Using imageLoad/imageStore to perform atomic add I have a rgba16f texture that I fill with values using nvidia GL_NV_shader_atomic_fp16_vector extension, which allows to perform imageAtomicAdd on half float RGBA images, with multiple shader threads using same index. However, it doesn't support rgba32f.
Can I use imageLoad/imageStore to perform same thing with such image buffer as written below?
vec4 prevVal = imageLoad(tex, index);
prevVal += currVal;
imageStore(tex, index, prevVal);

I'm not sure how correctly set the coherency of such operations with correct barriers usage because I have not found any example. Or if it is even possible.
If you could use imageLoad/Store to do atomic operations, there would be no need for atomic operations as a distinct class of operations. So no, you can't. There is no correct set of barriers or other properties that will allow this to work generally the way atomic operations do.