[PATCH] D94655: [Driver] -gsplit-dwarf: Produce .dwo regardless of -gN for IR input

[Fangrui Song via Phabricator via cfe-commits]

MaskRay added a comment.

In D94655#2498669 <https://reviews.llvm.org/D94655#2498669>, @dblaikie wrote:

> In D94655#2498548 <https://reviews.llvm.org/D94655#2498548>, @MaskRay wrote:
>
>> In D94655#2498504 <https://reviews.llvm.org/D94655#2498504>, @dblaikie wrote:
>>
>>> Is there any way to condition this on the type of the output, rather than the input? (or, more specifically, on whether machine code is being generated)
>>>
>>> Or maybe we could always pass the split-dwarf-file down through LLVM and not need to conditionalize it at all? It'd be a no-op if there's no DWARF in the IR anyway?
>>
>> I tried replacing `if (IRInput || Args.hasArg(options::OPT_g_Group)) {` with `if (1)`, -gsplit-dwarf may produce .dwo for regular non-g .c compile.
>
> Are you saying that if you make that change -gsplit-dwarf does cause .dwo files to be created for non-g .c compiles? Do the dwo files have anything in them? I had modified llvm to dynamically choose split or non-split based on whether there was enough data to be worth splitting into a .dwo file, but I guess that situation might still be producing an empty .dwo file which isn't ideal - I haven't tested that.



  % clang a.c -gsplit-dwarf -c
  % readelf -WS a.dwo                
  There are 2 section headers, starting at offset 0x50:
  
  Section Headers:
    [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
    [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
    [ 1] .strtab           STRTAB          0000000000000000 000040 000009 00      0   0  1



>> Since we already have the
>>
>>   // For -g0 or -gline-tables-only, drop -gsplit-dwarf. This gets a bit more
>>   // complicated if you've disabled inline info in the skeleton CUs
>>   // (SplitDWARFInlining) - then there's value in composing split-dwarf and
>>   // line-tables-only, so let those compose naturally in that case.
>>
>> logic, I think altering `DwarfFission` in the driver is fine. If not, I'd hope the backend to process `DwarfFission` ...
>
> Sorry, I'm not understanding this comment - could you describe/rephrase it in more detail?

The driver already decides that DwarfFission should be disabled in -g0 and -g1 cases. If the driver does not already do this, passing through DwarfFission in the driver and letting CC1 handle it seems right to me.

Since the driver already has some logic, I think adding more logic about IR input types is fine.


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https://reviews.llvm.org/D94655