PRFM (literal)

Prefetch memory (literal)

This instruction signals the memory system that data memory accesses from a specified address are likely to occur in the near future. The memory system can respond by taking actions that are expected to speed up the memory accesses when they do occur, such as making the cache line containing the specified address available at the level of cache specified by the instruction.

The effect of a PRFM instruction is IMPLEMENTATION DEFINED. For more information, see Prefetch memory.

For information about addressing modes, see Load/Store addressing modes.

Encoding: Literal

313029282726252423222120191817161514131211109876543210
11011000
opcVRimm19Rt

PRFM (<target> is one of: L1 : Level 1 cache, encoded in the "Rt<2:1>" field as 0b00. L2 : Level 2 cache, encoded in the "Rt<2:1>" field as 0b01. L3 : Level 3 cache, encoded in the "Rt<2:1>" field as 0b10. SLC : When FEAT_PRFMSLC is implemented, system level cache, encoded in the "Rt<2:1>" field as 0b11. <policy> is one of: KEEP : Retained or temporal prefetch, allocated in the cache normally. Encoded in the "Rt<0>" field as 0. STRM : Streaming or non-temporal prefetch, for data that is used only once. Encoded in the "Rt<0>" field as 1. For more information on these prefetch operations, see x[Prefetch memory](CEGGGIDE). For other encodings of the "Rt" field, use <imm5>." class="text-blue-400 hover:text-yellow-300"><prfop>|#<prfop>." class="text-blue-400 hover:text-yellow-300"><imm5>), <label>

Decoding algorithm

constant integer t = UInt(Rt);

constant bits(64) offset = SignExtend(imm19:'00', 64);

Operation

constant bits(64) address = PC64 + offset;

Prefetch(address, t<4:0>);

Explanations

<prfop>: <imm5>: Is the prefetch operation encoding as an immediate, in the range 0 to 31, encoded in the "Rt" field.
This syntax is only for encodings that are not accessible using <prfop>.
<label>: Is the program label from which the data is to be loaded. Its offset from the address of this instruction, in the range +/-1MB, is encoded as "imm19" times 4.