LSL (immediate, predicated) -- A64

This instruction shifts left by immediate each active element of the source vector, and destructively places the results in the corresponding elements of the source vector. The immediate shift amount is an unsigned value in the range 0 to number of bits per element minus 1. Inactive elements in the destination vector register remain unmodified.

SVE
(FEAT_SVE || FEAT_SME)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let tsize : bits(4) = tszh::tszl; if tsize == '0000' then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8 << HighestSetBitNZ(tsize); let g : integer = UInt(Pg); let dn : integer = UInt(Zdn); let shift : integer = UInt(tsize::imm3) - esize;

Assembler Symbols

<Zdn>

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

<T>

Is the size specifier, encoded in (tszh :: tszl):

tszh	tszl	<T>
00	00	RESERVED
00	01	B
00	1x	H
01	xx	S
1x	xx	D

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

<const>

Is the immediate shift amount, in the range 0 to number of bits per element minus 1, encoded in "tszh:tszl:imm3".

Operation

CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let elements : integer = VL DIV esize; let PL : integer{} = VL DIV 8; let operand1 : bits(VL) = Z{}(dn); let mask : bits(PL) = P{}(g); var result : bits(VL); for e = 0 to elements-1 do let element1 : bits(esize) = operand1[e*:esize]; if ActivePredicateElement{PL}(mask, e, esize) then result[e*:esize] = LSL(element1, shift); else result[e*:esize] = operand1[e*:esize]; end; end; Z{VL}(dn) = result;

Operational information

This instruction is a data-independent-time instruction as described in About PSTATE.DIT.

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:

The MOVPRFX can be predicated or unpredicated.
A predicated MOVPRFX must use the same governing predicate register as this instruction.
A predicated MOVPRFX must use the larger of the destination element size and first source element size in the preferred disassembly of this instruction.
The MOVPRFX 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.

2026-03_rel 2026-03-26 20:48:11

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	0	tszh		0	0	0	0	1	1	1	0	0	Pg			tszl		imm3			Zdn
												opc		L	U