rusyaev-roman added inline comments.
================ Comment at: clang/lib/Sema/Scope.cpp:152-154 + // Consider the variable as NRVO candidate if the return slot is available + // for it in the current scope, or if it can be available in outer scopes. + NRVO = CanBePutInReturnSlot ? VD : nullptr; ---------------- ChuanqiXu wrote: > rusyaev-roman wrote: > > ChuanqiXu wrote: > > > What if NRVO contains a value already? It is possible due to the value of > > > NRVO could be set by its children. > > Actually this is intention. If the parent has already NRVO candidate, then > > it should be invalidated (or not). Let's consider the following examples: > > > > > > ``` > > X foo(bool b) { > > X x; > > X y; > > if (b) > > return x; > > else > > return y; // when we process this return statement, the parent has > > already NRVO and it will be invalidated (this is correct behavior) > > } > > ``` > > > > ``` > > X foo(bool b) { > > X x; > > if (b) > > return x; > > > > X y; > > // when we process this return statement, the parent has already NRVO > > and it WON't be invalidated > > // (this is correct behavior), because a return slot will be available > > for it > > return y; > > } > > ``` > > > > ``` > > X foo(bool b) { > > X x; > > if (b) > > return x; > > > > // when we process this return statement, the parent has already NRVO > > and it WON't be invalidated (this is correct behavior) > > return x; > > } > > ``` > > > > ``` > > X foo(bool b, X x) { > > X y; > > > > if (b) > > return x; > > > > // when we process this return statement, the parent contains nullptr > > (invalid candidate) and it will be invalidated (this is correct behavior) > > return y; > > } > > ``` > > > > ``` > > X foo(bool b, X x) { > > if (b) > > return x; > > > > X y; > > // when we process this return statement, the parent contains nullptr > > (invalid candidate) and it WON't be invalidated (this is correct behavior) > > return y; > > } > > ``` > Oh, I see. Tricky. I don't find invalid cases now. But I recommend to comment > that the children would maintain the `ReturnSlots` of their parents. (This is > anti-intuition) > > Have you tested any larger projects? Like libc++, libstdc++ or something like > folly. I feel we need to do such tests to avoid we get anything wrong. I've already added a comment at the beginning of `updateNRVOCandidate` function where this point is mentioned: ``` // ... Therefore, we need to clear return slots for other // variables defined before the current return statement in the current // scope and in outer scopes. ``` If it's not enough, please let me know. > Have you tested any larger projects? Yes, I've built the `clang` itself and `compiler-rt` project. Then I've checked them to run 'check-all' (on built clang and compiler-rt). Everything works. Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D119792/new/ https://reviews.llvm.org/D119792 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits