ba1c70c69d
The microMIPS instruction set is compatible with the MIPS instruction set at the assembly level but not in terms of encodings. `nop` in microMIPS is a special case as it has the same encoding as `nop` for MIPS. Fix this error by reducing the usage of NOP in the MIPS backend such that only that ISA correct variants are produced. Differential Revision: https://reviews.llvm.org/D124716