PRFH (scalar plus vector)

Gather prefetch halfwords (scalar plus vector)

Gather prefetch of halfwords from the active memory addresses generated by a 64-bit scalar base plus vector index. The index values are optionally first sign or zero-extended from 32 to 64 bits and then multiplied by 2. Inactive addresses are not prefetched from memory.

The <prfop> symbol specifies the prefetch hint as a combination of three options: access type PLD for load or PST for store; target cache level L1, L2 or L3; temporality (KEEP for temporal or STRM for non-temporal).

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

Encoding: 32-bit scaled offset

Variants: FEAT_SVE (PROFILE_A)

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	0	0	0	0	1	0	0	0		1						0	0	1									0
									xs		Zm						msz		Pg			Rn						prfop

PRFH <prfop>, <Pg>, [<Xn|SP>, <Zm>.S, <mod> #1]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF);
constant integer esize = 32;
constant integer g = UInt(Pg);
constant integer n = UInt(Rn);
constant integer m = UInt(Zm);
constant integer level = UInt(prfop<2:1>);
constant boolean stream = (prfop<0> == '1');
constant PrefetchHint pref_hint = if prfop<3> == '0' then Prefetch_READ else Prefetch_WRITE;
constant integer offs_size = 32;
constant boolean offs_unsigned = (xs == '0');
constant integer scale = 1;

Encoding: 32-bit unpacked scaled offset

Variants: FEAT_SVE (PROFILE_A)

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	0	0	0	1	0	0	0		1						0	0	1									0
									xs		Zm						msz		Pg			Rn						prfop

PRFH <prfop>, <Pg>, [<Xn|SP>, <Zm>.D, <mod> #1]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF);
constant integer esize = 64;
constant integer g = UInt(Pg);
constant integer n = UInt(Rn);
constant integer m = UInt(Zm);
constant integer level = UInt(prfop<2:1>);
constant boolean stream = (prfop<0> == '1');
constant PrefetchHint pref_hint = if prfop<3> == '0' then Prefetch_READ else Prefetch_WRITE;
constant integer offs_size = 32;
constant boolean offs_unsigned = (xs == '0');
constant integer scale = 1;

Encoding: 64-bit scaled offset

Variants: FEAT_SVE (PROFILE_A)

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	0	0	0	1	0	0	0	1	1						1	0	1									0
											Zm						msz		Pg			Rn						prfop

PRFH <prfop>, <Pg>, [<Xn|SP>, <Zm>.D, LSL #1]

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF);
constant integer esize = 64;
constant integer g = UInt(Pg);
constant integer n = UInt(Rn);
constant integer m = UInt(Zm);
constant integer level = UInt(prfop<2:1>);
constant boolean stream = (prfop<0> == '1');
constant PrefetchHint pref_hint = if prfop<3> == '0' then Prefetch_READ else Prefetch_WRITE;
constant integer offs_size = 64;
constant boolean offs_unsigned = TRUE;
constant integer scale = 1;

Operation

CheckNonStreamingSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(PL) mask = P[g, PL];
bits(64) base;
bits(VL) offset;

if AnyActiveElement(mask, esize) then
    base = if n == 31 then SP[64] else X[n, 64];
    offset = Z[m, VL];

for e = 0 to elements-1
    if ActivePredicateElement(mask, e, esize) then
        constant integer off = Int(Elem[offset, e, esize], offs_unsigned);
        constant bits(64) addr = base + (off << scale);
        Hint_Prefetch(addr, pref_hint, level, stream);

Explanations

<prfop>: <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.
<Zm>: Is the name of the offset scalable vector register, encoded in the "Zm" field.
<mod>: