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

[David Blaikie]

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
>
>
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>
>
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