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Refactor constant expression evaluation to associate the complete object of a 

materialized temporary with the corresponding MaterializeTemporaryExpr. This is
groundwork for providing C++11's guaranteed static initialization for global
references bound to lifetime-extended temporaries (if the initialization is a
constant expression).

In passing, fix a couple of bugs where some evaluation failures didn't trigger
diagnostics, and a rejects-valid where potential constant expression testing
would assume that it knew the dynamic type of *this and would reject programs
which relied on it being some derived type.

llvm-svn: 183093
This commit is contained in:
Richard Smith 2013-06-03 05:03:02 +00:00
parent 2fcb73984a
commit 844010455d
3 changed files with 178 additions and 89 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

248
clang/lib/AST/ExprConstant.cpp
View File

@ -63,7 +63,25 @@ namespace {
if (!B) return QualType();
if (const ValueDecl *D = B.dyn_cast<const ValueDecl*>())
return D->getType();
return B.get<const Expr*>()->getType();
const Expr *Base = B.get<const Expr*>();
// For a materialized temporary, the type of the temporary we materialized
// may not be the type of the expression.
if (const MaterializeTemporaryExpr *MTE =
dyn_cast<MaterializeTemporaryExpr>(Base)) {
SmallVector<const Expr *, 2> CommaLHSs;
SmallVector<SubobjectAdjustment, 2> Adjustments;
const Expr *Temp = MTE->GetTemporaryExpr();
const Expr *Inner = Temp->skipRValueSubobjectAdjustments(CommaLHSs,
Adjustments);
// Keep any cv-qualifiers from the reference if we generated a temporary
// for it.
if (Inner != Temp)
return Inner->getType();
}
return Base->getType();
}
/// Get an LValue path entry, which is known to not be an array index, as a
@ -625,31 +643,7 @@ CallStackFrame::~CallStackFrame() {
Info.CurrentCall = Caller;
}
/// Produce a string describing the given constexpr call.
static void describeCall(CallStackFrame *Frame, raw_ostream &Out) {
unsigned ArgIndex = 0;
bool IsMemberCall = isa<CXXMethodDecl>(Frame->Callee) &&
!isa<CXXConstructorDecl>(Frame->Callee) &&
cast<CXXMethodDecl>(Frame->Callee)->isInstance();
if (!IsMemberCall)
Out << *Frame->Callee << '(';
for (FunctionDecl::param_const_iterator I = Frame->Callee->param_begin(),
E = Frame->Callee->param_end(); I != E; ++I, ++ArgIndex) {
if (ArgIndex > (unsigned)IsMemberCall)
Out << ", ";
const ParmVarDecl *Param = *I;
const APValue &Arg = Frame->Arguments[ArgIndex];
Arg.printPretty(Out, Frame->Info.Ctx, Param->getType());
if (ArgIndex == 0 && IsMemberCall)
Out << "->" << *Frame->Callee << '(';
}
Out << ')';
}
static void describeCall(CallStackFrame *Frame, raw_ostream &Out);
void EvalInfo::addCallStack(unsigned Limit) {
// Determine which calls to skip, if any.
@ -921,6 +915,42 @@ static bool EvaluateAtomic(const Expr *E, APValue &Result, EvalInfo &Info);
// Misc utilities
//===----------------------------------------------------------------------===//
/// Produce a string describing the given constexpr call.
static void describeCall(CallStackFrame *Frame, raw_ostream &Out) {
unsigned ArgIndex = 0;
bool IsMemberCall = isa<CXXMethodDecl>(Frame->Callee) &&
!isa<CXXConstructorDecl>(Frame->Callee) &&
cast<CXXMethodDecl>(Frame->Callee)->isInstance();
if (!IsMemberCall)
Out << *Frame->Callee << '(';
if (Frame->This && IsMemberCall) {
APValue Val;
Frame->This->moveInto(Val);
Val.printPretty(Out, Frame->Info.Ctx,
Frame->This->Designator.MostDerivedType);
// FIXME: Add parens around Val if needed.
Out << "->" << *Frame->Callee << '(';
IsMemberCall = false;
}
for (FunctionDecl::param_const_iterator I = Frame->Callee->param_begin(),
E = Frame->Callee->param_end(); I != E; ++I, ++ArgIndex) {
