[PATCH] D158136: [clang][modules] Avoid storing command-line macro definitions into implicitly built PCM files

[Jan Svoboda via Phabricator via cfe-commits]

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With implicit modules, it's impossible to load a PCM file that was built using different command-line macro definitions. This is guaranteed by the fact that they contribute to the context hash. This means that we don't need to store those macros into PCM files for validation purposes. This patch avoids serializing them in those circumstances, since there's no other use for command-line macro definitions (besides "-module-file-info").

For a typical Apple project, this speeds up the dependency scan by 5.6% and shrinks the cache with scanning PCMs by 26%.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D158136

Files:
  clang/include/clang/Serialization/ASTReader.h
  clang/include/clang/Serialization/ASTWriter.h
  clang/lib/Frontend/ASTUnit.cpp
  clang/lib/Frontend/FrontendActions.cpp
  clang/lib/Serialization/ASTReader.cpp
  clang/lib/Serialization/ASTWriter.cpp
  clang/lib/Serialization/GeneratePCH.cpp
  clang/test/Modules/module_file_info.m

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