x86-64.net

Instruction

KSHIFTLD

Shifts a 32-bit mask left by an immediate count, filling with zeros.

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

KSHIFTLD shifts the low 32 bits of a mask register left by an immediate count, fills with zeros from the right, and writes the 32-bit result to another mask register with bits 63:32 cleared. It is the 32-bit form of KSHIFTLW, whose page explains why a mask is shifted and that the count is taken whole from the 8-bit immediate; it needs AVX512BW, like KSHIFTLQ, for masks of 32 elements, one per word of a ZMM register or per byte of a YMM register.

Recorded on Zen 5

  • Bits leave at bit 31. By one, 1AECA47580000001h gave 2: bit 31 was lost rather than moved to bit 32, and the upper half of the source played no part.
  • The count is not masked. Counts of 32, 33, 51, 63, 64, 128 and 255 all gave 0, even from all ones; by 0, all ones gave FFFFFFFFh.
  • One register. kshiftld k5, k5, 0x10 turned 27666C54B14992E9h into 92E90000h.

In compiled code

With GCC 14 and Clang 23 at -O2 and -march=x86-64-v4, the words of 'y' that follow a word of 'x', (m1 << 1) & m2 of two word compares used as a write mask, are kshiftld k1, k0, 1 in both, with the second compare run under the shifted mask; returned as an integer, GCC keeps that form and Clang shifts and ANDs on EAX, as for 64 bytes on KSHIFTLQ’s page. m ^ (m << 1) on the mask of 32 bytes in YMM registers is KSHIFTLD and KXORD in both, and _kshiftli_mask32(m, 16) is KSHIFTLD. GCC also uses it to join two 16-bit masks written in C as ((__mmask32)hi << 16) | lo: KSHIFTLD by 16 and KORD, where Clang emits one KUNPCKWD.

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

Forms

Every encoding of KSHIFTLD that Intel XED knows, one row per XED instruction form (iform). How to read the notation.
InstructionEncodingRequires
KSHIFTLD k, k, imm8 KSHIFTLD_MASKmskw_MASKmskw_IMM8_AVX512VEX.LZ.66.0F3A.W0 33 /r ibAVX10.1 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, imm8
Skylake-SP, Ice Lake, Sapphire Rapids4 / 1p5
Zen 41 / 0.5FP1 FP2

Operation

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

v = low(k2, 32)                  # bits 63:32 of k2 are ignored
n = imm8.read()                  # 0 to 255, not masked
k1.write(low(v << n, 32))        # bits past bit 31 are lost; bits
                                 # 63:32 of k1 cleared

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
KSHIFTLD k, k, imm8
kexplicitwrite
kexplicitread
imm8explicitread

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 KSHIFTLD, 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
_kshiftli_mask32 __mmask32 _kshiftli_mask32(__mmask32 A, const unsigned int I)

KSHIFTLD k, k, imm8 VEX.LZ -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_KOPD

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 3-523 (KSHIFTLW/KSHIFTLB/KSHIFTLQ/KSHIFTLD)
  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.