Author: Chuanqi Xu Date: 2023-05-10T09:59:50+08:00 New Revision: 7adf3849e40e0b9faa3512874e2a1dc4cf86387a
URL: https://github.com/llvm/llvm-project/commit/7adf3849e40e0b9faa3512874e2a1dc4cf86387a DIFF: https://github.com/llvm/llvm-project/commit/7adf3849e40e0b9faa3512874e2a1dc4cf86387a.diff LOG: [docs] [C++20] [Modules] Remove the section 'Source content consistency' Since the C++20 named modules won't check source files consistency after 5b388f8, it would be better to remove this section in the document. Added: Modified: clang/docs/StandardCPlusPlusModules.rst Removed: ################################################################################ diff --git a/clang/docs/StandardCPlusPlusModules.rst b/clang/docs/StandardCPlusPlusModules.rst index a59a3edbbbac..ee8ffe9ec8c9 100644 --- a/clang/docs/StandardCPlusPlusModules.rst +++ b/clang/docs/StandardCPlusPlusModules.rst @@ -461,109 +461,6 @@ Note that **currently** the compiler doesn't consider inconsistent macro definit Currently Clang would accept the above example. But it may produce surprising results if the debugging code depends on consistent use of ``NDEBUG`` also in other translation units. -Source content consistency -^^^^^^^^^^^^^^^^^^^^^^^^^^ - -When the compiler reads a BMI, the compiler will check the consistency of the corresponding -source files. For example: - -.. code-block:: c++ - - // M.cppm - export module M; - export template <class T> - T foo(T t) { - return t; - } - - // Use.cpp - import M; - void bar() { - foo(5); - } - -.. code-block:: console - - $ clang++ -std=c++20 M.cppm --precompile -o M.pcm - $ rm M.cppm - $ clang++ -std=c++20 Use.cpp -fmodule-file=M=M.pcm - -The compiler would reject the example since the compiler failed to find the source file to check the consistency. -So the following example would be rejected too. - -.. code-block:: console - - $ clang++ -std=c++20 M.cppm --precompile -o M.pcm - $ echo "int i=0;" >> M.cppm - $ clang++ -std=c++20 Use.cpp -fmodule-file=M=M.pcm - -The compiler would reject it too since the compiler detected the file was changed. - -But it is OK to move the BMI as long as the source files remain: - -.. code-block:: console - - $ clang++ -std=c++20 M.cppm --precompile -o M.pcm - $ mkdir -p tmp - $ mv M.pcm tmp/M.pcm - $ clang++ -std=c++20 Use.cpp -fmodule-file=M=tmp/M.pcm - -The above example would be accepted. - -If the user doesn't want to follow the consistency requirement due to some reasons (e.g., distributing BMI), -the user could try to use ``-Xclang -fmodules-embed-all-files`` when producing BMI. For example: - -.. code-block:: console - - $ clang++ -std=c++20 M.cppm --precompile -Xclang -fmodules-embed-all-files -o M.pcm - $ rm M.cppm - $ clang++ -std=c++20 Use.cpp -fmodule-file=M=M.pcm - -Now the compiler would accept the above example. -Important note: Xclang options are intended to be used by compiler internally and its semantics -are not guaranteed to be preserved in future versions. - -Also the compiler will record the path to the header files included in the global module fragment and compare the -headers when imported. For example, - -.. code-block:: c++ - - // foo.h - #include <iostream> - void Hello() { - std::cout << "Hello World.\n"; - } - - // foo.cppm - module; - #include "foo.h" - export module foo; - export using ::Hello; - - // Use.cpp - import foo; - int main() { - Hello(); - } - -Then it is problematic if we remove ``foo.h`` before import `foo` module. - -.. code-block:: console - - $ clang++ -std=c++20 foo.cppm --precompile -o foo.pcm - $ mv foo.h foo.orig.h - # The following one is rejected - $ clang++ -std=c++20 Use.cpp -fmodule-file=foo=foo.pcm -c - -The above case will rejected. And we're still able to workaround it by ``-Xclang -fmodules-embed-all-files`` option: - -.. code-block:: console - - $ clang++ -std=c++20 foo.cppm --precompile -Xclang -fmodules-embed-all-files -o foo.pcm - $ mv foo.h foo.orig.h - $ clang++ -std=c++20 Use.cpp -fmodule-file=foo=foo.pcm -c -o Use.o - $ clang++ Use.o foo.pcm - ABI Impacts ----------- _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
