Arm® A64 Instruction Set Architecture: Armv8, for Armv8-A architecture profile

RDFFR, RDFFRS (predicated)

Return predicate of succesfully loaded elements.

Read the first-fault register (FFR) and place active elements in the corresponding elements of the destination predicate. Inactive elements in the destination predicate register are set to zero. Optionally sets the First (N), None (Z), !Last (C) condition flags based on the predicate result, and the V flag to zero.

It has encodings from 2 classes: Not setting the condition flags and Setting the condition flags

Not setting the condition flags

if !HaveSVE() then UNDEFINED;
integer g = UInt(Pg);
integer d = UInt(Pd);
boolean setflags = FALSE;

Setting the condition flags

if !HaveSVE() then UNDEFINED;
integer g = UInt(Pg);
integer d = UInt(Pd);
boolean setflags = TRUE;

Assembler Symbols

CheckSVEEnabled();
bits(PL) mask = P[g];
bits(PL) ffr = FFR[];
bits(PL) result = ffr AND mask;

if setflags then
    PSTATE.<N,Z,C,V> = PredTest(mask, result, 8);
P[d] = result;