[llvm] [RemoveDIs] Read/write DbgRecords directly from/to bitcode (PR #83251)

[Orlando Cazalet-Hyams via llvm-commits]

https://github.com/OCHyams commented:

> The metadata reference sizes in the abbrev seem small though, is metadata packed in around each function? (I'd always imagined it was one massive block with an average node-count of several thousands).

VBR 7 yielded the best result for the samples I was looking, over a few different sizes that I tried. I've pushed some different VBR widths to OCHyams/perf/ddd-bitcode2 on the compiletime tracker, which agrees that 6 or 7 is best for CTMark (look at the per-file size comparisons).

> IMO: this patch should be landed in a default-off state for the write-out-removedis-bitcode flag

SGTM, done


> I've done some review of the structure and implementation here -- higher level thoughts such as "should we be using this number-space" and so forth are beyond me.

@dblaikie do you have any strong feelings about this? Is it alright to add 5 record types and a function block-info abbrev?

https://github.com/llvm/llvm-project/pull/83251