add new union_pair and ReduceCode

prepare replace SlashShrink

Signed-off-by: xiehuc <xiehuc@gmail.com>
ddg change key type to PointUnion, support Use*

Signed-off-by: xiehuc <xiehuc@gmail.com>
add new ResolveEngine, more powerful, more clear

Signed-off-by: xiehuc <xiehuc@gmail.com>
add GEPRule and find_store

Signed-off-by: xiehuc <xiehuc@gmail.com>