NOT

NOT inverts every bit of its operand, which is C’s ~x. Unlike AND, OR, XOR and NEG, it leaves all the flags alone, so it can sit between an instruction that sets them and the branch that reads them.

NOT and its relatives#

• XOR with -1 computes the same value but writes the flags, and in a 64-bit register takes a byte more. GCC 14 and Clang 23 at -O2 compile both ~x and x ^ -1 to not rax.
• NEG is the two’s complement, so the two differ by one: ~x == -x - 1. Both compilers compile -x - 1 and -(x + 1) to NOT, and ~x + 1 to NEG.
• Logical negation, C’s !x, is a comparison, not NOT: both emit xor eax, eax, test edi, edi and sete al.
• AND with an inverted operand, ~a & b, is a NOT and an AND, or one ANDN when BMI1 is enabled.

Memory and LOCK#

NOT can invert memory in place (*p = ~*p becomes not qword ptr [rdi]), and with LOCK it does so atomically. C has no atomic NOT, and compilers do not reach for LOCK NOT: both compile atomic_fetch_xor(p, -1) to lock xor qword ptr [rdi], -1 when the result is unused, and to a CMPXCHG loop with a NOT inside when it is used.

Other registers#

Vector registers have no NOT: compilers XOR with all ones, which SSE code makes with PCMPEQD of a register with itself, and AVX-512 code uses VPTERNLOGD or VPTERNLOGQ with the register in all three operands. The mask registers have their own, KNOTW and its kin.

Forms

Latency and throughput

Operation

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

dest.write(~dest)                # with LOCK: one atomic read-modify-write;
                                 # no flag changes

dest.write(~src)                 # the new destination: bits 63:OSIZE
                                 # cleared, even for 8 and 16 bits

Operands

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.

Legacy forms

none in XED

EVEX forms

APX-EVEX-INT

Attributes

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

Legacy memory forms without LOCK

accepts a LOCK prefix

LOCK forms

locked: atomic read-modify-write; accepts XACQUIRE; accepts XRELEASE

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.

More General-purpose instructions

• JRCXZ
• LDS
• LEA
• LEAVE
• LES
• LFS
• LGS
• LODS
• LOOP
• LOOPE
• LOOPNE
• LSS
• MOV
• MOVS
• MOVSX
• MOVSXD
• MOVZX
• MUL
• NEG
• NOP
• OR
• OUT
• OUTS
• PAUSE
• POP
• POPA
• POPF
• PUSH
• PUSHA
• PUSHF
• RCL
• RCR
• RET
• ROL
• ROR
• SALC
• SAR
• SBB
• SCAS
• SETcc

All 109 General-purpose instructions

More APX instructions

• IDIV
• IMUL
• INC
• INVEPT
• INVPCID
• INVVPID
• JMPABS
• KMOVB
• KMOVD
• KMOVQ
• KMOVW
• LDTILECFG
• LZCNT
• MOVBE
• MOVDIR64B
• MOVDIRI
• MOVRS
• MUL
• MULX
• NEG
• OR
• PDEP
• PEXT
• POP2
• POP2P
• POPCNT
• POPP
• PUSH2
• PUSH2P
• PUSHP
• RCL
• RCR
• RDMSR
• ROL
• ROR
• RORX
• SAR
• SARX
• SBB
• SETcc

All 88 APX instructions