问为什么仅在第二次打开vim之后才启用autoload cscope.out？

EN

if !filereadable("cscope.out")
    autocmd BufRead,BufNewFile *.py !find / -name "*.py" > ~/cscope.files; cscope -Rbq -i ~/cscope.files
    autocmd BufRead,BufNewFile *.java !find / -name "*.java" > ~/cscope.files; cscope -Rbq -i ~/cscope.files
    autocmd BufRead,BufNewFile *.c !find / -name "*.c" -o -name "*.h" > ~/cscope.files; cscope -Rbq -i ~/cscope.files
    autocmd BufRead,BufNewFile *.cpp !find / -name "*.cpp" -o -name "*.hpp" -o -name "*.h" > ~/cscope.files; cscope -Rbq -i ~/cscope.files
    autocmd BufRead,BufNewFile *.hpp !find / -name "*.cpp" -o -name "*.hpp" -o -name "*.h" > ~/cscope.files; cscope -Rbq -i ~/cscope.files
endif

" setting location of cscope db & cscopetag
let CSCOPE_DB="~/cscope.out"                
                                                                              
if has("cscope")
"   set csprg=/usr/local/bin/cscope
    set csto=0
    set cst
    set nocsverb
    " add any database in current directory
    if filereadable("cscope.out")
        cs add cscope.out
    " else add database pointed to by environment
    elseif $CSCOPE_DB != ""
        cs add $CSCOPE_DB
    endif
    set csverb
endif