Emit a -Wnull-dereference warning for "*null" not just "*null = something". Addresses rdar://9269271.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@130207 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 19 deletions

diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 6d46127d7d..c90c513250 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -282,6 +282,25 @@ ExprResult Sema::DefaultFunctionArrayConversion(Expr *E) {
   return Owned(E);
 }
 
+static void CheckForNullPointerDereference(Sema &S, Expr *E) {
+  // Check to see if we are dereferencing a null pointer.  If so,
+  // and if not volatile-qualified, this is undefined behavior that the
+  // optimizer will delete, so warn about it.  People sometimes try to use this
+  // to get a deterministic trap and are surprised by clang's behavior.  This
+  // only handles the pattern "*null", which is a very syntactic check.
+  if (UnaryOperator *UO = dyn_cast<UnaryOperator>(E->IgnoreParenCasts()))
+    if (UO->getOpcode() == UO_Deref &&
+        UO->getSubExpr()->IgnoreParenCasts()->
+          isNullPointerConstant(S.Context, Expr::NPC_ValueDependentIsNotNull) &&
+        !UO->getType().isVolatileQualified()) {
+    S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
+                          S.PDiag(diag::warn_indirection_through_null)
+                            << UO->getSubExpr()->getSourceRange());
+    S.DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
+                        S.PDiag(diag::note_indirection_through_null));
+  }
+}
+
 ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   // C++ [conv.lval]p1:
   //   A glvalue of a non-function, non-array type T can be
@@ -317,6 +336,8 @@ ExprResult Sema::DefaultLvalueConversion(Expr *E) {
   if (T->isVoidType())
     return Owned(E);
 
+  CheckForNullPointerDereference(*this, E);
+
   // C++ [conv.lval]p1:
   //   [...] If T is a non-class type, the type of the prvalue is the
   //   cv-unqualified version of T. Otherwise, the type of the
@@ -7993,25 +8014,7 @@ QualType Sema::CheckAssignmentOperands(Expr *LHS, ExprResult &RHS,
                                RHS.get(), AA_Assigning))
     return QualType();
 
-  
-  // Check to see if the destination operand is a dereferenced null pointer.  If
-  // so, and if not volatile-qualified, this is undefined behavior that the
-  // optimizer will delete, so warn about it.  People sometimes try to use this
-  // to get a deterministic trap and are surprised by clang's behavior.  This
-  // only handles the pattern "*null = whatever", which is a very syntactic
-  // check.
-  if (UnaryOperator *UO = dyn_cast<UnaryOperator>(LHS->IgnoreParenCasts()))
-    if (UO->getOpcode() == UO_Deref &&
-        UO->getSubExpr()->IgnoreParenCasts()->
-          isNullPointerConstant(Context, Expr::NPC_ValueDependentIsNotNull) &&
-        !UO->getType().isVolatileQualified()) {
-    DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
-                        PDiag(diag::warn_indirection_through_null)
-                          << UO->getSubExpr()->getSourceRange());
-    DiagRuntimeBehavior(UO->getOperatorLoc(), UO,
-                        PDiag(diag::note_indirection_through_null));
-  }
-  
+  CheckForNullPointerDereference(*this, LHS);
   // Check for trivial buffer overflows.
   CheckArrayAccess(LHS->IgnoreParenCasts());