repro.glsl

#version 430 core

layout(std430, binding=0) buffer debugbuf {
    int debug[128];
};

layout(binding=0) uniform isamplerBuffer zigzag8;
layout(binding=1) uniform isamplerBuffer coeff_data;
layout(binding=2) uniform isamplerBuffer dc_data;
layout(binding=3) uniform usampler2D i_img;
layout(binding=4) uniform isamplerBuffer motion_buf;

shared int magic_sink[1];

layout(local_size_x=64) in;

void main()
{
    uint invoc = gl_LocalInvocationID.x;

    // this should just copy the first 64 int pairs from "motion_buf"
    // to debug, but it doesn't.
    ivec2 rel_vec = texelFetch(motion_buf, int(invoc)).xy;
    debug[invoc*2 + 0] = rel_vec.x;
    debug[invoc*2 + 1] = rel_vec.y;

    //return; // uncomment this and the shader works.

    int magic = 0;
    
    // comment out any of the following lines and the shader works.
    magic += texelFetch(dc_data, 0).x & 0;
    magic += texelFetch(zigzag8, 0).x & 0;
    magic += texelFetch(coeff_data, 0).x & 0;
    magic += int(textureGather(i_img, vec2(0.0, 0.0)).x) & 0;
    magic_sink[0] = magic;
}