optimization options not working

[rohitgeek]

Your .2 euros turned into  high value , i got the point. And yes, gcc got
the hidden talent.


Cedric Roux-4 wrote:
> 
> rohitgeek wrote:
>> mentioned by Ian too, i get what i expect. But why does optimizer does
>> so?
> 
> because it can with respect to the semantics of the compiled language.
> Your statements assign values to local variables.
> There is no side effect.
> The values you assign are not used later on.
> So they are completely useless. Computing them or not won't change
> the semantics of your program. At all.
> It's cool that gcc finds that out for cases where your code actually
> does something, where optimization is useful. No?
> 
>> Where is the assembly or data gone when doing the earlier way, because if
>> we
> 
> You write programs in C, not in assembly language. The C compiler
> can compile the way it wants as long as the C semantics is
> respected.
> 
>> put some data into registers and done some manipulations, then where are
> 
> This is what you don't understand I guess. Your program doesn't "put some
> data into
> registers and [does] some manipulations." Your program assigns values to C
> variables.
> This is another world.
> C is not assembly language.
> 
> So in short, as others said, if you want the code to stay there
> after optimization, be sure it does real stuff, like returning
> the computed value. The computed value has to "escape" the local
> scope for it to be "respected" by the optimization.
> 
> My .2 euros.
> 
> 

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