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LDFF1SW (scalar plus scalar)

Contiguous load first-fault signed words to vector (scalar index).

Contiguous load with first-faulting behavior of signed words to elements of a vector register from the memory address generated by a 64-bit scalar base and scalar index which is multiplied by 4 and added to the base address. After each element access the index value is incremented, but the index register is not updated. Inactive elements will not not cause a read from Device memory or signal a fault, and are set to zero in the destination vector.

313029282726252423222120191817161514131211109876543210
10100100100Rm011PgRnZt
dtype<3:1>dtype<0>

LDFF1SW { <Zt>.D }, <Pg>/Z, [<Xn|SP>{, <Xm>, LSL #2}]

if !HaveSVE() then UNDEFINED;
integer t = UInt(Zt);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer g = UInt(Pg);
integer esize = 64;
integer msize = 32;
boolean unsigned = FALSE;

Assembler Symbols

<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 optional 64-bit name of the general-purpose offset register, defaulting to XZR, encoded in the "Rm" field.

Operation

CheckSVEEnabled();
integer elements = VL DIV esize;
bits(64) base;
bits(64) addr;
bits(PL) mask = P[g];
bits(VL) result;
bits(VL) orig = Z[t];
bits(msize) data;
bits(64) offset = X[m];
constant integer mbytes = msize DIV 8;
boolean first = TRUE;
boolean fault = FALSE;
boolean faulted = FALSE;
boolean unknown = FALSE;

if HaveMTEExt() then SetTagCheckedInstruction(TRUE);

if n == 31 then
    if LastActiveElement(mask, esize) >= 0 || 
          ConstrainUnpredictableBool(Unpredictable_CHECKSPNONEACTIVE) then 
        CheckSPAlignment();
    base = SP[];
else
    base = X[n];

for e = 0 to elements-1
    if ElemP[mask, e, esize] == '1' then
        addr = base + UInt(offset) * mbytes;
        if first then
            // Mem[] will not return if a fault is detected for the first active element
            data = Mem[addr, mbytes, AccType_NORMAL];
            first = FALSE;
        else
            // MemNF[] will return fault=TRUE if access is not performed for any reason
            (data, fault) = MemNF[addr, mbytes, AccType_CNOTFIRST];
    else
        (data, fault) = (Zeros(msize), FALSE);

    // FFR elements set to FALSE following a supressed access/fault
    faulted = faulted || fault;
    if faulted then
        ElemFFR[e, esize] = '0';

    // Value becomes CONSTRAINED UNPREDICTABLE after an FFR element is FALSE
    unknown = unknown || ElemFFR[e, esize] == '0';
    if unknown then
        if !fault && ConstrainUnpredictableBool(Unpredictable_SVELDNFDATA) then
            Elem[result, e, esize] = Extend(data, esize, unsigned);
        elsif ConstrainUnpredictableBool(Unpredictable_SVELDNFZERO) then
            Elem[result, e, esize] = Zeros();
        else  // merge
            Elem[result, e, esize] = Elem[orig, e, esize];
    else
        Elem[result, e, esize] = Extend(data, esize, unsigned);

    offset = offset + 1;

Z[t] = result;