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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

313029282726252423222120191817161514131211109876543210
00100101000110001111000Pg0Pd
S

RDFFR <Pd>.B, <Pg>/Z

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

Setting the condition flags

313029282726252423222120191817161514131211109876543210
00100101010110001111000Pg0Pd
S

RDFFRS <Pd>.B, <Pg>/Z

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

Assembler Symbols

<Pd>

Is the name of the destination scalable predicate register, encoded in the "Pd" field.

<Pg>

Is the name of the governing scalable predicate register, encoded in the "Pg" field.

Operation

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;

Operational information

If PSTATE.DIT is 1:

  • The execution time of this instruction is independent of:
    • The values of the data supplied in any of its operand registers when its governing predicate register contains the same value for each execution.
    • The values of the NZCV flags.
  • The response of this instruction to asynchronous exceptions does not vary based on:
    • The values of the data supplied in any of its operand registers when its governing predicate register contains the same value for each execution.
    • The values of the NZCV flags.