The imageAtomicCompSwap doesn't seem to be working.
I create a texture buffer like so (all texels set to value -1)
Code :
// build buffer
std::vector<GLint> bufferData(ELEM_CNT,-1);
glBindBuffer(GL_TEXTURE_BUFFER, buffer);
glBindBuffer(GL_TEXTURE_BUFFER, 0);
// build texture
glBindTexture(GL_TEXTURE_BUFFER, texture);
	glTexBuffer(GL_TEXTURE_BUFFER, GL_R32I, buffer);
I expect the following shader to set texel number i to value i.
Code :
#version 420 core
layout(r32i) coherent uniform iimageBuffer imgData;
void main() {
	imageAtomicCompSwap(imgData, gl_VertexID, -1, gl_VertexID);
However, it does not, values remain at -1. Replacing imageAtomicCompSwap by imageAtomicExchange gives the correct output.

Code can be downloaded here (gmake and vs2010 projects are provided).