[PATCH] D68620: DebugInfo: Use base address selection entries for debug_loc

[Paul Robinson via Phabricator via llvm-commits]

probinson added a subscriber: Orlando.
probinson added a comment.

In D68620#2266531 <https://reviews.llvm.org/D68620#2266531>, @dblaikie wrote:

> @probinson - do you have any state here? Whether this is an ongoing issue, whether the improvements to avoid unnecessary debug_loc have reduced the overhead sufficiently, etc?

@Orlando mentioned he was collecting some size data that would be relevant here, he'll post it when he's done.  Basically .debug_loc sizes at various points.

But naively, pre-v5, base-address entries can only make lists longer, and for short lists the size cost is big while the reduction in relocations is small.  I'd have to agree with @wolfgangp that the space-time tradeoff probably is not favorable for small lists, and maybe there should be some threshold.  I know that's more complicated on the emission side, but it's not a trivial thing in the final object.  Orlando showed me a preliminary chart where .debug_loc went from ~30% of all debug info in LLVM 5.0 to ~50% in LLVM 10.0, in one of our benchmarks.


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