Are VRGATHER.VX indices byte offsets?
No. VRGATHER indices select source-vector elements; byte offsets belong to indexed load/store instructions.
VRGATHER.VX
RISC-V VRGATHER.VX Instruction Details
Instruction ManualR-typeGather source-vector elements by index.
Instruction Syntax
vrgather.vx vd, vs2, rs1, 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 PermutationGather
Related Search Terms
Instruction Behavior
VRGATHER.VX uses indices from rs1 to select elements from vs2 into vd; an index outside VLMAX produces a zero result element.
Quick Understanding & Search Notes
VRGATHER.VX handles index-based rearrangement of vector elements, with source data coming from vs2.
The index selects an element of vs2; it is not a memory address.
An index outside VLMAX writes zero to the destination element.
VI/VX/VV forms take indices from an immediate, scalar register, or vector elements respectively.
Common Usage Scenarios
Table Lookup
Understand this scenario with real code like «vrgather.vx v8, v12, x5, v0.t».
Reorder
Understand this scenario with real code like «vrgather.vx v8, v12, x5, v0.t».
Compress/Decompress
Understand this scenario with real code like «vrgather.vx v8, v12, x5, v0.t».
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
OOB (>=VLMAX) returns 0, no exception
Dest cannot overlap source
SEW=8 vrgather.vv only 0-255; vrgatherei16→64K