The Opcode occupy 2 bytes in following test, we should use {{[0-9]+}}
to match the total value if it, not a part of it.
OPC_Decode(uleb128 Opcode, uleb128 DIdx)
and so do for OPC_TryDecode.
Just like the encoder directive for variable-length instructions, this
patch adds a new decoder directive to allow custom decoder function on
an operand.
Right now, due to the design of DecoderEmitter each operand can only
have a single custom decoder in a given instruction.
Differential Revision: https://reviews.llvm.org/D142079
Currently the DecoderEmitter constructor takes a bunch of string
parameters containing bits of code to interpolate.
However, there's only two ways it can be called. The one used for most
targets which doesn't handle the SoftFail DecoderStatus (not a
problem, because they don't use SoftFail). The other mode, which is
used for ARM/AArch64, does handle SoftFail, but requires an externally
defined helper function in those targets.
This is unnecessary complication; remove the parameters, and unify
onto a single version which does support SoftFail, defining the helper
itself.
To support variable length instructions, I think of them as fixed length instructions with the "maximum length". For example, if there're three instructions with 2, 6 and 9 bytes, we can fit them into the algorithm by treating them all as 9 bytes.
Also, since we can't know the length of the instruction in advance, there is a function object with type `void(APInt &, uint64_t)` added in the parameter list of `decodeInstruction` and `fieldFromInstruction`. We can use this to supply the additional bits the decoder needs after we know the opcode of the instruction.
Finally, `InstrLenTable` is added to let the decoder know the length of the instructions.
See D120960 for its usage.
Reviewed By: myhsu
Differential Revision: https://reviews.llvm.org/D120958
