• Douglas Anderson's avatar
    kbuild: Make NOSTDINC_FLAGS a simply expanded variable · 0c22be07
    Douglas Anderson authored
    During a simple no-op (nothing changed) build I saw 39 invocations of
    the C compiler with the argument "-print-file-name=include".  We don't
    need to call the C compiler 39 times for this--one time will suffice.
    
    Let's change NOSTDINC_FLAGS to a simply expanded variable to avoid
    this since there doesn't appear to be any reason it should be
    recursively expanded.
    
    On my build this shaved ~400 ms off my "no-op" build.
    
    Note that the recursive expansion seems to date back to the (really
    old) commit e8f5bdb0 ("[PATCH] Makefile include path ordering").
    It's a little unclear to me if the point of that patch was to switch
    the variable to be recursively expanded (which it did) or to avoid
    directly assigning to NOSTDINC_FLAGS (AKA to switch to +=) because
    someone else (out of tree?) was setting it.  I presume later since if
    the only goal was to switch to recursive expansion the patch would
    have just removed the ":".
    Signed-off-by: default avatarDouglas Anderson <dianders@chromium.org>
    Signed-off-by: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
    0c22be07
Makefile 58.3 KB