Allow for optional operands with non-zero default values.
ISA 2.07 (ie, POWER8) added the rfebb instruction which takes one operand
with the value of either a 0 or 1. It also defines an extended mnemonic
with no operands (ie, "rfebb") that is supposed to be equivalent to "rfebb 1".
I implemented rfebb's lone operand with PPC_OPERAND_OPTIONAL, but the
problem is, optional operands that are ommitted always default to the
value 0, which is wrong in this case. I have added support for allowing
non-zero default values by adding an additional flag PPC_OPERAND_OPTIONAL_VALUE
that specifies that the default operand value to be used is stored in the
SHIFT field of the operand field immediately following this one.
This fixes the rfebb issue. I also fixed the mftb and mfcr instructions
so they use the same mechanism. This allows us to flag invalid uses of
mfcr where we explicitly pass in a zero FXM value, like the use in a2.[sd].
include/opcode/
* ppc.h (PPC_OPERAND_OPTIONAL_VALUE): New.
(ppc_optional_operand_value): New inline function.