Disallow the use of UnknownVal as the index for ElementRegions. UnknownVals can be used as

the index when the value evaluation isn't powerful enough.  By creating ElementRegions with
UnknownVals as the index, this gives the false impression that they are the same element, when
they really aren't.  This becomes really problematic when deriving symbols from these regions
(e.g., those representing the initial value of the index), since two different indices will
get the same symbol for their binding.

This fixes an issue with the idempotent operations checker that would cause two indices that
are clearly not the same to make it appear as if they always had the same value.

Fixes <rdar://problem/8431728>.

llvm-svn: 113920

8 files changed, 55 insertions, 19 deletions

diff --git a/clang/include/clang/Checker/PathSensitive/GRState.h b/clang/include/clang/Checker/PathSensitive/GRState.h
index ac382898d8f..878f5644917 100644
--- a/clang/include/clang/Checker/PathSensitive/GRState.h
+++ b/clang/include/clang/Checker/PathSensitive/GRState.h
@@ -650,7 +650,9 @@ inline SVal GRState::getLValue(const FieldDecl* D, SVal Base) const {
 }
 
 inline SVal GRState::getLValue(QualType ElementType, SVal Idx, SVal Base) const{
-  return getStateManager().StoreMgr->getLValueElement(ElementType, Idx, Base);
+  if (NonLoc *N = dyn_cast<NonLoc>(&Idx))
+    return getStateManager().StoreMgr->getLValueElement(ElementType, *N, Base);
+  return UnknownVal();
 }
 
 inline const llvm::APSInt *GRState::getSymVal(SymbolRef sym) const {
diff --git a/clang/include/clang/Checker/PathSensitive/MemRegion.h b/clang/include/clang/Checker/PathSensitive/MemRegion.h
index 96f906af28e..82b0c14f20c 100644
--- a/clang/include/clang/Checker/PathSensitive/MemRegion.h
+++ b/clang/include/clang/Checker/PathSensitive/MemRegion.h
@@ -788,9 +788,9 @@ class ElementRegion : public TypedRegion {
   friend class MemRegionManager;
 
   QualType ElementType;
-  SVal Index;
+  NonLoc Index;
 
-  ElementRegion(QualType elementType, SVal Idx, const MemRegion* sReg)
+  ElementRegion(QualType elementType, NonLoc Idx, const MemRegion* sReg)
     : TypedRegion(sReg, ElementRegionKind),
       ElementType(elementType), Index(Idx) {
     assert((!isa<nonloc::ConcreteInt>(&Idx) ||
@@ -803,7 +803,7 @@ class ElementRegion : public TypedRegion {
 
 public:
 
-  SVal getIndex() const { return Index; }
+  NonLoc getIndex() const { return Index; }
 
   QualType getValueType() const {
     return ElementType;
@@ -942,7 +942,7 @@ public:
   
   /// getElementRegion - Retrieve the memory region associated with the
   ///  associated element type, index, and super region.
-  const ElementRegion *getElementRegion(QualType elementType, SVal Idx,
+  const ElementRegion *getElementRegion(QualType elementType, NonLoc Idx,
                                         const MemRegion *superRegion,
                                         ASTContext &Ctx);
 
diff --git a/clang/include/clang/Checker/PathSensitive/Store.h b/clang/include/clang/Checker/PathSensitive/Store.h
index a1a41847a20..1ead4661369 100644
--- a/clang/include/clang/Checker/PathSensitive/Store.h
+++ b/clang/include/clang/Checker/PathSensitive/Store.h
@@ -112,7 +112,7 @@ public:
     return getLValueFieldOrIvar(D, Base);
   }
 
-  virtual SVal getLValueElement(QualType elementType, SVal offset, SVal Base);
+  virtual SVal getLValueElement(QualType elementType, NonLoc offset, SVal Base);
 
