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perf(codegen): speed up building sourcemap line tables (#2591)
Speed up building the line tables for source maps, using same kind of techniques as have been using in the lexer: * Iterate byte-by-byte not char-by-char (`chars` iterator is slow). * Fast path for ASCII (common case).
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overlookmotel
GitHub
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1 changed files with 89 additions and 53 deletions
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@ -118,68 +118,104 @@ impl SourcemapBuilder {
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fn generate_line_offset_tables(content: &str) -> Vec<LineOffsetTable> {
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let mut tables = vec![];
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let mut columns = None;
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let mut column = 0;
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// Process content line-by-line.
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// For each line, start by assuming line will be entirely ASCII, and read byte-by-byte.
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// If line is all ASCII, UTF-8 columns and UTF-16 columns are the same,
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// so no need to create a `columns` Vec. This is the fast path for common case.
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// If a Unicode character found, read rest of line char-by-char, populating `columns` Vec.
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// At end of line, go back to top of outer loop, and again assume ASCII for next line.
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let mut line_byte_offset = 0;
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let mut byte_offset_to_first = 0;
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for (i, ch) in content.char_indices() {
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// Mark the start of the next line
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if column == 0 {
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line_byte_offset = i;
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}
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'lines: loop {
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tables.push(LineOffsetTable {
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columns: None,
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// `usize::MAX` so `original_column >= line.byte_offset_to_first` check in
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// `search_original_line_and_column` fails if line is all ASCII
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byte_offset_to_first: usize::MAX,
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byte_offset_to_start_of_line: line_byte_offset,
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});
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// Start the mapping if this character is non-ASCII
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if !ch.is_ascii() && columns.is_none() {
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byte_offset_to_first = i - line_byte_offset;
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columns = Some(vec![]);
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}
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// Update the per-byte column offsets
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if let Some(columns) = &mut columns {
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for _ in 0..ch.len_utf8() {
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columns.push(column);
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}
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}
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match ch {
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'\r' | '\n' | LS | PS => {
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// Handle Windows-specific "\r\n" newlines
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if ch == '\r' && content.as_bytes().get(i + 1) == Some(&b'\n') {
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column += 1;
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let remaining = &content.as_bytes()[line_byte_offset..];
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for (mut byte_offset_from_line_start, b) in remaining.iter().copied().enumerate() {
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match b {
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b'\n' => {
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byte_offset_from_line_start += 1;
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}
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b'\r' => {
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byte_offset_from_line_start += 1;
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// Handle Windows-specific "\r\n" newlines
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if remaining.get(byte_offset_from_line_start) == Some(&b'\n') {
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byte_offset_from_line_start += 1;
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}
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}
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_ if b.is_ascii() => {
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continue;
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}
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_ => {
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// Unicode char found.
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// Create `columns` Vec, and set `byte_offset_to_first`.
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let table = tables.iter_mut().last().unwrap();
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table.byte_offset_to_first = byte_offset_from_line_start;
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table.columns = Some(vec![]);
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let columns = table.columns.as_mut().unwrap();
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tables.push(LineOffsetTable {
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columns,
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byte_offset_to_first,
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byte_offset_to_start_of_line: line_byte_offset,
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});
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column = 0;
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columns = None;
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byte_offset_to_first = 0;
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}
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_ => {
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// Mozilla's "source-map" library counts columns using UTF-16 code units
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column += ch.len_utf16();
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}
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// Loop through rest of line char-by-char.
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// `chunk_byte_offset` in this loop is byte offset from start of this 1st
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// Unicode char.
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let mut column = byte_offset_from_line_start;
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line_byte_offset += byte_offset_from_line_start;
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let remaining = &content[line_byte_offset..];
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for (mut chunk_byte_offset, ch) in remaining.char_indices() {
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for _ in 0..ch.len_utf8() {
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columns.push(column);
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}
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match ch {
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'\r' => {
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// Handle Windows-specific "\r\n" newlines
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chunk_byte_offset += 1;
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if remaining.as_bytes().get(chunk_byte_offset) == Some(&b'\n') {
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chunk_byte_offset += 1;
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columns.push(column + 1);
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}
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}
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'\n' => {
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chunk_byte_offset += 1;
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}
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LS | PS => {
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chunk_byte_offset += 3;
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}
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_ => {
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// Mozilla's "source-map" library counts columns using UTF-16 code units
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column += ch.len_utf16();
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continue;
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}
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}
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// Line break found.
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// `chunk_byte_offset` is now the offset of *end* of the line break.
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line_byte_offset += chunk_byte_offset;
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// Revert back to outer loop for next line
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continue 'lines;
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}
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// EOF.
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// One last column entry for EOF position.
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columns.push(column);
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break 'lines;
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}
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};
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// Line break found.
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// `byte_offset_from_line_start` is now the length of line *including* line break.
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line_byte_offset += byte_offset_from_line_start;
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continue 'lines;
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}
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}
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// Mark the start of the next line
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if column == 0 {
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line_byte_offset = content.len();
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}
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// Do one last update for the column at the end of the file
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if let Some(columns) = &mut columns {
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columns.push(column);
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// EOF
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break;
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}
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tables.push(LineOffsetTable {
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columns,
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byte_offset_to_first,
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byte_offset_to_start_of_line: line_byte_offset,
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});
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tables
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}
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}
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