LD1RQW (scalar plus scalar)

Contiguous load and replicate four words (scalar index)

Load four contiguous words to elements of a short, 128-bit (quadword) vector from the memory address generated by a 64-bit scalar base address and scalar index which is multiplied by 4 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. The resulting short vector is then replicated to fill the long destination vector. Only the first four predicate elements are used and higher numbered predicate elements are ignored.

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	1	0	0	0	!= 11111					0	0	0
							msz		ssz		Rm								Pg			Rn					Zt

LD1RQW { <Zt>.S }, <Pg>/Z, [<Xn|SP>, <Xm>, LSL #2]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
if Rm == '11111' then EndOfDecode(Decode_UNDEF);
constant integer t = UInt(Zt);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer g = UInt(Pg);
constant integer esize = 32;

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = 128 DIV esize;
bits(64) base;
constant bits(PL) mask = P[g, PL]; // low 16 bits only
bits(64) offset;
bits(64) addr;
bits(128) result;
constant integer mbytes = esize DIV 8;
constant boolean contiguous = TRUE;
constant boolean nontemporal = FALSE;
constant boolean tagchecked = TRUE;
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];
offset = X[m, 64];
addr = AddressAdd(base, UInt(offset) * mbytes, accdesc);

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

Z[t, VL] = Replicate(result, VL DIV 128);

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.
<Xm>: Is the 64-bit name of the general-purpose offset register, encoded in the "Rm" 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.