Conditionally extract last element to vector register
This instruction extracts, from the second source vector register, the Last active element, and then replicates that element to destructively fill the destination and first source vector.
If there are no Active elements, the destination and source vector are unmodified.
| 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 |
| 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | size | 1 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | Pg | Zm | Zdn | |||||||||||
| B | |||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << UInt(size); let g : integer = UInt(Pg); let dn : integer = UInt(Zdn); let m : integer = UInt(Zm); let isBefore : boolean = TRUE;
| <Zdn> |
Is the name of the first source and destination scalable vector register, encoded in the "Zdn" field. |
| <T> |
Is the size specifier,
encoded in
|
| <Pg> |
Is the name of the governing scalable predicate register P0-P7, encoded in the "Pg" field. |
| <Zm> |
Is the name of the second source scalable vector register, encoded in the "Zm" field. |
CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let mask : bits(PL) = P{}(g); let operand1 : bits(VL) = Z{}(dn); let operand2 : bits(VL) = Z{}(m); var result : bits(VL); var last : integer = LastActiveElement{PL}(mask, esize); if last < 0 then result = operand1; else if !isBefore then last = last + 1; if last >= elements then last = 0; end; end; for e = 0 to elements-1 do result[e*:esize] = operand2[last*:esize]; end; end; Z{VL}(dn) = result;
This instruction might be immediately preceded in program order by a MOVPRFX instruction. The MOVPRFX must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is CONSTRAINED UNPREDICTABLE:
2025-09_diff_tag 2025-11-28 16:29:05
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