Cache buffer lines ArrayView in BufferIterator

The extra indirection of going through the buffer can be costly as
the compiler does not know the buffer is not supposed to be mutated
during iteration, so it has to actually reload the values which adds
memory accesses in the Buffer instance which can be costly in say
regex searches where memory access tends to dominate performance.

Storing this in the BufferIterator lets the compiler put this
info in registers and not reload it.

2 files changed, 6 insertions, 4 deletions

diff --git a/src/buffer.hh b/src/buffer.hh
index ec2b9620..fd748213 100644
--- a/src/buffer.hh
+++ b/src/buffer.hh
@@ -95,6 +95,7 @@ public:
 
 private:
     SafePtr<const Buffer> m_buffer;
+    ArrayView<const StringDataPtr> m_lines;
     BufferCoord m_coord;
     StringView m_line;
 };
@@ -122,6 +123,7 @@ public:
         ReadOnly = 1 << 6,
     };
     friend constexpr bool with_bit_ops(Meta::Type<Flags>) { return true; }
+    friend class BufferIterator;
 
     enum class HistoryId : size_t { First = 0, Invalid = (size_t)-1 };
 
diff --git a/src/buffer.inl.hh b/src/buffer.inl.hh
index acaa699f..f3e46378 100644
--- a/src/buffer.inl.hh
+++ b/src/buffer.inl.hh
@@ -99,7 +99,7 @@ inline BufferCoord Buffer::end_coord() const
 }
 
 inline BufferIterator::BufferIterator(const Buffer& buffer, BufferCoord coord) noexcept
-    : m_buffer{&buffer}, m_coord{coord},
+    : m_buffer{&buffer}, m_lines{buffer.m_lines}, m_coord{coord},
       m_line{coord.line < buffer.line_count() ? (*m_buffer)[coord.line] : StringView{}} {}
 
 inline bool BufferIterator::operator==(const BufferIterator& iterator) const noexcept
@@ -165,8 +165,8 @@ inline BufferIterator& BufferIterator::operator++()
 {
     if (++m_coord.column == m_line.length())
     {
-        m_line = (++m_coord.line < m_buffer->line_count()) ?
-            (*m_buffer)[m_coord.line] : StringView{};
+        m_line = ((size_t)++m_coord.line < m_lines.size()) ?
+            m_lines[(size_t)m_coord.line]->strview() : StringView{};
         m_coord.column = 0;
     }
     return *this;
@@ -176,7 +176,7 @@ inline BufferIterator& BufferIterator::operator--()
 {
     if (m_coord.column == 0)
     {
-        m_line = (*m_buffer)[--m_coord.line];
+        m_line = m_lines[(size_t)--m_coord.line]->strview();
         m_coord.column = m_line.length() - 1;
     }
     else