llvm-project

7f482aa8 - [clang modules] Setting `DebugCompilationDir` when it is safe to ignore current working directory (#128446)

[clang modules] Setting `DebugCompilationDir` when it is safe to ignore current working directory (#128446) This PR explicitly sets `DebugCompilationDir` to the system's root directory if it is safe to ignore the current working directory. This fixes a problem where a PCM file's embedded debug information can lead to compilation failure. The compiler may have decided it is indeed safe to ignore the current working directory. In this case, the PCM file's content is functionally correct regardless of the current working directory because no inputs use relative paths (see https://github.com/llvm/llvm-project/pull/124786). However, a PCM may contain debug info. If debug info is requested, the compiler uses the current working directory value to set `DW_AT_comp_dir`. This may lead to the following situation: 1. Two different compilations need the same PCM file. 2. The PCM file is compiled assuming a working directory, which is embedded in the debug info, but otherwise has no effect. 3. The second compilation assumes a different working directory, and expects an identically-sized pcm file. However, it cannot find such a PCM, because the existing PCM file has been compiled assuming a different `DW_AT_comp_dir `, which is embedded in the debug info. This PR resets the `DebugCompilationDir` if it is functionally safe to ignore the working directory so the above situation is avoided, since all debug information will share the same working directory. rdar://145249881