Normally, generic processor does not have any SubtargetFeature. And it
can just generate most basic instructions which have no Predicates to
guard.
But it needs to enbale predicate for the btsti16 instruction as one of the most basic instructions.
Or the generic processor can't finish codegen process. So Add FeatureBTST16 SubtargetFeature to generic ProcessorModel.
- Test cases for arch only has 16-bit instruction such as ck801/ck802 need
compile with -mattr=+btst16
- Fix the GPR copy instruction with MOV16 for 16-bit only arch.
In FPUv3, there is fsel.32/64 instruction to select float/double type data.
In FPUv2, split block and use branch and move instruction to select float/double type data.
CSKY arch has multiple FPU instruction versions such as FPU, FPUv2 and FPUv3 to implement floating operations.
For now, we just only support FPUv2 and FPUv3.
It includes the encoding, asm parsing of instructions and codegen of DAG nodes.
