Volatile and compiler optimization

Question

Is it OK to say that 'volatile' keyword makes no difference if the compiler optimization is turned off i.e (gcc -o0 ....)?

I had made some sample 'C' program and seeing the difference between volatile and non-volatile in the generated assembly code only when the compiler optimization is turned on i.e ((gcc -o1 ....).

Answer 1

No, there is no basis for making such a statement.

volatile has specific semantics that are spelled out in the standard. You are asserting that gcc -O0 always generates code such that every variable -- volatile or not -- conforms to those semantics. This is not guaranteed; even if it happens to be the case for a particular program and a particular version of gcc, it could well change when, for example, you upgrade your compiler.