http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47379
--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> 2011-01-20 23:28:32 UTC --- When fwprop props subreg, it should check 1. If inner register is dead after use. 2. If subreg is used in multi-word operations. 3. If subreg is a paradoxical subreg.
