Fix PR31843: Clang-4.0 crashes/assert while evaluating __builtin_object_size

[george.burgess.iv]

Summary

We're currently using a special EvaluationMode to determine whether
we're OK with invalid base expressions during objectsize evaluation.
Using it to figure out how we handle UB/etc. is fine, but I think it's
too far-reaching to use for checking whether we're OK with an invalid
base expression. This is because an EvaluationMode applies by default to
all subexpressions of the expression we're evaluating, which causes
issues like in https://llvm.org/bugs/show_bug.cgi?id=31843 .

What I think we actually want to do is allow this relaxed behavior only
for "top-level" member/pointer expressions. In other words, we should
only allow it when we're evaluating the top-level pointers/lvalues
involved in an expression. As soon as we need to evaluate something else
(an int, ...), we should drop these relaxed rules and go back to
stricter evaluation. For example, in:

foo(whatever->a ? b() : 1)->bar->baz.quux

We don't care if whatever->a is evaluated using these relaxed rules,
since the only invalid base that's actually useful to the objectsize
evaluator is foo(...)->bar.

...As a lower level issue, one idea I had to make this less awkward was
to just define EvaluatePointer(const Expr *, LValue&, EvalInfo&) as a
method on LValueExprEvaluator/PointerExprEvaluator that called
::EvaluatePointer with the right fourth arg, but that seemed a bit too
subtle to me. Happy to swap to it if you think it's better.

Finally, if we make this change, ISTM we can just replace OffsetFold
with ConstantFold. I'd rather to that in another patch, since whatever
we choose to do here gets put into 4.0.

---

With all of that said, if we want the minimal fix for PR31843, it's
adding an InvalidBase check or two to Evaluate. My concern with that
approach is that we'd just end up playing whack-a-bug. It's possible
that this fix puts us in a similar situation, but I'm honestly at a loss
for a better approach. ¯\_(ツ)_/¯ (...And I'd kinda prefer to play
whack-a-bug with "clang could do a better job in this case" reports,
rather than "clang crashes on my code" reports.)

[mehdi_amini]

My concern with that approach is that we'd just end up playing whack-a-bug. It's possible that this fix puts us in a similar situation, but I'm honestly at a loss for a better approach. ¯\_(ツ)_/¯ (...And I'd kinda prefer to play whack-a-bug with "clang could do a better job in this case" reports, rather than "clang crashes on my code" reports.)

Agree, thanks :)

This patch LGTM but I have little confidence in myself in this area of the compiler, so I rather have someone else stamping it!

[mehdi_amini]

Ping? This is hitting 4.0

[george.burgess.iv]

End of week ping :)

[dexonsmith]

+Nuno, who worked on objectsize in the past.

[rsmith]

LGTM, I think this is also OK for Clang 4 if Hans is willing to take it.

lib/AST/ExprConstant.cpp

607–612

[nit] "We", "We", "Then" should not be capitalized, and please remove blank line prior to "Then we [...]"

[george.burgess.iv]

Thanks!

lib/AST/ExprConstant.cpp

enum EvaluationMode {
       /// construct that we can't evaluate yet (because we don't yet know the
       /// value of something) but stop if we hit something that could never be
       /// a constant expression. Some expressions can be retried in the
       /// optimizer if we don't constant fold them here, but in an unevaluated
       /// context we try to fold them immediately since the optimizer never
       /// gets a chance to look at it.
       EM_PotentialConstantExpressionUnevaluated,
 
-      /// Evaluate as a constant expression. Continue evaluating if either:
-      /// - We find a MemberExpr with a base that can't be evaluated.
+      /// Evaluate as a constant expression. In certain scenarios, if:
+      /// - We find a MemberExpr with a base that can't be evaluated, or
       /// - We find a variable initialized with a call to a function that has
-      ///   the alloc_size attribute on it.
+      ///   the alloc_size attribute on it
+      ///
+      /// Then we may consider evaluation to have succeeded.
+      ///
       /// In either case, the LValue returned shall have an invalid base; in the
       /// former, the base will be the invalid MemberExpr, in the latter, the
       /// base will be either the alloc_size CallExpr or a CastExpr wrapping
       /// said CallExpr.
       EM_OffsetFold,
     } EvalMode;
 
