x86-64.net

Instruction

VPSUBUSB

Subtracts packed unsigned bytes with unsigned saturation.

Extensions
Forms
10 (4 VEX, 6 EVEX)
Data
Intel XED v2026.08.23

VPSUBUSB subtracts the unsigned bytes of its second source from those of its first and stops at zero: the VEX and EVEX form of SSE2’s PSUBUSB, whose page shows how the result doubles as an unsigned comparison. The newer encodings add what VPADDSB’s page lists for the saturating family: a separate destination, memory at any alignment, zeroing above the vector length, AVX2 for the ymm form, AVX512BW (or AVX10.1) for the EVEX forms with a mask bit per byte, and no broadcast. On Zen 5, vpsubusb xmm1, xmm2, xmmword ptr [mem] turned 01h minus FFh and 80h minus FFh into 00h, FFh minus 01h into FEh and 80h minus 01h into 7Fh.

A register minus itself

A register minus itself gives zero here too: vpsubusb xmm4, xmm4, xmm4 cleared XMM4 and the bits above it. AMD’s Zen 5 guide names the wrapping VPSUBB to VPSUBQ, but not the saturating subtractions, among the zeroing idioms that skip the wait for the old value (Section 2.9.2). In our builds at -march=x86-64-v4, _mm256_subs_epu8(a, a) stays VPSUBUSB in GCC 14 and becomes VXORPS in Clang 23.

AVX-512 replaces the trick

In our builds at -O2 over fixed-size uint8_t arrays:

  • Differences that stop at zero. b[i] > c[i] ? b[i] - c[i] : 0 is one VPSUBUSB per 32 bytes in Clang at -march=x86-64-v3 and -v4. GCC computes the wrapped difference with VPSUBB and clears it where VPSUBUSB and VPCMPEQB find b[i] not greater, with VPANDN, at -v3; at -v4 it compares with VPCMPUB into a mask and subtracts with VPSUBB under zeroing.
  • The comparison. For b[i] > c[i] ? 0xFF : 0, GCC takes VPSUBUSB and two VPCMPEQBs against zero at -v3, and at -v4 a VPCMPNLEUB and a zero-masked VMOVDQU8 of all ones. Clang uses VPMINUB at -v3 and VPCMPNLEUB at -v4, as VPMINUB’s page shows.

AMD’s latency spreadsheet for Zen 5 gives the VEX and EVEX rows alike two cycles and two per cycle, on pipes FP0 and FP3, where VPSUBB takes one cycle at four per cycle.

