ARM: Thumb2 LDRD/STRD supports independent input/output regs
The existing code would unnecessarily break LDRD/STRD apart with
non-adjacent registers, on thumb2 this is not necessary.
Ideally on thumb2 we shouldn't match for ldrd/strd pre-regalloc anymore
as there is not reason to set register hints anymore, changing that is
something for a future patch however.
Differential Revision: http://reviews.llvm.org/D9694
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238795
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