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CMP (shifted register)

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

This is an alias of SUBS (shifted register). This means:

313029282726252423222120191817161514131211109876543210
sf1101011shift0Rmimm6Rn11111
opSRd

32-bit (sf == 0)

CMP <Wn>, <Wm>{, <shift> #<amount>}

is equivalent to

SUBS WZR, <Wn>, <Wm> {, <shift> #<amount>}

and is always the preferred disassembly.

64-bit (sf == 1)

CMP <Xn>, <Xm>{, <shift> #<amount>}

is equivalent to

SUBS XZR, <Xn>, <Xm> {, <shift> #<amount>}

and is always the preferred disassembly.

Assembler Symbols

<Wn>

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

<Wm>

Is the 32-bit name of the second general-purpose source register, encoded in the "Rm" field.

<Xn>

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

<Xm>

Is the 64-bit name of the second general-purpose source register, encoded in the "Rm" field.

<shift> Is the optional shift type to be applied to the second source operand, defaulting to LSL and encoded in shift:
shift <shift>
00 LSL
01 LSR
10 ASR
11 RESERVED
<amount>

For the 32-bit variant: is the shift amount, in the range 0 to 31, defaulting to 0 and encoded in the "imm6" field.

For the 64-bit variant: is the shift amount, in the range 0 to 63, defaulting to 0 and encoded in the "imm6" field.

Operation

The description of SUBS (shifted register) 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.
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