dblaikie added a comment. In D90719#2376388 <https://reviews.llvm.org/D90719#2376388>, @rnk wrote:
> In D90719#2372656 <https://reviews.llvm.org/D90719#2372656>, @dblaikie wrote: > >> My understanding is that such code is UB, is that right? > > I guess I'm not convinced it's UB, and need some language lawyering help to > decide. Fair enough. The code we're talking about essentially boils down to this, right: struct non_trivially_constructible { non_trivially_constructible(); int i; }; struct implicitly_non_trivially_constructible : non_trivially_constructible { }; void f1() { using T = implicitly_non_trivially_constructible; alignas(T) unsigned char data[sizeof(T)]; T* t = static_cast<T*>(&data); t->i = 3; ... } Yeah? My understanding is that the lifetime of the T object hasn't started, because its ctor hasn't been run. For trivial types that's a bit fuzzier (eg: `int *i = (int*)malloc(sizeof(int)); *i = 3;` - we don't usually bother to call the pseudodestructor on this type) but for a non-trivially constructible thing, I'd think that was pretty well required/guaranteed by the language? (sort of by definition of non-trivially constructible) Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D90719/new/ https://reviews.llvm.org/D90719 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
