[analyzer] For now, treat pointers-to-members as non-null void * symbols.

Until we have full support for pointers-to-members, we can at least
approximate some of their use by tracking null and non-null values.
We thus treat &A::m_ptr as a non-null void * symbol, and MemberPointer(0)
as a pointer-sized null constant.

This enables support for what is sometimes called the "safe bool" idiom,
demonstrated in the test case.

llvm-svn: 162495

clang/lib/StaticAnalyzer/Core/ExprEngine.cpp

@@ -1428,7 +1428,12 @@ void ExprEngine::VisitCommonDeclRefExpr(const Expr *Ex, const NamedDecl *D,
   }
   if (isa<FieldDecl>(D)) {
     // FIXME: Compute lvalue of field pointers-to-member.
-    Bldr.generateNode(Ex, Pred, state->BindExpr(Ex, LCtx, UnknownVal()), 0,
+    // Right now we just use a non-null void pointer, so that it gives proper
+    // results in boolean contexts.
+    SVal V = svalBuilder.conjureSymbolVal(Ex, LCtx, getContext().VoidPtrTy,
+                                          currBldrCtx->blockCount());
+    state = state->assume(cast<DefinedOrUnknownSVal>(V), true);
+    Bldr.generateNode(Ex, Pred, state->BindExpr(Ex, LCtx, V), 0,
 		      ProgramPoint::PostLValueKind);
     return;
   }

clang/lib/StaticAnalyzer/Core/ExprEngineC.cpp

@@ -274,6 +274,9 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
         Bldr.generateNode(CastE, Pred, state);
         continue;
       }
+      case CK_MemberPointerToBoolean:
+        // FIXME: For now, member pointers are represented by void *.
+        // FALLTHROUGH
       case CK_Dependent:
       case CK_ArrayToPointerDecay:
       case CK_BitCast:
@@ -359,16 +362,21 @@ void ExprEngine::VisitCast(const CastExpr *CastE, const Expr *Ex,
         Bldr.generateNode(CastE, Pred, state);
         continue;
       }
+      case CK_NullToMemberPointer: {
+        // FIXME: For now, member pointers are represented by void *.
+        SVal V = svalBuilder.makeIntValWithPtrWidth(0, true);
+        state = state->BindExpr(CastE, LCtx, V);
+        Bldr.generateNode(CastE, Pred, state);
+        continue;
+      }
       // Various C++ casts that are not handled yet.
       case CK_ToUnion:
       case CK_BaseToDerived:
-      case CK_NullToMemberPointer:
       case CK_BaseToDerivedMemberPointer:
       case CK_DerivedToBaseMemberPointer:
       case CK_ReinterpretMemberPointer:
       case CK_ConstructorConversion:
       case CK_VectorSplat:
-      case CK_MemberPointerToBoolean:
       case CK_LValueBitCast: {
         // Recover some path-sensitivty by conjuring a new value.
         QualType resultType = CastE->getType();

clang/test/Analysis/pointer-to-member.cpp

@@ -0,0 +1,44 @@
+// RUN: %clang_cc1 -analyze -analyzer-checker=core,debug.ExprInspection -analyzer-ipa=inlining -verify %s
+
+void clang_analyzer_eval(bool);
+
+struct A {
+  // This conversion operator allows implicit conversion to bool but not to other integer types.
+  typedef A * (A::*MemberPointer);
+  operator MemberPointer() const { return m_ptr ? &A::m_ptr : 0; }
+
+  A *m_ptr;
+};
+
+void testConditionalUse() {
+  A obj;
+
+  obj.m_ptr = &obj;
+  clang_analyzer_eval(obj.m_ptr); // expected-warning{{TRUE}}
+  clang_analyzer_eval(&A::m_ptr); // expected-warning{{TRUE}}
+  clang_analyzer_eval(obj); // expected-warning{{TRUE}}
+
+  obj.m_ptr = 0;
+  clang_analyzer_eval(obj.m_ptr); // expected-warning{{FALSE}}
+  clang_analyzer_eval(A::MemberPointer(0)); // expected-warning{{FALSE}}
+  clang_analyzer_eval(obj); // expected-warning{{FALSE}}
+}
+
+// ---------------
+// FALSE NEGATIVES
+// ---------------
+
+bool testDereferencing() {
+  A obj;
+  obj.m_ptr = 0;
+
+  A::MemberPointer member = &A::m_ptr;
+
+  // FIXME: Should be TRUE.
+  clang_analyzer_eval(obj.*member == 0); // expected-warning{{UNKNOWN}}
+
+  member = 0;
+
+  // FIXME: Should emit a null dereference.
+  return obj.*member; // no-warning
+}