http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47763
--- Comment #9 from Jie Zhang <jiez at gcc dot gnu.org> 2011-02-16 11:29:50 UTC --- The clobber is optimized away in 172r.cprop3 because the register renaming in 171r.web breaks the def-use relationship between the clobber and the use in the following instruction when -funroll-loops is used. My patch prevents the renaming in such case.
