rsmith requested changes to this revision. rsmith added a comment. This revision now requires changes to proceed.
I'd like to see some testcases for the C++ side of this. The following things all seem like they might be interesting: passing and returning classes and unions, especially ones that aren't trivially-copyable, `nullptr_t`, pointers to members, `this` parameters, VTTs, the "complete object" flag for MS ABI constructors, the `this` return from constructors in the ARM ABI, parameters and return values of virtual adjustment thunks. ================ Comment at: clang/lib/CodeGen/CGCall.cpp:1892 + return true; + if (QTy->isScalarType()) { + if (const ComplexType *Complex = dyn_cast<ComplexType>(QTy)) ---------------- This includes `nullptr_t` (which is never ` noundef`) and member pointers (which are sometimes `noundef`, and you'll need to ask the `CXXABI` implementation if you don't want to conservatively return `false`). ================ Comment at: clang/lib/CodeGen/CGCall.cpp:2110 + DetermineNoUndef(RetTy, getTypes(), DL, RetAI)) { + RetAttrs.addAttribute(llvm::Attribute::NoUndef); + } ---------------- This only applies in C++. In C, it's valid for a function to omit its `return` statement if the result value is unused, and in that case the returned value will legitimately be `undef`. Even in C++, we're conservative about enforcing the constraint that functions return a proper value and control flow doesn't just fall off the bottom of the function. See the full set of checks here: https://github.com/llvm/llvm-project/blob/master/clang/lib/CodeGen/CodeGenFunction.cpp#L1322 Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D81678/new/ https://reviews.llvm.org/D81678 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits