It's common knowledge that you shouldn't use a StringBuilder in place of a small number of concatenations:

string s = "Hello";
if (greetingWorld)
{
    s += " World";
}

s += "!";

However, in loops of a significant size, StringBuilder is the obvious choice:

string s = "";
foreach (var i in Enumerable.Range(1,5000))
{
    s += i.ToString();
}

Console.WriteLine(s);

Is there a tool that I can run on either raw C# source or a compiled assembly to identify where in the source code that String.Concat is being called? (If you're not familiar, s += "foo" is mapped to String.Concat in the IL output.) Obviously, I can't realistically search through an entire project and evaluate every += to identify whether the lvalue is a string.

Ideally, it would only point out calls inside a for/foreach loop, but I would even put up with all the false positives of noting every String.Concat. Also, I'm aware that there are some refactoring tools that will automatically refactor my code to use StringBuilder, but I am only interested in identifying the Concat usage at this point.

I routinely run Gendarme and FxCop on my code, and neither of those tools identify what I've described.