     /// Are we checking whether the expression is a potential constant
LLVM_NODISCARD bool noteFailure() {
       // subexpression implies that a side-effect has potentially happened. We
       // skip setting the HasSideEffects flag to true until we decide to
       // continue evaluating after that point, which happens here.
       bool KeepGoing = keepEvaluatingAfterFailure();
       EvalStatus.HasSideEffects |= KeepGoing;
       return KeepGoing;
     }
 
-    bool allowInvalidBaseExpr() const {
-      return EvalMode == EM_OffsetFold;
-    }
-
     class ArrayInitLoopIndex {
       EvalInfo &Info;
       uint64_t OuterIndex;
 
     public:
       ArrayInitLoopIndex(EvalInfo &Info)
           : Info(Info), OuterIndex(Info.ArrayInitIndex) {
         Info.ArrayInitIndex = 0;
static bool operator==(const MemberPtr &LHS, const MemberPtr &RHS) {
     return LHS.Path == RHS.Path;
   }
 }
 
 static bool Evaluate(APValue &Result, EvalInfo &Info, const Expr *E);
 static bool EvaluateInPlace(APValue &Result, EvalInfo &Info,
                             const LValue &This, const Expr *E,
                             bool AllowNonLiteralTypes = false);
-static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info);
-static bool EvaluatePointer(const Expr *E, LValue &Result, EvalInfo &Info);
+static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info,
+                           bool InvalidBaseOK = false);
+static bool EvaluatePointer(const Expr *E, LValue &Result, EvalInfo &Info,
+                            bool InvalidBaseOK = false);
 static bool EvaluateMemberPointer(const Expr *E, MemberPtr &Result,
                                   EvalInfo &Info);
 static bool EvaluateTemporary(const Expr *E, LValue &Result, EvalInfo &Info);
 static bool EvaluateInteger(const Expr *E, APSInt &Result, EvalInfo &Info);
 static bool EvaluateIntegerOrLValue(const Expr *E, APValue &Result,
                                     EvalInfo &Info);
 static bool EvaluateFloat(const Expr *E, APFloat &Result, EvalInfo &Info);
 static bool EvaluateComplex(const Expr *E, ComplexValue &Res, EvalInfo &Info);

 // Common base class for lvalue and temporary evaluation.
 //===----------------------------------------------------------------------===//
 namespace {
 template<class Derived>
 class LValueExprEvaluatorBase
   : public ExprEvaluatorBase<Derived> {
 protected:
   LValue &Result;
+  bool InvalidBaseOK;
   typedef LValueExprEvaluatorBase LValueExprEvaluatorBaseTy;
   typedef ExprEvaluatorBase<Derived> ExprEvaluatorBaseTy;
 
   bool Success(APValue::LValueBase B) {
     Result.set(B);
     return true;
   }
 
+  bool evaluatePointer(const Expr *E, LValue &Result) {
+    return EvaluatePointer(E, Result, this->Info, InvalidBaseOK);
+  }
+
 public:
-  LValueExprEvaluatorBase(EvalInfo &Info, LValue &Result) :
-    ExprEvaluatorBaseTy(Info), Result(Result) {}
+  LValueExprEvaluatorBase(EvalInfo &Info, LValue &Result, bool InvalidBaseOK)
+      : ExprEvaluatorBaseTy(Info), Result(Result),
+        InvalidBaseOK(InvalidBaseOK) {}
 
   bool Success(const APValue &V, const Expr *E) {
     Result.setFrom(this->Info.Ctx, V);
     return true;
   }
 
   bool VisitMemberExpr(const MemberExpr *E) {
     // Handle non-static data members.
     QualType BaseTy;
     bool EvalOK;
     if (E->isArrow()) {
-      EvalOK = EvaluatePointer(E->getBase(), Result, this->Info);
+      EvalOK = evaluatePointer(E->getBase(), Result);
       BaseTy = E->getBase()->getType()->castAs<PointerType>()->getPointeeType();
     } else if (E->getBase()->isRValue()) {
       assert(E->getBase()->getType()->isRecordType());
       EvalOK = EvaluateTemporary(E->getBase(), Result, this->Info);
       BaseTy = E->getBase()->getType();
     } else {
       EvalOK = this->Visit(E->getBase());
       BaseTy = E->getBase()->getType();
     }
     if (!EvalOK) {
-      if (!this->Info.allowInvalidBaseExpr())
+      if (!InvalidBaseOK)
         return false;
       Result.setInvalid(E);
       return true;
     }
 
     const ValueDecl *MD = E->getMemberDecl();
     if (const FieldDecl *FD = dyn_cast<FieldDecl>(E->getMemberDecl())) {
       assert(BaseTy->getAs<RecordType>()->getDecl()->getCanonicalDecl() ==