if (ArgIndex > (unsigned)IsMemberCall)
Out << ", ";
const ParmVarDecl *Param = *I;
const APValue &Arg = Frame->Arguments[ArgIndex];
Arg.printPretty(Out, Frame->Info.Ctx, Param->getType());
if (ArgIndex == 0 && IsMemberCall)
Out << "->" << *Frame->Callee << '(';
}
Out << ')';
}
/// Evaluate an expression to see if it had side-effects, and discard its
/// result.
/// \return \c true if the caller should keep evaluating.
@ -1541,6 +1571,19 @@ static bool HandleLValueBase(EvalInfo &Info, const Expr *E, LValue &Obj,
return true;
}
static bool HandleLValueBasePath(EvalInfo &Info, const CastExpr *E,
QualType Type, LValue &Result) {
for (CastExpr::path_const_iterator PathI = E->path_begin(),
PathE = E->path_end();
PathI != PathE; ++PathI) {
if (!HandleLValueBase(Info, E, Result, Type->getAsCXXRecordDecl(),
*PathI))
return false;
Type = (*PathI)->getType();
}
return true;
}
/// Update LVal to refer to the given field, which must be a member of the type
/// currently described by LVal.
static bool HandleLValueMember(EvalInfo &Info, const Expr *E, LValue &LVal,
@ -2152,7 +2195,7 @@ CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E, AccessKinds AK,
// Compute value storage location and type of base object.
APValue *BaseVal = 0;
QualType BaseType;
QualType BaseType = getType(LVal.Base);
if (const ValueDecl *D = LVal.Base.dyn_cast<const ValueDecl*>()) {
// In C++98, const, non-volatile integers initialized with ICEs are ICEs.
@ -2173,7 +2216,6 @@ CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E, AccessKinds AK,
}
// Accesses of volatile-qualified objects are not allowed.
BaseType = VD->getType();
if (BaseType.isVolatileQualified()) {
if (Info.getLangOpts().CPlusPlus) {
Info.Diag(E, diag::note_constexpr_access_volatile_obj, 1)
@ -2241,7 +2283,6 @@ CompleteObject findCompleteObject(EvalInfo &Info, const Expr *E, AccessKinds AK,
return CompleteObject();
}
BaseType = Base->getType();
BaseVal = &Frame->Temporaries[Base];
// Volatile temporary objects cannot be accessed in constant expressions.
@ -2630,54 +2671,53 @@ static bool EvaluateObjectArgument(EvalInfo &Info, const Expr *Object,
/// lvalue referring to the result.
///
/// \param Info - Information about the ongoing evaluation.
/// \param BO - The member pointer access operation.
/// \param LV - Filled in with a reference to the resulting object.
/// \param LV - An lvalue referring to the base of the member pointer.
/// \param RHS - The member pointer expression.
/// \param IncludeMember - Specifies whether the member itself is included in
/// the resulting LValue subobject designator. This is not possible when
/// creating a bound member function.
/// \return The field or method declaration to which the member pointer refers,
/// or 0 if evaluation fails.
static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
const BinaryOperator *BO,
QualType LVType,
LValue &LV,
const Expr *RHS,
bool IncludeMember = true) {
assert(BO->getOpcode() == BO_PtrMemD || BO->getOpcode() == BO_PtrMemI);
bool EvalObjOK = EvaluateObjectArgument(Info, BO->getLHS(), LV);
if (!EvalObjOK && !Info.keepEvaluatingAfterFailure())
return 0;
MemberPtr MemPtr;
if (!EvaluateMemberPointer(BO->getRHS(), MemPtr, Info))
if (!EvaluateMemberPointer(RHS, MemPtr, Info))
return 0;
// C++11 [expr.mptr.oper]p6: If the second operand is the null pointer to
// member value, the behavior is undefined.
if (!MemPtr.getDecl())
return 0;
if (!EvalObjOK)
if (!MemPtr.getDecl()) {
// FIXME: Specific diagnostic.
Info.Diag(RHS);
return 0;
}
if (MemPtr.isDerivedMember()) {
// This is a member of some derived class. Truncate LV appropriately.
// The end of the derived-to-base path for the base object must match the
// derived-to-base path for the member pointer.
