i#6662 public traces, part 1: synthetic ISA

[edeiana]

A synthetic ISA that has the purpose of preserving register dependencies and giving
hints on the type of operation an instruction performs. This PR implements the
encoding/decoding functionalities for this new ISA, which we call #DR_ISA_REGDEPS.

Note that being a synthetic ISA, some routines that work on instructions coming from an
actual ISA (such as #DR_ISA_AMD64) are not supported (e.g., decode_sizeof()).

Currently we support:

• instr_convert_to_isa_regdeps(): to convert an #instr_t of an actual ISA to a
  #DR_ISA_REGDEPS #instr_t.
• instr_encode() and instr_encode_to_copy(): to encode a #DR_ISA_REGDEPS #instr_t
  into a sequence of contiguous bytes.
• decode() and decode_from_copy(): to decode an encoded #DR_ISA_REGDEPS instruction
  into an #instr_t.

A #DR_ISA_REGDEPS #instr_t contains the following information:

• categories: composed by #dr_instr_category_t values, they indicate the type of
  operation performed (e.g., a load, a store, a floating point math operation, a
  branch, etc.). Note that categories are composable, hence more than one category
  can be set. This information can be obtained using instr_get_category().
• arithmetic flags: we don't distinguish between different flags, we only report if
  at least one arithmetic flag was read (all arithmetic flags will be set to read)
  and/or written (all arithmetic flags will be set to written). This information
  can be obtained using instr_get_arith_flags().
• number of source and destination operands: we only consider register operands.
  This information can be obtained using instr_num_srcs() and instr_num_dsts().
• source operation size: is the largest source operand the instruction operates on.
  This information can be obtained by accessing the #instr_t operation_size field.
• list of register operand identifiers: they are contained in #opnd_t lists,
  separated in source and destination. Note that these #reg_id_t identifiers are
  virtual and it should not be assumed that they belong to any DR_REG_ enum value
  of any specific architecture. These identifiers are meant for tracking register
  dependencies with respect to other #DR_ISA_REGDEPS instructions only. These
  lists can be obtained by walking the #instr_t operands with instr_get_dst() and
  instr_get_src().
• ISA mode: is always #DR_ISA_REGDEPS. This information can be obtained using
  instr_get_isa_mode().
• encoding bytes: an array of bytes containing the #DR_ISA_REGDEPS #instr_t
  encoding. Note that this information is present only for decoded instructions
  (i.e., #instr_t generated by decode() or decode_from_copy()). This information
  can be obtained using instr_get_raw_bits().
• length: the length of the encoded instruction in bytes. Note that this
  information is present only for decoded instructions (i.e., #instr_t generated by
  decode() or decode_from_copy()). This information can be obtained by accessing
  the #instr_t length field.

Note that all routines that operate on #instr_t and #opnd_t are also supported for
#DR_ISA_REGDEPS instructions. However, querying information outside of those
described above (e.g., the instruction opcode with instr_get_opcode()) will return
the zeroed value set by instr_create() or instr_init() when the #instr_t was
created (e.g., instr_get_opcode() would return OP_INVALID).

[derekbruening]

I think we're almost there; probably just one more round after we finalize the last couple of decisions.