[PATCH] D19236: Add DITypeIndex for CodeView and emit it for locals

[Aboud, Amjad via llvm-commits]

I am not convinced that you are going the right direction.
Not only that, now you are confusing me with the double motivation, I asked you before on the proposal of improving debug info if the motivation was CodeView and you said “no”.
Now, you claim that the motivation is fast implementation for CodeView.
I think it is easier/faster/doable to emit CodeView from current Dwarf Metadata, for sure more than you will be able to do with the Blobs/MDStrings that you do not explain yet how it will look like.

I can simply let you commit this patch that adds nothing to what we can do today, but you will need to prove that the next patch (when you support compound types) will work more than we can implement today with what we have in dwarf.
If your approach will fail, will you consider revert and go back to one representation of debug info (Dwarf based or whatever) and do the simple extra work in the backend to emit the format needed by the target?

Thanks,
Amjad

From: Reid Kleckner [mailto:rnk at google.com]
Sent: Thursday, April 21, 2016 23:44
To: David Blaikie <dblaikie at gmail.com>
Cc: reviews+D19236+public+b02ee3c2b2d2b281 at reviews.llvm.org; Aboud, Amjad <amjad.aboud at intel.com>; Duncan P. N. Exon Smith <dexonsmith at apple.com>; Eric Christopher <echristo at gmail.com>; Adrian Prantl <aprantl at apple.com>; llvm-commits <llvm-commits at lists.llvm.org>
Subject: Re: [PATCH] D19236: Add DITypeIndex for CodeView and emit it for locals

On Thu, Apr 21, 2016 at 10:45 AM, David Blaikie <dblaikie at gmail.com<mailto:dblaikie at gmail.com>> wrote:
2.d. Do you have estimation on how much size the "llvm.dbg.cvtypes" will consume? Can you assure we will end up reducing the IR size and not increasing it?
3. If the idea is to reduce the size of the LTO IR, why we are not doing this also for DWARF, why just for CV types?

Because that's a lot of work that's not needed right now. Right now the need is to emit CodeView debug info. The goal is to use the motivation here to experiment with something we've been considering for a while and, if it seems like a good path forward we can port DWARF over to it at some point in the future when someone decides they want to save a few more bytes and cycles.

Yes, thanks for writing that! That's a good way to put it: collectively, we think emitting debug types in the frontend is the right design long term, for both coupling and efficiency reasons. Doing it for DWARF is a large amount of work, and nobody has immediate plans to do it. CodeView, however, does need work, and this is a good opportunity to experiment with up front type emission.

I meant to respond to the RFC with something along those lines, but writing patches is so much more attractive than writing email...
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