LD1SW (scalar plus immediate)

Contiguous load signed words to vector (immediate index)

Contiguous load of signed words to elements of a vector register from the memory address generated by a 64-bit scalar base and immediate index in the range -8 to 7 which is multiplied by the vector's in-memory size, irrespective of predication, and added to the base address. Inactive elements will not cause a read from Device memory or signal a fault, and are set to zero in the destination vector.

Encoding: SVE

Variants: FEAT_SVE || FEAT_SME (FEAT_SVE || FEAT_SME)

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
1	0	1	0	0	1	0	0	1	0	0	0					1	0	1
							dtype					imm4							Pg			Rn					Zt

LD1SW { <Zt>.D }, <Pg>/Z, [<Xn|SP>{, #<imm>, MUL VL}]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
constant integer t = UInt(Zt);
constant integer n = UInt(Rn);
constant integer g = UInt(Pg);
constant integer esize = 64;
constant integer msize = 32;
constant boolean unsigned = FALSE;
constant integer offset = SInt(imm4);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
bits(64) base;
constant bits(PL) mask = P[g, PL];
bits(64) addr;
bits(VL) result;
bits(msize) data;
constant integer mbytes = msize DIV 8;
constant boolean contiguous = TRUE;
constant boolean nontemporal = FALSE;
constant boolean tagchecked = n != 31;
constant AccessDescriptor accdesc = CreateAccDescSVE(MemOp_LOAD, nontemporal, contiguous,
                                                     tagchecked);

if !AnyActiveElement(mask, esize) then
    if n == 31 && ConstrainUnpredictableBool(Unpredictable_CHECKSPNONEACTIVE) then
        CheckSPAlignment();
else
    if n == 31 then CheckSPAlignment();

base = if n == 31 then SP[64] else X[n, 64];
addr = AddressAdd(base, offset * elements * mbytes, accdesc);

for e = 0 to elements-1
    if ActivePredicateElement(mask, e, esize) then
        data = Mem[addr, mbytes, accdesc];
        Elem[result, e, esize] = Extend(data, esize, unsigned);
    else
        Elem[result, e, esize] = Zeros(esize);
    addr = AddressIncrement(addr, mbytes, accdesc);

Z[t, VL] = result;

Explanations

<Zt>: Is the name of the scalable vector register to be transferred, encoded in the "Zt" field.
<Pg>: Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.
<Xn|SP>: Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.
<imm>: Is the optional signed immediate vector offset, in the range -8 to 7, defaulting to 0, encoded in the "imm4" field.

Operational Notes

If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored when its governing predicate register contains the same value for each execution.