Patch. Fix redundent copies between nodes with different but compatible register classes

[Yin Ma]

Hello,

 

This patch will remove the copy between def-use nodes with two different but
compatible register classes. 

This problem is found for ARM architecture but apply for all architectures.
In the ARM mode, most of instructions 

are defined to use the same register class like GPR. The problem is not
exposed. However, in the Thumb mode, 

instructions are defined in different register classes tGPR, GPR. Actually,
one is a superset of another register class.

There is not necessary to generate copy between them.  

 

Please review,

 

Yin 

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