if (LV.Designator.MostDerivedPathLength + MemPtr.Path.size() >
LV.Designator.Entries.size())
LV.Designator.Entries.size()) {
Info.Diag(RHS);
return 0;
}
unsigned PathLengthToMember =
LV.Designator.Entries.size() - MemPtr.Path.size();
for (unsigned I = 0, N = MemPtr.Path.size(); I != N; ++I) {
const CXXRecordDecl *LVDecl = getAsBaseClass(
LV.Designator.Entries[PathLengthToMember + I]);
const CXXRecordDecl *MPDecl = MemPtr.Path[I];
if (LVDecl->getCanonicalDecl() != MPDecl->getCanonicalDecl())
if (LVDecl->getCanonicalDecl() != MPDecl->getCanonicalDecl()) {
Info.Diag(RHS);
return 0;
}
}
// Truncate the lvalue to the appropriate derived class.
if (!CastToDerivedClass(Info, BO, LV, MemPtr.getContainingRecord(),
if (!CastToDerivedClass(Info, RHS, LV, MemPtr.getContainingRecord(),
PathLengthToMember))
return 0;
} else if (!MemPtr.Path.empty()) {
@ -2686,7 +2726,6 @@ static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
MemPtr.Path.size() + IncludeMember);
// Walk down to the appropriate base class.
QualType LVType = BO->getLHS()->getType();
if (const PointerType *PT = LVType->getAs<PointerType>())
LVType = PT->getPointeeType();
const CXXRecordDecl *RD = LVType->getAsCXXRecordDecl();
@ -2694,23 +2733,24 @@ static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
// The first class in the path is that of the lvalue.
for (unsigned I = 1, N = MemPtr.Path.size(); I != N; ++I) {
const CXXRecordDecl *Base = MemPtr.Path[N - I - 1];
if (!HandleLValueDirectBase(Info, BO, LV, RD, Base))
if (!HandleLValueDirectBase(Info, RHS, LV, RD, Base))
return 0;
RD = Base;
}
// Finally cast to the class containing the member.
if (!HandleLValueDirectBase(Info, BO, LV, RD, MemPtr.getContainingRecord()))
if (!HandleLValueDirectBase(Info, RHS, LV, RD,
MemPtr.getContainingRecord()))
return 0;
}
// Add the member. Note that we cannot build bound member functions here.
if (IncludeMember) {
if (const FieldDecl *FD = dyn_cast<FieldDecl>(MemPtr.getDecl())) {
if (!HandleLValueMember(Info, BO, LV, FD))
if (!HandleLValueMember(Info, RHS, LV, FD))
return 0;
} else if (const IndirectFieldDecl *IFD =
dyn_cast<IndirectFieldDecl>(MemPtr.getDecl())) {
if (!HandleLValueIndirectMember(Info, BO, LV, IFD))
if (!HandleLValueIndirectMember(Info, RHS, LV, IFD))
return 0;
} else {
llvm_unreachable("can't construct reference to bound member function");
@ -2720,6 +2760,24 @@ static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
return MemPtr.getDecl();
}
static const ValueDecl *HandleMemberPointerAccess(EvalInfo &Info,
const BinaryOperator *BO,
LValue &LV,
bool IncludeMember = true) {
assert(BO->getOpcode() == BO_PtrMemD || BO->getOpcode() == BO_PtrMemI);
if (!EvaluateObjectArgument(Info, BO->getLHS(), LV)) {
if (Info.keepEvaluatingAfterFailure()) {
MemberPtr MemPtr;
EvaluateMemberPointer(BO->getRHS(), MemPtr, Info);
}
return 0;
}
return HandleMemberPointerAccess(Info, BO->getLHS()->getType(), LV,
BO->getRHS(), IncludeMember);
}
/// HandleBaseToDerivedCast - Apply the given base-to-derived cast operation on
/// the provided lvalue, which currently refers to the base object.
static bool HandleBaseToDerivedCast(EvalInfo &Info, const CastExpr *E,
@ -3842,24 +3900,14 @@ public:
return ExprEvaluatorBaseTy::VisitCastExpr(E);
case CK_DerivedToBase:
case CK_UncheckedDerivedToBase: {
case CK_UncheckedDerivedToBase:
if (!this->Visit(E->getSubExpr()))
return false;
// Now figure out the necessary offset to add to the base LV to get from
// the derived class to the base class.
QualType Type = E->getSubExpr()->getType();
for (CastExpr::path_const_iterator PathI = E->path_begin(),
PathE = E->path_end(); PathI != PathE; ++PathI) {
if (!HandleLValueBase(this->Info, E, Result, Type->getAsCXXRecordDecl(),
