================ @@ -652,6 +652,134 @@ in the future. The expected roadmap for Reduced BMIs as of Clang 19.x is: comes, the term BMI will refer to the Reduced BMI and the Full BMI will only be meaningful to build systems which elect to support two-phase compilation. +Experimental No Transitive Change +--------------------------------- + +Starting with clang19.x, we introduced an experimental feature: the non-transitive +change for modules, aimed at reducing unnecessary recompilations. For example, + +.. code-block:: c++ + + // m-partA.cppm + export module m:partA; + + // m-partB.cppm + export module m:partB; + export int getB() { return 44; } + + // m.cppm + export module m; + export import :partA; + export import :partB; + + // useBOnly.cppm + export module useBOnly; + import m; + export int B() { + return getB(); + } + + // Use.cc + import useBOnly; + int get() { + return B(); + } + +Now let's compile the project (For brevity, some commands are omitted.): + +.. code-block:: console + + $ clang++ -std=c++20 m-partA.cppm --precompile -o m-partA.pcm + $ clang++ -std=c++20 m-partB.cppm --precompile -o m-partB.pcm + $ clang++ -std=c++20 m.cppm --precompile -o m.pcm -fprebuilt-module-path=. + $ clang++ -std=c++20 useBOnly.cppm --precompile -o useBOnly.pcm -fprebuilt-module-path=. + $ md5sum useBOnly.pcm + 07656bf4a6908626795729295f9608da useBOnly.pcm + +then let's change the interface of ``m-partA.cppm`` to: + +.. code-block:: c++ + + // m-partA.v1.cppm + export module m:partA; + export int getA() { return 43; } + +Let's compile the BMI for `useBOnly` again: + +.. code-block:: console + + $ clang++ -std=c++20 m-partA.cppm --precompile -o m-partA.pcm + $ clang++ -std=c++20 m-partB.cppm --precompile -o m-partB.pcm + $ clang++ -std=c++20 m.cppm --precompile -o m.pcm -fprebuilt-module-path=. + $ clang++ -std=c++20 useBOnly.cppm --precompile -o useBOnly.pcm -fprebuilt-module-path=. + $ md5sum useBOnly.pcm + 07656bf4a6908626795729295f9608da useBOnly.pcm + +We observed that the contents of useBOnly.pcm remain unchanged. +Consequently, if the build system bases recompilation decisions on directly imported modules only, ---------------- ChuanqiXu9 wrote:
Done https://github.com/llvm/llvm-project/pull/96453 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits