diff options
| -rw-r--r-- | src/libsyntax/tokenstream.rs | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/src/libsyntax/tokenstream.rs b/src/libsyntax/tokenstream.rs index f5d2d6f18ee..7d6ffceb2c0 100644 --- a/src/libsyntax/tokenstream.rs +++ b/src/libsyntax/tokenstream.rs @@ -255,7 +255,13 @@ impl TokenStream { 0 => TokenStream::empty(), 1 => streams.pop().unwrap(), _ => { - let mut vec = vec![]; + // rust-lang/rust#57735: pre-allocate vector to avoid + // quadratic blow-up due to on-the-fly reallocations. + let tree_count = streams.iter() + .map(|ts| match &ts.0 { None => 0, Some(s) => s.len() }) + .sum(); + let mut vec = Vec::with_capacity(tree_count); + for stream in streams { match stream.0 { None => {}, |