diff options
Diffstat (limited to 'clang/lib/Sema')
| -rw-r--r-- | clang/lib/Sema/SemaDeclCXX.cpp | 109 |
1 files changed, 99 insertions, 10 deletions
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp index 45b03badb2a..8b04f8dfcf5 100644 --- a/clang/lib/Sema/SemaDeclCXX.cpp +++ b/clang/lib/Sema/SemaDeclCXX.cpp @@ -9627,6 +9627,94 @@ CXXMethodDecl *Sema::DeclareImplicitMoveAssignment(CXXRecordDecl *ClassDecl) { return MoveAssignment; } +/// Check if we're implicitly defining a move assignment operator for a class +/// with virtual bases. Such a move assignment might move-assign the virtual +/// base multiple times. +static void checkMoveAssignmentForRepeatedMove(Sema &S, CXXRecordDecl *Class, + SourceLocation CurrentLocation) { + assert(!Class->isDependentContext() && "should not define dependent move"); + + // Only a virtual base could get implicitly move-assigned multiple times. + // Only a non-trivial move assignment can observe this. We only want to + // diagnose if we implicitly define an assignment operator that assigns + // two base classes, both of which move-assign the same virtual base. + if (Class->getNumVBases() == 0 || Class->hasTrivialMoveAssignment() || + Class->getNumBases() < 2) + return; + + llvm::SmallVector<CXXBaseSpecifier *, 16> Worklist; + typedef llvm::DenseMap<CXXRecordDecl*, CXXBaseSpecifier*> VBaseMap; + VBaseMap VBases; + + for (CXXRecordDecl::base_class_iterator BI = Class->bases_begin(), + BE = Class->bases_end(); + BI != BE; ++BI) { + Worklist.push_back(&*BI); + while (!Worklist.empty()) { + CXXBaseSpecifier *BaseSpec = Worklist.pop_back_val(); + CXXRecordDecl *Base = BaseSpec->getType()->getAsCXXRecordDecl(); + + // If the base has no non-trivial move assignment operators, + // we don't care about moves from it. + if (!Base->hasNonTrivialMoveAssignment()) + continue; + + // If there's nothing virtual here, skip it. + if (!BaseSpec->isVirtual() && !Base->getNumVBases()) + continue; + + // If we're not actually going to call a move assignment for this base, + // or the selected move assignment is trivial, skip it. + Sema::SpecialMemberOverloadResult *SMOR = + S.LookupSpecialMember(Base, Sema::CXXMoveAssignment, + /*ConstArg*/false, /*VolatileArg*/false, + /*RValueThis*/true, /*ConstThis*/false, + /*VolatileThis*/false); + if (!SMOR->getMethod() || SMOR->getMethod()->isTrivial() || + !SMOR->getMethod()->isMoveAssignmentOperator()) + continue; + + if (BaseSpec->isVirtual()) { + // We're going to move-assign this virtual base, and its move + // assignment operator is not trivial. If this can happen for + // multiple distinct direct bases of Class, diagnose it. (If it + // only happens in one base, we'll diagnose it when synthesizing + // that base class's move assignment operator.) + CXXBaseSpecifier *&Existing = + VBases.insert(std::make_pair(Base->getCanonicalDecl(), BI)) + .first->second; + if (Existing && Existing != BI) { + S.Diag(CurrentLocation, diag::warn_vbase_moved_multiple_times) + << Class << Base; + S.Diag(Existing->getLocStart(), diag::note_vbase_moved_here) + << (Base->getCanonicalDecl() == + Existing->getType()->getAsCXXRecordDecl()->getCanonicalDecl()) + << Base << Existing->getType() << Existing->getSourceRange(); + S.Diag(BI->getLocStart(), diag::note_vbase_moved_here) + << (Base->getCanonicalDecl() == + BI->getType()->getAsCXXRecordDecl()->getCanonicalDecl()) + << Base << BI->getType() << BaseSpec->getSourceRange(); + + // Only diagnose each vbase once. + Existing = 0; + } + } else { + // Only walk over bases that have defaulted move assignment operators. + // We assume that any user-provided move assignment operator handles + // the multiple-moves-of-vbase case itself somehow. + if (!SMOR->getMethod()->isDefaulted()) + continue; + + // We're going to move the base classes of Base. Add them to the list. + for (CXXRecordDecl::base_class_iterator BI = Base->bases_begin(), + BE = Base->bases_end(); + BI != BE; ++BI) + Worklist.push_back(&*BI); + } + } + } +} + void Sema::DefineImplicitMoveAssignment(SourceLocation CurrentLocation, CXXMethodDecl *MoveAssignOperator) { assert((MoveAssignOperator->isDefaulted() && @@ -9656,16 +9744,9 @@ void Sema::DefineImplicitMoveAssignment(SourceLocation CurrentLocation, // are assigned, in the order in which they were declared in the class // definition. - // FIXME: Issue a warning if our implicit move assignment operator will move - // from a virtual base more than once. For instance, given: - // - // struct A { A &operator=(A&&); }; - // struct B : virtual A {}; - // struct C : virtual A {}; - // struct D : B, C {}; - // - // If the move assignment operator of D is synthesized, we should warn, - // because the A vbase will be moved from multiple times. + // Issue a warning if our implicit move assignment operator will move + // from a virtual base more than once. + checkMoveAssignmentForRepeatedMove(*this, ClassDecl, CurrentLocation); // The statements that form the synthesized function body. SmallVector<Stmt*, 8> Statements; @@ -9692,6 +9773,14 @@ void Sema::DefineImplicitMoveAssignment(SourceLocation CurrentLocation, bool Invalid = false; for (CXXRecordDecl::base_class_iterator Base = ClassDecl->bases_begin(), E = ClassDecl->bases_end(); Base != E; ++Base) { + // C++11 [class.copy]p28: + // It is unspecified whether subobjects representing virtual base classes + // are assigned more than once by the implicitly-defined copy assignment + // operator. + // FIXME: Do not assign to a vbase that will be assigned by some other base + // class. For a move-assignment, this can result in the vbase being moved + // multiple times. + // Form the assignment: // static_cast<Base*>(this)->Base::operator=(static_cast<Base&&>(other)); QualType BaseType = Base->getType().getUnqualifiedType(); |
