[llvm-dev] Improving the rich disassembly output

[Craig Topper via llvm-dev]

I'm not sure how to add annotations to these instructions. But I can tell
you that ADC64i32 is created by the last def at the bottom of the
ArithBinOp_RF multiclass in X86InstrArithmetic.td.

~Craig

On Wed, Dec 9, 2020 at 6:10 AM Alain Carlucci via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi,
>
> I'm trying to use the annotation support for the LLVM disassembler, which
> seems
> to be implemented only on ARM and x86.
>
> It was easy to add annotations also on SystemZ, AArch64 and MIPS (at least
> <imm:> and <reg:>) and I'm going to send you soon all the patches.
>
> But now I'm facing a problem with the annotations in x86: there are some
> instructions that emit registers directly from the AsmString written in the
> TableGen file.
>
> For example, llvm/lib/Target/X86/X86InstrInfo.td:1631, this line defines
> the
> instruction with the `al` register hardcoded, which is emitted without
> markup:
> ```
> def MOV8o32a : Ii32<0xA2, RawFrmMemOffs, (outs), (ins offset32_8:$dst),
>                      "mov{b}\t{%al, $dst|$dst, al}", []>, AdSize32;
> ```
>
> In this case, I tried to change "al" with "$al" (at first by creating a new
> RegisterClass "AL8" with only one register (AL) and forwarding it to
> MOV8o32a)
> but I got a crash while trying to emit the instruction.
> And, honestly, creating RegisterClass with only one register doesn't seem
> to be
> the best way to approach this problem.
>
> For the record, the crash was:
> ```
> Unhandled relocation encoding AL8
> Unhandled relocation encoding
> UNREACHABLE executed at
> llvm/llvm/utils/TableGen/X86RecognizableInstr.cpp:1212!
> ```
>
> There are instructions like ADC64i32, ADD64i32 that emit an hardcoded
> register
> in the generated file (something like `O << ", %rax"`) in
> build/lib/Target/X86/X86GenAsmWriter.inc but I can't find them in the any
> tablegen file.
>
> So I'd like to ask you, can you give me some advice about how to enable
> annotations for this kind of instructions?
>
> Thanks,
> Alain
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