SWPB, SWPAB, SWPALB, SWPLB -- A64

SWPB, SWPAB, SWPALB, SWPLB

Swap byte in memory atomically loads an 8-bit byte 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 WZR, SWPAB and SWPALB load from memory with acquire semantics.
SWPLB and SWPALB store to memory with release semantics.
SWPB has no memory ordering requirements.

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)

31	30	29	28	27	26	25	24	23	22	21	20	19	18	17	16	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
0	0	1	1	1	0	0	0	A	R	1	Rs					1	0	0	0	0	0	Rn					Rt
size

SWPAB (A == 1 && R == 0)

SWPAB <Ws>, <Wt>, [<Xn|SP>] // (PSTATE.C64 == '0')

SWPAB <Ws>, <Wt>, [<Cn|CSP>] // (PSTATE.C64 == '1')

SWPALB (A == 1 && R == 1)

SWPALB <Ws>, <Wt>, [<Xn|SP>] // (PSTATE.C64 == '0')

SWPALB <Ws>, <Wt>, [<Cn|CSP>] // (PSTATE.C64 == '1')

SWPB (A == 0 && R == 0)

SWPB <Ws>, <Wt>, [<Xn|SP>] // (PSTATE.C64 == '0')

SWPB <Ws>, <Wt>, [<Cn|CSP>] // (PSTATE.C64 == '1')

SWPLB (A == 0 && R == 1)

SWPLB <Ws>, <Wt>, [<Xn|SP>] // (PSTATE.C64 == '0')

SWPLB <Ws>, <Wt>, [<Cn|CSP>] // (PSTATE.C64 == '1')

if !HaveAtomicExt() then UNDEFINED; integer t = UInt(Rt); integer n = UInt(Rn); integer s = UInt(Rs); integer datasize = 8 << UInt(size); integer regsize = if datasize == 64 then 64 else 32; AccType ldacctype = if A == '1' && Rt != '11111' then AccType_ORDEREDATOMICRW else AccType_ATOMICRW; AccType stacctype = if R == '1' then AccType_ORDEREDATOMICRW else AccType_ATOMICRW;

Assembler Symbols

<Ws>	Is the 32-bit name of the general-purpose register to be stored, encoded in the "Rs" field.

<Wt>	Is the 32-bit name of the general-purpose register to be loaded, encoded in the "Rt" field.

<Xn|SP>

Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

<Cn|CSP>

Is the name of the capability register or capability stack pointer holding the base address, encoded in the "Rn" field.

Operation

bits(64) address; bits(datasize) data; bits(datasize) store_value; store_value = X[s]; VirtualAddress base = BaseReg[n]; data = MemAtomic(base, MemAtomicOp_SWP, store_value, ldacctype, stacctype); X[t] = ZeroExtend(data, regsize);

Internal version only: isa v32.13, AdvSIMD v29.04, pseudocode morello-2022-01_rc2, capabilities morello-2022-01_rc2 ; Build timestamp: 2022-01-11T11:23