how good is dmd at optimising away the default initialisers when it is guaranteed that a variable will be initialised later than the variable declaration? I am concerned about this because my program is very time critical. I think it would be cool if there was an attribute for variable declarations not to be initialised by default.

"imr1984" <imr1984_member@pathlink.com> wrote in message news:c5mttq$la8$1@digitaldaemon.com...
> how good is dmd at optimising away the default initialisers when it is guaranteed that a variable will be initialised later than the variable declaration? I am concerned about this because my program is very time
critical.
> I think it would be cool if there was an attribute for variable
declarations not
> to be initialised by default.

But if they arent given a default value, dont they
then just contain garbage anyway? If so, isnt it better to have a default
value?

Phill.




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"imr1984" <imr1984_member@pathlink.com> wrote in message news:c5mttq$la8$1@digitaldaemon.com...
> how good is dmd at optimising away the default initialisers when it is guaranteed that a variable will be initialised later than the variable declaration? I am concerned about this because my program is very time
critical.
> I think it would be cool if there was an attribute for variable
declarations not
> to be initialised by default.

The compiler uses 'data flow analysis' to detect and remove dead assignments, and it works reasonably well. Try it and see.

Walter wrote:

> The compiler uses 'data flow analysis' to detect and remove dead assignments, and it works reasonably well. Try it and see.

WinXP dmd 0.82

<code>
import std.c.windows.windows;
void main(){
  double dtime(){
    return (cast(double) GetTickCount) / 1000;
  }
  const long size=1_400_000_000;
  double start= dtime;
  int[] arr=new int[size/4];
  //arr[1]=1;
  double end= dtime;
  printf("%20.20f\n", end - start);
}
</code>

Although I commented the access out, the runtime stays by more than 1.5 seconds, whereas the according C program hushes by.

So long!