incr.comp.: Precompute small hash for filenames to save some work.

src/libsyntax/codemap.rs

@@ -246,6 +246,7 @@ impl CodeMap {
                                 name_was_remapped: bool,
                                 crate_of_origin: u32,
                                 src_hash: u128,
+                                name_hash: u128,
                                 source_len: usize,
                                 mut file_local_lines: Vec<BytePos>,
                                 mut file_local_multibyte_chars: Vec<MultiByteChar>,
@@ -282,6 +283,7 @@ impl CodeMap {
             lines: RefCell::new(file_local_lines),
             multibyte_chars: RefCell::new(file_local_multibyte_chars),
             non_narrow_chars: RefCell::new(file_local_non_narrow_chars),
+            name_hash,
         });
 
         files.push(filemap.clone());