 //  * A MaterializeTemporaryExpr that has static storage duration, with no
 //    CallIndex, for a lifetime-extended temporary.
 // plus an offset in bytes.
 //===----------------------------------------------------------------------===//
 namespace {
 class LValueExprEvaluator
   : public LValueExprEvaluatorBase<LValueExprEvaluator> {
 public:
-  LValueExprEvaluator(EvalInfo &Info, LValue &Result) :
-    LValueExprEvaluatorBaseTy(Info, Result) {}
+  LValueExprEvaluator(EvalInfo &Info, LValue &Result, bool InvalidBaseOK) :
+    LValueExprEvaluatorBaseTy(Info, Result, InvalidBaseOK) {}
 
   bool VisitVarDecl(const Expr *E, const VarDecl *VD);
   bool VisitUnaryPreIncDec(const UnaryOperator *UO);
 
   bool VisitDeclRefExpr(const DeclRefExpr *E);
   bool VisitPredefinedExpr(const PredefinedExpr *E) { return Success(E); }
   bool VisitMaterializeTemporaryExpr(const MaterializeTemporaryExpr *E);
   bool VisitCompoundLiteralExpr(const CompoundLiteralExpr *E);

 };
 } // end anonymous namespace
 
 /// Evaluate an expression as an lvalue. This can be legitimately called on
 /// expressions which are not glvalues, in three cases:
 ///  * function designators in C, and
 ///  * "extern void" objects
 ///  * @selector() expressions in Objective-C
-static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info) {
+static bool EvaluateLValue(const Expr *E, LValue &Result, EvalInfo &Info,
+                           bool InvalidBaseOK) {
   assert(E->isGLValue() || E->getType()->isFunctionType() ||
          E->getType()->isVoidType() || isa<ObjCSelectorExpr>(E));
-  return LValueExprEvaluator(Info, Result).Visit(E);
+  return LValueExprEvaluator(Info, Result, InvalidBaseOK).Visit(E);
 }
 
 bool LValueExprEvaluator::VisitDeclRefExpr(const DeclRefExpr *E) {
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(E->getDecl()))
     return Success(FD);
   if (const VarDecl *VD = dyn_cast<VarDecl>(E->getDecl()))
     return VisitVarDecl(E, VD);
   if (const BindingDecl *BD = dyn_cast<BindingDecl>(E->getDecl()))
bool LValueExprEvaluator::VisitMemberExpr(const MemberExpr *E) {
   return LValueExprEvaluatorBaseTy::VisitMemberExpr(E);
 }
 
 bool LValueExprEvaluator::VisitArraySubscriptExpr(const ArraySubscriptExpr *E) {
   // FIXME: Deal with vectors as array subscript bases.
   if (E->getBase()->getType()->isVectorType())
     return Error(E);
 
-  if (!EvaluatePointer(E->getBase(), Result, Info))
+  if (!evaluatePointer(E->getBase(), Result))
     return false;
 
   APSInt Index;
   if (!EvaluateInteger(E->getIdx(), Index, Info))
     return false;
 
   return HandleLValueArrayAdjustment(Info, E, Result, E->getType(),
                                      getExtValue(Index));
 }
 
 bool LValueExprEvaluator::VisitUnaryDeref(const UnaryOperator *E) {
-  return EvaluatePointer(E->getSubExpr(), Result, Info);
+  return evaluatePointer(E->getSubExpr(), Result);
 }
 
 bool LValueExprEvaluator::VisitUnaryReal(const UnaryOperator *E) {
   if (!Visit(E->getSubExpr()))
     return false;
   // __real is a no-op on scalar lvalues.
   if (E->getSubExpr()->getType()->isAnyComplexType())
     HandleLValueComplexElement(Info, E, Result, E->getType(), false);

