================ @@ -444,53 +435,57 @@ For example, the following example is allowed: # Inconsistent debugging level. $ clang++ -std=c++20 -g Use.cpp -fprebuilt-module-path=. -Although the two examples have inconsistent optimization and debugging level, both of them are accepted. +Although the optimization and debugging levels are inconsistent, these +compilations are accepted because the compiler options do not impact the +language dialect. -Note that **currently** the compiler doesn't consider inconsistent macro definition a problem. For example: +Note that the compiler **currently** doesn't reject inconsistent macro +definitions (this may change in the future). For example: .. code-block:: console $ clang++ -std=c++20 M.cppm --precompile -o M.pcm # Inconsistent optimization level. $ clang++ -std=c++20 -O3 -DNDEBUG Use.cpp -fprebuilt-module-path=. -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. - -Definitions consistency -^^^^^^^^^^^^^^^^^^^^^^^ - -The C++ language defines that same declarations in different translation units should have -the same definition, as known as ODR (One Definition Rule). Prior to modules, the translation -units don't dependent on each other and the compiler itself can't perform a strong -ODR violation check. With the introduction of modules, now the compiler have -the chance to perform ODR violations with language semantics across translation units. - -However, in the practice, we found the existing ODR checking mechanism is not stable -enough. Many people suffers from the false positive ODR violation diagnostics, AKA, -the compiler are complaining two identical declarations have different definitions -incorrectly. Also the true positive ODR violations are rarely reported. -Also we learned that MSVC don't perform ODR check for declarations in the global module -fragment. - -So in order to get better user experience, save the time checking ODR and keep consistent -behavior with MSVC, we disabled the ODR check for the declarations in the global module -fragment by default. Users who want more strict check can still use the -``-Xclang -fno-skip-odr-check-in-gmf`` flag to get the ODR check enabled. It is also -encouraged to report issues if users find false positive ODR violations or false negative ODR -violations with the flag enabled. +Currently, Clang accepts the above example though it may produce surprising +results if the debugging code depends on consistent use of ``NDEBUG`` in other +translation units. + +Object definition consistency +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The C++ language requires that the same declarations in different translation +units have the same definition, which is known as the One Definition Rule (ODR). +Prior to modules, the compiler cannot perform strong ODR violation checking +because it only sees one translation unit at a time. With use of modules, the +compiler can perform checks for ODR violations across translation units. + +However, the current ODR checking mechanisms are not perfect. There are a +significant number of false positive ODR violation diagnostics, where the +compiler incorrectly diagnoses two identical declarations as having different +definitions. Further, true positive ODR violations are not always reported. +Additionally, MSVC does not currently perform ODR checking for declarations in +the global module fragment. + ---------------- cor3ntin wrote:
Why are we talking about msvc? The mention below is sufficient https://github.com/llvm/llvm-project/pull/90237 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
