XZR
alias WZRarchitectural number 31Zero register
XZR64-bit view
X only
shared with WZR
WZR32-bit view
bits 31:0 of XZR
write
Writing WZR does not simply deposit 32 bits. Bits 63:32 of XZR are reset to zero as a side effect, so a W write always clears the upper half. This is the reason WSP and WZR can never hold unrelated values at the same time.
Notes
Reads as zero and discards writes. Shared encoding with the stack pointer: the meaning is decided by the instruction, not the register. In AArch64 there is no way to name SP and ZR in the same operand.