Advanced Vector Extensions 512

AVX-512 are 512-bit extensions to the 256-bit Advanced Vector Extensions SIMD instructions for x86 instruction set architecture (ISA) proposed by Intel in July 2013, and is supported in Intel's Xeon Phi x200 (Knights Landing) and Skylake-X Core i7 and i9 models. AVX-512 is not the first 512-bit SIMD instruction set that Intel has introduced in processors. The earlier 512-bit SIMD instructions used in Xeon Phi coprocessors, derived from Intel's Larrabee project, are similar but not binary compatible and only partially source compatible.

AVX-512 consists of multiple extensions not all meant to be supported by all processors implementing them. Only the core extension AVX-512F (AVX-512 Foundation) is required by all implementations.

The AVX-512 instruction set consists of several separate sets each having their own unique CPUID feature bit; however, they are typically grouped by supporting processor generation.

The VEX prefix used by AVX and AVX2, while flexible, did not leave enough room for the features Intel wanted to add to AVX-512. This has led them to define a new prefix called EVEX.

Compared to VEX, EVEX adds the following benefits:

The extended registers, SIMD width bit, and opmask registers of AVX-512 are mandatory and all require support from the OS.

The AVX-512 instructions are designed to mix with 128/256-bit AVX/AVX2 instructions without a performance penalty. However, AVX-512VL extensions allows the use of AVX-512 instructions on 128/256-bit registers XMM/YMM, so most SSE and AVX/AVX2 instructions have new AVX-512 versions encoded with the EVEX prefix which allow access to new features such as opmask and additional registers. Unlike AVX-256, the new instructions do not have new mnemonics but share namespace with AVX, making the distinction between VEX and EVEX encoded versions of an instruction ambiguous in the source code. Since AVX-512F only supports 32- and 64-bit values, SSE and AVX/AVX2 instructions that operate on bytes or words are only supported with the AVX-512BW extension (Byte & Word support).

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