how to use this tools for autoLIPO（autoFDO + LIPO）in gcc google 4_9 branch ?

hi, @danielcdh
I recently read the code of [LIPO](https://gcc.gnu.org/wiki/LightweightIpo) (Profile Feedback Based Lightweight IPO) in gcc and find that the theory is very good. In [this paper](https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7559528) and [this patches](http://gcc.1065356.n8.nabble.com/GOOGLE-Enhance-LIPO-support-in-AutoFDO-tc933847.html) , I see that LIPO has realized the combination with autoFDO, avoiding the disadvantage of LIPO having to recompile the FDO process.

I tried to use the autoFDO tool to generate the gcda and imports files required by LIPO, and although imports were automatically generated, it was always empty, causing LIPO not to optimize the program.

Therefore, I want to know how to make the imports file generated by the autoFDO tool have content instead of empty and make LIPO effective.

Looking forward to your reply!

thanks，
ijinma