How can we make it easier to experiment with the compiler?

[zjh]

We need `big changes`.
We need `todolist`(order by important).
We need to split big files into directories.
Small refactoring is useless.
`Big changes` are necessary.
We separate the `stable part` from the `unstable part` of the big 
file.And divided into `small files`.
According to dependence, change from `the most dependent`.
Interfacs or func name need not to change.
It's just that the `organization` has to be changed.
Nobody reads `thousands of lines` functions.
No one reads `>100kb` coding files because they are too large.
We just `split up` large files, not modify the function 
implementation.
Because modifying the function implementation is `most likely` to 
make mistakes.