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Advanced Vector Extensions (AVX, also known as Gesher New Instructions and then Sandy Bridge New Instructions) are SIMD extensions to the x86 instruction set architecture for microprocessors from Intel and Advanced Micro Devices (AMD). They were proposed by Intel in March 2008 and first supported by Intel with the Sandy Bridge[1] microarchitecture shipping in Q1 2011 and later by AMD with the Bulldozer[2] microarchitecture shipping in Q4 2011. AVX provides new features, new instructions, and a new coding scheme.
AVX2 (also known as Haswell New Instructions) expands most integer commands to 256 bits and introduces new instructions. They were first supported by Intel with the Haswell microarchitecture, which shipped in 2013.
AVX-512 expands AVX to 512-bit support using a new EVEX prefix encoding proposed by Intel in July 2013 and first supported by Intel with the Knights Landing co-processor, which shipped in 2016.[3][4] In conventional processors, AVX-512 was introduced with Skylake server and HEDT processors in 2017.
Advanced Vector Extensions
AVX uses sixteen YMM registers to perform a single instruction on multiple pieces of data (see SIMD). Each YMM register can hold and do simultaneous operations (math) on:
- eight 32-bit single-precision floating point numbers or
- four 64-bit double-precision floating point numbers.
The width of the SIMD registers is increased from 128 bits to 256 bits, and renamed from XMM0–XMM7 to YMM0–YMM7 (in x86-64 mode, from XMM0–XMM15 to YMM0–YMM15). The legacy SSE instructions can be still utilized via the VEX prefix to operate on the lower 128 bits of the YMM registers.
| 511 256 | 255 128 | 127 0 |
| ZMM0 | YMM0 | XMM0 |
| ZMM1 | YMM1 | XMM1 |
| ZMM2 | YMM2 | XMM2 |
| ZMM3 | YMM3 | XMM3 |
| ZMM4 | YMM4 | XMM4 |
| ZMM5 | YMM5 | XMM5 |
| ZMM6 | YMM6 | XMM6 |
| ZMM7 | YMM7 | XMM7 |
| ZMM8 | YMM8 | XMM8 |
| ZMM9 | YMM9 | XMM9 |
| ZMM10 | YMM10 | XMM10 |
| ZMM11 | YMM11 | XMM11 |
| ZMM12 | YMM12 | XMM12 |
| ZMM13 | YMM13 | XMM13 |
| ZMM14 | YMM14 | XMM14 |
| ZMM15 | YMM15 | XMM15 |
| ZMM16 | YMM16 | XMM16 |
| ZMM17 | YMM17 | XMM17 |
| ZMM18 | YMM18 | XMM18 |
| ZMM19 | YMM19 | XMM19 |
| ZMM20 | YMM20 | XMM20 |
| ZMM21 | YMM21 | XMM21 |
| ZMM22 | YMM22 | XMM22 |
| ZMM23 | YMM23 | XMM23 |
| ZMM24 | YMM24 | XMM24 |
| ZMM25 | YMM25 | XMM25 |
| ZMM26 | YMM26 | XMM26 |
| ZMM27 | YMM27 | XMM27 |
| ZMM28 | YMM28 | XMM28 |
| ZMM29 | YMM29 | XMM29 |
| ZMM30 | YMM30 | XMM30 |
| ZMM31 | YMM31 | XMM31 |
AVX introduces a three-operand SIMD instruction format called VEX coding scheme, where the destination register is distinct from the two source operands. For example, an SSE instruction using the conventional two-operand form a ← a + b can now use a non-destructive three-operand form c ← a + b, preserving both source operands. Originally, AVX's three-operand format was limited to the instructions with SIMD operands (YMM), and did not include instructions with general purpose registers (e.g. EAX). It was later used for coding new instructions on general purpose registers in later extensions, such as BMI. 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. Notably, the VMOVDQA instruction still requires its memory operand to be aligned.
The new VEX coding scheme introduces a new set of code prefixes that extends the opcode space, allows instructions to have more than two operands, and allows SIMD vector registers to be longer than 128 bits. The VEX prefix can also be used on the legacy SSE instructions giving them a three-operand form, and making them interact more efficiently with AVX instructions without the need for VZEROUPPER and VZEROALL.
