+ // Is the instruction decoder method able to completely determine if the
+ // given instruction is valid or not. If the TableGen definition of the
+ // instruction specifies bitpattern A??B where A and B are static bits, the
+ // hasCompleteDecoder flag says whether the decoder method fully handles the
+ // ?? space, i.e. if it is a final arbiter for the instruction validity.
+ // If not then the decoder attempts to continue decoding when the decoder
+ // method fails.
+ //
+ // This allows to handle situations where the encoding is not fully
+ // orthogonal. Example:
+ // * InstA with bitpattern 0b0000????,
+ // * InstB with bitpattern 0b000000?? but the associated decoder method
+ // DecodeInstB() returns Fail when ?? is 0b00 or 0b11.
+ //
+ // The decoder tries to decode a bitpattern that matches both InstA and
+ // InstB bitpatterns first as InstB (because it is the most specific
+ // encoding). In the default case (hasCompleteDecoder = 1), when
+ // DecodeInstB() returns Fail the bitpattern gets rejected. By setting
+ // hasCompleteDecoder = 0 in InstB, the decoder is informed that
+ // DecodeInstB() is not able to determine if all possible values of ?? are
+ // valid or not. If DecodeInstB() returns Fail the decoder will attempt to
+ // decode the bitpattern as InstA too.
+ bit hasCompleteDecoder = 1;
+