[clang] [flang] [llvm] [mlir] [polly] [CMake][LLVM] Add PCH infrastructure and LLVMSupport PCH (PR #176420)

[Chuanqi Xu via llvm-commits]

ChuanqiXu9 wrote:


> * But the results for Clang appear to be correct and there is the expected number of cache hits from source files. It appears that Clang doesn't include macro definitions in the PCH? At least in my tests, the PCH ended up being identical (same hash sum)? (@ChuanqiXu9 @Bigcheese is this correct?)


I think clang include the macro definition in the PCH. You can verify this by inserting outputs to ASTWriter::WritePreprocessor

https://github.com/llvm/llvm-project/pull/176420