splice
SVE Splice Vectors
Splices two vectors based on the last active element of the first.
Pseudocode Operation
integer esize = 8 << UInt(sz);
integer elements = VL / esize;
integer last_active = -1;
for e = 0 to elements-1
if Pg[e] == '1' then
last_active = e;
integer start_pos = last_active + 1;
for e = 0 to elements-1
if (start_pos + e) < elements then
Zdn[e * esize +: esize] = Zdn[(start_pos + e) * esize +: esize];
else
Zdn[e * esize +: esize] = Zm[(start_pos + e - elements) * esize +: esize];Example
Encoding
Operands
-
Zdn
Dest/First -
Pg
Predicate -
Zm
Second
Related
More in SVE
Reference
Instruction Forms
| Encoding | Instruction | ISA | Bit pattern | ||
|---|---|---|---|---|---|
| 0x052D8000 | SPLICE <Zd>.<T>, <Pv>, { <Zn1>.<T>, <Zn2>.<T> } | A64 | 00000101 | size | 101101100 | Pv | Zn | Zd | ||
| 0x052C8000 | SPLICE <Zdn>.<T>, <Pv>, <Zdn>.<T>, <Zm>.<T> | A64 | 00000101 | size | 101100100 | Pv | Zm | Zdn |
Description
Select a region from the first source vector and copy it 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 region is selected using the first and last true elements in the vector select predicate register. The result is placed destructively in the destination and first source vector, or constructively in the destination vector. The Destructive encoding of this instruction might be immediately preceded in program order by a MOVPRFX instruction. The MOVPRFX instruction must conform to all of the following requirements, otherwise the behavior of the MOVPRFX and this instruction is UNPREDICTABLE: The MOVPRFX instruction must be unpredicated. 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.
Operation
CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
bits(PL) mask = P[v, PL];
bits(VL) operand1 = if AnyActiveElement(mask, esize) then Z[s1, VL] else Zeros(VL);
bits(VL) operand2 = Z[s2, VL];
bits(VL) result;
integer x = 0;
boolean active = FALSE;
constant integer lastnum = LastActiveElement(mask, esize);
if lastnum >= 0 then
for e = 0 to lastnum
active = active || ActivePredicateElement(mask, e, esize);
if active then
Elem[result, x, esize] = Elem[operand1, e, esize];
x = x + 1;
constant integer nelements = (elements - x) - 1;
for e = 0 to nelements
Elem[result, x, esize] = Elem[operand2, e, esize];
x = x + 1;
Z[dst, VL] = result;