The files in the dmd subdirectory are part of the front-end for the Digital Mars D compiler, hosted at https://github.com/dlang/dmd/. They cover the lexical analysis, parsing, and semantic analysis of the D Programming Language defined in the documents at https://dlang.org/. To report a problem or look up known issues with the dmd front-end, please visit the issue tracker at https://issues.dlang.org/. All changes to dmd should go through the upstream repository first, then merged back to GCC.