Write the first-fault register
This instruction reads the source predicate register, and writes the value in the register to the first-fault register (FFR). This instruction is intended to restore a saved FFR and is not recommended for general use by applications.
This instruction requires that the source predicate contains a monotonic predicate value, in which starting from bit 0 there are zero or more 1 bits, followed only by 0 bits in any remaining bit positions. If the source is not a monotonic predicate value, then the resulting value in the FFR will be UNPREDICTABLE. It is not possible to generate a non-monotonic value in FFR when using SETFFR followed by first-fault or non-fault loads.
This instruction is illegal when executed in Streaming SVE mode, unless FEAT_SME_FA64 is implemented and enabled.
| 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 |
| 0 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | Pn | 0 | 0 | 0 | 0 | 0 | |||
| opc | |||||||||||||||||||||||||||||||
if !IsFeatureImplemented(FEAT_SVE) then EndOfDecode(Decode_UNDEF); end; let n : integer = UInt(Pn);
CheckNonStreamingSVEEnabled(); let VL : integer{} = CurrentVL(); let PL : integer{} = VL DIV 8; let operand : bits(PL) = P{}(n); let hsb : integer{} = HighestSetBit(operand); if hsb < 0 || IsOnes(operand[hsb:0]) then FFR{PL}() = operand; else // not a monotonic predicate FFR{PL}() = ARBITRARY : bits(PL); end;
2025-12_rel 2025-12-10 16:41:45
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