When generating CodeView debug information, LLVM emits SourceLanguage::Masm for any unsupported source language (see AsmPrinter/CodeViewDebug.cpp, function MapDWLangToCVLang). The Visual Studio debugger falls back to the C++ engine for this which is ok for many languages. But the D programming language has debugger support (http://rainers.github.io/visuald/visuald/Debugging.html#concord) that is loaded by the VS debugger depending on the source language found in the debug information.

Unfortunately, I haven't been able to draw Microsofts attention to adding a constant to the respective headers (https://github.com/Microsoft/microsoft-pdb/issues/21). 

Would it still be possible to add a D specific source language identifier to the CodeView output for dwarf::DW_LANG_D, so that the LLVM based D compiler could benefit from this integration, too? The reference compiler emits constant 'D' (0x44) as the source language.