[PATCH] D124420: [Serialization] Compress serialized macro expansion SLocEntries

[Sam McCall via Phabricator via cfe-commits]

sammccall created this revision.
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Macro expansion SLocEntries are significant to PCH size (7-10% in my tests).
These store the expansion end location as vbr8. However it's highly predictable:

- for macro arg expansion it's zero
- for object macros it equals the expansion start
- for function macros it's usually shortly after the expansion start

Instead, this change stores (bool relative, unsigned value).
If relative is true, ExpEnd is ExpBegin+value, otherwise it's just value.
We define abbreviations to cover the common cases above.

This saves ~15% of SM_SLOC_EXPANSION, which is 1-1.5% of overall PCH size.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D124420

Files:
  clang/lib/Serialization/ASTReader.cpp
  clang/lib/Serialization/ASTWriter.cpp

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