LDFF1B (scalar plus vector)

Gather load with first-faulting behavior of unsigned bytes to active elements of a vector register from memory addresses generated by a 64-bit scalar base plus vector index. The index values are optionally sign or zero-extended from 32 to 64 bits. Inactive elements will not cause a read from Device memory or signal faults, and are set to zero in the destination vector.

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

32-bit unpacked unscaled offset

if !IsFeatureImplemented(FEAT_SVE) then UNDEFINED; constant integer t = UInt(Zt); constant integer n = UInt(Rn); constant integer m = UInt(Zm); constant integer g = UInt(Pg); constant integer esize = 64; constant integer msize = 8; constant integer offs_size = 32; constant boolean unsigned = TRUE; constant boolean offs_unsigned = xs == '0'; constant integer scale = 0;

32-bit unscaled offset

if !IsFeatureImplemented(FEAT_SVE) then UNDEFINED; constant integer t = UInt(Zt); constant integer n = UInt(Rn); constant integer m = UInt(Zm); constant integer g = UInt(Pg); constant integer esize = 32; constant integer msize = 8; constant integer offs_size = 32; constant boolean unsigned = TRUE; constant boolean offs_unsigned = xs == '0'; constant integer scale = 0;

64-bit unscaled offset

if !IsFeatureImplemented(FEAT_SVE) then UNDEFINED; constant integer t = UInt(Zt); constant integer n = UInt(Rn); constant integer m = UInt(Zm); constant integer g = UInt(Pg); constant integer esize = 64; constant integer msize = 8; constant integer offs_size = 64; constant boolean unsigned = TRUE; constant boolean offs_unsigned = TRUE; constant integer scale = 0;

Assembler Symbols

<Zt>	Is the name of the scalable vector register to be transferred, encoded in the "Zt" field.

<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>

Is the index extend and shift specifier, encoded in xs:

xs	<mod>
0	UXTW
1	SXTW

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; bits(VL) result; constant bits(VL) orig = Z[t, VL]; bits(msize) data; constant integer mbytes = msize DIV 8; boolean fault = FALSE; boolean faulted = FALSE; boolean unknown = FALSE; constant boolean contiguous = FALSE; constant boolean tagchecked = TRUE; AccessDescriptor accdesc = CreateAccDescSVEFF(contiguous, tagchecked); if !AnyActiveElement(mask, esize) then if n == 31 && ConstrainUnpredictableBool(Unpredictable_CHECKSPNONEACTIVE) then CheckSPAlignment(); else if n == 31 then CheckSPAlignment(); base = if n == 31 then SP[] else X[n, 64]; offset = Z[m, VL]; assert accdesc.first; for e = 0 to elements-1 if ActivePredicateElement(mask, e, esize) then constant integer off = Int(Elem[offset, e, esize]<offs_size-1:0>, offs_unsigned); constant bits(64) addr = AddressAdd(base, off << scale, accdesc); if accdesc.first then // Mem[] will not return if a fault is detected for the first active element data = Mem[addr, mbytes, accdesc]; accdesc.first = FALSE; else // MemNF[] will return fault=TRUE if access is not performed for any reason (data, fault) = MemNF[addr, mbytes, accdesc]; else (data, fault) = (Zeros(msize), FALSE); // FFR elements set to FALSE following a suppressed access/fault faulted = faulted || fault; if faulted then ElemFFR[e, esize] = '0'; // Value becomes CONSTRAINED UNPREDICTABLE after an FFR element is FALSE unknown = unknown || ElemFFR[e, esize] == '0'; if unknown then if !fault && ConstrainUnpredictableBool(Unpredictable_SVELDNFDATA) then Elem[result, e, esize] = Extend(data, esize, unsigned); elsif ConstrainUnpredictableBool(Unpredictable_SVELDNFZERO) then Elem[result, e, esize] = Zeros(esize); else // merge Elem[result, e, esize] = Elem[orig, e, esize]; else Elem[result, e, esize] = Extend(data, esize, unsigned); Z[t, VL] = result;

Internal version only: aarchmrs v2024-03_relA, pseudocode v2024-03_rel, sve v2024-03_rel ; Build timestamp: 2024-03-26T09:45

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	xs	0	Zm					0	1	1	Pg			Rn					Zt
							msz<1>	msz<0>									U	ff

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	xs	0	Zm					0	1	1	Pg			Rn					Zt
																	U	ff

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	Zm					1	1	1	Pg			Rn					Zt
							msz<1>	msz<0>									U	ff