perf(sourcemap): improve perf of search_original_line_and_column

crates/oxc_codegen/src/sourcemap_builder.rs

@@ -71,6 +71,7 @@ pub struct SourcemapBuilder {
     sourcemap_builder: oxc_sourcemap::SourceMapBuilder,
     generated_line: u32,
     generated_column: u32,
+    last_line_lookup: usize,
 }
 
 impl SourcemapBuilder {
@@ -88,6 +89,7 @@ impl SourcemapBuilder {
             sourcemap_builder,
             generated_line: 0,
             generated_column: 0,
+            last_line_lookup: 0,
         }
     }
 
@@ -131,12 +133,29 @@ impl SourcemapBuilder {
 
     #[allow(clippy::cast_possible_truncation)]
     fn search_original_line_and_column(&mut self, position: u32) -> (u32, u32) {
-        let result = self
-            .line_offset_tables
-            .lines
-            .partition_point(|table| table.byte_offset_to_start_of_line <= position);
-        let original_line = if result > 0 { result - 1 } else { 0 };
-        let line = &self.line_offset_tables.lines[original_line];
+        let lines = &self.line_offset_tables.lines;
+        let mut idx = self.last_line_lookup;
+
+        // Ensure we have a valid starting point
+        // If position < lines[idx].byte_offset_to_start_of_line, fallback to a full binary search.
+        if position < lines[idx].byte_offset_to_start_of_line {
+            #[cold]
+            fn fallback_binary_search(lines: &[Line], position: u32) -> usize {
+                let mut i =
+                    lines.partition_point(|line| line.byte_offset_to_start_of_line <= position);
+                i = i.saturating_sub(1);
+                i
+            }
+            idx = fallback_binary_search(lines, position);
+        } else {
+            while idx + 1 < lines.len() && lines[idx + 1].byte_offset_to_start_of_line <= position {
+                idx += 1;
+            }
+        }
+
+        self.last_line_lookup = idx;
+
+        let line = &lines[idx];
         let mut original_column = position - line.byte_offset_to_start_of_line;
         if let Some(column_offsets_id) = line.column_offsets_id {
             let column_offsets = &self.line_offset_tables.column_offsets[column_offsets_id];
@@ -145,7 +164,7 @@ impl SourcemapBuilder {
                     [(original_column - column_offsets.byte_offset_to_first) as usize];
             }
         }
-        (original_line as u32, original_column)
+        (idx as u32, original_column)
     }
 
     #[allow(clippy::cast_possible_truncation)]