x86-64.net

Instruction

KXORQ

Computes the bitwise XOR of two 64-bit masks.

Extensions
Forms
1 (1 VEX)
Data
Intel XED v2026.08.23

KXORQ XORs all 64 bits of two mask registers into a third: a bit is 1 where the two sources differ. It is the AVX512BW form of KXORW, for masks with one bit per byte of a ZMM register; KXORW’s page explains what the XOR of two masks selects and how it marks the edges of a run, and KXORD is the 32-bit form. KXNORQ inverts the result.

Recorded on Zen 5

  • Opposite patterns give all ones. 5555555555555555h against AAAAAAAAAAAAAAAAh gave FFFFFFFFFFFFFFFFh, and AAAAAAAAAAAAAAAAh against all ones gave its inverse, 5555555555555555h.
  • Equal sources give 0. All ones against all ones, two registers each holding 5555555555555555h, and kxorq k7, k7, k7 all wrote 0.
  • All 64 bits. 9B21DA987C4984A7h against 2977685307EDEF8Bh gave B256B2CB7BA46B2Ch.

In compiled code

With GCC 14 and Clang 23 at -O2 and -march=x86-64-v4, the bytes that equal exactly one of b and c, _mm512_cmpeq_epi8_mask(a, b) ^ _mm512_cmpeq_epi8_mask(a, c) used as the zero mask of a VMOVDQU8, are one KXORQ in both, after two VPCMPB with predicate 0 in GCC and two VPCMPEQB in Clang. A mask XORed with a shifted copy of itself stays in the mask registers as well: m ^ (m << 1) is KSHIFTLQ by 1 and KXORQ in both, and KSHIFTRQ’s page shows the same for m >> 1. _kxor_mask64 of two __mmask64 arguments is KMOVQ twice, KXORQ and a KMOVQ back in GCC, and XOR on RAX in Clang.

AMD’s Zen 5 latency spreadsheet gives KXORQ one cycle and two per cycle on pipes FP0 and FP3, as KXORW.

Forms

Every encoding of KXORQ that Intel XED knows, one row per XED instruction form (iform). How to read the notation.
InstructionEncodingRequires
KXORQ k, k, k KXORQ_MASKmskw_MASKmskw_MASKmskw_AVX512VEX.L1.NP.0F.W1 47 /rAVX10.1 or AVX512BW

Latency and throughput

What the scheduling models of LLVM 23.1.2 give for each form, not measurements: latency / reciprocal throughput in cycles, the ports under them. A row is a model, or models that agree; a dash, a form that its processors lack. Memory forms: latency from the address, ports without the load and store units. Which processors each model covers.
Modelk, k, k
Skylake-SP, Ice Lake, Sapphire Rapids1 / 1p0
Zen 41 / 0.5FP2 FP3

Operation

What the forms do, in pseudocode that our tests run against results recorded on real processors. How to read.

k1.q[0] = k2.q[0] ^ k3.q[0]

Run on AMD Zen 5 (EPYC 9645): 11 cases.

Operands

What each form reads and writes, as Intel XED records it: the operands of its syntax, in order, and the implicit ones that the syntax does not name. How to read.
OperandKindAction
KXORQ k, k, k
kexplicitwrite
kexplicitread
kexplicitread

Flags

None: XED records no flag that the forms test or change.

Exceptions

The exception class is XED's name for the set of exception conditions that a form follows. How to read.

All forms
AVX512-K20

Intrinsics

The C intrinsics of Clang 23.1.2 that compile to KXORQ, each with the form it compiles to and the Clang options it needs. The forms come from compiling every intrinsic and decoding the result with Intel XED; all intrinsics A–Z explains the method.

IntrinsicCompiles to
_kxor_mask64 __mmask64 _kxor_mask64(__mmask64 __A, __mmask64 __B)

KXORQ k, k, k VEX.L1 -mavx512bw

CPUID and processors

Each form belongs to an XED ISA set. A form can be used when the processor reports every CPUID bit of one of its ISA set's alternatives.

CPUID requirements and processors of the XED ISA sets above. Alternatives are separated by “or”; processors follow XED’s chip model, whose AMD processors end with Zen 2, and the CPU data of this site for Zen 3 to Zen 6.
ISA setCPUIDProcessors
AVX512BW_KOPQ

AVX10.1
CPUID.(EAX=07H,ECX=1):EDX[19] AVX10
CPUID.(EAX=24H,ECX=0):EBX[7:0] ≥ 1 AVX10 version

or

AVX512BW
CPUID.(EAX=07H,ECX=0):EBX[30] AVX512BW

Cannon Lake, Ice Lake (client), Tiger Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Zen 4, Zen 5, Zen 6

More AVX10.1 instructions

All 686 AVX10.1 instructions

Sources

  1. Intel XED v2026.08.23 (commit 0bcb6237345c): forms, encodings, operands, flags, exception classes, attributes, ISA sets, CPUID bits and chip model.
  2. The CPU data of x86-64.net: Zen 3 to Zen 6, from GCC’s -march feature sets and AMD’s Processor Programming References, which the page of each processor cites.
  3. Clang's x86 intrinsic headers, LLVM 23.1.2 (commit 85ac56026243): the intrinsics, their signatures and doc comments, and the Clang of that release, which compiled each of them.
  4. LLVM 23.1.2's x86 scheduling models (commit 85ac56026243): the latency, reciprocal throughput and ports of each form, as llvm-mca reports them.
  5. Intel Advanced Vector Extensions 10.2 Architecture Specification, revision 7.0 (361050-007, April 2026)
  6. Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 2 (325383-093, September 2026): Volume 2A, page 3-531 (KXORW/KXORB/KXORQ/KXORD)
  7. Software Optimization Guide for the AMD Zen5 Microarchitecture (58455, rev. 1.00, August 2024), Wayback Machine copy of AMD's ZIP

The tables are derived from Intel XED, Copyright Intel Corporation, licensed under the Apache License 2.0; x86-64.net converted and reformatted them. The intrinsics and their signatures come from Clang and the timings from LLVM's scheduling models, both part of the LLVM Project, licensed under the Apache License 2.0 with LLVM Exceptions. The text is our own.