b65f6b0820
This allows rematerialization during register coalescing to handle
more cases involving operations like SUBREG_TO_REG which might need to
be rematerialized using sub-register indices.
For example, code like:
v1(GPR64):sub_32 = MOVZ something
v2(GPR64) = COPY v1(GPR64)
should be convertable to:
v2(GPR64):sub_32 = MOVZ something
but previously we just gave up in places like this
llvm-svn: 182872