[flang] Flang does not accept -gdwarf- option

[abidh]

clang accepts flags from -gdwarf-2 to -gdwarf-5. Flang does not accept any of them.

flang -gdwarf-4 test.f90
flang-20: error: unknown argument: '-gdwarf-4'

[llvmbot]

@llvm/issue-subscribers-flang-driver

Author: Abid Qadeer (abidh)

clang accepts flags from -gdwarf-2 to -gdwarf-5. Flang does not accept any of them.

flang -gdwarf-4 test.f90
flang-20: error: unknown argument: '-gdwarf-4'

[abidh]

Hi @tarunprabhu

Thanks for working on this ticket. I looked at this issue a bit more. As you said that it is a little confusing because clang seems to have a lot of different debug related options. To attach this problem in incremental way, this is what I think we should be doing.

For -gdwarf-n switch, I think we should add an option in CodeGenOptions.def and the propagate it to AddDebugInfo which will generate the correct version info. I see that clang has more debug options in DebugOptions.def which we can adopt in future PRs as need arise.

As you have noticed that clang also accepts many other -g related options. I think those could be handled separately but here are some quick comments. The frontend's (DebugInfoKind) has more options than the DICompileUnit::DebugEmissionKind. So we see that clang maps many of them to FullDebugInfo in CGDebugInfo::CreateCompileUnit. I think we should do a similar thing in flang. The parseDebugArgs could be extended to allow those extra options. Then getEmissionKind can do similar mapping as clang does in CGDebugInfo::CreateCompileUnit. AddDebugInfo pass will be responsible to generate the debug data accordingly.