LD2 (single structure)

Load single 2-element structure to one lane of two registers. This instruction loads a 2-element structure from memory and writes the result to the corresponding elements of the two SIMD&FP registers without affecting the other bits of the registers.

Depending on the settings in the CPACR_EL1, CPTR_EL2, and CPTR_EL3 registers, and the current Security state and Exception level, an attempt to execute the instruction might be trapped.

It has encodings from 2 classes: No offset and Post-index

No offset

313029282726252423222120191817161514131211109876543210
0Q00110101100000xx0SsizeRnRt
LRo2opcode

8-bit (opcode == 000)

LD2 { <Vt>.B, <Vt2>.B }[<index>], [<Xn|SP>]

16-bit (opcode == 010 && size == x0)

LD2 { <Vt>.H, <Vt2>.H }[<index>], [<Xn|SP>]

32-bit (opcode == 100 && size == 00)

LD2 { <Vt>.S, <Vt2>.S }[<index>], [<Xn|SP>]

64-bit (opcode == 100 && S == 0 && size == 01)

LD2 { <Vt>.D, <Vt2>.D }[<index>], [<Xn|SP>]

integer t = UInt(Rt); integer n = UInt(Rn); integer m = integer UNKNOWN; boolean wback = FALSE; boolean nontemporal = FALSE; boolean tagchecked = wback || n != 31;

Post-index

313029282726252423222120191817161514131211109876543210
0Q001101111Rmxx0SsizeRnRt
LRopcode

8-bit, immediate offset (Rm == 11111 && opcode == 000)

LD2 { <Vt>.B, <Vt2>.B }[<index>], [<Xn|SP>], #2

8-bit, register offset (Rm != 11111 && opcode == 000)

LD2 { <Vt>.B, <Vt2>.B }[<index>], [<Xn|SP>], <Xm>

16-bit, immediate offset (Rm == 11111 && opcode == 010 && size == x0)

LD2 { <Vt>.H, <Vt2>.H }[<index>], [<Xn|SP>], #4

16-bit, register offset (Rm != 11111 && opcode == 010 && size == x0)

LD2 { <Vt>.H, <Vt2>.H }[<index>], [<Xn|SP>], <Xm>

32-bit, immediate offset (Rm == 11111 && opcode == 100 && size == 00)

LD2 { <Vt>.S, <Vt2>.S }[<index>], [<Xn|SP>], #8

32-bit, register offset (Rm != 11111 && opcode == 100 && size == 00)

LD2 { <Vt>.S, <Vt2>.S }[<index>], [<Xn|SP>], <Xm>

64-bit, immediate offset (Rm == 11111 && opcode == 100 && S == 0 && size == 01)

LD2 { <Vt>.D, <Vt2>.D }[<index>], [<Xn|SP>], #16

64-bit, register offset (Rm != 11111 && opcode == 100 && S == 0 && size == 01)

LD2 { <Vt>.D, <Vt2>.D }[<index>], [<Xn|SP>], <Xm>

integer t = UInt(Rt); integer n = UInt(Rn); integer m = UInt(Rm); boolean wback = TRUE; boolean nontemporal = FALSE; boolean tagchecked = wback || n != 31;

Assembler Symbols

<Vt>

Is the name of the first or only SIMD&FP register to be transferred, encoded in the "Rt" field.

<Vt2>

Is the name of the second SIMD&FP register to be transferred, encoded as "Rt" plus 1 modulo 32.

<index>

For the 8-bit variant: is the element index, encoded in "Q:S:size".

For the 16-bit variant: is the element index, encoded in "Q:S:size<1>".

For the 32-bit variant: is the element index, encoded in "Q:S".

For the 64-bit variant: is the element index, encoded in "Q".

<Xn|SP>

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

<Xm>

Is the 64-bit name of the general-purpose post-index register, excluding XZR, encoded in the "Rm" field.

Shared Decode

bits(2) scale = opcode<2:1>; integer selem = UInt(opcode<0>:R) + 1; boolean replicate = FALSE; integer index; case scale of when '11' // load and replicate if L == '0' || S == '1' then UNDEFINED; scale = size; replicate = TRUE; when '00' index = UInt(Q:S:size); // B[0-15] when '01' if size<0> == '1' then UNDEFINED; index = UInt(Q:S:size<1>); // H[0-7] when '10' if size<1> == '1' then UNDEFINED; if size<0> == '0' then index = UInt(Q:S); // S[0-3] else if S == '1' then UNDEFINED; index = UInt(Q); // D[0-1] scale = '11'; constant integer datasize = 64 << UInt(Q); constant integer esize = 8 << UInt(scale);

Operation

CheckFPAdvSIMDEnabled64(); bits(64) address; bits(64) eaddr; bits(64) offs; bits(128) rval; bits(esize) element; constant integer ebytes = esize DIV 8; AccessDescriptor accdesc = CreateAccDescASIMD(MemOp_LOAD, nontemporal, tagchecked); if n == 31 then CheckSPAlignment(); address = SP[]; else address = X[n, 64]; offs = Zeros(64); if replicate then // load and replicate to all elements for s = 0 to selem-1 eaddr = AddressIncrement(address, offs, accdesc); element = Mem[eaddr, ebytes, accdesc]; // replicate to fill 128- or 64-bit register V[t, datasize] = Replicate(element, datasize DIV esize); offs = offs + ebytes; t = (t + 1) MOD 32; else // load/store one element per register for s = 0 to selem-1 rval = V[t, 128]; eaddr = AddressIncrement(address, offs, accdesc); Elem[rval, index, esize] = Mem[eaddr, ebytes, accdesc]; V[t, 128] = rval; offs = offs + ebytes; t = ( t + 1 ) MOD 32; if wback then if m != 31 then offs = X[m, 64]; address = AddressAdd(address, offs, accdesc); if n == 31 then SP[] = address; else X[n, 64] = address;

Operational information

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 v2024-03_relA, pseudocode v2024-03_rel, sve v2024-03_rel ; Build timestamp: 2024-03-26T09:45

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