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

[David Jones via llvm-dev]

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> 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
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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