   // FIXME: This should soon be eliminated altogether; clients should deal with
   // region extents directly.
diff --git a/clang/lib/Checker/MemRegion.cpp b/clang/lib/Checker/MemRegion.cpp
index 3f706e145a8..ddcb7d2687a 100644
--- a/clang/lib/Checker/MemRegion.cpp
+++ b/clang/lib/Checker/MemRegion.cpp
@@ -624,7 +624,7 @@ MemRegionManager::getCompoundLiteralRegion(const CompoundLiteralExpr* CL,
 }
 
 const ElementRegion*
-MemRegionManager::getElementRegion(QualType elementType, SVal Idx,
+MemRegionManager::getElementRegion(QualType elementType, NonLoc Idx,
                                    const MemRegion* superRegion,
                                    ASTContext& Ctx){
 
diff --git a/clang/lib/Checker/RegionStore.cpp b/clang/lib/Checker/RegionStore.cpp
index 4051f4d39b8..91f7cfaf6c8 100644
--- a/clang/lib/Checker/RegionStore.cpp
+++ b/clang/lib/Checker/RegionStore.cpp
@@ -786,7 +786,7 @@ SVal RegionStoreManager::ArrayToPointer(Loc Array) {
   ArrayType *AT = cast<ArrayType>(T);
   T = AT->getElementType();
 
-  SVal ZeroIdx = ValMgr.makeZeroArrayIndex();
+  NonLoc ZeroIdx = ValMgr.makeZeroArrayIndex();
   return loc::MemRegionVal(MRMgr.getElementRegion(T, ZeroIdx, ArrayR, Ctx));
 }
 
@@ -828,14 +828,14 @@ SVal RegionStoreManager::EvalBinOp(BinaryOperator::Opcode Op, Loc L, NonLoc R,
       else
         EleTy = T->getAs<ObjCObjectPointerType>()->getPointeeType();
 
-      SVal ZeroIdx = ValMgr.makeZeroArrayIndex();
+      const NonLoc &ZeroIdx = ValMgr.makeZeroArrayIndex();
       ER = MRMgr.getElementRegion(EleTy, ZeroIdx, SR, Ctx);
       break;
     }
     case MemRegion::AllocaRegionKind: {
       const AllocaRegion *AR = cast<AllocaRegion>(MR);
       QualType EleTy = Ctx.CharTy; // Create an ElementRegion of bytes.
-      SVal ZeroIdx = ValMgr.makeZeroArrayIndex();
+      NonLoc ZeroIdx = ValMgr.makeZeroArrayIndex();
       ER = MRMgr.getElementRegion(EleTy, ZeroIdx, AR, Ctx);
       break;
     }
@@ -889,8 +889,12 @@ SVal RegionStoreManager::EvalBinOp(BinaryOperator::Opcode Op, Loc L, NonLoc R,
       SVal NewIdx =
         Base->evalBinOp(ValMgr, Op,
                 cast<nonloc::ConcreteInt>(ValMgr.convertToArrayIndex(*Offset)));
+
+      if (!isa<NonLoc>(NewIdx))
+        return UnknownVal();
+
       const MemRegion* NewER =
-        MRMgr.getElementRegion(ER->getElementType(), NewIdx,
+        MRMgr.getElementRegion(ER->getElementType(), cast<NonLoc>(NewIdx),
                                ER->getSuperRegion(), Ctx);
       return ValMgr.makeLoc(NewER);
     }
@@ -1449,7 +1453,7 @@ Store RegionStoreManager::BindArray(Store store, const TypedRegion* R,
     if (VI == VE)
       break;
 
-    SVal Idx = ValMgr.makeArrayIndex(i);
+    const NonLoc &Idx = ValMgr.makeArrayIndex(i);
     const ElementRegion *ER = MRMgr.getElementRegion(ElementTy, Idx, R, Ctx);
 
     if (ElementTy->isStructureOrClassType())
diff --git a/clang/lib/Checker/SVals.cpp b/clang/lib/Checker/SVals.cpp
index 97ba74e9487..937b948fc9c 100644
--- a/clang/lib/Checker/SVals.cpp
+++ b/clang/lib/Checker/SVals.cpp
@@ -270,7 +270,7 @@ void SVal::dump() const { dumpToStream(llvm::errs()); }
 void SVal::dumpToStream(llvm::raw_ostream& os) const {
   switch (getBaseKind()) {
     case UnknownKind:
-      os << "Invalid";
+      os << "Unknown";
       break;
     case NonLocKind:
       cast<NonLoc>(this)->dumpToStream(os);
diff --git a/clang/lib/Checker/Store.cpp b/clang/lib/Checker/Store.cpp
index 1cb5cd70cae..aaa518edc8a 100644
--- a/clang/lib/Checker/Store.cpp
+++ b/clang/lib/Checker/Store.cpp
@@ -28,7 +28,7 @@ Store StoreManager::EnterStackFrame(const GRState *state,
 
