• Kirill Smelkov's avatar
    tree-walk: finally switch over tree descriptors to contain a pre-parsed entry · 7146e66f
    Kirill Smelkov authored
    This continues 4651ece8 (Switch over tree descriptors to contain a
    pre-parsed entry) and moves the only rest computational part
    
        mode = canon_mode(mode)
    
    from tree_entry_extract() to tree entry decode phase - to
    decode_tree_entry().
    
    The reason to do it, is that canon_mode() is at least 2 conditional
    jumps for regular files, and that could be noticeable should canon_mode()
    be invoked several times.
    
    That does not matter for current Git codebase, where typical tree
    traversal is
    
        while (t->size) {
            sha1 = tree_entry_extract(t, &path, &mode);
            ...
            update_tree_entry(t);
        }
    
    i.e. we do t -> sha1,path.mode "extraction" only once per entry. In such
    cases, it does not matter performance-wise, where that mode
    canonicalization is done - either once in tree_entry_extract(), or once
    in decode_tree_entry() called by update_tree_entry() - it is
    approximately the same.
    
    But for future code, which could need to work with several tree_desc's
    in parallel, it could be handy to operate on tree_desc descriptors, and
    do "extracts" only when needed, or at all, access only relevant part of
    it through structure fields directly.
    
    And for such situations, having canon_mode() be done once in decode
    phase is better - we won't need to pay the performance price of 2 extra
    conditional jumps on every t->mode access.
    
    So let's move mode canonicalization to decode_tree_entry(). That was the
    final bit. Now after tree entry is decoded, it is fully ready and could
    be accessed either directly via field, or through tree_entry_extract()
    which this time got really "totally trivial".
    Signed-off-by: default avatarKirill Smelkov <kirr@mns.spb.ru>
    Signed-off-by: default avatarJunio C Hamano <gitster@pobox.com>
    7146e66f
tree-walk.h 2.19 KB