*PathI))
return false;
Type = (*PathI)->getType();
}
return true;
}
return HandleLValueBasePath(this->Info, E, E->getSubExpr()->getType(),
Result);
}
}
};
@ -3888,8 +3936,10 @@ public:
// * BlockExpr
// * CallExpr for a MakeStringConstant builtin
// - Locals and temporaries
// * MaterializeTemporaryExpr
// * Any Expr, with a CallIndex indicating the function in which the temporary
// was evaluated.
// was evaluated, for cases where the MaterializeTemporaryExpr is missing
// from the AST (FIXME).
// plus an offset in bytes.
//===----------------------------------------------------------------------===//
namespace {
@ -3984,12 +4034,51 @@ bool LValueExprEvaluator::VisitVarDecl(const Expr *E, const VarDecl *VD) {
bool LValueExprEvaluator::VisitMaterializeTemporaryExpr(
const MaterializeTemporaryExpr *E) {
if (E->getType()->isRecordType())
return EvaluateTemporary(E->GetTemporaryExpr(), Result, Info);
// Walk through the expression to find the materialized temporary itself.
SmallVector<const Expr *, 2> CommaLHSs;
SmallVector<SubobjectAdjustment, 2> Adjustments;
const Expr *Inner = E->GetTemporaryExpr()->
skipRValueSubobjectAdjustments(CommaLHSs, Adjustments);
// If we passed any comma operators, evaluate their LHSs.
for (unsigned I = 0, N = CommaLHSs.size(); I != N; ++I)
if (!EvaluateIgnoredValue(Info, CommaLHSs[I]))
return false;
// Materialize the temporary itself.
APValue *Value = &Info.CurrentCall->Temporaries[E];
Result.set(E, Info.CurrentCall->Index);
return EvaluateInPlace(Info.CurrentCall->Temporaries[E], Info,
Result, E->GetTemporaryExpr());
if (!EvaluateInPlace(*Value, Info, Result, Inner))
return false;
// Adjust our lvalue to refer to the desired subobject.
QualType Type = Inner->getType();
for (unsigned I = Adjustments.size(); I != 0; /**/) {
--I;
switch (Adjustments[I].Kind) {
case SubobjectAdjustment::DerivedToBaseAdjustment:
if (!HandleLValueBasePath(Info, Adjustments[I].DerivedToBase.BasePath,
Type, Result))
return false;
Type = Adjustments[I].DerivedToBase.BasePath->getType();
break;
case SubobjectAdjustment::FieldAdjustment:
if (!HandleLValueMember(Info, E, Result, Adjustments[I].Field))
return false;
Type = Adjustments[I].Field->getType();
break;
case SubobjectAdjustment::MemberPointerAdjustment:
if (!HandleMemberPointerAccess(this->Info, Type, Result,
Adjustments[I].Ptr.RHS))
return false;
Type = Adjustments[I].Ptr.MPT->getPointeeType();
break;
}
}
return true;
}
bool
@ -4167,6 +4256,9 @@ public:
return Error(E);
}
bool VisitCXXThisExpr(const CXXThisExpr *E) {
// Can't look at 'this' when checking a potential constant expression.
if (Info.CheckingPotentialConstantExpression)
return false;
if (!Info.CurrentCall->This)
return Error(E);
Result = *Info.CurrentCall->This;
@ -4240,7 +4332,7 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
return true;
case CK_DerivedToBase:
case CK_UncheckedDerivedToBase: {
case CK_UncheckedDerivedToBase:
if (!EvaluatePointer(E->getSubExpr(), Result, Info))
return false;
if (!Result.Base && Result.Offset.isZero())
@ -4248,19 +4340,9 @@ bool PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
// Now figure out the necessary offset to add to the base LV to get from
// the derived class to the base class.
QualType Type =
E->getSubExpr()->getType()->castAs<PointerType>()->getPointeeType();
for (CastExpr::path_const_iterator PathI = E->path_begin(),
PathE = E->path_end(); PathI != PathE; ++PathI) {
if (!HandleLValueBase(Info, E, Result, Type->getAsCXXRecordDecl(),
*PathI))
return false;
Type = (*PathI)->getType();
}
return true;
}
return HandleLValueBasePath(Info, E, E->getSubExpr()->getType()->
castAs<PointerType>()->getPointeeType(),
Result);
case CK_BaseToDerived:
if (!Visit(E->getSubExpr()))

