SWP, SWPA, SWPAL, SWPL

Swap word or doubleword in memory atomically loads a 32-bit word or 64-bit doubleword from a memory location, and stores the value held in a register back to the same memory location. The value initially loaded from memory is returned in the destination register.

• If the destination register is not one of WZR or XZR, SWPA and SWPAL load from memory with acquire semantics.
• SWPL and SWPAL store to memory with release semantics.
• SWP has neither acquire nor release semantics.

For more information about memory ordering semantics, see Load-Acquire, Store-Release.

For information about memory accesses, see Load/Store addressing modes.

Integer
(FEAT_LSE)

if !IsFeatureImplemented(FEAT_LSE) then UNDEFINED; integer t = UInt(Rt); integer n = UInt(Rn); integer s = UInt(Rs); constant integer datasize = 8 << UInt(size); integer regsize = if datasize == 64 then 64 else 32; boolean acquire = A == '1' && Rt != '11111'; boolean release = R == '1'; boolean tagchecked = n != 31;