Loong64 extension: invalid LSX arrangement type: {ext}

Error message

Loong64 extension: invalid LSX arrangement type: {ext}

What it means

Thrown by Loong64RegisterExtension in the non-index (arrangement) branch when simdType is LSX (register is V0-V31) and `ext` is not a key in loong64LsxArngExtMap. LSX arrangement suffixes are restricted to B16, H8, W4, and V2, which describe a 128-bit LSX vector's lane layout.

Source

Thrown at src/cmd/asm/internal/arch/loong64.go:109

	}

	if isIndex {
		arngType, ok = loong64ElemExtMap[ext]
		if !ok {
			return errors.New("Loong64 extension: invalid LSX/LASX arrangement type: " + ext)
		}

		a.Reg = loong64.REG_ELEM
		a.Reg += ((simdReg & loong64.EXT_REG_MASK) << loong64.EXT_REG_SHIFT)
		a.Reg += ((arngType & loong64.EXT_TYPE_MASK) << loong64.EXT_TYPE_SHIFT)
		a.Reg += ((simdType & loong64.EXT_SIMDTYPE_MASK) << loong64.EXT_SIMDTYPE_SHIFT)
		a.Index = num
	} else {
		switch simdType {
		case loong64.LSX:
			arngType, ok = loong64LsxArngExtMap[ext]
			if !ok {
				return errors.New("Loong64 extension: invalid LSX arrangement type: " + ext)
			}

		case loong64.LASX:
			arngType, ok = loong64LasxArngExtMap[ext]
			if !ok {
				return errors.New("Loong64 extension: invalid LASX arrangement type: " + ext)
			}
		}

		a.Reg = loong64.REG_ARNG
		a.Reg += ((simdReg & loong64.EXT_REG_MASK) << loong64.EXT_REG_SHIFT)
		a.Reg += ((arngType & loong64.EXT_TYPE_MASK) << loong64.EXT_TYPE_SHIFT)
		a.Reg += ((simdType & loong64.EXT_SIMDTYPE_MASK) << loong64.EXT_SIMDTYPE_SHIFT)
	}

	return nil
}

View on GitHub (pinned to b6b368adc5)

Solutions

Use one of the LSX arrangements: B16, H8, W4, or V2.
If you need a wider arrangement, switch the register to an LASX X-register (X0-X31) so the LASX map applies.
Verify the intended lane width and count against the 128-bit LSX register size (16 bytes total).

Example fix

// before (LASX suffix on LSX register)
VADD V0.B32, V1, V2
// after (correct LSX arrangement)
VADD V0.B16, V1, V2

Defensive patterns

Strategy: validation

Validate before calling

var validLsxArng = map[string]bool{"B16":true,"H8":true,"W4":true,"V2":true}
func isValidLsxArrangement(ext string) bool { return validLsxArng[ext] }

Type guard

func isLsxArrangement(ext string) bool {
    switch ext { case "B16","H8","W4","V2": return true }
    return false
}

Prevention

Remember LSX is 128-bit: B16/H8/W4/V2 are the only valid full-vector arrangements.
Do not reuse LASX (256-bit) suffixes on V-registers.
Validate generated assembly against the arrangement maps in loong64.go before emitting.

When it happens

Trigger: Calling Loong64RegisterExtension with isIndex==false, a V-register (LSX), and an arrangement suffix not equal to B16/H8/W4/V2. In assembly this is an operand like `V0.B8` or `V0.H4` where the suffix does not match a 128-bit LSX arrangement.

Common situations: Copying an LASX (256-bit) arrangement suffix (B32, H16, W8, V4, Q2) onto an LSX V-register; using ARM NEON-style suffixes (8B, 4H) directly; typos in the lane count.

Related errors

AI-assisted analysis of golang/go@b6b368adc5 (2026-08-12). Data as JSON: /api/errors/b881eadc7ae2ee3d. Report an issue: GitHub.