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Bit manipulation instructions. For all of the VEX-encoded instructions defined by BMI1 and BMI2, the operand size may be 32 or 64 bits, controlled by the VEX.W bit – none of these instructions are available in 16-bit variants. The VEX-encoded instructions are not available in Real Mode and Virtual-8086 mode - other than that, the bit ...
The use of the 8F byte requires that the m-bits (see VEX coding scheme) have a value larger than or equal to 8 in order to avoid overlap with existing instructions. [Note 1] The C4 byte used in the VEX scheme has no such restriction. This may prevent the use of the m-bits for other purposes in the future in the XOP scheme, but not in the VEX ...
AVX-512 introduced 8 mask registers and added VEX-coded instructions to manipulate them. (VEX.B̅ is ignored when the field is used to encode a mask register, but VEX.R̅ and VEX.v̅ 3 are not, and must be set to 1 in 64-bit mode. [5]) AMX introduced 8 tile registers and added VEX-coded instructions to manipulate them. The VEX prefix's initial ...
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Unlike the rest of the AVX-512 instructions, these instructions are all VEX encoded. The initial opmask instructions are all 16-bit (Word) versions. With AVX-512DQ 8-bit (Byte) versions were added to better match the needs of masking 8 64-bit values, and with AVX-512BW 32-bit (Double) and 64-bit (Quad) versions were added so they can mask up to ...
The EVEX scheme is a 4-byte extension to the VEX scheme which supports the AVX-512 instruction set and allows addressing new 512-bit ZMM registers and new 64-bit operand mask registers. With Advanced Performance Extensions , the Extended EVEX prefix redefines the semantics of several payload bits.
VEX coding is also used for instructions operating on the k0-k7 mask registers that were introduced with AVX-512. The alignment requirement of SIMD memory operands is relaxed. [5] Unlike their non-VEX coded counterparts, most VEX coded vector instructions no longer require their memory operands to be aligned to the vector size.
A new coding scheme (DREX) is introduced for allowing instructions to have three operands. [13] April 2008: Intel announces their AVX and FMA instruction sets, including 4-operand FMA instructions. The coding of these instructions uses the new VEX coding scheme, [14] which is more flexible than AMD's DREX scheme.