[BUG] Adding 0.0 to an expression causes significant visual difference

The following issue is also logged here, which links to the relevant files

Platform details are at the end.

This fragment shader:

https://github.com/mc-imperial/shader-compiler-bugs/raw/master/ARM-Mali-T628-Chromebook-WebGL/wrong_images/small-v100-we…

causes this image to be rendered:

In contrast, this shader:

https://raw.githubusercontent.com/mc-imperial/shader-compiler-bugs/master/ARM-Mali-T628-Chromebook-WebGL/wrong_images/sm…

causes the following similar but visually distinct image to be rendered:

The shaders are identical, except in the second shader, this line from the first shader:

    vec3 b = fract(sin(co.x * 0.3e-3 + co.y) * vec3(8.1e5, 1.0e5, 0.1e5)); 

has been replaced by:

    vec3 b = fract(sin(co.x * 0.3e-3 + co.y) * (vec3(8.1e5, 1.0e5, 0.1e5) + vec3(injectionSwitch.x, 0.0, 0.0))); 

At runtime, we set injectionSwitch to (0.0, 1.0), so adding vec3(injectionSwitch.x, 0.0, 0.0) should be like adding a vector of zeroes; i.e., it should have no effect. Yet making this change causes a visible difference in the image that is rendered.

Platform details:

- Samsung Chromebook

- Chrome OS

     * Version: 54.0.2840.101

     * Platform: 8743.85.0 (Official Build) stable-channel peach_pit

     * Firmware: Google_Peach_Pit.4482.95.0

- GPU: ARM Mali-T628

Version and renderer info obtained via WebGL API: