PRFW (scalar plus vector)

Gather prefetch words (scalar plus vector)

This instruction performs a gather prefetch of words from the active memory addresses generated by a 64-bit scalar base plus vector index. The index values are optionally first sign-extended or zero-extended from 32 to 64 bits and then multiplied by 4. Inactive addresses are not prefetched from memory.

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

• Access type:
  • PLD for prefetch for load.
  • PST for prefetch for store.
• Target cache level:
  • L1 for Level 1 cache.
  • L2 for Level 2 cache.
  • L3 for Level 3 cache.
• Policy:
  • KEEP for retained or temporal prefetch, allocated in the cache normally.
  • STRM for streaming or non-temporal prefetch, for data that is used only once.

This instruction is illegal when executed in Streaming SVE mode, unless FEAT_SME_FA64 is implemented and enabled.

It has encodings from 3 classes: 32-bit scaled offset , 32-bit unpacked scaled offset and 64-bit scaled offset

32-bit scaled offset
(FEAT_SVE)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 32; let g : integer = UInt(Pg); let n : integer = UInt(Rn); let m : integer = UInt(Zm); 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 offs_size : integer{} = 32; let offs_unsigned : boolean = (xs == '0'); let scale : integer = 2;

32-bit unpacked scaled offset
(FEAT_SVE)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 64; let g : integer = UInt(Pg); let n : integer = UInt(Rn); let m : integer = UInt(Zm); 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 offs_size : integer{} = 32; let offs_unsigned : boolean = (xs == '0'); let scale : integer = 2;

64-bit scaled offset
(FEAT_SVE)

Decode for this encoding

if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let esize : integer{} = 64; let g : integer = UInt(Pg); let n : integer = UInt(Rn); let m : integer = UInt(Zm); 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 offs_size : integer{} = 64; let offs_unsigned : boolean = TRUE; let scale : integer = 2;