PRFB (scalar plus scalar)

Contiguous prefetch bytes (scalar index)

This instruction prefetches contiguous byte elements from the memory address generated by a 64-bit scalar base and scalar index that is added to the base address. After each element prefetch the index value is incremented, but the index register is not updated.

The <prfop> operand specifies the prefetch hint as follows:


Note

Arm strongly recommends the following for this instruction:


SVE
(FEAT_SVE || FEAT_SME)

313029282726252423222120191817161514131211109876543210
10000100000!= 11111110PgRn0prfop
mszRm

Encoding

PRFB <prfop>, <Pg>, [<Xn|SP>, <Xm>]

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) && !IsFeatureImplemented(FEAT_SME) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 8; let g : integer = UInt(Pg); let n : integer = UInt(Rn); let m : integer = UInt(Rm); let level : integer = UInt(prfop[2:1]); let stream : boolean = (prfop[0] == '1'); let pref_hint : PrefetchHint = if prfop[3] == '0' then Prefetch_READ else Prefetch_WRITE; let scale : integer = 0;

Assembler Symbols

<prfop>

Is the prefetch operation specifier, encoded in prfop:

prfop <prfop>
0000 PLDL1KEEP
0001 PLDL1STRM
0010 PLDL2KEEP
0011 PLDL2STRM
0100 PLDL3KEEP
0101 PLDL3STRM
x11x #uimm4
1000 PSTL1KEEP
1001 PSTL1STRM
1010 PSTL2KEEP
1011 PSTL2STRM
1100 PSTL3KEEP
1101 PSTL3STRM
<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 64-bit name of the general-purpose offset register, encoded in the "Rm" field.

Operation

CheckSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let mask : bits(PL) = P{}(g); var base : bits(64); var offset : bits(64); if AnyActiveElement{PL}(mask, esize) then base = if n == 31 then SP{64}() else X{64}(n); offset = X{64}(m); end; for e = 0 to elements-1 do if ActivePredicateElement{PL}(mask, e, esize) then let eoff : integer = UInt(offset) + e; let addr : bits(64) = base + (eoff << scale); Hint_Prefetch(addr, pref_hint, level, stream); end; end;


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

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