How to turn off all optimizations in GCC

Question

How to turn off all optimizations in GCC? Using -O0 does not work since it still optimizes out the statements that have no effects, or any code that is after an infinite loop without any break statements.

Answer 1

There is no way to make gcc not ignore unreachable code and statments that have no effect.

What you can do is make code that is unreachable appear to be reachable by using volatile variables.

volatile bool always_true = true;

if( always_true  )
{
     //infinite loop
     //return something
}

//Useless code

in the above example, gcc won't optomize out useless code because it cannot know it is infact useless

int a = 5;
int b = 5;
volatile int c = 9;

c += 37;
return a + b;

In this example, integer c won't be optimized out because gcc does can't know it is dead weight code.

Answer 2

You have to make your code nearly impossible to be optimized by the compiler. For example:

• use volatile keyword on variables that you wish not to be optimized
• make sure the code has effect, for example: not just only changing the variable value but also print the value or store it to another variable or do arithmetic to the variable and store it in another variable
• reference/change the variable in other function to make sure the compiler cannot judge it is not used in compile time