armcc是否使用-O0优化非易失性变量？

Question

int* Register = 0x00FF0000; // Address of micro-seconds timer
while(*Register != 0);

Should I declare *Register as volatile while using armcc compiler and -O0 optimization ?

In other words: Does -O0 optimization requires qualifying that sort of variables as volatile ? (which is probably required in -O2 optimization)

Answer 1

It seems to me that you should declare Register as volatile regardless, since it is volatile. There's no harm in marking it volatile , since you're depending on the compiler not optimizing away the accesses through the pointer.

int volatile* Register = (int*) 0x00FF0000;

You shouldn't depend on the compiler optimization settings to hope this gets compiled correctly. I'd guess that forgetting to mark things volatile appropriately is a major reason that cranking up optimizations on embedded C code often causes things to start breaking.