From: Douglas Gregor Date: Thu, 20 May 2010 08:36:28 +0000 (+0000) Subject: Rework our handling of binding a reference to a temporary X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=60dcb8432cff2455488b9226b9cc65b80356146e;p=clang 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 --- 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); } } diff --git a/test/CodeGenCXX/references.cpp b/test/CodeGenCXX/references.cpp index 3ae1e474f8..ed162492b3 100644 --- a/test/CodeGenCXX/references.cpp +++ b/test/CodeGenCXX/references.cpp @@ -1,4 +1,4 @@ -// RUN: %clang_cc1 -verify -emit-llvm -o - %s | FileCheck %s +// RUN: %clang_cc1 -triple x86_64-apple-darwin -verify -emit-llvm -o - %s | FileCheck %s void t1() { extern int& a; int b = a; @@ -168,3 +168,56 @@ namespace N1 { const int* const args_array[] = { &arg }; } } + +// Bind to subobjects while extending the life of the complete object. +namespace N2 { + class X { + public: + X(const X&); + X &operator=(const X&); + ~X(); + }; + + struct P { + X first; + }; + + P getP(); + + // CHECK: define void @_ZN2N21fEi + // CHECK: call void @_ZN2N24getPEv + // CHECK: getelementptr inbounds + // CHECK: store i32 17 + // CHECK: call void @_ZN2N21PD1Ev + void f(int i) { + const X& xr = getP().first; + i = 17; + } + + struct SpaceWaster { + int i, j; + }; + + struct ReallyHasX { + X x; + }; + + struct HasX : ReallyHasX { }; + + struct HasXContainer { + HasX has; + }; + + struct Y : SpaceWaster, HasXContainer { }; + struct Z : SpaceWaster, Y { }; + + Z getZ(); + + // CHECK: define void @_ZN2N21gEi + // CHECK: call void @_ZN2N24getZEv + // FIXME: Not treated as an lvalue! + void g(int i) { + const X &xr = getZ().has.x; + i = 19; + } +}