If there is a def of a super-register followed by a use of a sub-register, do *not...

If there is a def of a super-register followed by a use of a sub-register, do *not* add an implicit def of the sub-register. e.g.
EAX = ..., AX<imp-def>
...
    = AX

This creates a double-def. Apparently this used to be necessary but is no longer needed.

Thanks to Anton for pointing this out. Anton, I cannot create a test case without your uncommitted ARM patches. Please check in a test case for me.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@72755 91177308-0d34-0410-b5e6-96231b3b80d8