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LDP

Load Pair of Registers calculates an address from a base register value and an immediate offset, loads two 32-bit words or two 64-bit doublewords from memory, and writes them to two registers. For information about memory accesses, see Load/Store addressing modes.

It has encodings from 3 classes: Post-index , Pre-index and Signed offset

Post-index

313029282726252423222120191817161514131211109876543210
x010100011imm7Rt2RnRt
opcL

32-bit (opc == 00)

LDP <Wt1>, <Wt2>, [<Xn|SP>], #<imm>

64-bit (opc == 10)

LDP <Xt1>, <Xt2>, [<Xn|SP>], #<imm>

boolean wback = TRUE;
boolean postindex = TRUE;

Pre-index

313029282726252423222120191817161514131211109876543210
x010100111imm7Rt2RnRt
opcL

32-bit (opc == 00)

LDP <Wt1>, <Wt2>, [<Xn|SP>, #<imm>]!

64-bit (opc == 10)

LDP <Xt1>, <Xt2>, [<Xn|SP>, #<imm>]!

boolean wback = TRUE;
boolean postindex = FALSE;

Signed offset

313029282726252423222120191817161514131211109876543210
x010100101imm7Rt2RnRt
opcL

32-bit (opc == 00)

LDP <Wt1>, <Wt2>, [<Xn|SP>{, #<imm>}]

64-bit (opc == 10)

LDP <Xt1>, <Xt2>, [<Xn|SP>{, #<imm>}]

boolean wback = FALSE;
boolean postindex = FALSE;

For information about the constrained unpredictable behavior of this instruction, see Architectural Constraints on UNPREDICTABLE behaviors, and particularly LDP.

Assembler Symbols

<Wt1>

Is the 32-bit name of the first general-purpose register to be transferred, encoded in the "Rt" field.

<Wt2>

Is the 32-bit name of the second general-purpose register to be transferred, encoded in the "Rt2" field.

<Xt1>

Is the 64-bit name of the first general-purpose register to be transferred, encoded in the "Rt" field.

<Xt2>

Is the 64-bit name of the second general-purpose register to be transferred, encoded in the "Rt2" field.

<Xn|SP>

Is the 64-bit name of the general-purpose base register or stack pointer, encoded in the "Rn" field.

<imm>

For the 32-bit post-index and 32-bit pre-index variant: is the signed immediate byte offset, a multiple of 4 in the range -256 to 252, encoded in the "imm7" field as <imm>/4.

For the 32-bit signed offset variant: is the optional signed immediate byte offset, a multiple of 4 in the range -256 to 252, defaulting to 0 and encoded in the "imm7" field as <imm>/4.

For the 64-bit post-index and 64-bit pre-index variant: is the signed immediate byte offset, a multiple of 8 in the range -512 to 504, encoded in the "imm7" field as <imm>/8.

For the 64-bit signed offset variant: is the optional signed immediate byte offset, a multiple of 8 in the range -512 to 504, defaulting to 0 and encoded in the "imm7" field as <imm>/8.

Shared Decode

integer n = UInt(Rn);
integer t = UInt(Rt);
integer t2 = UInt(Rt2);
if L:opc<0> == '01' || opc == '11' then UNDEFINED;
boolean signed = (opc<0> != '0');
integer scale = 2 + UInt(opc<1>);
integer datasize = 8 << scale;
bits(64) offset = LSL(SignExtend(imm7, 64), scale);
boolean tag_checked = wback || n != 31;

Operation

bits(64) address;
bits(datasize) data1;
bits(datasize) data2;
constant integer dbytes = datasize DIV 8;
boolean rt_unknown = FALSE;

if HaveMTEExt() then
    SetNotTagCheckedInstruction(!tag_checked);

boolean wb_unknown = FALSE;

if wback && (t == n || t2 == n) && n != 31 then
    Constraint c = ConstrainUnpredictable(Unpredictable_WBOVERLAPLD);
    assert c IN {Constraint_WBSUPPRESS, Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP};
    case c of
        when Constraint_WBSUPPRESS wback = FALSE;    // writeback is suppressed
        when Constraint_UNKNOWN    wb_unknown = TRUE;    // writeback is UNKNOWN
        when Constraint_UNDEF      UNDEFINED;
        when Constraint_NOP        EndOfInstruction();

if t == t2 then
    Constraint c = ConstrainUnpredictable(Unpredictable_LDPOVERLAP);
    assert c IN {Constraint_UNKNOWN, Constraint_UNDEF, Constraint_NOP};
    case c of
        when Constraint_UNKNOWN rt_unknown = TRUE;    // result is UNKNOWN
        when Constraint_UNDEF   UNDEFINED;
        when Constraint_NOP     EndOfInstruction();

if n == 31 then
    CheckSPAlignment();
    address = SP[];
else
    address = X[n];

if !postindex then
    address = address + offset;

data1 = Mem[address, dbytes, AccType_NORMAL];
data2 = Mem[address+dbytes, dbytes, AccType_NORMAL];
if rt_unknown then
    data1 = bits(datasize) UNKNOWN;
    data2 = bits(datasize) UNKNOWN;
if signed then
    X[t] = SignExtend(data1, 64);
    X[t2] = SignExtend(data2, 64);
else
    X[t] = data1;
    X[t2] = data2;

if wback then
    if wb_unknown then
        address = bits(64) UNKNOWN;
    elsif postindex then
        address = address + offset;
    if n == 31 then
        SP[] = address;
    else
        X[n] = address;

Operational information

If PSTATE.DIT is 1, the timing of this instruction is insensitive to the value of the data being loaded or stored.

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