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Splice two vectors under predicate control.

Copy the first active to last active elements (inclusive) from the first source vector to the lowest-numbered elements of the result. Then set any remaining elements of the result to a copy of the lowest-numbered elements from the second source vector. The result is placed destructively in the first source vector.



SPLICE <Zdn>.<T>, <Pg>, <Zdn>.<T>, <Zm>.<T>

if !HaveSVE() then UNDEFINED;
integer esize = 8 << UInt(size);
integer g = UInt(Pg);
integer dn = UInt(Zdn);
integer m = UInt(Zm);

Assembler Symbols


Is the name of the first source and destination scalable vector register, encoded in the "Zdn" field.

<T> Is the size specifier, encoded in size:
size <T>
00 B
01 H
10 S
11 D

Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field.


Is the name of the second source scalable vector register, encoded in the "Zm" field.


integer elements = VL DIV esize;
bits(PL) mask = P[g];
bits(VL) operand1 = Z[dn];
bits(VL) operand2 = Z[m];
bits(VL) result;
integer x = 0;
boolean active = FALSE;
integer lastnum = LastActiveElement(mask, esize);

if lastnum >= 0 then
    for e = 0 to lastnum
        active = active || ElemP[mask, e, esize] == '1';
        if active then
            Elem[result, x, esize] = Elem[operand1, e, esize];
            x = x + 1;

elements = elements - x - 1;
for e = 0 to elements
    Elem[result, x, esize] = Elem[operand2, e, esize];
    x = x + 1;

Z[dn] = result;

Operational information

This instruction might be immediately preceded in program order by a MOVPRFX instruction that conforms to all of the following requirements, otherwise the behavior of either or both instructions is unpredictable:

  • The MOVPRFX instruction must specify the same destination register as this instruction.
  • The destination register must not refer to architectural register state referenced by any other source operand register of this instruction.
The MOVPRFX instructions that can be used with this instruction are as follows:
  • An unpredicated MOVPRFX instruction.
  • A predicated MOVPRFX instruction using the same governing predicate register and source element size as this instruction.