UIImageFromCGLayer.swift

extension UIImage {
    class func imageWithLayer(layer: CALayer) -> UIImage? {
        UIGraphicsBeginImageContextWithOptions(layer.bounds.size, layer.isOpaque, 0.0)
        layer.render(in: UIGraphicsGetCurrentContext()!)
        
        guard let img = UIGraphicsGetImageFromCurrentImageContext() else {
            return nil
        }
        
        UIGraphicsEndImageContext()
        return img
    }
}

// Get UIImage from CAGradientLayer
let gradientOverlayLayer = CAGradientLayer()
UIImage.imageWithLayer(layer: gradientOverlayLayer)?.draw(at: CGPoint.zero, blendMode: .multiply, alpha: 1.0)
            

As a side not define extensions with class func to allow them to be initialized in the form of UIImage.imageWithLayer() instead of UIImage().imageWithLayer()