The AVX instructions support both 128-bit and 256-bit SIMD. The 128-bit versions can be useful to improve old code without needing to widen the vectorization, and avoid the penalty of going from SSE to AVX, they are also faster on some early AMD implementations of AVX. This mode is sometimes known as AVX-128.[6]
New instructions
These AVX instructions are in addition to the ones that are 256-bit extensions of the legacy 128-bit SSE instructions; most are usable on both 128-bit and 256-bit operands.
| Instruction | Description |
|---|---|
VBROADCASTSS, VBROADCASTSD, VBROADCASTF128
|
Copy a 32-bit, 64-bit or 128-bit memory operand to all elements of a XMM or YMM vector register. |
VINSERTF128
|
Replaces either the lower half or the upper half of a 256-bit YMM register with the value of a 128-bit source operand. The other half of the destination is unchanged. |
VEXTRACTF128
|
Extracts either the lower half or the upper half of a 256-bit YMM register and copies the value to a 128-bit destination operand. |
VMASKMOVPS, VMASKMOVPD
|
Conditionally reads any number of elements from a SIMD vector memory operand into a destination register, leaving the remaining vector elements unread and setting the corresponding elements in the destination register to zero. Alternatively, conditionally writes any number of elements from a SIMD vector register operand to a vector memory operand, leaving the remaining elements of the memory operand unchanged. On the AMD Jaguar processor architecture, this instruction with a memory source operand takes more than 300 clock cycles when the mask is zero, in which case the instruction should do nothing. This appears to be a design flaw.[7] |
VPERMILPS, VPERMILPD
|
Permute In-Lane. Shuffle the 32-bit or 64-bit vector elements of one input operand. These are in-lane 256-bit instructions, meaning that they operate on all 256 bits with two separate 128-bit shuffles, so they can not shuffle across the 128-bit lanes.[8] |
VPERM2F128
|
Shuffle the four 128-bit vector elements of two 256-bit source operands into a 256-bit destination operand, with an immediate constant as selector. |
VTESTPS, VTESTPD
|
Packed bit test of the packed single-precision or double-precision floating-point sign bits, setting or clearing the ZF flag based on AND and CF flag based on ANDN. |
VZEROALL
|
Set all YMM registers to zero and tag them as unused. Used when switching between 128-bit use and 256-bit use. |
VZEROUPPER
|
Set the upper half of all YMM registers to zero. Used when switching between 128-bit use and 256-bit use. |
CPUs with AVX
- Intel
- Sandy Bridge processors (Q1 2011) and newer, except models branded as Celeron and Pentium.[9]
- Pentium and Celeron branded processors starting with Tiger Lake (Q3 2020) and newer.[10]
- AMD:
Issues regarding compatibility between future Intel and AMD processors are discussed under XOP instruction set.
Compiler and assembler support
- Absoft supports with -mavx flag.
- The Free Pascal compiler supports AVX and AVX2 with the -CfAVX and -CfAVX2 switches from version 2.7.1.
- RAD studio (v11.0 Alexandria) supports AVX2 and AVX512.[12]
- The GNU Assembler (GAS) inline assembly functions support these instructions (accessible via GCC), as do Intel primitives and the Intel inline assembler (closely compatible to GAS, although more general in its handling of local references within inline code). GAS supports AVX starting with binutils version 2.19.[13]
- GCC starting with version 4.6 (although there was a 4.3 branch with certain support) and the Intel Compiler Suite starting with version 11.1 support AVX.
- The Open64 compiler version 4.5.1 supports AVX with -mavx flag.
- PathScale supports via the -mavx flag.
- The Vector Pascal compiler supports AVX via the -cpuAVX32 flag.
- The Visual Studio 2010/2012 compiler supports AVX via intrinsic and /arch:AVX switch.
- NASM starting with version 2.03 and newer. There were numerous bug fixes and updates related to AVX in version 2.04.[14]
- Other assemblers such as MASM VS2010 version, YASM,[15] FASM and JWASM.
Operating system support
AVX adds new register-state through the 256-bit wide YMM register file, so explicit operating system support is required to properly save and restore AVX's expanded registers between context switches. The following operating system versions support AVX:
- DragonFly BSD: support added in early 2013.
