Re: [DotGNU]callvirt change to cscc

[Rhys Weatherley]

Gopal V wrote:

> this totally destroys the efficency of using non-virtual methods ...
> Because if we're going to lookup each and every method .... It's just
> one lookup per method for every call . IMHO we should try to optimise
> rather than correct non-existent bugs for non-existent compatibility..

Actually, the runtime impact isn't as big as you think.  The verifier
notices that "callvirt" is being used on a non-virtual method and
inserts a normal CVM "call" opcode, rather than CVM's "call_virtual".
The only runtime change is to do a "cknull" before the "call".
It doesn't have to do a virtual method lookup for every call - it
can call the destination method directly.

> The correct NullReferenceException will be thrown when the called
> method accesses 'this' anyway...
> 
> Sorry, I don't like this change ... This is neither good or bad ..
> it's UGLY ...

I agree with you.  Unfortunately, compatibility trumps efficiency
in this case.  Under MS'es compiler/runtime, the following throws
a NullReferenceException even though "this" is never touched by
the "DoNothing" method:

    using System;

    public class Test
    {
        public void DoNothing()
        {
        }

        public static void Main()
        {
            ((Test)null).DoNothing();
        }
    }

Cheers,

Rhys.