[Bug middle-end/47379] fwprop1 generates bad codes for x32

[hjl.tools at gmail dot com]

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.