- FreeBSD: support added in a patch submitted on January 21, 2012,[16] which was included in the 9.1 stable release.[17]
- Linux: supported since kernel version 2.6.30,[18] released on June 9, 2009.[19]
- macOS: support added in 10.6.8 (Snow Leopard) update[20][unreliable source?] released on June 23, 2011. In fact, macOS Ventura does not support x86 processors without the AVX2 instruction set. [21]
- OpenBSD: support added on March 21, 2015.[22]
- Solaris: supported in Solaris 10 Update 10 and Solaris 11.
- Windows: supported in Windows 7 SP1, Windows Server 2008 R2 SP1,[23] Windows 8, Windows 10.
- Windows Server 2008 R2 SP1 with Hyper-V requires a hotfix to support AMD AVX (Opteron 6200 and 4200 series) processors, KB2568088
- Windows XP and Windows Server 2003 do not support AVX in both kernel drivers and user applications.
Advanced Vector Extensions 2
Advanced Vector Extensions 2 (AVX2), also known as Haswell New Instructions,[24] is an expansion of the AVX instruction set introduced in Intel's Haswell microarchitecture. AVX2 makes the following additions:
- expansion of most vector integer SSE and AVX instructions to 256 bits
- Gather support, enabling vector elements to be loaded from non-contiguous memory locations
- DWORD- and QWORD-granularity any-to-any permutes
- vector shifts.
Sometimes three-operand fused multiply-accumulate (FMA3) extension is considered part of AVX2, as it was introduced by Intel in the same processor microarchitecture. This is a separate extension using its own CPUID flag and is described on its own page and not below.
New instructions
| Instruction | Description |
|---|---|
VBROADCASTSS, VBROADCASTSD
|
Copy a 32-bit or 64-bit register operand to all elements of a XMM or YMM vector register. These are register versions of the same instructions in AVX1. There is no 128-bit version however, but the same effect can be simply achieved using VINSERTF128. |
VPBROADCASTB, VPBROADCASTW, VPBROADCASTD, VPBROADCASTQ
|
Copy an 8, 16, 32 or 64-bit integer register or memory operand to all elements of a XMM or YMM vector register. |
VBROADCASTI128
|
Copy a 128-bit memory operand to all elements of a YMM vector register. |
VINSERTI128
|
Replaces either the lower half or the upper half of a 256-bit YMM register with the value of a 128-bit source operand. The other half of the destination is unchanged. |
VEXTRACTI128
|
Extracts either the lower half or the upper half of a 256-bit YMM register and copies the value to a 128-bit destination operand. |
VGATHERDPD, VGATHERQPD, VGATHERDPS, VGATHERQPS
|
Gathers single or double precision floating point values using either 32 or 64-bit indices and scale. |
VPGATHERDD, VPGATHERDQ, VPGATHERQD, VPGATHERQQ
|
Gathers 32 or 64-bit integer values using either 32 or 64-bit indices and scale. |
VPMASKMOVD, VPMASKMOVQ
|
Conditionally reads any number of elements from a SIMD vector memory operand into a destination register, leaving the remaining vector elements unread and setting the corresponding elements in the destination register to zero. Alternatively, conditionally writes any number of elements from a SIMD vector register operand to a vector memory operand, leaving the remaining elements of the memory operand unchanged. |
VPERMPS, VPERMD
|
Shuffle the eight 32-bit vector elements of one 256-bit source operand into a 256-bit destination operand, with a register or memory operand as selector. |
VPERMPD, VPERMQ
|
Shuffle the four 64-bit vector elements of one 256-bit source operand into a 256-bit destination operand, with a register or memory operand as selector. |
VPERM2I128
|
Shuffle (two of) the four 128-bit vector elements of two 256-bit source operands into a 256-bit destination operand, with an immediate constant as selector. |
VPBLENDD
|
Doubleword immediate version of the PBLEND instructions from SSE4. |
VPSLLVD, VPSLLVQ
|
Shift left logical. Allows variable shifts where each element is shifted according to the packed input. |
VPSRLVD, VPSRLVQ
|
Shift right logical. Allows variable shifts where each element is shifted according to the packed input. |
VPSRAVD
|
Shift right arithmetically. Allows variable shifts where each element is shifted according to the packed input. |
CPUs with AVX2
- Intel
- Haswell processors (Q2 2013) and newer, except models branded as Celeron and Pentium.
