[analyzer] Check that a member expr is valid even when the result is an lvalue.

We want to catch cases like this early, so that we can produce better
diagnostics and path notes:

  Point *p = 0;
  int *px = &p->x; // should warn here
  *px = 1;

llvm-svn: 164441

clang/lib/StaticAnalyzer/Core/ExprEngine.cpp

@@ -1515,22 +1515,30 @@ void ExprEngine::VisitMemberExpr(const MemberExpr *M, ExplodedNode *Pred,
     return;
   }
 
-  // FIXME: Should we insert some assumption logic in here to determine
-  // if "Base" is a valid piece of memory?  Before we put this assumption
-  // later when using FieldOffset lvals (which we no longer have).
-
   // For all other cases, compute an lvalue.    
   SVal L = state->getLValue(field, baseExprVal);
   if (M->isGLValue()) {
+    ExplodedNodeSet Tmp;
+    Bldr.takeNodes(Pred);
+    evalLocation(Tmp, M, M, Pred, state, baseExprVal,
+                 /*Tag=*/0, /*isLoad=*/true);
+    Bldr.addNodes(Tmp);
+
+    const MemRegion *ReferenceRegion = 0;
     if (field->getType()->isReferenceType()) {
-      if (const MemRegion *R = L.getAsRegion())
-        L = state->getSVal(R);
-      else
+      ReferenceRegion = L.getAsRegion();
+      if (!ReferenceRegion)
         L = UnknownVal();
     }
 
-    Bldr.generateNode(M, Pred, state->BindExpr(M, LCtx, L), 0,
+    for (ExplodedNodeSet::iterator I = Tmp.begin(), E = Tmp.end(); I != E; ++I){
+      state = (*I)->getState();
+      if (ReferenceRegion)
+        L = state->getSVal(ReferenceRegion);
+
+      Bldr.generateNode(M, (*I), state->BindExpr(M, LCtx, L), 0,
                         ProgramPoint::PostLValueKind);
+    }
   } else {
     Bldr.takeNodes(Pred);
     evalLoad(Dst, M, M, Pred, state, L);

clang/test/Analysis/fields.c

@@ -26,3 +26,10 @@ void test() {
   Point p;
   (void)(p = getit()).x;
 }
+
+
+void testNullAddress() {
+  Point *p = 0;
+  int *px = &p->x; // expected-warning{{Access to field 'x' results in a dereference of a null pointer (loaded from variable 'p')}}
+  *px = 1; // No warning because analysis stops at the previous line.
+}

clang/test/Analysis/nullptr.cpp

@@ -23,10 +23,11 @@ void foo3(void) {
   };
   char *np = nullptr;
   // casting a nullptr to anything should be caught eventually
-  int *ip = &(((struct foo *)np)->f);
-  *ip = 0;  // expected-warning{{Dereference of null pointer}}
-  // should be error here too, but analysis gets stopped
-//  *np = 0;
+  int *ip = &(((struct foo *)np)->f);  // expected-warning{{Access to field 'f' results in a dereference of a null pointer (loaded from variable 'np')}}
+
+  // Analysis stops at the first problem case, so we won't actually warn here.
+  *ip = 0;
+  *np = 0;
 }
 
 // nullptr is implemented as a zero integer value, so should be able to compare