[Bug rtl-optimization/51447] [4.4/4.5/4.6/4.7 Regression] global register variable definition incorrectly removed as dead code

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51447

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-12-15 
11:32:06 UTC ---
Created attachment 26100
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=26100
gcc47-pr51447.patch

While that fixes the testcase at -O1, at -O2 and above it still fails. 
Apparently ud_dce pass removes it.