The Q flag in AArch64 state
In AArch64 state, you cannot read or write to the Q flag because in A64 there are no saturating arithmetic instructions that operate on the general purpose registers.
The Advanced SIMD saturating arithmetic instructions set the
QC bit in the floating-point status register (FPSR) to indicate
that saturation has occurred. You can identify such instructions
by the Q mnemonic modifier, for example