combine two id<MTLTexture>

Hi,
Perhaps the textures are too complicated for something like this to be done simply, but...
I have two depth textures, same size, same pixel format, each created with a separate rendering pass. One to calculate shadows created by stationary objects, the other to calculate shadows created by moving objects.
Is there an easy way to combine the two textures, so that I end up with a single texture that I can use "sample_compare" inside a shader? Or is the best way to pass both textures to the shader and do samplecompare twice?
Thanks