Arvids Blog

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SIMD Instruction Format

Did you know, that Intel has a naming scheme for their SIMD instructions? Neither did I.

I found, by watching a CppCon talk by Tim Haines, that
SIMD instruction have a pre-defined scheme which can be used to easily decode the, sometimes, cryptic mnemonics.
To much of my surprise, it’s not mentioned nor explained in any of Intel’s manuals.


An instruction is composed of these parts:


PREFIX (Optional): Whether the instruction is AVX or SSE. Possible values: A[V]X, or left out

OPCODE: The operation to perform. Possible values: Any basic arithmetic instruction (e.g ADD/SUB/MUL), MOV

ALIGNMENT (Optional): The alignment requirements of the data, only applicable to a few instructions. Possible values: [A]ligned, [U]naligned

PACKING: Whether it’s a packed operation or operation on a single scalar. Possible values: [P]acked, [S]calar

PRECISION: Whether it operates on single or double precision floats. Possible values: [S]ingle-Precision float, [D]ouble-Precision float


MOVAPD: [MOV][A][P][D]. [MOV]e [A]ligned [P]acked [D]ouble-Precision float

SUBSS: [SUB][S][S]. [SUB]tract [S]calar [S]ingle-Precision float

VMOVSS: [V][MOV][S][S]. A[V]X [MOV]e [S]calar [S]ingle-Precision float


This does only apply to a few basic instructions, namely the basic arithmetic and MOV instructions.

Many instructions, added later in SSE2/3/4 are very specialized, which can be applied vertically or horizontally, use non-temporal stores, etc.


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