efriedma added a comment. There are multiple notions of "constant" here:
- Whether a value is invariant at runtime. - Whether a value is legal in a "constexpr" expression. - Whether we can emit a constant without emitting code that runs at startup to initialize it. The third is generally a superset of the second; most targets have relocations that allow us emit the address of a global variable into another global variable. dllimport variables are an exception: even though the address is constant, we can't emit a relocation. To make this work, what we need to do is: - Extend the notion of a "constant" in the AST/Sema to allow dllimport variables. (There should be code specifically checking for dllimport variables; we just need to drop that check.) - Teach IR generation (clang/lib/CodeGen) how to emit constants that don't have a relocation. This probably means a check that if we're generating the initializer for a global variable, and the initializer refers to the address of a dllimport variable, we instead emit a global constructor. (Maybe with a higher priority that normal global constructor, so the user can't accidentally observe an uninitialized variable? I forget if MSVC actually has constructor priorities...). Or I guess as an initial patch, we could just emit an error if we detect this case. CHANGES SINCE LAST ACTION https://reviews.llvm.org/D137107/new/ https://reviews.llvm.org/D137107 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
