Question about find modifiable mems

[shmeel gutl]

find_modifiable_mems was introduced to gcc 4.8 in september 2012. Is 
there any documentation as to how it is supposed to help the haifa 
scheduler?

In my private port of gcc it make the following type of transformations
    from
        a= *(b+20)
        b+=30

    to
        b+=30
        a=*(b-10)

Although this is functionally correct, it has changed an ANTI_DEP into a 
TRUE_DEP and thus introduced stalls. If it went the other way, that 
would be good. Any pointers?

Thanks,
Shmeel