[Bug rtl-optimization/47763] Useless initialization of register

[jiez at gcc dot gnu.org]

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.