 }
 
 /// \brief Attempts to evaluate the given LValueBase as the result of a call to
 /// a function with the alloc_size attribute. If it was possible to do so, this
 /// function will return true, make Result's Base point to said function call,
 /// and mark Result's Base as invalid.
 static bool evaluateLValueAsAllocSize(EvalInfo &Info, APValue::LValueBase Base,
                                       LValue &Result) {
-  if (!Info.allowInvalidBaseExpr() || Base.isNull())
+  if (Base.isNull())
     return false;
 
   // Because we do no form of static analysis, we only support const variables.
   //
   // Additionally, we can't support parameters, nor can we support static
   // variables (in the latter case, use-before-assign isn't UB; in the former,
   // we have no clue what they'll be assigned to).
   const auto *VD =
static bool evaluateLValueAsAllocSize(EvalInfo &Info, APValue::LValueBase Base,
   Result.addUnsizedArray(Info, Pointee);
   return true;
 }
 
 namespace {
 class PointerExprEvaluator
   : public ExprEvaluatorBase<PointerExprEvaluator> {
   LValue &Result;
+  bool InvalidBaseOK;
 
   bool Success(const Expr *E) {
     Result.set(E);
     return true;
   }
 
+  bool evaluateLValue(const Expr *E, LValue &Result) {
+    return EvaluateLValue(E, Result, Info, InvalidBaseOK);
+  }
+
+  bool evaluatePointer(const Expr *E, LValue &Result) {
+    return EvaluatePointer(E, Result, Info, InvalidBaseOK);
+  }
+
   bool visitNonBuiltinCallExpr(const CallExpr *E);
 public:
 
-  PointerExprEvaluator(EvalInfo &info, LValue &Result)
-    : ExprEvaluatorBaseTy(info), Result(Result) {}
+  PointerExprEvaluator(EvalInfo &info, LValue &Result, bool InvalidBaseOK)
+      : ExprEvaluatorBaseTy(info), Result(Result),
+        InvalidBaseOK(InvalidBaseOK) {}
 
   bool Success(const APValue &V, const Expr *E) {
     Result.setFrom(Info.Ctx, V);
     return true;
   }
   bool ZeroInitialization(const Expr *E) {
     auto Offset = Info.Ctx.getTargetNullPointerValue(E->getType());
     Result.set((Expr*)nullptr, 0, false, true, Offset);
bool VisitCXXThisExpr(const CXXThisExpr *E) {
     Result = *Info.CurrentCall->This;
     return true;
   }
 
   // FIXME: Missing: @protocol, @selector
 };
 } // end anonymous namespace
 
-static bool EvaluatePointer(const Expr* E, LValue& Result, EvalInfo &Info) {
+static bool EvaluatePointer(const Expr* E, LValue& Result, EvalInfo &Info,
+                            bool InvalidBaseOK) {
   assert(E->isRValue() && E->getType()->hasPointerRepresentation());
-  return PointerExprEvaluator(Info, Result).Visit(E);
+  return PointerExprEvaluator(Info, Result, InvalidBaseOK).Visit(E);
 }
 
 bool PointerExprEvaluator::VisitBinaryOperator(const BinaryOperator *E) {
   if (E->getOpcode() != BO_Add &&
       E->getOpcode() != BO_Sub)
     return ExprEvaluatorBaseTy::VisitBinaryOperator(E);
 
   const Expr *PExp = E->getLHS();
   const Expr *IExp = E->getRHS();
   if (IExp->getType()->isPointerType())
     std::swap(PExp, IExp);
 
-  bool EvalPtrOK = EvaluatePointer(PExp, Result, Info);
+  bool EvalPtrOK = evaluatePointer(PExp, Result);
   if (!EvalPtrOK && !Info.noteFailure())
     return false;
 
   llvm::APSInt Offset;
   if (!EvaluateInteger(IExp, Offset, Info) || !EvalPtrOK)
     return false;
 
   int64_t AdditionalOffset = getExtValue(Offset);
   if (E->getOpcode() == BO_Sub)
     AdditionalOffset = -AdditionalOffset;
 
