Data Proc R15 Dest Edge Case

[reissGRVS]

Writing to R15
When Rd is a register other than R15, the condition code
flags in the CPSR may be updated from the ALU flags as
described above.
When Rd is R15 and the S flag in the instruction is not set
the result of the operation is placed in R15 and the CPSR is
unaffected.
When Rd is R15 and the S flag is set the result of the operation
is placed in R15 and the SPSR corresponding to the
current mode is moved to the CPSR. This allows state
changes which atomically restore both PC and CPSR. This
form of instruction should not be used in User mode.