Intel® Architecture Instruction Set Extensions Programming Reference

INSTRUCTION FORMAT
NOTES:
1. If ModR/M.mod = 00b, the base address is zero, then effective address is computed as [scaled vector index] + disp32. Otherwise the
base address is computed as [EBP/R13]+ disp, the displacement is either 8 bit or 32 bit depending on the value of ModR/M.mod:
MOD Effective Address
00b [Scaled Vector Register] + Disp32
01b [Scaled Vector Register] + Disp8 + [EBP/R13]
10b [Scaled Vector Register] + Disp32 + [EBP/R13]
4.2.1 64-bit Mode VSIB Memory Addressing
In 64-bit mode VSIB memory addressing uses the VEX.B field and the base field of the SIB byte to encode one of
the 16 general-purpose register as the base register. The VEX.X field and the index field of the SIB byte encode one
of the 16 vector registers as the vector index register.
In 64-bit mode the top row of Table 4-6 base register should be interpreted as the full 64-bit of each register.
4.3 VEX ENCODING SUPPORT FOR GPR INSTRUCTIONS
VEX prefix may be used to encode instructions that operate on neither YMM nor XMM registers. VEX-encoded
general-purpose-register instructions have the following properties:
• Instruction syntax support for three encodable operands.
• Encoding support for instruction syntax of non-destructive source operand, destination operand encoded via
VEX.vvvv, and destructive three-operand syntax.
• Elimination of escape opcode byte (0FH), two-byte escape via a compact bit field representation within the VEX
prefix.
• Elimination of the need to use REX prefix to encode the extended half of general-purpose register sets (R8-R15)
for direct register access or memory addressing.
• Flexible and more compact bit fields are provided in the VEX prefix to retain the full functionality provided by
REX prefix. REX.W, REX.X, REX.B functionalities are provided in the three-byte VEX prefix only.
• VEX-encoded GPR instructions are encoded with VEX.L=0.
Any VEX-encoded GPR instruction with a 66H, F2H, or F3H prefix preceding VEX will #UD.
Any VEX-encoded GPR instruction with a REX prefix proceeding VEX will #UD.
VEX-encoded GPR instructions are not supported in real and virtual 8086 modes.
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4-10 Ref. # 319433-014