[analyzer] Add LocationContext information to SymbolMetadata.

Like SymbolConjured, SymbolMetadata also needs to be uniquely
identified by the moment of its birth.

Such moments are coded by the (Statement, LocationContext, Block count) triples.
Each such triple represents the moment of analyzing a statement with a certain
call backtrace, with corresponding CFG block having been entered a given amount
of times during analysis of the current code body.

The LocationContext information was accidentally omitted for SymbolMetadata,
which leads to reincarnation of SymbolMetadata upon re-entering a code body
with a different backtrace; the new symbol is incorrectly unified with
the old symbol, which leads to unsound assumptions.

Patch by Alexey Sidorin!

Differential Revision: https://reviews.llvm.org/D21978

llvm-svn: 278937

clang/include/clang/StaticAnalyzer/Core/PathSensitive/SValBuilder.h

@@ -198,9 +198,11 @@ class SValBuilder {
   DefinedOrUnknownSVal getDerivedRegionValueSymbolVal(
       SymbolRef parentSymbol, const TypedValueRegion *region);
 
-  DefinedSVal getMetadataSymbolVal(
-      const void *symbolTag, const MemRegion *region,
-      const Expr *expr, QualType type, unsigned count);
+  DefinedSVal getMetadataSymbolVal(const void *symbolTag,
+                                   const MemRegion *region,
+                                   const Expr *expr, QualType type,
+                                   const LocationContext *LCtx,
+                                   unsigned count);
 
   DefinedSVal getFunctionPointer(const FunctionDecl *func);
 

clang/include/clang/StaticAnalyzer/Core/PathSensitive/SymbolManager.h

@@ -186,15 +186,18 @@ class SymbolMetadata : public SymbolData {
   const MemRegion* R;
   const Stmt *S;
   QualType T;
+  const LocationContext *LCtx;
   unsigned Count;
   const void *Tag;
 public:
   SymbolMetadata(SymbolID sym, const MemRegion* r, const Stmt *s, QualType t,
-                 unsigned count, const void *tag)
-  : SymbolData(SymbolMetadataKind, sym), R(r), S(s), T(t), Count(count), Tag(tag) {}
+                 const LocationContext *LCtx, unsigned count, const void *tag)
+  : SymbolData(SymbolMetadataKind, sym), R(r), S(s), T(t), LCtx(LCtx),
+    Count(count), Tag(tag) {}
 
   const MemRegion *getRegion() const { return R; }
   const Stmt *getStmt() const { return S; }
+  const LocationContext *getLocationContext() const { return LCtx; }
   unsigned getCount() const { return Count; }
   const void *getTag() const { return Tag; }
 
@@ -203,18 +206,19 @@ class SymbolMetadata : public SymbolData {
   void dumpToStream(raw_ostream &os) const override;
 
   static void Profile(llvm::FoldingSetNodeID& profile, const MemRegion *R,
-                      const Stmt *S, QualType T, unsigned Count,
-                      const void *Tag) {
+                      const Stmt *S, QualType T, const LocationContext *LCtx,
+                      unsigned Count, const void *Tag) {
     profile.AddInteger((unsigned) SymbolMetadataKind);
     profile.AddPointer(R);
     profile.AddPointer(S);
     profile.Add(T);
+    profile.AddPointer(LCtx);
     profile.AddInteger(Count);
     profile.AddPointer(Tag);
   }
 
   void Profile(llvm::FoldingSetNodeID& profile) override {
-    Profile(profile, R, S, T, Count, Tag);
+    Profile(profile, R, S, T, LCtx, Count, Tag);
   }
 
   // Implement isa<T> support.
@@ -435,7 +439,9 @@ class SymbolManager {
   /// VisitCount can be used to differentiate regions corresponding to
   /// different loop iterations, thus, making the symbol path-dependent.
   const SymbolMetadata *getMetadataSymbol(const MemRegion *R, const Stmt *S,
-                                          QualType T, unsigned VisitCount,
+                                          QualType T,
+                                          const LocationContext *LCtx,
+                                          unsigned VisitCount,
                                           const void *SymbolTag = nullptr);
 
   const SymbolCast* getCastSymbol(const SymExpr *Operand,

clang/lib/StaticAnalyzer/Checkers/CStringChecker.cpp

@@ -685,6 +685,7 @@ SVal CStringChecker::getCStringLengthForRegion(CheckerContext &C,
   QualType sizeTy = svalBuilder.getContext().getSizeType();
   SVal strLength = svalBuilder.getMetadataSymbolVal(CStringChecker::getTag(),
                                                     MR, Ex, sizeTy,
+                                                    C.getLocationContext(),
                                                     C.blockCount());
 
   if (!hypothetical) {

clang/lib/StaticAnalyzer/Core/SValBuilder.cpp

@@ -182,11 +182,12 @@ SValBuilder::getConjuredHeapSymbolVal(const Expr *E,
 DefinedSVal SValBuilder::getMetadataSymbolVal(const void *symbolTag,
                                               const MemRegion *region,
                                               const Expr *expr, QualType type,
+                                              const LocationContext *LCtx,
                                               unsigned count) {
   assert(SymbolManager::canSymbolicate(type) && "Invalid metadata symbol type");
 
   SymbolRef sym =
-      SymMgr.getMetadataSymbol(region, expr, type, count, symbolTag);
+      SymMgr.getMetadataSymbol(region, expr, type, LCtx, count, symbolTag);
 
   if (Loc::isLocType(type))
     return loc::MemRegionVal(MemMgr.getSymbolicRegion(sym));

clang/lib/StaticAnalyzer/Core/SymbolManager.cpp

@@ -216,17 +216,18 @@ SymbolManager::getExtentSymbol(const SubRegion *R) {
   return cast<SymbolExtent>(SD);
 }
 
-const SymbolMetadata*
+const SymbolMetadata *
 SymbolManager::getMetadataSymbol(const MemRegion* R, const Stmt *S, QualType T,
+                                 const LocationContext *LCtx,
                                  unsigned Count, const void *SymbolTag) {
 
   llvm::FoldingSetNodeID profile;
-  SymbolMetadata::Profile(profile, R, S, T, Count, SymbolTag);
+  SymbolMetadata::Profile(profile, R, S, T, LCtx, Count, SymbolTag);
   void *InsertPos;
   SymExpr *SD = DataSet.FindNodeOrInsertPos(profile, InsertPos);
   if (!SD) {
     SD = (SymExpr*) BPAlloc.Allocate<SymbolMetadata>();
-    new (SD) SymbolMetadata(SymbolCounter, R, S, T, Count, SymbolTag);
+    new (SD) SymbolMetadata(SymbolCounter, R, S, T, LCtx, Count, SymbolTag);
     DataSet.InsertNode(SD, InsertPos);
     ++SymbolCounter;
   }

clang/test/Analysis/string.c

@@ -154,6 +154,23 @@ void strlen_liveness(const char *x) {
   clang_analyzer_eval(strlen(x) < 5); // expected-warning{{FALSE}}
 }
 
+
+size_t strlenWrapper(const char *str) {
+  return strlen(str);
+}
+
+extern void invalidate(char *s);
+
+void testStrlenCallee() {
+  char str[42];
+  invalidate(str);
+  size_t lenBefore = strlenWrapper(str);
+  invalidate(str);
+  size_t lenAfter = strlenWrapper(str);
+  clang_analyzer_eval(lenBefore == lenAfter); // expected-warning{{UNKNOWN}}
+}
+
+
 //===----------------------------------------------------------------------===
 // strnlen()
 //===----------------------------------------------------------------------===