Where is `AsmVerbose` or `IsVerboseAsm` set?

Beginners
1

I am learning LLVM backend. I would like to enable IsVerboseAsm for AsmPrinter on my new target machine so that I can print comments.

I tried to do this by referring to Target/X86. Because I noticed that on my target machine, IsVerboseAsm is always false, while for X86 it is always true.

However, I could not find any code to configure IsVerboseAsm. I traced it with gdb and found that the source of this data came from a macro under include/clang/Driver/Options.inc generated when LLVM compiled:

CODEGEN_OPTION_WITH_MARSHALLING(prefix_1, &"-fno-verbose-asm"[1], fno_verbose_asm, Flag, f_Group, INVALID, nullptr, CC1Option, 0, nullptr. nullptr, nullptr, "-fno-verbose-asm", true, 0, CodeGenOpts.AsmVerbose, true, false, true, normalizeSimpleNegativeFlag, denormalizeSimpleFlag , mergeForwardValue, extractForwardValue, -1)

Further tracing is unnecessarily complicated for me. On the other hand, I also wonder why it would appear in such a place if this is target-independent code.

So, what keywords should I be looking at so I can know how to enable IsVerboseAsm for the AsmPrinter of the target machine I’m adding? I know I can always write some code to directly set the options in TargetOptions to true, but I’d like to know how other backends do it.

2

The handling is automatically set for CodeGenOpts under clang/include/llvm/MC/TargetRegistry.h via marshalling callbacks used by llvm::opt::PrecomputedOptTable. The key information is here in clang/lib/Driver/Toolchains/Clang.cpp:

  // Decide whether to use verbose asm. Verbose assembly is the default on
  // toolchains which have the integrated assembler on by default.
  bool IsIntegratedAssemblerDefault = TC.IsIntegratedAssemblerDefault();
  if (!Args.hasFlag(options::OPT_fverbose_asm, options::OPT_fno_verbose_asm,
                    IsIntegratedAssemblerDefault))
    CmdArgs.push_back("-fno-verbose-asm");

Under clang -cc1, CodeGenOpts::AsmVerbose is set based on these arguments. That information is then passed MC options in BackendUtil.cpp:

Options.MCOptions.AsmVerbose = CodeGenOpts.AsmVerbose;

And finally, it’s used as the IsVerboseAsm argument to createAsmStreamer in llvm/lib/CodeGen/LLVMTargetMachine.cpp:

    MCStreamer *S = getTarget().createAsmStreamer(
        Context, std::move(FOut), Options.MCOptions.AsmVerbose,
        UseDwarfDirectory, InstPrinter, std::move(MCE), std::move(MAB),
        Options.MCOptions.ShowMCInst);

So the backends don’t actually handle it themselves: if a target machine is known to have an integrated assembler in Clang, the default is to have verbose ASM enabled by default.

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