 const MemRegion *StoreManager::MakeElementRegion(const MemRegion *Base,
                                               QualType EleTy, uint64_t index) {
-  SVal idx = ValMgr.makeArrayIndex(index);
+  NonLoc idx = ValMgr.makeArrayIndex(index);
   return MRMgr.getElementRegion(EleTy, idx, Base, ValMgr.getContext());
 }
 
@@ -45,7 +45,7 @@ static bool IsCompleteType(ASTContext &Ctx, QualType Ty) {
 
 const ElementRegion *StoreManager::GetElementZeroRegion(const MemRegion *R, 
                                                         QualType T) {
-  SVal idx = ValMgr.makeZeroArrayIndex();
+  NonLoc idx = ValMgr.makeZeroArrayIndex();
   assert(!T.isNull());
   return MRMgr.getElementRegion(T, idx, R, Ctx);
 }
@@ -267,7 +267,7 @@ SVal StoreManager::getLValueFieldOrIvar(const Decl* D, SVal Base) {
   return loc::MemRegionVal(MRMgr.getFieldRegion(cast<FieldDecl>(D), BaseR));
 }
 
-SVal StoreManager::getLValueElement(QualType elementType, SVal Offset, 
+SVal StoreManager::getLValueElement(QualType elementType, NonLoc Offset, 
                                     SVal Base) {
 
   // If the base is an unknown or undefined value, just return it back.
@@ -283,7 +283,7 @@ SVal StoreManager::getLValueElement(QualType elementType, SVal Offset,
   const ElementRegion *ElemR = dyn_cast<ElementRegion>(BaseRegion);
 
   // Convert the offset to the appropriate size and signedness.
-  Offset = ValMgr.convertToArrayIndex(Offset);
+  Offset = cast<NonLoc>(ValMgr.convertToArrayIndex(Offset));
 
   if (!ElemR) {
     //
@@ -322,8 +322,8 @@ SVal StoreManager::getLValueElement(QualType elementType, SVal Offset,
   assert(BaseIdxI.isSigned());
 
   // Compute the new index.
-  SVal NewIdx = nonloc::ConcreteInt(
-                      ValMgr.getBasicValueFactory().getValue(BaseIdxI + OffI));
+  nonloc::ConcreteInt NewIdx(ValMgr.getBasicValueFactory().getValue(BaseIdxI +
+                                                                    OffI));
 
   // Construct the new ElementRegion.
   const MemRegion *ArrayR = ElemR->getSuperRegion();
diff --git a/clang/test/Analysis/idempotent-operations.c b/clang/test/Analysis/idempotent-operations.c
index d88bf49485e..c673f0062f0 100644
--- a/clang/test/Analysis/idempotent-operations.c
+++ b/clang/test/Analysis/idempotent-operations.c
@@ -194,3 +194,33 @@ void false8() {
   a = (short)a; // no-warning
   test(a);
 }
+
+// This test case previously flagged a warning at 'b == c' because the
+// analyzer previously allowed 'UnknownVal' as the index for ElementRegions.
+typedef struct RDar8431728_F {
+  int RDar8431728_A;
+  unsigned char *RDar8431728_B;
+  int RDar8431728_E[6];
+} RDar8431728_D;
+static inline int RDar8431728_C(RDar8431728_D * s, int n,
+    unsigned char **RDar8431728_B_ptr) {
+  int xy, wrap, pred, a, b, c;
+
+  xy = s->RDar8431728_E[n];
+  wrap = s->RDar8431728_A;
+
+  a = s->RDar8431728_B[xy - 1];
+  b = s->RDar8431728_B[xy - 1 - wrap];
+  c = s->RDar8431728_B[xy - wrap];
+
+  if (b == c) { // no-warning
+    pred = a;
+  } else {
+    pred = c;
+  }
+
+  *RDar8431728_B_ptr = &s->RDar8431728_B[xy];
+
+  return pred;
+}
+