[llvm-dev] Can creating new forms of debug info metadata be simplified? [formatting fixed]

[David Blaikie via llvm-dev]

+some of the debug info cabal (& Duncan, as an emeritus member, and person
who plumbed a lot of the current debug info syntax support in)

Visitor seems plausible though I haven't looked at the code in detail to
see if it'd work perfectly.

On Tue, May 29, 2018 at 7:56 AM Sohail Somani (Fizz Buzz Inc.) via llvm-dev
<llvm-dev at lists.llvm.org> wrote:

> [Resending due to accidental markdown rendering - sorry]
>
> Hi list,
>
> Let's talk about adding a new type of debug info metadata. Here are the
> steps (at minimum - probably incomplete) one needs to take:
>
> 1. Create a new class in the hierarchy
> 2. Implement two forms of `MD_NODE_GET`
> 3. Specialize `MDNodeKeyImpl`
> 4. Modify `LLParser.cpp` and add serialization code for your special type
> 5. Modify `AsmWriter.cpp` and add serialization code for your special type
>
> I believe we can accomplish everything needed for debug info with just
> step 1 using a pattern found in Boost Serialization. Imagine a new API
> based on this concept:
>
> ```
> class DIMyFancyType : public MDNode {
>   StringRef FileName;
>
>   template<typename Visitor>
>   void visit(Visitor & v) {
>      DINode::visit(s); // or not, if you stay true to boost.serialization
>      v.name("DIMyFancyType");
>      v.property("FileName",FileName);
>   }
> };
> ```
>
> With this, we could implement steps 2-5 using a little bit of template
> meta-programming and we could also implement escape hatches where needed to
> get more specific, allowing us to keep many things in one place.
>
> I imagine since there is now a `.def` file for the metadata (very useful!)
> that this is on somebody's mind and not just my own, so I'm curious about
> what people think. I realize that "new forms of debug metadata" is possibly
> not a very popular use case as there has been only one new kind added in
> the last few years. However, in my humble opinion, it would make it easier
> to add richer information allowing those of us extending LLVM to create
> better debuggers/debugging experiences.
>
> Thanks for your time!
>
> --
> Sohail Somani
> Fizz Buzz Inc.
> Booking schedule: https://sohailsomani.youcanbook.me
>
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