[all-commits] [llvm/llvm-project] 904b4f: [clang][timers][modules] Fix a timer being started...

[Alan Zhao via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 904b4f5a27d42a5c76bb485cbdafa94a6f381906
      https://github.com/llvm/llvm-project/commit/904b4f5a27d42a5c76bb485cbdafa94a6f381906
  Author: Alan Zhao <ayzhao at google.com>
  Date:   2025-08-20 (Wed, 20 Aug 2025)

  Changed paths:
    M clang/include/clang/Serialization/ASTReader.h
    M clang/lib/Serialization/ASTReader.cpp

  Log Message:
  -----------
  [clang][timers][modules] Fix a timer being started when it's running (#154231)

`ASTReader::FinishedDeserializing()` calls
`adjustDeductedFunctionResultType(...)` [0], which in turn calls
`FunctionDecl::getMostRecentDecl()`[1]. In modules builds,
`getMostRecentDecl()` may reach out to the `ASTReader` and start
deserializing again. Starting deserialization starts `ReadTimer`;
however, `FinishedDeserializing()` doesn't call `stopTimer()` until
after it's call to `adjustDeductedFunctionResultType(...)` [2]. As a
result, we hit an assert checking that we don't start an already started
timer [3]. To fix this, we simply don't start the timer if it's already
running.

Unfortunately I don't have a test case for this yet as modules builds
are notoriously difficult to reduce.

[0]:
https://github.com/llvm/llvm-project/blob/4d2288d31866013bd361800df4746fbc2fcf742a/clang/lib/Serialization/ASTReader.cpp#L11053
[1]:
https://github.com/llvm/llvm-project/blob/4d2288d31866013bd361800df4746fbc2fcf742a/clang/lib/AST/ASTContext.cpp#L3804
[2]:
https://github.com/llvm/llvm-project/blob/4d2288d31866013bd361800df4746fbc2fcf742a/clang/lib/Serialization/ASTReader.cpp#L11065-L11066
[3]:
https://github.com/llvm/llvm-project/blob/4d2288d31866013bd361800df4746fbc2fcf742a/llvm/lib/Support/Timer.cpp#L150



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