Add support for MCS 2.6.4 pinned region with string variable

[ElektroKill]

Link to issue(s) this covers:
N/A

Problem

Decompilation of the following code compiled with MCS 2.6.4 was not properly supported and resulted in ugly and invalid code:

fixed (char* ptr = text, userName = Environment.UserName, ptr2 = text)
{
	*ptr = 'c';
	*userName = 'd';
	*ptr2 = 'e';
}

would result in:

fixed (string text2 = text)
{
	fixed (char* ptr = &System.Runtime.CompilerServices.Unsafe.AsRef<char>((char*)((long)(IntPtr)text2 + (long)RuntimeHelpers.OffsetToStringData)))
	{
		fixed (string text3 = Environment.UserName)
		{
			fixed (char* ptr2 = &System.Runtime.CompilerServices.Unsafe.AsRef<char>((char*)((long)(IntPtr)text3 + (long)RuntimeHelpers.OffsetToStringData)))
			{
				fixed (string text4 = text)
				{
					fixed (char* ptr3 = &System.Runtime.CompilerServices.Unsafe.AsRef<char>((char*)((long)(IntPtr)text4 + (long)RuntimeHelpers.OffsetToStringData)))
					{
						*ptr = 'c';
						*ptr2 = 'd';
						*ptr3 = 'e';
					}
				}
			}
		}
	}
}
text3 = null;
text4 = null;

The code is now decompiled as:

fixed (char* ptr = text)
{
	fixed (char* ptr2 = Environment.UserName)
	{
		fixed (char* ptr3 = text)
		{
			*ptr = 'c';
			*ptr2 = 'd';
			*ptr3 = 'e';
		}
	}
}

Solution

• Adjusted login in the DetectPinnedRegion transform to handle the alternate code generation from the MCS 2.6.4 compiler.
• No unit test was added as the current Pretty tests don't support the MCS 2.6.4 compiler.

[dgrunwald]

You could add an ILPretty test instead.

[siegfriedpammer]

Thank you very much for your contribution!