Optimization level not working

Hi , I am working on LPC1788 with RTX , my code size is much bigger , so i want to optimize my code, after sarching through internet , there is optimization level(-O1 to -O3) specified by keil , but when i am using that optimization level(tried each level)in my code,but it is not working , not in debug mode also , why is this happened , please help or suggest.

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