PLI (register) -- AArch32

PLI (register)

Preload Instruction signals the memory system that instruction memory accesses from a specified address are likely 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 pre-loading the cache line containing the specified address into the instruction cache.

The effect of a PLI instruction is implementation defined. For more information, see Preloading caches.

It has encodings from the following instruction sets: A32 ( A1 ) and T32 ( T1 ) .

A1

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
1	1	1	1	0	1	1	0	U	1	0	1	Rn				(1)	(1)	(1)	(1)	imm5					stype		0	Rm

Encoding for the Rotate right with extend variant

Applies when (imm5 == 00000 && stype == 11)

PLI{<c>}{<q>} [<Rn>, {+/-}<Rm> , RRX]

Encoding for the Shift or rotate by value variant

Applies when (!(imm5 == 00000 && stype == 11))

PLI{<c>}{<q>} [<Rn>, {+/-}<Rm> {, <shift> #<amount>}]

Decode for all variants of this encoding

constant n = UInt(Rn); constant m = UInt(Rm); constant add = (U == '1'); constant (shift_t, shift_n) = DecodeImmShift(stype, imm5); if m == 15 then UNPREDICTABLE;

T1

15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0	15	14	13	12	11	10	9	8	7	6	5	4	3	2	1	0
1	1	1	1	1	0	0	1	0	0	0	1	!= 1111				1	1	1	1	0	0	0	0	0	0	imm2		Rm
												Rn

Encoding for the T1 variant

PLI{<c>}{<q>} [<Rn>, {+}<Rm> {, LSL #<amount>}]

Decode for this encoding

if Rn == '1111' then SEE "PLI (immediate, literal)"; constant n = UInt(Rn); constant m = UInt(Rm); constant add = TRUE; constant (shift_t, shift_n) = (SRType_LSL, UInt(imm2)); // Armv8-A removes UNPREDICTABLE for R13 if m == 15 then UNPREDICTABLE;

For more information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors.

Assembler Symbols

<c>	For encoding A1: see Standard assembler syntax fields. <c> must be AL or omitted.
	For encoding T1: see Standard assembler syntax fields.

<q>	See Standard assembler syntax fields.

<Rn>	Is the general-purpose base register, encoded in the "Rn" field.

+/-

Specifies the index register is added to or subtracted from the base register, defaulting to + if omitted and encoded in U:

U	+/-
0	-
1	+

+	Specifies the index register is added to the base register.

<Rm>	Is the general-purpose index register, encoded in the "Rm" field.

<shift>

Is the type of shift to be applied to the index register, encoded in stype:

stype	<shift>
00	LSL
01	LSR
10	ASR
11	ROR

<amount>	For encoding A1: is the shift amount, in the range 1 to 31 (when <shift> = LSL or ROR) or 1 to 32 (when <shift> = LSR or ASR) encoded in the "imm5" field as <amount> modulo 32.
	For encoding T1: is the shift amount, in the range 0 to 3, defaulting to 0 and encoded in the "imm2" field.

Operation

if ConditionPassed() then EncodingSpecificOperations(); constant offset = Shift(R[m], shift_t, shift_n, PSTATE.C); constant address = if add then (R[n] + offset) else (R[n] - offset); Hint_PreloadInstr(address);

Internal version only: isa v01_32, pseudocode v2024-12_rel ; Build timestamp: 2024-12-16T10:54