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Write the first-fault register.

Read the source predicate register and place in 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.




if !HaveSVE() then UNDEFINED;
integer n = UInt(Pn);

Assembler Symbols


Is the name of the source scalable predicate register, encoded in the "Pn" field.


bits(PL) operand = P[n];

hsb = HighestSetBit(operand);
if hsb < 0 || IsOnes(operand<hsb:0>) then  
    FFR[] = operand;
else // not a monotonic predicate
    FFR[] = bits(PL) UNKNOWN;