Forms

Every encoding of VPSUBUSB that Intel XED knows, one row per XED instruction form (iform). How to read the notation.
InstructionEncodingRequires
VPSUBUSB xmm, xmm, m128 VPSUBUSB_XMMdq_XMMdq_MEMdqVEX.128.66.0F.WIG D8 /rAVX
VPSUBUSB xmm, xmm, xmm VPSUBUSB_XMMdq_XMMdq_XMMdqVEX.128.66.0F.WIG D8 /rAVX
VPSUBUSB ymm, ymm, m256 VPSUBUSB_YMMqq_YMMqq_MEMqqVEX.256.66.0F.WIG D8 /rAVX2
VPSUBUSB ymm, ymm, ymm VPSUBUSB_YMMqq_YMMqq_YMMqqVEX.256.66.0F.WIG D8 /rAVX2
VPSUBUSB xmm {k}{z}, xmm, xmm VPSUBUSB_XMMu8_MASKmskw_XMMu8_XMMu8_AVX512EVEX.128.66.0F.WIG D8 /rAVX10.1 or AVX512BW + AVX512VL
VPSUBUSB xmm {k}{z}, xmm, m128 VPSUBUSB_XMMu8_MASKmskw_XMMu8_MEMu8_AVX512EVEX.128.66.0F.WIG D8 /rAVX10.1 or AVX512BW + AVX512VL
VPSUBUSB ymm {k}{z}, ymm, ymm VPSUBUSB_YMMu8_MASKmskw_YMMu8_YMMu8_AVX512EVEX.256.66.0F.WIG D8 /rAVX10.1 or AVX512BW + AVX512VL
VPSUBUSB ymm {k}{z}, ymm, m256 VPSUBUSB_YMMu8_MASKmskw_YMMu8_MEMu8_AVX512EVEX.256.66.0F.WIG D8 /rAVX10.1 or AVX512BW + AVX512VL
VPSUBUSB zmm {k}{z}, zmm, zmm VPSUBUSB_ZMMu8_MASKmskw_ZMMu8_ZMMu8_AVX512EVEX.512.66.0F.WIG D8 /rAVX10.1 or AVX512BW
VPSUBUSB zmm {k}{z}, zmm, m512 VPSUBUSB_ZMMu8_MASKmskw_ZMMu8_MEMu8_AVX512EVEX.512.66.0F.WIG D8 /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.
Modelxmm, xmm, m128
xmm {k}{z}, xmm, m128no mask		xmm, xmm, xmm
xmm {k}{z}, xmm, xmmno mask		ymm, ymm, m256
ymm {k}{z}, ymm, m256no mask		ymm, ymm, ymmxmm {k}{z}, xmm, xmmwith a mask, zeroingxmm {k}{z}, xmm, m128with a mask, zeroingymm {k}{z}, ymm, ymmno maskymm {k}{z}, ymm, ymmwith a mask, zeroingymm {k}{z}, ymm, m256with a mask, zeroingzmm {k}{z}, zmm, zmmno maskzmm {k}{z}, zmm, zmmwith a mask, zeroingzmm {k}{z}, zmm, m512no maskzmm {k}{z}, zmm, m512with a mask, zeroing
Sandy Bridge7 / 0.5p151 / 0.5p15
Haswell7 / 0.5p151 / 0.5p158 / 0.5p151 / 0.5p15
Broadwell6 / 0.5p151 / 0.5p157 / 0.5p151 / 0.5p15
Skylake7 / 0.5p011 / 0.5p018 / 0.5p011 / 0.5p01
Skylake-SP, Ice Lake7 / 0.5p011 / 0.5p018 / 0.5p011 / 0.5p011 / 0.5p017 / 0.5p011 / 0.5p011 / 0.5p018 / 0.5p011 / 1p01 / 1p08 / 1p08 / 1p0
Alder Lake8 / 0.5p011 / 0.5p019 / 0.5p011 / 0.5p01
Sapphire Rapids8 / 0.5p011 / 0.5p019 / 0.5p011 / 0.5p013 / 0.5p0111 / 0.5p011 / 0.5p013 / 0.5p0111 / 0.5p011 / 1p03 / 1p09 / 1p011 / 1p0
Lunar Lake7 / 2V0 V11 / 0.5V0 V18 / 2.33V0 V11 / 0.5V0 V1
Piledriver7 / 1.5FPMAL2 / 0.5FPMAL FPU2 FPU3
Zen8 / 0.5FPU0 FPU1 FPU31 / 0.33FPU0 FPU1 FPU38 / 0.67FPU0 FPU1 FPU31 / 0.67FPU0 FPU1 FPU3
Zen 28 / 0.33FPU0 FPU1 FPU31 / 0.33FPU0 FPU1 FPU38 / 0.33FPU0 FPU1 FPU31 / 0.33FPU0 FPU1 FPU3
Zen 38 / 0.5FP0 FP1 FP2 FP31 / 0.5FP0 FP18 / 0.5FP0 FP1 FP2 FP31 / 0.5FP0 FP1
Zen 48 / 0.5FP0 FP1 FP2 FP32 / 11FP0 FP18 / 0.5FP0 FP1 FP2 FP31 / 0.5FP0 FP12 / 12FP0 FP18 / 0.5FP0 FP1 FP2 FP31 / 0.253FP0 FP1 FP2 FP31 / 0.253FP0 FP1 FP2 FP38 / 0.5FP0 FP1 FP2 FP31 / 0.54FP0 FP1 FP2 FP31 / 0.54FP0 FP1 FP2 FP38 / 0.5FP0 FP1 FP2 FP38 / 0.5FP0 FP1 FP2 FP3
Jaguar6 / 1FPU0 FPU1 VALU0 VALU11 / 0.5FPU0 FPU1 VALU0 VALU1
  1. Zen 4 model: AMD's spreadsheets give reciprocal throughput 0.5 for Zen 4 and Zen 5 (AMD 57647, row 3051; AMD 58455, row 1188).
  2. Zen 4 model: AMD's spreadsheets give reciprocal throughput 0.5 for Zen 4 and Zen 5 (AMD 57647, row 3052; AMD 58455, row 340).
  3. Zen 4 model: AMD's spreadsheets give latency 2 for Zen 4 and Zen 5 (AMD 57647, row 3054; AMD 58455, row 340).
  4. Zen 4 model: AMD's spreadsheets give latency 2 for Zen 4 and Zen 5 (AMD 57647, row 3055; AMD 58455, row 340).

