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Conditional execution in AArch64 state

In AArch64 state, the NZCV register holds copies of the N, Z, C, and V condition flags. The processor uses them to determine whether or not to execute conditional instructions. The NZCV register contains the flags in bits[31:28].

The condition flags are accessible in all exception levels, using the MSR and MRS instructions.

A64 makes less use of conditionality than A32. For example, in A64:

  • Only a few instructions can set or test the condition flags.

  • There is no equivalent of the T32 IT instruction.

  • The only conditionally executed instruction, which behaves as a NOP if the condition is false, is the conditional branch, B.cond.

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