This is realized by two changes: first, GP and vector operand size are
completely separated using one extra bit. If the operand size of an
instruction is derived from VEX.L (or EVEX.L'L), then the "opsize" bits
indicate how to derive a smaller vector size (half/quarter/eighth).
Now, an instruction cannot refer to the GP operand size and the vector
operand size at the same time. This isn't necessary, all necessary
distinguishing could also be achieved manually using W0/W1/66 selectors.
Some instructions honor an address-size override or a segment override,
even in the absence of a directly encoded memory operand.
These annotations are not yet used, but may be used in future to
optimize the size of encoded instructions.
This changes the instruction description format:
- Use Intel/AMD terminology for describing operands (where applicable)
- Group instructions by ISA extension
- Indicate read/written status flags
These instructions have plenty of corner cases and some instructions
have a different usage of the memory operand. Given that MPX is already
deprecated by Intel, it seems that the better option is to decode these
(rarely occuring) instructions as NOPs.
The new trie implementation is more flexible and allows omitting
prefixes even with a ModRM specifier in the opcode. Use this flexibility
to simplify instruction descriptions.
- 3DNow! instructions have a trailing immediate byte which indicates the
opcode. Decoding this with the existing table structure requires more
effort (in particular, a new lookup table after decoding ModRM would
be required). Given that AMD even removed 3DNow! over 10 years ago, it
appears unlikely that this will ever be fully supported. Adding the
RMI-encoded pseudo-instruction "3DNOW" just to support that opcode.
- FEMMS is a legacy 3DNow! instruction.
- EXTRQ/INSERTQ are instructions with an "unusual" encoding and
operation mode. This is another instance of 16-bit immediates.
- SVM (AMD's variant of VMX) and SNP instructions are AMD-only.
