[Bug target/63404] [5 Regression] gcc 5 miscompiles linux block layer

[jiwang at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63404

--- Comment #4 from Jiong Wang <jiwang at gcc dot gnu.org> ---
sorry for causing the trouble.

the reason might be the "flag" is an implified register while it's not take
into account in current shrink-wrap reg read/write analysis.

I will revert my patch temperarily if I couldn't find a proper fix today.