Darren Cook <darren@dcook.org> writes:
I'm hoping Thorsten Ottosen's contract programming will make it into the standard so the compiler will understand asserts and be able to optimize away the redundant ones. Compilers are already allowed to do that, and I predict no proposal that requires it to be done will ever be accepted into the standard.
"be able" falls somewhere between "allowed to" and "required to". An optimizer will have a hard job analyzing all the code in a function so see if any can be skipped. But if it can see a precondition is always satisfied then it can jump directly to the body of the function and skip the precondition.
E.g. void f(int x){ precondition{ x>=0 && x<=99; } //1 ... //2 }
f(atoi(argv[2])); //Jumps to f, at 1 f(34); //Jumps to f, at 2
If f is inlined, I'm positive that compilers today can do that.
void g(int z){ precondition{ z>=10 && z<50; } f(z*2); //Can also jump to f at 2, as range is 20..98 }
And I'm pretty sure that compilers today can do that one.
I don't think Thorsten's proposal requires optimizations like this. But I don't know enough about compiler writing to know if the above is ever likely to be implemented.
It is just as implementable for assert as it is with Thorsten's proposal. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com