Data flow

Where the elements of the sources go, element 0 on the right; results that depend on a control value are drawn for an example. How to read.

Element-wise: each byte of the result comes from the byte in the same place in each source.
VPSUBUSB: element by elementResult byte i comes from byte i of xmm2 and xmm3. Result bytes 7 to 0: a7-b7, unchanged (bit 6 of k1 is 0), a5-b5, a4-b4, a3-b3, a2-b2, a1-b1, a0-b0.…01234567xmm2a11111110k1…a0-b0a1-b1a2-b2a3-b3a4-b4a5-b5a7-b7xmm1…01234567xmm3or m128b

Shown: bytes 7 to 0. Every byte works alike: 16, 32 and 64 bytes in the xmm, ymm and zmm forms. The EVEX forms write under a mask: where its bit is 0, the element keeps its old value, or zeroes it with {z}.

Result byte i comes from byte i of xmm2 and xmm3. Result bytes 7 to 0: a7-b7, unchanged (bit 6 of k1 is 0), a5-b5, a4-b4, a3-b3, a2-b2, a1-b1, a0-b0.

Operation

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

for i in range(VL // 8):
    if k1[i]:  # 1 without a write mask
        a = zmm2.b[i]
        b = src3.b[i]
        zmm1.b[i] = usat(a - b, 8)
    elif zeroing:
        zmm1.b[i] = 0
    # else: zmm1.b[i] keeps its value
# zmm1 is zeroed from bit VL up

Run on AMD Zen 5 (EPYC 9645): 10 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
VPSUBUSB xmm, xmm, xmm/m128 VPSUBUSB ymm, ymm, ymm/m256
xmm, ymmexplicitwrite
xmm, ymmexplicitread
xmm/m128, ymm/m256explicitread
VPSUBUSB xmm {k}{z}, xmm, xmm/m128 VPSUBUSB ymm {k}{z}, ymm, ymm/m256 VPSUBUSB zmm {k}{z}, zmm, zmm/m512
xmm, ymm, zmmexplicitwrite (masked)
{k}explicitread (write mask)
xmm, ymm, zmmexplicitread
xmm/m128, ymm/m256, zmm/m512explicitread

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.

VEX forms
avx-type-4
EVEX forms
AVX512-E4

Attributes

What else XED records about the forms. How to read.

