VPCOMB instruction (XOP)

Forms

Every encoding of VPCOMB that Intel XED knows, one row per XED instruction form (iform). How to read the notation.

Instruction	Encoding	Requires
`VPCOMB xmm, xmm, m128, imm8` VPCOMB_XMMdq_XMMdq_MEMdq_IMMb	`XOP.128.NP.08.W0 CC /r ib`	XOP
`VPCOMB xmm, xmm, xmm, imm8` VPCOMB_XMMdq_XMMdq_XMMdq_IMMb	`XOP.128.NP.08.W0 CC /r ib`	XOP

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.

Shown: bytes 7 to 0. Every byte works alike: 16 bytes in the xmm form.

Result byte i comes from byte i of xmm2 and xmm3. Result bytes 7 to 0: r7, r6, r5, r4, r3, r2, r1, r0.

Operation

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

features = cpuid_leaf(0x80000001, 0)[2]
if not features >> 11 & 1:
    fault(UD)  # CPUID: no XOP
for i in range(16):
    sa = xmm2.sb[i]
    sb = src3.sb[i]
    if xop_compare(imm8, sa, sb):
        xmm1.b[i] = -1
    else:
        xmm1.b[i] = 0
# imm8 & 7: 0 <, 1 <=, 2 >, 3 >=, 4 ==, 5 !=, 6 false, 7 true
# xmm1 is zeroed from bit 128 up

Run on AMD Zen 5 (EPYC 9645): 2 cases. Its cases ran where CPUID reported no XOP, and every one raised an exception.

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.

Operand	Kind	Action
`VPCOMB xmm, xmm, xmm/m128, imm8`
`xmm`	explicit	write
`xmm`	explicit	read
`xmm/m128`	explicit	read
`imm8`	explicit	read

Flags

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

Intrinsics

The C intrinsics of Clang 23.1.2 that compile to VPCOMB, 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.

Intrinsic	Compiles to
`_mm_com_epi8` `__m128i _mm_com_epi8(__m128i A, __m128i B, const int N)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comeq_epi8` `__m128i _mm_comeq_epi8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comeq_epu8` `__m128i _mm_comeq_epu8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comge_epi8` `__m128i _mm_comge_epi8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comgt_epi8` `__m128i _mm_comgt_epi8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comle_epi8` `__m128i _mm_comle_epi8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comlt_epi8` `__m128i _mm_comlt_epi8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comneq_epi8` `__m128i _mm_comneq_epi8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop
`_mm_comneq_epu8` `__m128i _mm_comneq_epu8(__m128i __A, __m128i __B)`	`VPCOMB xmm, xmm, xmm, imm8` XOP.128 -mxop

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 set	CPUID	Processors
`XOP` XOP	XOP `CPUID.80000001H:ECX[11]` XOP	Bulldozer, Piledriver

More XOP instructions

All 55 XOP instructions