[all-commits] [llvm/llvm-project] 44af53: [clang][modules] Avoid calling expensive `SourceMa...

[Jan Svoboda via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 44af53b22aaa1fe382b22329bbc7e4610ecbacc8
      https://github.com/llvm/llvm-project/commit/44af53b22aaa1fe382b22329bbc7e4610ecbacc8
  Author: Jan Svoboda <jan_svoboda at apple.com>
  Date:   2024-03-28 (Thu, 28 Mar 2024)

  Changed paths:
    M clang/include/clang/Lex/ModuleMap.h
    M clang/lib/Frontend/CompilerInstance.cpp
    M clang/lib/Frontend/FrontendAction.cpp
    M clang/lib/Lex/ModuleMap.cpp
    M clang/lib/Serialization/ASTWriter.cpp
    M clang/test/ClangScanDeps/modules-extern-unrelated.m

  Log Message:
  -----------
  [clang][modules] Avoid calling expensive `SourceManager::translateFile()` (#86216)

The `ASTWriter` algorithm for computing affecting module maps uses
`SourceManager::translateFile()` to get a `FileID` from a `FileEntry`.
This is slow (O(n)) since the function performs a linear walk over
`SLocEntries` until it finds one with a matching `FileEntry`.

This patch removes this use of `SourceManager::translateFile()` by
tracking `FileID` instead of `FileEntry` in couple of places in
`ModuleMap`, giving `ASTWriter` the desired `FileID` directly. There are
no changes required for clients that still want a `FileEntry` from
`ModuleMap`: the existing APIs internally use `SourceManager` to perform
the reverse `FileID` to `FileEntry` conversion in O(1).



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