For some simple InstAlias, we can implement it in td files. But for some complex InstAlias,
td can't implement it, we should implement those complex InstAlias it in PPCInstrPrinter.cpp.
For example:
asm sldi ra,rs,n (n < 64) <=====> rldicr ra,rs,n,63-n
This patch will implement some complex InstAlias in PPCInstrPrinter.cpp for below instructions:
RLDIMI: insrdi RLWIMI: inslwi, insrwi RLWINM: slwi srwi clrrwi clrlslwi extlwi extrwi RLDIC: clrlsldi RLDIC: srdi extrdi RLDICR: sldi clrrdi extldi