LD1Q

Gather load quadwords

Gather load of quadwords to active elements of a vector register from memory addresses generated by a vector base plus a 64-bit unscaled scalar register offset. Inactive elements will not cause a read from Device memory or signal faults, and are set to zero in the destination vector.

This instruction is illegal when executed in Streaming SVE mode, unless FEAT_SME_FA64 is implemented and enabled.

Encoding: SVE2

Variants: FEAT_SVE2p1 (ARMv9.4)

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	1	0	0	0	1	0	0	0	0	0						1	0	1
											Rm								Pg			Zn					Zt

LD1Q { <Zt>.Q }, <Pg>/Z, [<Zn>.D{, <Xm>}]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE2p1) then EndOfDecode(Decode_UNDEF);
constant integer t = UInt(Zt);
constant integer n = UInt(Zn);
constant integer m = UInt(Rm);
constant integer g = UInt(Pg);

Operation

constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
CheckNonStreamingSVEEnabled();
constant integer elements = VL DIV 128;
constant bits(PL) mask = P[g, PL];
bits(VL) base;
bits(64) offset;
bits(VL) result;
constant boolean contiguous = FALSE;
constant boolean nontemporal = FALSE;
constant boolean tagchecked = TRUE;
constant AccessDescriptor accdesc = CreateAccDescSVE(MemOp_LOAD, nontemporal, contiguous,
                                                     tagchecked);

if AnyActiveElement(mask, 128) then
    base = Z[n, VL];
    offset = X[m, 64];

for e = 0 to elements-1
    if ActivePredicateElement(mask, e, 128) then
        constant bits(64) baddr = Elem[base, 2*e, 64];
        constant bits(64) addr = AddressAdd(baddr, offset, accdesc);
        Elem[result, e, 128] = Mem[addr, 16, accdesc];
    else
        Elem[result, e, 128] = Zeros(128);

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.
<Zn>: Is the name of the base scalable vector register, encoded in the "Zn" field.
<Xm>: Is the optional 64-bit name of the general-purpose offset register, defaulting to XZR, 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.