Fix checking for a null pointer constant when the expression itself is

value-dependent. Audit (and fixed) all calls to
Expr::isNullPointerConstant() to provide the correct behavior with
value-dependent expressions. Fixes PR5041 and a crash in libstdc++
<locale>.

In the same vein, properly compute value- and type-dependence for
ChooseExpr. Fixes PR4996.

llvm-svn: 82748

1 files changed, 19 insertions, 7 deletions

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index dc9cee13a9c..dcfd1474f16 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1625,9 +1625,21 @@ bool Expr::isIntegerConstantExpr(llvm::APSInt &Result, ASTContext &Ctx,
 /// isNullPointerConstant - C99 6.3.2.3p3 -  Return true if this is either an
 /// integer constant expression with the value zero, or if this is one that is
 /// cast to void*.
-bool Expr::isNullPointerConstant(ASTContext &Ctx) const {
-  // Ignore value dependent expressions.
-  assert(!isValueDependent() && "Unexpect value dependent expression!");
+bool Expr::isNullPointerConstant(ASTContext &Ctx,
+                                 NullPointerConstantValueDependence NPC) const {
+  if (isValueDependent()) {
+    switch (NPC) {
+    case NPC_NeverValueDependent:
+      assert(false && "Unexpected value dependent expression!");
+      // If the unthinkable happens, fall through to the safest alternative.
+        
+    case NPC_ValueDependentIsNull:
+      return isTypeDependent() || getType()->isIntegralType();
+        
+    case NPC_ValueDependentIsNotNull:
+      return false;
+    }
+  }
 
   // Strip off a cast to void*, if it exists. Except in C++.
   if (const ExplicitCastExpr *CE = dyn_cast<ExplicitCastExpr>(this)) {
@@ -1638,20 +1650,20 @@ bool Expr::isNullPointerConstant(ASTContext &Ctx) const {
         if (!Pointee.hasQualifiers() &&
             Pointee->isVoidType() &&                              // to void*
             CE->getSubExpr()->getType()->isIntegerType())         // from int.
-          return CE->getSubExpr()->isNullPointerConstant(Ctx);
+          return CE->getSubExpr()->isNullPointerConstant(Ctx, NPC);
       }
     }
   } else if (const ImplicitCastExpr *ICE = dyn_cast<ImplicitCastExpr>(this)) {
     // Ignore the ImplicitCastExpr type entirely.
-    return ICE->getSubExpr()->isNullPointerConstant(Ctx);
+    return ICE->getSubExpr()->isNullPointerConstant(Ctx, NPC);
   } else if (const ParenExpr *PE = dyn_cast<ParenExpr>(this)) {
     // Accept ((void*)0) as a null pointer constant, as many other
     // implementations do.
-    return PE->getSubExpr()->isNullPointerConstant(Ctx);
+    return PE->getSubExpr()->isNullPointerConstant(Ctx, NPC);
   } else if (const CXXDefaultArgExpr *DefaultArg
                = dyn_cast<CXXDefaultArgExpr>(this)) {
     // See through default argument expressions
-    return DefaultArg->getExpr()->isNullPointerConstant(Ctx);
+    return DefaultArg->getExpr()->isNullPointerConstant(Ctx, NPC);
   } else if (isa<GNUNullExpr>(this)) {
     // The GNU __null extension is always a null pointer constant.
     return true;