RPRFM

Range Prefetch Memory signals the memory system that data memory accesses from a specified range of addresses are likely to occur in the near future. The instruction may also signal the memory system about the likelihood of data reuse of the specified range of addresses. The memory system can respond by taking actions that are expected to speed up the memory accesses when they do occur, such as prefetching locations within the specified address ranges into one or more caches. The memory system may also exploit the data reuse hints to decide whether to retain the data in other caches upon eviction from the innermost caches or to discard it.

The effect of an RPRFM instruction is IMPLEMENTATION DEFINED. For more information, see Prefetch memory.

An RPRFM instruction specifies the type of accesses and range of addresses using the following parameters:

• 'Type', in the <rprfop> operand opcode bits, specifies whether the prefetched data will be accessed by load or store instructions.
• 'Policy', in the <rprfop> operand opcode bits, specifies whether the data is likely to be reused or if it is a streaming, non-temporal prefetch. If a streaming prefetch is specified, then the 'ReuseDistance' parameter is ignored.
• 'BaseAddress', in the 64-bit base register, holds the initial block address for the accesses.
• 'ReuseDistance', in the metadata register bits[63:60], indicates the maximum number of bytes to be accessed by this PE before executing the next RPRFM instruction that specifies the same range. This includes the total number of bytes inside and outside of the range that will be accessed by the same PE. This parameter can be used to influence cache eviction and replacement policies, in order to retain the data in the most optimal levels of the memory hierarchy after each access. If software cannot easily determine the amount of other memory that will be accessed, these bits can be set to zero to indicate that 'ReuseDistance' is not known. Otherwise, these four bits encode decreasing powers of two in the range 512MiB (0b0001) to 32KiB (0b1111).
• 'Stride', in the metadata register bits[59:38], is a signed, two's complement integer encoding of the number of bytes to advance the block address after 'Length' bytes have been accessed, in the range -2MiB to +2MiB-1B. A negative value indicates that the block address is advanced in a descending direction.
• 'Count', in the metadata register bits[37:22], is an unsigned integer encoding of the number of blocks of data to be accessed minus 1, representing the range 1 to 65536 blocks. If 'Count' is 0, then the 'Stride' parameter is ignored and only a single block of contiguous bytes from 'BaseAddress' to ('BaseAddress' + 'Length' - 1) is described.
• 'Length', in the metadata register bits[21:0], is a signed, two's complement integer encoding of the number of contiguous bytes to be accessed starting from the current block address, without changing the block address, in the range -2MiB to +2MiB-1B. A negative value indicates that the bytes are accessed in a descending direction.

Integer
(FEAT_RPRFM)

bits(6) operation = option<2>:option<0>:S:Rt<2:0>; integer n = UInt(Rn); integer m = UInt(Rm);