[nem-bug] [Nemerle 0000603]: callvirt is emitted when call is sufficient

[feedback at nemerle.org]

A NOTE has been added to this issue.
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<https://nemerle.org/bugs/view.php?id=603> 
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Reported By:                nazgul
Assigned To:                
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Project:                    Nemerle
Issue ID:                   603
Category:                   Compiler
Reproducibility:            always
Severity:                   minor
Priority:                   normal
Status:                     confirmed
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Date Submitted:             01-26-2006 21:34 CET
Last Modified:              02-11-2006 12:09 CET
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Summary:                    callvirt is emitted when call is sufficient
Description: 
#pragma indent

using System

class A
  public foo () : void 
    ()
    
A().foo ()


produces:
...
    IL_0000:  newobj     instance void A::.ctor()
    IL_0005:  callvirt   instance void A::foo()
    IL_000a:  ret
...

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----------------------------------------------------------------------
 nazgul - 02-11-06 11:19 
----------------------------------------------------------------------
This patch seems to fix the basic behaviour, but it causes strange
regressions in frommcs testcases, like:

[IL]: Error: [C:\cygwin\home\nazgul\nemerle\ncc\testsuite\test-147.exe :
Test::Main][offset 0x00000037] The 'this' parameter to the call must be
the calling method's 'this' parameter.
1 Error Verifying ../test-147.exe


My guess is that it is unrelated to callvirt, which must have just hidden
the real bug...

----------------------------------------------------------------------
 nazgul - 02-11-06 11:42 
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Funny, csc seems to emit 'call' only in cases when it knows for sure, that
the object is actual class, which we are trying to call. If it is first
stored for example in local variable, then it emits 'callvirt' even when
not calling virtual methods. 
So it is probably optimized by runtime.

----------------------------------------------------------------------
 steffen - 02-11-06 12:01 
----------------------------------------------------------------------
As far as I know the difference between call and callvirt when calling
non-virtual functions is that callvirt checks whether the called instance
is null while call doesn't.

So if you compile the following C# program:

public class A {
  public void f() {
    System.Console.WriteLine(this == null);
  }
  
  public static void Main() {
    ((A)null).f();
  }
}

and disassemble it and replace the line 
	IL_0001:  callvirt instance void class A::f()
by
	IL_0001:  call instance void class A::f()
it will run and output

True

----------------------------------------------------------------------
 nazgul - 02-11-06 12:09 
----------------------------------------------------------------------
Nice! I didn't know that. Also 'call' is emitted for "base" calls in
override method chain, so it seems that only there it makes difference in
"virtual" way of calling the method.

Issue History
Date Modified  Username       Field                    Change              
======================================================================
01-26-06 21:34 nazgul         New Issue                                    
02-11-06 11:18 nazgul         Status                   new => confirmed    
02-11-06 11:18 nazgul         Description Updated                          
02-11-06 11:18 nazgul         Additional Information Updated                    
02-11-06 11:18 nazgul         File Added: nonvirt.patch                    
02-11-06 11:19 nazgul         Note Added: 0001077                          
02-11-06 11:42 nazgul         Note Added: 0001078                          
02-11-06 12:01 steffen        Note Added: 0001079                          
02-11-06 12:09 nazgul         Note Added: 0001080                          
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