How do you debug DMD?

[%u]

I tried using Visual Studio to set breakpoints in DMD and everything
(after compiling with -g), but it said that the source file is a
"different version" (it isn't), and so it doesn't really let me set
breakpoints.

What tools (aka debuggers) do you guys use to debug DMD? Any free
tools we can use to help find bugs? (Or is there some trick to getting
Visual Studio to debug this?)