Read Check Write Software Swap quadword in memory atomically loads a 128-bit quadword from a memory location, and conditionally stores the value held in a pair of registers back to the same memory location. Storing back to memory is conditional on RCW Checks and RCWS Checks. The value initially loaded from memory is returned in the same pair of registers. This instruction updates the condition flags based on the result of the update of memory.
| 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 | 1 | 0 | 1 | 1 | 0 | 0 | 1 | A | R | 1 | Rt2 | 1 | 0 | 1 | 0 | 0 | 0 | Rn | Rt | ||||||||||||
| S | o3 | opc | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_D128) || !IsFeatureImplemented(FEAT_THE) then UNDEFINED; if Rt == '11111' then UNDEFINED; if Rt2 == '11111' then UNDEFINED; integer t = UInt(Rt); integer t2 = UInt(Rt2); integer n = UInt(Rn); boolean acquire = A == '1'; boolean release = R == '1'; boolean tagchecked = n != 31; boolean rt_unknown = FALSE; if t == t2 then Constraint c = ConstrainUnpredictable(Unpredictable_LSE128OVERLAP); assert c IN {Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP}; case c of when Constraint_UNKNOWN rt_unknown = TRUE; // result is UNKNOWN when Constraint_UNDEF UNDEFINED; when Constraint_NOP EndOfInstruction();
For information about the CONSTRAINED UNPREDICTABLE behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors, and particularly CONSTRAINED UNPREDICTABLE behavior for A64 instructions.
| <Xt1> |
Is the 64-bit name of the first general-purpose register to be transferred, encoded in the "Rt" field. |
| <Xt2> |
Is the 64-bit name of the second general-purpose register to be transferred, encoded in the "Rt2" field. |
| <Xn|SP> |
Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field. |
if !IsD128Enabled(PSTATE.EL) then UNDEFINED; bits(64) address; bits(64) value1; bits(64) value2; bits(128) newdata; bits(128) readdata; bits(4) nzcv; AccessDescriptor accdesc = CreateAccDescRCW(MemAtomicOp_SWP, TRUE, acquire, release, tagchecked); if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; value1 = X[t, 64]; value2 = X[t2, 64]; newdata = if BigEndian(accdesc.acctype) then value1:value2 else value2:value1; bits(128) compdata = bits(128) UNKNOWN; // Irrelevant when not executing CAS (nzcv, readdata) = MemAtomicRCW(address, compdata, newdata, accdesc); PSTATE.<N,Z,C,V> = nzcv; if rt_unknown then readdata = bits(128) UNKNOWN; if BigEndian(accdesc.acctype) then X[t, 64] = readdata<127:64>; X[t2, 64] = readdata<63:0>; else X[t, 64] = readdata<63:0>; X[t2, 64] = readdata<127:64>;
If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.
Internal version only: aarchmrs v2023-12_rel, pseudocode v2023-12_rel, sve v2023-12_rel ; Build timestamp: 2023-12-15T16:46
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