   QualType Pointee = PExp->getType()->castAs<PointerType>()->getPointeeType();
   return HandleLValueArrayAdjustment(Info, E, Result, Pointee,
                                      AdditionalOffset);
 }
 
 bool PointerExprEvaluator::VisitUnaryAddrOf(const UnaryOperator *E) {
-  return EvaluateLValue(E->getSubExpr(), Result, Info);
+  return evaluateLValue(E->getSubExpr(), Result);
 }
 
 bool PointerExprEvaluator::VisitCastExpr(const CastExpr* E) {
   const Expr* SubExpr = E->getSubExpr();
 
   switch (E->getCastKind()) {
   default:
     break;
if (!E->getType()->isVoidPointerType()) {
         CCEDiag(E, diag::note_constexpr_invalid_cast) << 2;
     }
     if (E->getCastKind() == CK_AddressSpaceConversion && Result.IsNullPtr)
       ZeroInitialization(E);
     return true;
 
   case CK_DerivedToBase:
   case CK_UncheckedDerivedToBase:
-    if (!EvaluatePointer(E->getSubExpr(), Result, Info))
+    if (!evaluatePointer(E->getSubExpr(), Result))
       return false;
     if (!Result.Base && Result.Offset.isZero())
       return true;
 
     // Now figure out the necessary offset to add to the base LV to get from
     // the derived class to the base class.
     return HandleLValueBasePath(Info, E, E->getSubExpr()->getType()->
                                   castAs<PointerType>()->getPointeeType(),
case CK_IntegralToPointer: {
     } else {
       // Cast is of an lvalue, no need to change value.
       Result.setFrom(Info.Ctx, Value);
       return true;
     }
   }
   case CK_ArrayToPointerDecay:
     if (SubExpr->isGLValue()) {
-      if (!EvaluateLValue(SubExpr, Result, Info))
+      if (!evaluateLValue(SubExpr, Result))
         return false;
     } else {
       Result.set(SubExpr, Info.CurrentCall->Index);
       if (!EvaluateInPlace(Info.CurrentCall->createTemporary(SubExpr, false),
                            Info, Result, SubExpr))
         return false;
     }
     // The result is a pointer to the first element of the array.
     if (const ConstantArrayType *CAT
           = Info.Ctx.getAsConstantArrayType(SubExpr->getType()))
       Result.addArray(Info, E, CAT);
     else
       Result.Designator.setInvalid();
     return true;
 
   case CK_FunctionToPointerDecay:
-    return EvaluateLValue(SubExpr, Result, Info);
+    return evaluateLValue(SubExpr, Result);
 
   case CK_LValueToRValue: {
     LValue LVal;
-    if (!EvaluateLValue(E->getSubExpr(), LVal, Info))
+    if (!evaluateLValue(E->getSubExpr(), LVal))
       return false;
 
     APValue RVal;
     // Note, we use the subexpression's type in order to retain cv-qualifiers.
     if (!handleLValueToRValueConversion(Info, E, E->getSubExpr()->getType(),
                                         LVal, RVal))
-      return evaluateLValueAsAllocSize(Info, LVal.Base, Result);
+      return InvalidBaseOK &&
+             evaluateLValueAsAllocSize(Info, LVal.Base, Result);
     return Success(RVal, E);
   }
   }
 
   return ExprEvaluatorBaseTy::VisitCastExpr(E);
 }
 
 static CharUnits GetAlignOfType(EvalInfo &Info, QualType T) {
static CharUnits GetAlignOfExpr(EvalInfo &Info, const Expr *E) {
   return GetAlignOfType(Info, E->getType());
 }
 
 // To be clear: this happily visits unsupported builtins. Better name welcomed.
 bool PointerExprEvaluator::visitNonBuiltinCallExpr(const CallExpr *E) {
   if (ExprEvaluatorBaseTy::VisitCallExpr(E))
     return true;
 
-  if (!(Info.allowInvalidBaseExpr() && getAllocSizeAttr(E)))
+  if (!(InvalidBaseOK && getAllocSizeAttr(E)))
     return false;
 
   Result.setInvalid(E);
   QualType PointeeTy = E->getType()->castAs<PointerType>()->getPointeeType();
   Result.addUnsizedArray(Info, PointeeTy);
   return true;
 }
 
 bool PointerExprEvaluator::VisitCallExpr(const CallExpr *E) {
   if (IsStringLiteralCall(E))
     return Success(E);
 
   if (unsigned BuiltinOp = E->getBuiltinCallee())
     return VisitBuiltinCallExpr(E, BuiltinOp);
 
   return visitNonBuiltinCallExpr(E);
 }
 
 bool PointerExprEvaluator::VisitBuiltinCallExpr(const CallExpr *E,
                                                 unsigned BuiltinOp) {
   switch (BuiltinOp) {
   case Builtin::BI__builtin_addressof:
-    return EvaluateLValue(E->getArg(0), Result, Info);
+    return evaluateLValue(E->getArg(0), Result);
   case Builtin::BI__builtin_assume_aligned: {
     // We need to be very careful here because: if the pointer does not have the
     // asserted alignment, then the behavior is undefined, and undefined
     // behavior is non-constant.
-    if (!EvaluatePointer(E->getArg(0), Result, Info))
+    if (!evaluatePointer(E->getArg(0), Result))
       return false;
 
