator& it, const ExecConfig& config)
     {
-        return utf8::codepoint(forward ? it : utf8::previous(it, config.subject_begin),
-                               config.subject_end);
+        if constexpr (forward)
+        {
+            return utf8::read_codepoint(it, config.end);
+        }
+        else
+        {
+            utf8::to_previous(it, config.end);
+            return utf8::codepoint(it, config.begin);
+        }
     }
 
     const CompiledRegex& m_program;