Check vl first
The current vl determines the number of body elements. Typical code executes vsetvli, vsetivli, or vsetvl before this instruction.
VSLL.VX
RISC-V VSLL.VX Instruction Details
Instruction ManualR-typeElement-wise logical left shift.
Instruction Syntax
vsll.vx vd, vs2, rs1, vm
Operand Breakdown
vd: destination vector register group.
vs2/vs1 or scalar source: selected by suffixes such as .vv, .vx, .vi, or .vf.
vm: when present, vm=0 uses v0 as the execution mask and vm=1 is unmasked.
VVector Operations
Instruction Behavior
VSLL.VX performs RVV single-width integer logical left shift. Each active element reads vs2[i], takes the shift amount from x[rs1], uses only the low bits selected by SEW as specified by the V extension, and writes the result to vd. With vm=0, v0.t selects which body elements participate in this shift.
VSLL.VX Decode And Execute Animation
Starts from OP-V encoding fields, then shows how VSLL takes the low shift-count bits, shifts active elements left, and writes the low SEW result.
Instruction input
vsll.vx
OP-V encodingvsll.vx
funct6
100101
vm
0
vs2
01000
rs1
01011
funct3
100
vd
00100
opcode
1010111
lane
0
1
2
3
4
5
6
7
v8
0x00fa
0x010b
0x011c
0x012d
0x013e
0x014f
0x0160
0x0171
<<
<<
<<
<<
<<
<<
<<
<<
x11
0x0013
0x0013
0x0013
0x0013
0x0013
0x0013
0x0013
0x0013
v0.t
1
0
1
1
1
0
1
1
v4
...
-
...
...
...
-
...
...
Current step
Show OP-V 32-bit encoding fields
vsll.vx uses OP-V encoding. The animation places fixed fields, register fields, vm, and the rs1 field in one encoding strip.
This animation shows only ISA-visible relationships from the official V extension: OP-V field decode, active-element reads, SEW-width integer logical left shift, mask control, and vd writeback. It does not model pipelines, caches, or timing.
Quick Understanding & Search Notes
VSLL.VX applies logical left shift lane by lane to active elements within the current vl. The full shift source is not used as a count directly; the count uses only the low log2(SEW) bits, and mask-off or tail elements follow the current vtype policies.
VSLL uses OP-V vector-arithmetic encoding with funct6=100101; the .vx form is selected by funct3=100.
The VX form takes the shift-count source from integer register x[rs1]. The actual count uses only the low log2(SEW) bits.
VSLL.VX shifts left and fills low bits with zero; it keeps the low SEW bits. Ordinary VSLL/VSRL/VSRA do not use vxrm rounding and do not set vxsat.
vm=0 uses the v0 mask and vm=1 is unmasked; mask-off body elements and tail elements follow the current mask/tail policy.
Vector Execution Context
When reading VSLL.VX, do not stop at the mnemonic. Official V-extension semantics also depend on the current vl, vtype, and mask state. .vx: one vector source and one integer scalar source participate.
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.
Common Usage Scenarios
Bit Operations & Masks
Understand this scenario with real code like «vsll.vx v8, v12, x5, v0.t».
Vector Operations
Understand this scenario with real code like «vsll.vx v8, v12, x5, v0.t».
Power-of-2 Multiply
Understand this scenario with real code like «vsll.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
Do not treat the full VSLL.VX shift source as the shift count; the actual count uses only the low bits specified by SEW.
VSLL.VX is an ordinary integer shift; it does not use vxrm rounding and does not set vxsat because bits were shifted out.
A mask-off body element is not a deterministic zero write; the destination element follows the current mask policy.
FAQ
Can the VSLL.VX shift count exceed SEW?
The encoded or source value can be wider, but ordinary RVV shifts use only the low log2(SEW) bits selected by SEW as the actual shift count.
How is VSLL.VX different from nearby shift instructions?
VSLL shifts left and fills low bits with zero; VSRL shifts right logically and fills high bits with zero; VSRA shifts right arithmetically and copies the signed element sign bit.