[cfe-dev] output metadata for extern declared functions?

[David Blaikie]

Generally we don't encourage source to source translation via code
generation from the AST even - its best to use the AST to motivate edits to
the original source. The AST just doesn't have the fidelity to regenerate
the original source perfectly.

As for your current problem, I guess 'is it cheaper to rewrite in a better
way' depends on the complexity, but i assume its hard to justify a rewrite
unless this tool is going to live a long time further and need new
features/maintenance.

That said, I'm not sure how much I can help you produce debug info for
every function declaration. If I were doing this I'd go back and look at
the support I added for imported directives (using declarations and
directives) and look at other unhandled decks that could be supported.
On Nov 9, 2013 10:18 AM, "Lewis Burns" <lewisurn at gmail.com> wrote:

>  I'm fixing an existing source-to-source translator, and it was
> unfortunately written by someone using LLVM as the intermediate step before
> Clang was mature. I don't need to generate object code at all, and
> performance is not a concern here.
>
> Sounds like that the only way for me to save this translator is to patch
> Clang by generating debug info metadata for declarations whose definitions
> are not available. Is this a feasible approach? I mean how difficult it
> would be comparing with hacking into Clang AST and start from there? I
> guessed that it would be much easier than starting over with Clang AST from
> scratch. Since I haven't worked on Clang before, any suggestion and help
> would be greatly appreciated.
>
>
>
> On 11/09/2013 04:14 PM, David Blaikie wrote:
>
> For those following this thread a critical detail would be that you want
> debug info metadata.
>
> There's no simple flag for this as we don't attach the function debug info
> metadata to every declaration, just to definitions (there's no filtering
> step)
>
> But why do you want this anyway? If you're performing
> optimizations/transformations based on debug info metadata, that's not
> really the desired approach. Debug info is not meant to affect code
> generation.
> On Nov 9, 2013 7:59 AM, "Lewis Burns" <lewisurn at gmail.com> wrote:
>
>>  Hi,
>>
>> I haven't worked on Clang before and have a simple question (supposedly)
>> for those who are familiar with metadata and LLVM bitcode generation.
>> Assume that I have a function which is declared as extern as the following:
>>
>> extern int convert(unsigned u);
>>
>> I want to have Clang generate metadata nodes for it by adding a metadata
>> node of subprogram into the list of subprograms defined in the current
>> compilation unit. The subprogram metadata node and its associated nodes
>> should have the info of the type signature. For example, I get the
>> following set of metadata nodes for function
>>
>> int convert(unsigned u) {return 0;}
>>
>> !3 = metadata !{metadata !4, metadata !10, metadata !33}
>> !4 = metadata !{i32 786478, metadata !1, metadata !5, metadata
>> !"convert", metadata !"convert", metadata !"", i32 23, metadata !6, i1
>> false, i1 true, i32 0, i32 0, null, i32 256, i1 false, i32 (i32)* @convert,
>> null, null, metadata !2, i32 23} ; [ DW_TAG_subprogram ] [line 23] [def]
>> [convert]
>> !7 = metadata !{metadata !8, metadata !9}
>> !8 = metadata !{i32 786468, null, null, metadata !"int", i32 0, i64 32,
>> i64 32, i64 0, i32 0, i32 5} ; [ DW_TAG_base_type ] [int] [line 0, size 32,
>> align 32, offset 0, enc DW_ATE_signed]
>> !9 = metadata !{i32 786468, null, null, metadata !"unsigned int", i32 0,
>> i64 32, i64 32, i64 0, i32 0, i32 7} ; [ DW_TAG_base_type ] [unsigned int]
>> [line 0, size 32, align 32, offset 0, enc DW_ATE_unsigned]
>>
>> which allows me to extract the source-level type signature for the
>> function by using LLVM debug info APIs. I'd like to get the source-level
>> type signature of the extern declared function, but Clang does not produce
>> metadata for it.
>>
>> By looking at the Clang AST for the extern declared function
>>
>> |-FunctionDecl 0x70598c0 <line:23:1, col:30> convert 'int (unsigned int)'
>> extern
>> | |-ParmVarDecl 0x7059800 <col:20, col:29> u 'unsigned int'
>>
>> I know that Clang has the information I need, and I just need to turn off
>> or remove the filter that ignores functions whose bodies are not available
>> during metadata node or/and code generation. Are there simple switches that
>> do this? If not, can anyone please explain how to do it by pointing me to
>> the right code snippets?
>>
>> Thanks very much,
>>
>>
>> --
>> Lewis
>>
>>
>> _______________________________________________
>> cfe-dev mailing list
>> cfe-dev at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev
>>
>>
>
> --
> Lewis
>
>
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