[all-commits] [llvm/llvm-project] 2e5af5: [C++20] [Modules] Allow to compile a pcm with and ...

[Chuanqi Xu via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 2e5af56b05c2d39ab2c829bf4c13190523b67ddd
      https://github.com/llvm/llvm-project/commit/2e5af56b05c2d39ab2c829bf4c13190523b67ddd
  Author: Chuanqi Xu <yedeng.yd at linux.alibaba.com>
  Date:   2024-02-23 (Fri, 23 Feb 2024)

  Changed paths:
    M clang/include/clang/Frontend/ASTUnit.h
    M clang/include/clang/Frontend/CompilerInstance.h
    M clang/include/clang/Frontend/CompilerInvocation.h
    M clang/lib/Frontend/ASTUnit.cpp
    M clang/lib/Frontend/FrontendAction.cpp
    A clang/test/Modules/compile-pcm-with-pic.cppm
    M clang/tools/c-index-test/core_main.cpp
    M clang/tools/libclang/CIndex.cpp

  Log Message:
  -----------
  [C++20] [Modules] Allow to compile a pcm with and without -fPIC
seperately

We can compile a module unit in 2 phase compilaton:

```
clang++ -std=c++20 a.cppm --precompile -o a.pcm
clang++ -std=c++20 a.pcm -c -o a.o
```

And it is a general requirement that we need to compile a translation
unit with and without -fPIC for static and shared libraries.

But for C++20 modules with 2 phase compilation, it may be waste of time
to compile them 2 times completely. It may be fine to generate one BMI
and compile it with and without -fPIC seperately.

e.g.,

```
clang++ -std=c++20 a.cppm --precompile -o a.pcm
clang++ -std=c++20 a.pcm -c -o a.o
clang++ -std=c++20 a.pcm -c -fPIC -o a-PIC.o
```

Then we can save the time to parse a.cppm repeatedly.



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