Gather load first-fault unsigned words to vector (vector index)
This instruction performs a gather load with first-faulting behavior of unsigned words 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 first sign-extended or zero-extended from 32 to 64 bits and then optionally multiplied by 4. 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.
It has encodings from 6 classes: 32-bit scaled offset , 32-bit unpacked scaled offset , 32-bit unpacked unscaled offset , 32-bit unscaled offset , 64-bit scaled offset and 64-bit unscaled offset
| 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 | 1 | 0 | xs | 1 | Zm | 0 | 1 | 1 | Pg | Rn | Zt | ||||||||||||||
| U | ff | ||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let t : integer = UInt(Zt); let n : integer = UInt(Rn); let m : integer = UInt(Zm); let g : integer = UInt(Pg); let esize : integer{} = 32; let msize : integer{} = 32; let offs_size : integer{} = 32; let unsigned : boolean = TRUE; let offs_unsigned : boolean = xs == '0'; let scale : integer = 2;
| 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 | 1 | 0 | xs | 1 | Zm | 0 | 1 | 1 | Pg | Rn | Zt | ||||||||||||||
| opc | U | ff | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let t : integer = UInt(Zt); let n : integer = UInt(Rn); let m : integer = UInt(Zm); let g : integer = UInt(Pg); let esize : integer{} = 64; let msize : integer{} = 32; let offs_size : integer{} = 32; let unsigned : boolean = TRUE; let offs_unsigned : boolean = xs == '0'; let scale : integer = 2;
| 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 | 1 | 0 | xs | 0 | Zm | 0 | 1 | 1 | Pg | Rn | Zt | ||||||||||||||
| msz | U | ff | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let t : integer = UInt(Zt); let n : integer = UInt(Rn); let m : integer = UInt(Zm); let g : integer = UInt(Pg); let esize : integer{} = 64; let msize : integer{} = 32; let offs_size : integer{} = 32; let unsigned : boolean = TRUE; let offs_unsigned : boolean = xs == '0'; let scale : integer = 0;
| 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 | 1 | 0 | xs | 0 | Zm | 0 | 1 | 1 | Pg | Rn | Zt | ||||||||||||||
| opc | U | ff | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let t : integer = UInt(Zt); let n : integer = UInt(Rn); let m : integer = UInt(Zm); let g : integer = UInt(Pg); let esize : integer{} = 32; let msize : integer{} = 32; let offs_size : integer{} = 32; let unsigned : boolean = TRUE; let offs_unsigned : boolean = xs == '0'; let scale : integer = 0;
| 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 | 1 | 0 | 1 | 1 | Zm | 1 | 1 | 1 | Pg | Rn | Zt | ||||||||||||||
| opc | U | ff | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let t : integer = UInt(Zt); let n : integer = UInt(Rn); let m : integer = UInt(Zm); let g : integer = UInt(Pg); let esize : integer{} = 64; let msize : integer{} = 32; let offs_size : integer{} = 64; let unsigned : boolean = TRUE; let offs_unsigned : boolean = TRUE; let scale : integer = 2;
| 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 | 1 | 0 | 1 | 0 | Zm | 1 | 1 | 1 | Pg | Rn | Zt | ||||||||||||||
| msz | U | ff | |||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let t : integer = UInt(Zt); let n : integer = UInt(Rn); let m : integer = UInt(Zm); let g : integer = UInt(Pg); let esize : integer{} = 64; let msize : integer{} = 32; let offs_size : integer{} = 64; let unsigned : boolean = TRUE; let offs_unsigned : boolean = TRUE; let scale : integer = 0;
| <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
|
CheckNonStreamingSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let elements : integer = VL DIV esize; let mask : bits(PL) = P{}(g); var base : bits(64); var offset : bits(VL); var result : bits(VL); let orig : bits(VL) = Z{}(t); var data : bits(msize); let mbytes : integer{} = msize DIV 8; var fault : boolean = FALSE; var faulted : boolean = FALSE; var unknown : boolean = FALSE; let contiguous : boolean = FALSE; let tagchecked : boolean = TRUE; var accdesc : AccessDescriptor = CreateAccDescSVEFF(contiguous, tagchecked); if !AnyActiveElement{PL}(mask, esize) then if n == 31 && ConstrainUnpredictableBool(Unpredictable_CHECKSPNONEACTIVE) then CheckSPAlignment(); end; else if n == 31 then CheckSPAlignment(); end; base = if n == 31 then SP{64}() else X{64}(n); offset = Z{VL}(m); end; assert accdesc.first; for e = 0 to elements-1 do if ActivePredicateElement{PL}(mask, e, esize) then let offselt : bits(offs_size) = offset[e*:esize][offs_size-1:0]; let off : integer = if offs_unsigned then UInt(offselt) else SInt(offselt); let addr : bits(64) = 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{msize}(addr, accdesc); accdesc.first = FALSE; else // MemNF[] will return fault=TRUE if access is not performed for any reason (data, fault) = MemNF{msize}(addr, accdesc); faulted = faulted || ConstrainUnpredictableBool(Unpredictable_NONFAULT); end; else (data, fault) = (Zeros{msize}, FALSE); end; // FFR elements set to FALSE following a suppressed access/fault faulted = faulted || fault; if faulted then ElemFFR(e, esize) = '0'; end; // 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 result[e*:esize] = Extend{esize}(data, unsigned); elsif ConstrainUnpredictableBool(Unpredictable_SVELDNFZERO) then result[e*:esize] = Zeros{esize}; else // merge result[e*:esize] = orig[e*:esize]; end; else result[e*:esize] = Extend{esize}(data, unsigned); end; end; Z{VL}(t) = result;
2026-03_rel 2026-03-26 20:48:11
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