gep

type Index struct {
	// HasVal specifies whether Val has a valid value. If index is a constant
	// integer or a constant integer vector of which all elements have the same
	// value, then HasVal is set. Note, this is a requirement to index into
	// structure types.
	HasVal bool
	// Index integer value. Val is only valid if HasVal is set.
	Val int64
	// Length of index vector; or 0 if index is scalar. VectorLen may be non-zero
	// even if HasVal is false.
	VectorLen uint64
}