AC6 Optimization Level

Hi,

    I am new to coding environment. My question is reading the optimization levels in build command. In some documents and sample code i have seen the build command as shown below, in which the two optimization level is given in a build command. 

    armclang --target=arm-arm-none-eabi -Oz -O2

1) Is this method is correct? can i give multiple optimization level in single build command

2) I am getting liker error(the code will not fit in flash) while using command a shown above. But the code will build if the optimization order is changed(armclang --target=arm-arm-none-eabi -O2 -Oz). Why it the code is buildable while changing the order of optimization level.

3) With ac6 is it possible to set optimization level(-O0, -O2, -O3) and optimization for ( -Oz, -Os)

Best Regards

Ranjith