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VID.V

RISC-V VID.V Instruction Details

Instruction ManualR-type

Write each active element index i to destination integer vector vd.

Instruction Syntax

vid.v vd, vm
Operand Breakdown
Destination rd: register receiving the operation result.
Source rs1: register holding the first operand.
Source rs2: register holding the second operand.
VVector PermutationPermutation
Related Search Terms
VID.V instructionRISC-V VID.Vvid.v syntaxvid.v RVVelement indexRVV mask

Instruction Behavior

VID.V is a RISC-V V element-index generation instruction. For each active element i, it writes the unsigned index value i to vd, starting at 0 and bounded by the current vl.

Quick Understanding & Search Notes

VID.V generates element numbers; it does not read memory or an ordinary source vector.

Index values are generated from current element numbers and written to SEW-width destination elements.
vm=0 uses v0 as the execution mask and vm=1 is unmasked; inactive and tail elements follow the current vma/vta policy.
Often combined with mask comparisons, compression, or indexed memory access.
RISC-V Unprivileged ISA Manual: V Standard Extension for Vector Operations

Common Usage Scenarios

Sequence Gen

Understand this scenario with real code like «vsetvli t0, a0, e32, m1, ta, ma vid.v v1 # v1[i] = i».

Loop Counter

Understand this scenario with real code like «vsetvli t0, a0, e32, m1, ta, ma vid.v v1 # v1[i] = i».

Gather Index

Understand this scenario with real code like «vsetvli t0, a0, e32, m1, ta, ma vid.v v1 # v1[i] = i».

Pre-Use Checklist

Syntax Check
  • Confirm the current instruction format is R-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

vid.v outputs 0,1,2,... (element position) — not byte offset in register.
vs2 operand is ignored but must be specified. Masked-off positions not written (or agnostically overwritten).

FAQ

How does VID.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.