- The goal of this patch is improve option compatible with RISCV-V GCC,
-mcpu support on GCC side will sent patch in next few days.
- -mtune only affect the pipeline model and non-arch/extension related
target feature, e.g. instruction fusion; in td file it called
TuneFeatures, which is introduced by X86 back-end[1].
- -mtune accept all valid option for -mcpu and extra alias processor
option, e.g. `generic`, `rocket` and `sifive-7-series`, the purpose is
option compatible with RISCV-V GCC.
- Processor alias for -mtune will resolve according the current target arch,
rv32 or rv64, e.g. `rocket` will resolve to `rocket-rv32` or `rocket-rv64`.
- Interaction between -mcpu and -mtune:
* -mtune has higher priority than -mcpu for pipeline model and
TuneFeatures.
[1] https://reviews.llvm.org/D85165
Reviewed By: luismarques
Differential Revision: https://reviews.llvm.org/D89025
56f8ee5d8e