WHILEWR

While free of write-after-read/write conflicts

This instruction checks two addresses for a conflict or overlap between address ranges of the form [addr,addr+VL÷8), where VL is the accessible vector length in bits, that could result in a loop-carried dependency through memory due to the use of these addresses by contiguous load and store instructions within the same iteration of a loop. Generate a predicate whose elements are true while the addresses cannot conflict within the same iteration, and false thereafter. Sets the First (N), None (Z), !Last (C) condition flags based on the predicate result, and the V flag to zero.

Encoding: SVE2

Variants: FEAT_SVE2 || FEAT_SME (FEAT_SVE2 || FEAT_SME)

313029282726252423222120191817161514131211109876543210
0010010110011000
sizeRmRnrwPd

WHILEWR <Pd>.<T>, <Xn>, <Xm>

Decoding algorithm

if !IsFeatureImplemented(FEAT_SVE2) && !IsFeatureImplemented(FEAT_SME) then
    EndOfDecode(Decode_UNDEF);
constant integer esize = 8 << UInt(size);
constant integer n = UInt(Rn);
constant integer m = UInt(Rm);
constant integer d = UInt(Pd);

Operation

CheckSVEEnabled();
constant integer VL = CurrentVL;
constant integer PL = VL DIV 8;
constant integer elements = VL DIV esize;
constant bits(PL) mask = Ones(PL);
constant bits(64) src1 = X[n, 64];
constant bits(64) src2 = X[m, 64];
constant integer operand1 = UInt(src1);
constant integer operand2 = UInt(src2);
bits(PL) result;
constant integer psize = esize DIV 8;

constant integer diff = (operand2 - operand1) DIV (esize DIV 8);
for e = 0 to elements-1
    if diff <= 0 || e < diff then
        Elem[result, e, psize] = ZeroExtend('1', psize);
    else
        Elem[result, e, psize] = ZeroExtend('0', psize);

PSTATE. = PredTest(mask, result, esize);
P[d, PL] = result;

Explanations

<Pd>: Is the name of the destination scalable predicate register, encoded in the "Pd" field.
<T>: <Xn>: Is the 64-bit name of the first source general-purpose register, encoded in the "Rn" field.
<Xm>: Is the 64-bit name of the second source general-purpose register, encoded in the "Rm" field.