CMP (immediate)

Compare (immediate) subtracts an optionally-shifted immediate value from a register value. It updates the condition flags based on the result, and discards the result.

This is an alias of SUBS (immediate). This means:

The encodings in this description are named to match the encodings of SUBS (immediate).
The description of SUBS (immediate) gives the operational pseudocode, any CONSTRAINED UNPREDICTABLE behavior, and any operational information for this instruction.

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
sf	1	1	1	0	0	0	1	0	sh	imm12												Rn					1	1	1	1	1
	op	S																									Rd

32-bit (sf == 0)

CMP <Wn|WSP>, #<imm>{, <shift>}

is equivalent to

SUBS WZR, <Wn|WSP>, #<imm> {, <shift>}

and is always the preferred disassembly.

64-bit (sf == 1)

CMP <Xn|SP>, #<imm>{, <shift>}

is equivalent to

SUBS XZR, <Xn|SP>, #<imm> {, <shift>}

and is always the preferred disassembly.

Assembler Symbols

<Wn|WSP>

Is the 32-bit name of the source general-purpose register or stack pointer, encoded in the "Rn" field.

<Xn|SP>

Is the 64-bit name of the source general-purpose register or stack pointer, encoded in the "Rn" field.

<imm>

Is an unsigned immediate, in the range 0 to 4095, encoded in the "imm12" field.

<shift>

Is the optional left shift to apply to the immediate, defaulting to LSL #0 and encoded in sh:

sh	<shift>
0	LSL #0
1	LSL #12

Operation

The description of SUBS (immediate) gives the operational pseudocode for this instruction.

Operational information

If PSTATE.DIT is 1:

The execution time of this instruction is independent of:
- The values of the data supplied in any of its registers.
- The values of the NZCV flags.
The response of this instruction to asynchronous exceptions does not vary based on:
- The values of the data supplied in any of its registers.
- The values of the NZCV flags.