The new encoder directive can be used to specify custom encoder for a
single operand or slice. This is different from the EncoderMethod field
within an Operand, which affects every operands in the target.
In addition, this patch also changes the function signature of the
encoder method -- a new argument, InsertPost, is added to both the
default one (i.e. getMachineValue) and the custom one. This argument
provides the bit position where the operand will eventually be inserted.
Differential Revision: https://reviews.llvm.org/D119100
Full write up:
https://gist.github.com/mshockwave/66e98d099256deefc062633909bb7b5b
The existing CodeEmitterGen infrastructure is unable to generate encoder
function for ISAs with variable-length instructions. This patch
introduces a new infrastructure to support variable-length instruction
encoding, including a new TableGen syntax for writing instruction
encoding directives and a new TableGen backend component,
VarLenCodeEmitterGen, built on top of CodeEmitterGen.
Differential Revision: https://reviews.llvm.org/D115128
