[llvm-dev] How to resolve debug info forward types

[Rodney M. Bates via llvm-dev]

Thanks, this got me going.  I had to do things a bit differently for 3.6.1.
But the body of DIBuilder::replaceTemporary of 3.7.1 led me to what I need
in MDNodeFwdDecl::replaceAllUsesWith, in Metadata.h of 3.6.1.


On 02/24/2016 04:15 PM, David Jones wrote:
> It's now a multi-stage process.
>
> First, there is a difference between a permanent forward declaration (i.e. the actual definition is in a different file) and a temporary forward declaration (i.e. it will appear later in the same file).
>
> To create a permanent forward declaration:
>
>      DICompositeType     *result = m_DIBuilder->createForwardDecl(
>              dwarf::DW_TAG_structure_type,
>              name,
>              m_DICompileUnit,
>              file,
>              loc.m_Line);
>
> To create a temporary forward declaration:
>
>      DICompositeType     *result = m_DIBuilder->createReplaceableCompositeType(
>              dwarf::DW_TAG_structure_type,
>              name,
>              m_DICompileUnit,
>              file,
>              loc.m_Line);
>
> And then, once the final value of the temporary is known (and you GOTTA do this step otherwise you get an assert):
>
>      DICompositeType     *result = m_DIBuilder->createStructType(
>              m_DICompileUnit,
>              name,
>              file,
>              loc.m_Line,
>              sizeOf(actual) * 8, alignOf(actual) * 8,
>              0, nullptr, elts);
>
>      it = m_TmpStructDI.find(name);
>      if (it != m_TmpStructDI.end()) {
>          MDNode          *node = /* the result from createReplaceableCompositeType earlier */
>          llvm::TempMDNode fwd_decl(node);
>
>          m_DIBuilder->replaceTemporary(std::move(fwd_decl), result);
>
> You will need to keep a map of outstanding temporary forward declarations to do this.
>
> On Wed, Feb 24, 2016 at 5:09 PM, Rodney M. Bates via llvm-dev <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>     Before metadata was separated from values, I could create a debug info forward
>     declaration and eventually resolve it using LLVMReplaceAllUsesWith in core.h.
>     Now, I can't figure out how to resolve it.  I can find no function that seems
>     to do this.  My one wild guess that giving the forward decl and the resolving
>     decl the same UniqueId might do it is not working.
>
>     I am currently using 3.6.1, but I see nothing the voluminous diff of DIBuilder
>     from 3.6.1 to 3.7.1 that looks like it has anything to do with this.
>     --
>     Rodney Bates
>     rodney.m.bates at acm.org <mailto:rodney.m.bates at acm.org>
>     _______________________________________________
>     LLVM Developers mailing list
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>
>

-- 
Rodney Bates
rodney.m.bates at acm.org