ChuanqiXu added a comment. In D145639#4198837 <https://reviews.llvm.org/D145639#4198837>, @ilya-biryukov wrote:
> In D145639#4198794 <https://reviews.llvm.org/D145639#4198794>, @ChuanqiXu > wrote: > >>> ! In D145639#4198815 <https://reviews.llvm.org/D145639#4198815>, @ChuanqiXu >>> wrote: >>> The RVO seems to be mandated by the standard. >> >> Yeah, I thought so... But WG21 decided to not make it in a recent meeting... >> So we can only make it as a non-mandated compiler optimization. > > That's unexpected. Are there any wording change proposals published? > Our understanding comes from the reading of dcl.fct.def.coroutine/7 > <https://timsong-cpp.github.io/cppwp/n4868/dcl.fct.def.coroutine#7> > >> The expression promise.get_return_object() is used to initialize the glvalue >> result or prvalue result object of a call to a coroutine. > > And we **think** RVO is mandated when initializing the **result objects** > mentioned in general. > Also, from https://github.com/llvm/llvm-project/issues/56532: > >> Q: if the initialization does occur later, by what mechanism the prvalue >> result of get_return_object is forwarded to that initialization. >> A: (see below) >> Case 1/2. Same type of get_return_object and coroutine return type. >> **Constructed in the return slot.** >> Case 3. Different types: >> (1) Constructed temporary object prior to initial suspend initialized with a >> call to get_return_object() >> (2) when coroutine needs to to return to the caller and needs to construct >> return value for the coroutine it is initialized with expiring value of the >> temporary obtained in step 1. The formal file shouldn't be released yet. But we can find the issue report and the proposed solution in https://cplusplus.github.io/CWG/issues/2563.html. The words you quoted is the recording of the wg21's discussion during the meeting. And that's the **intention** of the designers but it is not reflected to the wording. What issue 2563 discussed is that if we should delay the conversion. And the RVO is a conclusion of that. But according to the result, we should say the compiler is allowed to do RVO if the types matched but it is not required. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D145639/new/ https://reviews.llvm.org/D145639 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
