[SystemZ] Replace subreg_r with subreg_h
Change
subreg_r32 -> subreg_h32
subreg_r64 -> subreg_h64
subreg_hr32 -> subreg_hh32
The subregisters subreg_r32 and subreg_r64 were added to emphasize the
fact that modifying these subregisters may clobber the entire register.
This is not necessarily the case for subreg_h32, et al.
However, the ability to compose subreg_h64 with subreg_r32, and with
subreg_h32 and subreg_l32 at the same time makes the compositions be
treated as non-overlapping (leading to problems when tracking subreg
liveness). See D50468 for more details.
Differential Revision: https://reviews.llvm.org/D50725
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339778
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