- Celeron and Pentium branded processors starting with Tiger Lake (Q3 2020) and newer.[10]
- AMD
- Excavator processors (Q2 2015) and newer.
- VIA:
- Nano QuadCore
- Eden X4
AVX-512
AVX-512 are 512-bit extensions to the 256-bit Advanced Vector Extensions SIMD instructions for x86 instruction set architecture proposed by Intel in July 2013, and are supported with Intel's Knights Landing processor.[3]
AVX-512 instructions are encoded with the new EVEX prefix. It allows 4 operands, 8 new 64-bit opmask registers, scalar memory mode with automatic broadcast, explicit rounding control, and compressed displacement memory addressing mode. The width of the register file is increased to 512 bits and total register count increased to 32 (registers ZMM0-ZMM31) in x86-64 mode.
AVX-512 consists of multiple instruction subsets, not all of which are meant to be supported by all processors implementing them. The instruction set consists of the following:
- AVX-512 Foundation (F) – adds several new instructions and expands most 32-bit and 64-bit floating point SSE-SSE4.1 and AVX/AVX2 instructions with EVEX coding scheme to support the 512-bit registers, operation masks, parameter broadcasting, and embedded rounding and exception control
- AVX-512 Conflict Detection Instructions (CD) – efficient conflict detection to allow more loops to be vectorized, supported by Knights Landing[3]
- AVX-512 Exponential and Reciprocal Instructions (ER) – exponential and reciprocal operations designed to help implement transcendental operations, supported by Knights Landing[3]
- AVX-512 Prefetch Instructions (PF) – new prefetch capabilities, supported by Knights Landing[3]
- AVX-512 Vector Length Extensions (VL) – extends most AVX-512 operations to also operate on XMM (128-bit) and YMM (256-bit) registers (including XMM16-XMM31 and YMM16-YMM31 in x86-64 mode)[25]
- AVX-512 Byte and Word Instructions (BW) – extends AVX-512 to cover 8-bit and 16-bit integer operations[25]
- AVX-512 Doubleword and Quadword Instructions (DQ) – enhanced 32-bit and 64-bit integer operations[25]
- AVX-512 Integer Fused Multiply Add (IFMA) – fused multiply add for 512-bit integers.[26]: 746
- AVX-512 Vector Byte Manipulation Instructions (VBMI) adds vector byte permutation instructions which are not present in AVX-512BW.
- AVX-512 Vector Neural Network Instructions Word variable precision (4VNNIW) – vector instructions for deep learning.
- AVX-512 Fused Multiply Accumulation Packed Single precision (4FMAPS) – vector instructions for deep learning.
- VPOPCNTDQ – count of bits set to 1.[27]
- VPCLMULQDQ – carry-less multiplication of quadwords.[27]
- AVX-512 Vector Neural Network Instructions (VNNI) – vector instructions for deep learning.[27]
- AVX-512 Galois Field New Instructions (GFNI) – vector instructions for calculating Galois field.[27]
- AVX-512 Vector AES instructions (VAES) – vector instructions for AES coding.[27]
- AVX-512 Vector Byte Manipulation Instructions 2 (VBMI2) – byte/word load, store and concatenation with shift.[27]
- AVX-512 Bit Algorithms (BITALG) – byte/word bit manipulation instructions expanding VPOPCNTDQ.[27]
- AVX-512 Bfloat16 Floating-Point Instructions (BF16) – vector instructions for AI acceleration.
- AVX-512 Half-Precision Floating-Point Instructions (FP16) – vector instructions for operating on floating-point and complex numbers with reduced precision.
Only the core extension AVX-512F (AVX-512 Foundation) is required by all implementations, though all current implementations also support CD (conflict detection). All central processors with AVX-512 also support VL, DQ and BW. The ER, PF, 4VNNIW and 4FMAPS instruction set extensions are currently only implemented in Intel computing coprocessors.
The updated SSE/AVX instructions in AVX-512F use the same mnemonics as AVX versions; they can operate on 512-bit ZMM registers, and will also support 128/256 bit XMM/YMM registers (with AVX-512VL) and byte, word, doubleword and quadword integer operands (with AVX-512BW/DQ and VBMI).[26]: 23