zequanwu added a comment. In D96832#2569987 <https://reviews.llvm.org/D96832#2569987>, @ahatanak wrote:
> In D96832#2569481 <https://reviews.llvm.org/D96832#2569481>, @zequanwu wrote: > >> In D96832#2568257 <https://reviews.llvm.org/D96832#2568257>, @aaron.ballman >> wrote: >> >>> It was explicitly disallowed in the initial patch: >>> https://reviews.llvm.org/D12922 and the original author said "I'm still >>> trying to figure out the best way to handle c++ virtual functions: this >>> attribute is not very useful for someone who is looking for a way to >>> reliably prevent tail-call to a virtual function." and "I made this change >>> because this attribute isn't useful when the compiler cannot resolve the >>> function call statically at compile time and it isn't important for the use >>> case I have." Has this situation changed in the backend? >> >> Oh, I didn't see that. But when I tested `not_tail_called` on normal >> functions, it seems like not working(https://godbolt.org/z/znr5b5, `f1` is >> marked as `not_tail_called`, it still get inlined). Or, I misunderstand how >> to use it properly? > > I'm still trying to remember the discussions we had, but I think we banned > the attribute on virtual functions because you can't in general promise a > call to an annotated function won't be tail called if the function is virtual. > > This patch doesn't prevent the call to `method` in the code below from being > tail called, but I suppose users would except the attribute to prevent the > tail call? > > struct B { > virtual void method(); > }; > > struct D : B { > [[clang::not_tail_called]] void method() override; > }; > > void test(D *d) { > B *b = D; > b->method(); > } I got the point about why preventing it on virtual functions. But, on the above godbolt link, I provided a example where `not_tail_called` doesn't prevent a non-virtual function from tail call. I wonder if I use it correctly. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D96832/new/ https://reviews.llvm.org/D96832 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
