Reference type non-null-checks produce incorrect code

switchbladeswitchblade Posts: 4
edited June 23, 2017 3:40AM in .NET Reflector
I've noticed this bug for a while now, I'm not sure when it was introduced but take this simple example here:
private static void ABC(byte[] b)
{
    if (b != null)
    {
        Environment.Exit(0);
    }
}

private static void ABC(List<string> b)
{
    if (b != null)
    {
        Environment.Exit(0);
    }
}

This is the decompiled output:
private static void ABC(byte[] b)
{
    if (b > null)
    {
        Environment.Exit(0);
    }
}

private static void ABC(List<string> b)
{
    if (b > null)
    {
        Environment.Exit(0);
    }
}

It seems to replace the expected "!=" with ">" which is not valid C# code. The same occurs on VB decompilation as well.

PS - The forum seems to be encoding "<" and ">" incorrectly using the code tags, would be nice if you could fix that too.
Tagged:

Comments

  • Sorry to hear you're running into an issue!

    It's odd though, I'm not able to reproduce this at the moment.

    w11k59nrdo7h.png

    May I ask the project type and the .NET Framework version of the assembly you're decompiling?

    Thanks!
    Product Support Engineer | Redgate Software
  • switchbladeswitchblade Posts: 4
    edited July 3, 2017 12:30AM
    The project type is a console application and is compiled with .NET Core 1.0. However I can also repro this issue with a .NET Framework 4 WinForms app. Changing the C# version at the top of Reflector also seems to have no effect. For reference here is the IL which may explain the problem:
    .method private hidebysig static void ABC(uint8[] b) cil managed
    {
        .maxstack 2
        .locals init (
            [0] bool flag)
        L_0000: nop 
        L_0001: ldarg.0 
        L_0002: ldnull 
        L_0003: cgt.un // -- here?
        L_0005: stloc.0 
        L_0006: ldloc.0 
        L_0007: brfalse.s L_0012
        L_0009: nop 
        L_000a: ldc.i4.0 
        L_000b: call void [mscorlib]System.Environment::Exit(int32)
        L_0010: nop 
        L_0011: nop 
        L_0012: ret 
    }
    

    https://stackoverflow.com/questions/28781839/why-does-the-c-sharp-compiler-translate-this-comparison-as-if-it-were-a-com
  • Hi @switchblade, thanks very much for those details and for the helpful stackoverflow post!

    I have been able to reproduce this and as .NET Reflector should still be able to decompile != correctly, I have gone ahead and logged a bug for this internally with reference RP-4045. Thank you and I will let you know once I have any updates.

    Just a note that we are also working on the bug where our forum is encoding code incorrectly--thanks for reporting this as well!
    Product Support Engineer | Redgate Software
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