OpenCL reduced available memory for OpenCL applications on your system, usually it is related to environment variables and size of RAM installed.
But detecting 3GB instead of 4GB will not change your mining speed. So what's the problem?
The miner exits just after the "start building OpenCL program...".
I've had the same problem but with my RX480. My problem was that it needs more ram, I was with only 2GB, then put 2GB more and everything is OK. How much ram do you have?
That's it. BINGO!
Machine had only 2GB of RAM. Replacing a 1GB memory card for a 2GB one (3GB total) solved.
Thank you very much to everyone to replied.
Regards, Brusque