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VLUXEI64.V

RISC-V VLUXEI64.V Instruction Details

Instruction ManualV-type

Use x[rs1] plus 64-bit unsigned byte offsets from vs2 for unordered indexed loads.

Instruction Syntax

vluxei64.v vd, (rs1), vs2, vm
Operand Breakdown
vd: destination vector register group receiving loaded active elements.
rs1: integer base-address register; unit-stride forms read elements from consecutive addresses.
vm: when present, vm=0 uses v0 as the execution mask and vm=1 is unmasked.
VVector MemoryIndexed Vector Load
Related Search Terms
VLUXEI64.V instructionRISC-V VLUXEI64.Vvluxei64.v syntaxvluxei64.v encodingRVV indexed loadei64 indexunordered indexed load

Instruction Behavior

VLUXEI64.V is a RISC-V V-extension unordered indexed vector load instruction. Each active element forms its address as x[rs1] + zero_extend(vs2[i]); ei64 is the index EEW, so the index is an unsigned byte offset, not an element number. The unordered form does not guarantee observation in element-number order. With vm=0, elements disabled by v0.t do not access memory.

VLUXEI64.V Decode And Execute Animation

Decode the 64-bit indexed load, then compute each element address as x[rs1] + zero_extend(vs2[i]).

Instruction input
vluxei64.v
Execution context: index EEW=64, data SEW=32, address=x[rs1]+zero_extend(vs2[i]), unordered indexed accesses do not guarantee element order, LMUL=m1. These are not assembly syntax operands.
Encoding fieldsvluxei64.v / LOAD-FP
31..29
nf
000
28
mew
0
27..26
mop
01
25
vm
0
24..20
vs2
00100
19..15
rs1
01010
14..12
width
111
11..7
vd/vs3
01000
6..0
opcode
0000111
Address and data pathaddr[i] = 0x8000 + vs2[i]
i=0
i=1
i=2
i=3
i=4
i=5
i=6
i=7
i=8
i=9
i=10
i=11
i=12
i=13
i=14
i=15
vs2 byte offset
0x0000000000000000
0x000000000000000c
0x0000000000000018
0x0000000000000018
0x0000000000000024
0x0000000000000030
0x0000000000000030
0x000000000000003c
0x0000000000000048
0x0000000000000048
0x0000000000000054
0x0000000000000060
0x0000000000000060
0x000000000000006c
0x0000000000000078
0x0000000000000078
addr
0x8000
0x800c
0x8018
0x8018
0x8024
0x8030
0x8030
0x803c
0x8048
0x8048
0x8054
0x8060
0x8060
0x806c
0x8078
0x8078
mem
0x00000101
0x00000202
0x00000303
0x00000404
0x00000505
0x00000606
0x00000707
0x00000808
0x00000909
0x00000a0a
0x00000b0b
0x00000c0c
0x00000d0d
0x00000e0e
0x00000f0f
0x00001010
active
1
1
0
1
1
1
1
0
1
1
1
1
0
1
1
1
v8
...
...
-
...
...
...
...
-
...
...
...
...
-
...
...
...
Step 1 / 22

Show vector memory instruction encoding

The animation starts from the 32-bit vector memory encoding and shows the official bit fields: nf, mew, mop, vm, rs2/vs2 or lumop/sumop, width, register fields, and opcode.

Quick Understanding & Search Notes

VLUXEI64.V uses vs2 as byte offsets, not element numbers; the unordered form must not be used when element access order is required.

Index EEW=64; loaded data elements use the current SEW, and register-group use is constrained by data SEW/LMUL together with index EEW.
Unordered indexed loads allow accesses to be observed out of element order; offsets are unsigned byte offsets.
vm=0 uses v0 as the execution mask and vm=1 is unmasked; inactive and tail elements follow the current vma/vta policy.
RISC-V Unprivileged ISA Manual: V Standard Extension for Vector Operations

Vector Execution Context

When reading VLUXEI64.V, do not stop at the mnemonic. Official V-extension semantics also depend on the current vl, vtype, and mask state. The suffix and operand form determine whether sources are vector, scalar, or immediate values.

Check vl first

The current vl determines the number of body elements. Typical code executes vsetvli, vsetivli, or vsetvl before this instruction.

Then check vtype

The current vtype supplies SEW, LMUL, tail policy, and mask policy; these affect element width, register-group size, and inactive/tail destination elements.

Then check vm/v0

For ordinary vector instructions with vm, vm=0 uses v0 as the execution mask and vm=1 is unmasked. A few forms such as VMERGE use v0 as data-selection input.

Official source: RISC-V V Standard Extension for Vector Operations

Common Usage Scenarios

Sparse data reads

Understand this scenario with real code like «vsetvli t0, a0, e32, m1, ta, ma vluxei64.v v1, (a0), v2».

Gather access without ordering needs

Understand this scenario with real code like «vsetvli t0, a0, e32, m1, ta, ma vluxei64.v v1, (a0), v2».

Indirect array loads

Understand this scenario with real code like «vsetvli t0, a0, e32, m1, ta, ma vluxei64.v v1, (a0), v2».

Pre-Use Checklist

Syntax Check
  • Confirm the current instruction format is V-type.
  • Confirm the operand order matches the example.
Semantic Check
  • Ensure the destination register usage is compatible with the calling convention.
  • Confirm this is not the lower-level form of a pseudo-instruction expansion.

Pitfalls / Common Confusions

ei64 is the index EEW, not the SEW of the loaded data; data element width still comes from current vtype.
vs2[i] is an unsigned byte offset; the address is x[rs1] + zero_extend(vs2[i]), not x[rs1] + i * EEW and not an element number.
Unordered indexed loads do not guarantee element access order; use the ordered indexed form when an address space requires element order.
With vm=0, elements disabled by v0.t perform no memory read and must not be shown as writing zero.

FAQ

What unit is used for VLUXEI64.V address offsets?

Indexed-load vs2 elements are unsigned byte offsets.

How does VLUXEI64.V handle masking?

With vm=0, v0 selects active elements; with vm=1, all body elements participate. Inactive and tail elements follow the current policies.