[Mono-bugs] [Bug 570272] New: out parameter set with ternary ?: or ?? operator in generic function with 'struct' parameter constraint generates invalid code

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http://bugzilla.novell.com/show_bug.cgi?id=570272

http://bugzilla.novell.com/show_bug.cgi?id=570272#c0


           Summary: out parameter set with ternary ?: or ?? operator in
                    generic function with 'struct' parameter constraint
                    generates invalid code
    Classification: Mono
           Product: Mono: Compilers
           Version: 2.4.x
          Platform: x86
        OS/Version: Ubuntu
            Status: NEW
          Severity: Major
          Priority: P5 - None
         Component: C#
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: halfflat at gmail.com
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---
           Blocker: ---


User-Agent:       Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.6)
Gecko/20091215 Ubuntu/9.10 (karmic) Firefox/3.5.6

The following sample C# source, when compiled with gmcs [version 2.4.2.3
(Debian 2.4.2.3+dfsg-2] generates code which, when run with mono, raises an
Invalid IL System.InvalidProgramException.

class Q {
    static void bar<T>(out T t) where T: struct {
        t=true?new T():new T();
    }   

    public static void Main(string[] args) {
        int d=0;
        bar(out d);
    }   
}   


Similarly, when the ?? operator is used, the same exception is raised upon
execution:
    // also fails:
    static void bar<T>(out T t) where T: struct {
        T? u=null; 
        t=u??new T();
    }


However, the issue does not occur if the constraint is "where T: new()" instead
of "where T: struct":
    // executes correctly:
    static void bar<T>(out T t) where T: new() {
        t=true?new T():new T();
    }   



Reproducible: Always

Steps to Reproduce:
1. The sample code above is compiled with gmcs, with or without optimization:
    gmcs q.cs

2. The resulting .exe is executed:
    mono q.exe

Actual Results:  
On execution, mono reports:

Unhandled Exception: System.InvalidProgramException: Invalid IL code in
Q:bar<int> (int&): IL_002b: ret       


  at Q.Main (System.String[] args) [0x00000] 


Expected Results:  
No exception should be raised, and the correct program semantics should be
respected.

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