Flipping macOS metal texture

What is the best way to horizontally flip a texture in macOS metal?

I can use the following vertex shader and successfully flip the texture, but this code doesn't work (crashes) on older Macs (< 2015).

I could flip the texture before I submit it to the GPU but that seems very inefficient. I also checked the documentation. I can't see any way to change the anchor position from being the left top of the texture.

// Vertex Function
vertex RasterizerData
vertexShader(uint vertexID [[ vertex_id ]],
             constant AAPLVertex *vertexArray [[ buffer(AAPLVertexInputIndexVertices) ]],
             constant vector_uint2 *viewportSizePointer  [[ buffer(AAPLVertexInputIndexViewportSize) ]])

{

    RasterizerData out;

    vertexArray[vertexID].position.y *= -1;
    // Index into our array of positions to get the current vertex
    //   Our positions are specified in pixel dimensions (i.e. a value of 100 is 100 pixels from
    //   the origin)
    float2 pixelSpacePosition = vertexArray[vertexID].position.xy;

    // Get the size of the drawable so that we can convert to normalized device coordinates,
    float2 viewportSize = float2(*viewportSizePointer);

    // The output position of every vertex shader is in clip space (also known as normalized device
    //   coordinate space, or NDC). A value of (-1.0, -1.0) in clip-space represents the
    //   lower-left corner of the viewport whereas (1.0, 1.0) represents the upper-right corner of
    //   the viewport.

    // In order to convert from positions in pixel space to positions in clip space we divide the
    //   pixel coordinates by half the size of the viewport.
    out.clipSpacePosition.xy = pixelSpacePosition / (viewportSize / 2.0);

    // Set the z component of our clip space position 0 (since we're only rendering in
    //   2-Dimensions for this sample)
    out.clipSpacePosition.z = 0.0;

    // Set the w component to 1.0 since we don't need a perspective divide, which is also not
    //   necessary when rendering in 2-Dimensions
    out.clipSpacePosition.w = 1.0;

    // Pass our input textureCoordinate straight to our output RasterizerData. This value will be
    //   interpolated with the other textureCoordinate values in the vertices that make up the
    //   triangle.
    out.textureCoordinate = vertexArray[vertexID].textureCoordinate;

    return out;
}