Optimize unnecessary move due to the operator =

[hpcharles]

[hpcharles]

Too many mv due to the = operator.

[hpcharles]

Possible implementation level

• At tree generation / HybroLan.py/visitAffectexpr
• At code generation time H2CodeGeneration.py/codeGeneration/is SemName == "MV"
• At run-time with a specific optimization for genMV : return input register instead of generating insns