[PATCH] D97417: [clangd] use a compatible preamble for the first AST built

[Sam McCall via Phabricator via cfe-commits]

sammccall added a comment.

@kadircet who was doing (or planning!) some measurements around this idea. Maybe it's possible to use this patch for them?

My guess about risks:

- currently, preamble patching covers relatively few extra headers in practice. Here we're likely to end up with larger divergences which might lead to really terrible AST build times (e.g. what if we're missing 30% of a 500MB preamble...)
- maybe extra resource consumption from the +5 cached preambles (e.g. in preamble-in-ram case), but I guess this number can just be tuned


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D97417/new/

https://reviews.llvm.org/D97417