(optimize_reg_copy_1): Tighten up code to properly handle the case when...

(optimize_reg_copy_1): Tighten up code to properly handle the case when...

(optimize_reg_copy_1): Tighten up code to properly handle the case
when SRC or DEST is a multi-word hard register and only some parts of
the register are set or used.  Also, avoid updating register status
for DEST if we can't do the optimization.

From-SVN: r2380