Please see the following post. Some of you may know the answer.

[Luís Carlos Carneiro Gonçalves via Gcc]

https://community.intel.com/t5/GPU-Compute-Software/Intel-GPU-OpenCL-with-g-O3-flag/m-p/1512130/emcs_t/S2h8ZW1haWx8dG9waWNfc3Vic2NyaXB0aW9ufExMMkkxSjhRTU1HMjZZfDE1MTIxMzB8U1VCU0NSSVBUSU9OU3xoSw