6
clang/test/CXX/expr/expr.const/p2-0x.cpp
View File

@ -481,17 +481,19 @@ namespace UnspecifiedRelations {
public:
constexpr A() : a(0), b(0) {}
int a;
constexpr bool cmp() const { return &a < &b; } // expected-error {{constexpr function never produces a constant expression}} expected-note {{comparison of address of fields 'a' and 'b' of 'A' with differing access specifiers (public vs private) has unspecified value}}
constexpr bool cmp() const { return &a < &b; } // expected-note {{comparison of address of fields 'a' and 'b' of 'A' with differing access specifiers (public vs private) has unspecified value}}
private:
int b;
};
static_assert(A().cmp(), ""); // expected-error {{constant expression}} expected-note {{in call}}
class B {
public:
A a;
constexpr bool cmp() const { return &a.a < &b.a; } // expected-error {{constexpr function never produces a constant expression}} expected-note {{comparison of address of fields 'a' and 'b' of 'B' with differing access specifiers (public vs protected) has unspecified value}}
constexpr bool cmp() const { return &a.a < &b.a; } // expected-note {{comparison of address of fields 'a' and 'b' of 'B' with differing access specifiers (public vs protected) has unspecified value}}
protected:
A b;
};
static_assert(B().cmp(), ""); // expected-error {{constant expression}} expected-note {{in call}}
// If two pointers point to different base sub-objects of the same object, or
// one points to a base subobject and the other points to a member, the result

13
clang/test/SemaCXX/constant-expression-cxx11.cpp
View File

@ -778,21 +778,26 @@ namespace Temporaries {
struct S {
constexpr S() {}
constexpr int f() const;
constexpr int g() const;
};
struct T : S {
constexpr T(int n) : S(), n(n) {}
int n;
};
constexpr int S::f() const {
// 'this' must be the postfix-expression in a class member access expression,
// so we can't just use
// return static_cast<T*>(this)->n;
return this->*(int(S::*))&T::n;
return static_cast<const T*>(this)->n; // expected-note {{cannot cast}}
}
constexpr int S::g() const {
// FIXME: Better diagnostic for this.
return this->*(int(S::*))&T::n; // expected-note {{subexpression}}
}
// The T temporary is implicitly cast to an S subobject, but we can recover the
// T full-object via a base-to-derived cast, or a derived-to-base-casted member
// pointer.
static_assert(S().f(), ""); // expected-error {{constant expression}} expected-note {{in call to '&Temporaries::S()->f()'}}
static_assert(S().g(), ""); // expected-error {{constant expression}} expected-note {{in call to '&Temporaries::S()->g()'}}
static_assert(T(3).f() == 3, "");
static_assert(T(4).g() == 4, "");
constexpr int f(const S &s) {
return static_cast<const T&>(s).n;