EVEX forms
write masking
EVEX memory forms
memory fault suppression

Intrinsics

The C intrinsics of Clang 23.1.2 that compile to VPSUBUSB, 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
_mm_subs_epu8 __m128i _mm_subs_epu8(__m128i __a, __m128i __b)

VPSUBUSB xmm, xmm, xmm VEX.128 -mavxwith AVX enabled

_mm_mask_subs_epu8 __m128i _mm_mask_subs_epu8(__m128i __W, __mmask16 __U, __m128i __A, __m128i __B)

VPSUBUSB xmm {k}, xmm, xmm EVEX.128 -mavx512vl -mavx512bw

_mm_maskz_subs_epu8 __m128i _mm_maskz_subs_epu8(__mmask16 __U, __m128i __A, __m128i __B)

VPSUBUSB xmm {k}{z}, xmm, xmm EVEX.128 -mavx512vl -mavx512bw

_mm256_subs_epu8 __m256i _mm256_subs_epu8(__m256i __a, __m256i __b)

VPSUBUSB ymm, ymm, ymm VEX.256 -mavx2

_mm256_mask_subs_epu8 __m256i _mm256_mask_subs_epu8(__m256i __W, __mmask32 __U, __m256i __A, __m256i __B)

VPSUBUSB ymm {k}, ymm, ymm EVEX.256 -mavx512vl -mavx512bw

_mm256_maskz_subs_epu8 __m256i _mm256_maskz_subs_epu8(__mmask32 __U, __m256i __A, __m256i __B)

VPSUBUSB ymm {k}{z}, ymm, ymm EVEX.256 -mavx512vl -mavx512bw

_mm512_subs_epu8 __m512i _mm512_subs_epu8(__m512i __A, __m512i __B)

VPSUBUSB zmm, zmm, zmm EVEX.512 -mavx512bw

_mm512_mask_subs_epu8 __m512i _mm512_mask_subs_epu8(__m512i __W, __mmask64 __U, __m512i __A, __m512i __B)

VPSUBUSB zmm {k}, zmm, zmm EVEX.512 -mavx512bw

_mm512_maskz_subs_epu8 __m512i _mm512_maskz_subs_epu8(__mmask64 __U, __m512i __A, __m512i __B)

VPSUBUSB zmm {k}{z}, zmm, zmm EVEX.512 -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
AVX

AVX
CPUID.01H:ECX[28] AVX

Sandy Bridge, Ivy Bridge, Haswell, Broadwell, Skylake, Comet Lake, Cannon Lake, Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Sierra Forest, Clearwater Forest, Knights Landing, Knights Mill, Bulldozer, Piledriver, Zen, Zen+, Zen 2, Zen 3, Zen 4, Zen 5, Zen 6
AVX2

AVX2
CPUID.(EAX=07H,ECX=0):EBX[5] AVX2

Haswell, Broadwell, Skylake, Comet Lake, Cannon Lake, Ice Lake (client), Tiger Lake, Alder Lake, Arrow Lake, Panther Lake, Nova Lake, Skylake-SP, Cascade Lake, Cooper Lake, Ice Lake (server), Sapphire Rapids, Emerald Rapids, Granite Rapids, Diamond Rapids, Sierra Forest, Clearwater Forest, Knights Landing, Knights Mill, Zen, Zen+, Zen 2, Zen 3, Zen 4, Zen 5, Zen 6
AVX512BW_128

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

or

AVX512BW + AVX512VL
CPUID.(EAX=07H,ECX=0):EBX[30] AVX512BW
CPUID.(EAX=07H,ECX=0):EBX[31] AVX512VL

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
AVX512BW_256
Same as AVX512BW_128Same as AVX512BW_128
AVX512BW_512

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

Same as AVX512BW_128

More AVX instructions

All 253 AVX instructions

More AVX2 instructions

All 138 AVX2 instructions

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 64 and IA-32 Architectures Software Developer's Manual, Volume 2 (325383-093, September 2026): Volume 2B, page 4-494 (PSUBUSB/PSUBUSW)
  6. Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 1 (253665-093, September 2026)
  7. Intel Advanced Vector Extensions 10.2 Architecture Specification, revision 7.0 (361050-007, April 2026)
  8. 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.