Efficiency of branching in shaders

Question

I understand that this question may seem somewhat ungrounded, but if someone knows anything theoretical / has practical experience on this topic, it would be great

Answer 1

Here's a real world performance benchmark on a kindle Fire:

In the fragment shader...

This runs at 20fps:

lowp vec4 a = vec4(0.0, 0.0, 0.0, 0.0);
if (a.r == 0.0)
    gl_FragColor = texture2D ( texture1, TextureCoordOut );   

This runs at 60fps:

gl_FragColor = texture2D ( texture1, TextureCoordOut );