[llvm-dev] [LLVM][DISubprogram][LL format updation query] Question regarding moving DISubprogram DIFlags to DISPFlag.

[Djordje Todorovic via llvm-dev]

Hi Chirag,

On 20.2.20. 09:57, Chirag Patel wrote:
> Yes, removing the support for isLocal, isDefinition fields completely from ll files, currently the LLParser still parses it. I want to remove it and update the all the ll files which still uses it.

Could you please describe what is the benefit of that?

> Also the metadata read will support old format, no changes in that.
>
> so if ll file has isLocal and isDefinition it will result in parser error. But the bitcode read will work as usual.
>

AFAIK, there are no compatibility guarantees for textual LLVM IR, so we only need to support the bitcode auto-upgrade. So, that would be acceptable if there is motivation for doing that.
In addition, I'm not sure if this was documented somewhere, so we could improve the documentation for the metadata backward compatibility.
 
> - Chirag.
> 
> -----Original Message-----
> From: Djordje Todorovic <djordje.todorovic at rt-rk.com> 
> Sent: 20 February 2020 14:16
> To: Chirag Patel <Chirag at raincode.com>; llvm-dev at lists.llvm.org
> Subject: Re: [llvm-dev] [LLVM][DISubprogram][LL format updation query] Question regarding moving DISubprogram DIFlags to DISPFlag.
> 
> Hi Chirag,
> 
> On 20.2.20. 07:51, Chirag Patel via llvm-dev wrote:
>> Hello,
>>
>>  
>>
>> In regard to the review request https://reviews.llvm.org/D74470,
>>
>> I am trying to move five of the DIFlags to DISPFlag for the moment namely DIFlagExplicit, DIFlagPrototyped, DIFlagNoReturn, DIFlagThunk, DIFlagAllCallsDescribed.
>>
>> The llvm ir format for DISubprogram currently has backword compatibility where the isLocal, isDefinition, virtuality, isOptimized and SPFlags are mutually exclusive.
>>
>> My question is,
>>
>> is it a good idea to remove the booleans support'(isLocal, isDefinition) and move most of it to spflags and flags in llvm ir? 
> 
> But it was already "done", we currently have the 'DISPFlagLocalToUnit' and 'DISPFlagDefinition' (please take a look into the https://reviews.llvm.org/D54755 and https://reviews.llvm.org/D59288).
> 
> The llvm ir backward compatibility does not list the clear requirements on documentations page. This change affects more then 750 ll files.
>>
> 
> I am not sure what change will take 750 ll files? Removing the 'isLocal' and 'isDefinition'? I think the role of LLVM IR backward compatibility is to support interpretation of the old metadata in terms of the newest one. Therefore, if there is an 'isDefinition' metadata field, that should be interpreted as 'DISPFlagDefinition'.
> 
> 
>>
>> Regards,
>>
>> Chirag Partel.
>>

Best, 
Djordje