From 60dcb8432cff2455488b9226b9cc65b80356146e Mon Sep 17 00:00:00 2001 From: Douglas Gregor Date: Thu, 20 May 2010 08:36:28 +0000 Subject: Rework our handling of binding a reference to a temporary subobject. Previously, we could only properly bind to a base class subobject while extending the lifetime of the complete object (of a derived type); for non-static data member subobjects, we could memcpy (!) the result and bind to that, which is rather broken. Now, we pull apart the expression that we're binding to, to figure out which subobject we're accessing, then construct the temporary object (adding a destruction if needed) and, finally, dig out the subobject we actually meant to access. This fixes yet another instance where we were memcpy'ing rather than doing the right thing. However, note the FIXME in references.cpp: there's more work to be done for binding to subobjects, since the AST is incorrectly modeling some member accesses in base classes as lvalues when they are really rvalues. git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@104219 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/CodeGen/CGExpr.cpp | 118 +++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 100 insertions(+), 18 deletions(-) (limited to 'lib/CodeGen/CGExpr.cpp') diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp index 489a9a2044..80d38f250d 100644 --- a/lib/CodeGen/CGExpr.cpp +++ b/lib/CodeGen/CGExpr.cpp @@ -135,6 +135,39 @@ void CodeGenFunction::EmitAnyExprToMem(const Expr *E, } } +/// \brief An adjustment to be made to the temporary created when emitting a +/// reference binding, which accesses a particular subobject of that temporary. +struct SubobjectAdjustment { + enum { DerivedToBaseAdjustment, FieldAdjustment } Kind; + + union { + struct { + const CXXBaseSpecifierArray *BasePath; + const CXXRecordDecl *DerivedClass; + } DerivedToBase; + + struct { + FieldDecl *Field; + unsigned CVRQualifiers; + } Field; + }; + + SubobjectAdjustment(const CXXBaseSpecifierArray *BasePath, + const CXXRecordDecl *DerivedClass) + : Kind(DerivedToBaseAdjustment) + { + DerivedToBase.BasePath = BasePath; + DerivedToBase.DerivedClass = DerivedClass; + } + + SubobjectAdjustment(FieldDecl *Field, unsigned CVRQualifiers) + : Kind(FieldAdjustment) + { + this->Field.Field = Field; + this->Field.CVRQualifiers = CVRQualifiers; + } +}; + RValue CodeGenFunction::EmitReferenceBindingToExpr(const Expr* E, bool IsInitializer) { bool ShouldDestroyTemporaries = false; @@ -174,19 +207,34 @@ RValue CodeGenFunction::EmitReferenceBindingToExpr(const Expr* E, PopCXXTemporary(); } } else { - const CXXBaseSpecifierArray *BasePath = 0; - const CXXRecordDecl *DerivedClassDecl = 0; + QualType ResultTy = E->getType(); - if (const CastExpr *CE = - dyn_cast(E->IgnoreParenNoopCasts(getContext()))) { - if (CE->getCastKind() == CastExpr::CK_DerivedToBase) { - E = CE->getSubExpr(); - - BasePath = &CE->getBasePath(); - DerivedClassDecl = - cast(E->getType()->getAs()->getDecl()); + llvm::SmallVector Adjustments; + do { + if (const CastExpr *CE + = dyn_cast(E->IgnoreParenNoopCasts(getContext()))) { + if (CE->getCastKind() == CastExpr::CK_DerivedToBase) { + E = CE->getSubExpr(); + CXXRecordDecl *Derived + = cast(E->getType()->getAs()->getDecl()); + Adjustments.push_back(SubobjectAdjustment(&CE->getBasePath(), + Derived)); + continue; + } + } else if (const MemberExpr *ME + = dyn_cast( + E->IgnoreParenNoopCasts(getContext()))) { + if (ME->getBase()->isLvalue(getContext()) != Expr::LV_Valid && + ME->getBase()->getType()->isRecordType()) { + if (FieldDecl *Field = dyn_cast(ME->getMemberDecl())) { + E = ME->getBase(); + Adjustments.push_back(SubobjectAdjustment(Field, + E->getType().getCVRQualifiers())); + continue; + } + } } - } + } while (false); Val = EmitAnyExprToTemp(E, /*IsAggLocVolatile=*/false, IsInitializer); @@ -225,13 +273,47 @@ RValue CodeGenFunction::EmitReferenceBindingToExpr(const Expr* E, } } - // Check if need to perform the derived-to-base cast. - if (BasePath) { - llvm::Value *Derived = Val.getAggregateAddr(); - llvm::Value *Base = - GetAddressOfBaseClass(Derived, DerivedClassDecl, *BasePath, - /*NullCheckValue=*/false); - return RValue::get(Base); + // Check if need to perform derived-to-base casts and/or field accesses, to + // get from the temporary object we created (and, potentially, for which we + // extended the lifetime) to the subobject we're binding the reference to. + if (!Adjustments.empty()) { + llvm::Value *Object = Val.getAggregateAddr(); + for (unsigned I = Adjustments.size(); I != 0; --I) { + SubobjectAdjustment &Adjustment = Adjustments[I-1]; + switch (Adjustment.Kind) { + case SubobjectAdjustment::DerivedToBaseAdjustment: + Object = GetAddressOfBaseClass(Object, + Adjustment.DerivedToBase.DerivedClass, + *Adjustment.DerivedToBase.BasePath, + /*NullCheckValue=*/false); + break; + + case SubobjectAdjustment::FieldAdjustment: { + unsigned CVR = Adjustment.Field.CVRQualifiers; + LValue LV = EmitLValueForField(Object, Adjustment.Field.Field, CVR); + if (LV.isSimple()) { + Object = LV.getAddress(); + break; + } + + // For non-simple lvalues, we actually have to create a copy of + // the object we're binding to. + QualType T = Adjustment.Field.Field->getType().getNonReferenceType() + .getUnqualifiedType(); + Object = CreateTempAlloca(ConvertType(T), "lv"); + EmitStoreThroughLValue(EmitLoadOfLValue(LV, T), + LValue::MakeAddr(Object, + Qualifiers::fromCVRMask(CVR)), + T); + break; + } + } + } + + const llvm::Type *ResultPtrTy + = llvm::PointerType::get(ConvertType(ResultTy), 0); + Object = Builder.CreateBitCast(Object, ResultPtrTy, "temp"); + return RValue::get(Object); } } -- cgit v1.2.3-70-g09d2