     LValue OffsetResult(Result);
     APSInt Alignment;
     if (!EvaluateInteger(E->getArg(1), Alignment, Info))
       return false;
     CharUnits Align = CharUnits::fromQuantity(getExtValue(Alignment));
 

 // lvalues. The full-object of which the temporary is a subobject is implicitly
 // materialized so that a reference can bind to it.
 //===----------------------------------------------------------------------===//
 namespace {
 class TemporaryExprEvaluator
   : public LValueExprEvaluatorBase<TemporaryExprEvaluator> {
 public:
   TemporaryExprEvaluator(EvalInfo &Info, LValue &Result) :
-    LValueExprEvaluatorBaseTy(Info, Result) {}
+    LValueExprEvaluatorBaseTy(Info, Result, false) {}
 
   /// Visit an expression which constructs the value of this temporary.
   bool VisitConstructExpr(const Expr *E) {
     Result.set(E, Info.CurrentCall->Index);
     return EvaluateInPlace(Info.CurrentCall->createTemporary(E, false),
                            Info, Result, E);
   }
 
LValue LVal;
 
     if (E->isGLValue()) {
       // It's possible for us to be given GLValues if we're called via
       // Expr::tryEvaluateObjectSize.
       APValue RVal;
       if (!EvaluateAsRValue(Info, E, RVal))
         return false;
       LVal.setFrom(Info.Ctx, RVal);
-    } else if (!EvaluatePointer(ignorePointerCastsAndParens(E), LVal, Info))
+    } else if (!EvaluatePointer(ignorePointerCastsAndParens(E), LVal, Info,
+                                /*InvalidBaseOK=*/true))
       return false;
   }
 
   // If we point to before the start of the object, there are no accessible
   // bytes.
   if (LVal.getLValueOffset().isNegative()) {
     Size = 0;
     return true;

test/CodeGen/object-size.c

int incomplete_and_function_types() {
   gi = __builtin_object_size(incomplete_char_array, 0);
   // CHECK: call i64 @llvm.objectsize.i64.p0i8
   gi = __builtin_object_size(incomplete_char_array, 1);
   // CHECK: call i64 @llvm.objectsize.i64.p0i8
   gi = __builtin_object_size(incomplete_char_array, 2);
   // CHECK: store i32 0
   gi = __builtin_object_size(incomplete_char_array, 3);
 }
+
+// Flips between the pointer and lvalue evaluator a lot.
+void deeply_nested() {
+  struct {
+    struct {
+      struct {
+        struct {
+          int e[2];
+          char f; // Inhibit our writing-off-the-end check
+        } d[2];
+      } c[2];
+    } b[2];
+  } *a;
+
+  // CHECK: store i32 4
+  gi = __builtin_object_size(&a->b[1].c[1].d[1].e[1], 1);
+  // CHECK: store i32 4
+  gi = __builtin_object_size(&a->b[1].c[1].d[1].e[1], 3);
+}

test/Sema/builtin-object-size.c

int pr28314(void) {
 
   int a = 0;
   a += __builtin_object_size(&p->a, 0);
   a += __builtin_object_size(p->b, 0);
   a += __builtin_object_size(p2->b, 0);
   a += __builtin_object_size(p3->b, 0);
   return a;
 }
+
+int pr31843() {
+  int n = 0;
+
+  struct { int f; } a;
+  int b;
+  n += __builtin_object_size(({&(b ? &a : &a)->f; pr31843;}), 0); // expected-warning{{expression result unused}}
+
+  struct statfs { char f_mntonname[1024];};
+  struct statfs *outStatFSBuf;
+  n += __builtin_object_size(outStatFSBuf->f_mntonname ? "" : "", 1); // expected-warning{{address of array}}
+  n += __builtin_object_size(outStatFSBuf->f_mntonname ?: "", 1);
+
+  return n;
+}