Add a warning for when an array-to-pointer decay is performed on an array

temporary or an array subobject of a class temporary, and the resulting value
is used to initialize a pointer which outlives the temporary. Such a pointer
is always left dangling after the initialization completes and the array's
lifetime ends.

In order to detect this situation, this change also adds an
LValueClassification of LV_ArrayTemporary for temporaries of array type which
aren't subobjects of class temporaries. These occur in C++11 T{...} and GNU C++
(T){...} expressions, when T is an array type. Previously we treated the former
as a generic prvalue and the latter as a class temporary.

llvm-svn: 157955

1 files changed, 19 insertions, 4 deletions

diff --git a/clang/lib/AST/ExprClassification.cpp b/clang/lib/AST/ExprClassification.cpp
index f958ade..f16d70b 100644
--- a/clang/lib/AST/ExprClassification.cpp
+++ b/clang/lib/AST/ExprClassification.cpp
@@ -77,6 +77,7 @@ Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
   case Cl::CL_MemberFunction:
   case Cl::CL_SubObjCPropertySetting:
   case Cl::CL_ClassTemporary:
+  case Cl::CL_ArrayTemporary:
   case Cl::CL_ObjCMessageRValue:
   case Cl::CL_PRValue: assert(getValueKind() == VK_RValue); break;
   }
@@ -87,6 +88,18 @@ Cl Expr::ClassifyImpl(ASTContext &Ctx, SourceLocation *Loc) const {
   return Classification(kind, modifiable);
 }
 
+/// Classify an expression which creates a temporary, based on its type.
+static Cl::Kinds ClassifyTemporary(QualType T) {
+  if (T->isRecordType())
+    return Cl::CL_ClassTemporary;
+  if (T->isArrayType())
+    return Cl::CL_ArrayTemporary;
+
+  // No special classification: these don't behave differently from normal
+  // prvalues.
+  return Cl::CL_PRValue;
+}
+
 static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
   // This function takes the first stab at classifying expressions.
   const LangOptions &Lang = Ctx.getLangOpts();
@@ -124,10 +137,10 @@ static Cl::Kinds ClassifyInternal(ASTContext &Ctx, const Expr *E) {
     return Cl::CL_LValue;
 
     // C99 6.5.2.5p5 says that compound literals are lvalues.
-    // In C++, they're class temporaries.
+    // In C++, they're prvalue temporaries.
   case Expr::CompoundLiteralExprClass:
-    return Ctx.getLangOpts().CPlusPlus? Cl::CL_ClassTemporary 
-                                         : Cl::CL_LValue;
+    return Ctx.getLangOpts().CPlusPlus ? ClassifyTemporary(E->getType())
+                                       : Cl::CL_LValue;
 
     // Expressions that are prvalues.
   case Expr::CXXBoolLiteralExprClass:
@@ -417,7 +430,7 @@ static Cl::Kinds ClassifyUnnamed(ASTContext &Ctx, QualType T) {
     return Cl::CL_LValue;
   const RValueReferenceType *RV = T->getAs<RValueReferenceType>();
   if (!RV) // Could still be a class temporary, though.
-    return T->isRecordType() ? Cl::CL_ClassTemporary : Cl::CL_PRValue;
+    return ClassifyTemporary(T);
 
   return RV->getPointeeType()->isFunctionType() ? Cl::CL_LValue : Cl::CL_XValue;
 }
@@ -602,6 +615,7 @@ Expr::LValueClassification Expr::ClassifyLValue(ASTContext &Ctx) const {
   case Cl::CL_MemberFunction: return LV_MemberFunction;
   case Cl::CL_SubObjCPropertySetting: return LV_SubObjCPropertySetting;
   case Cl::CL_ClassTemporary: return LV_ClassTemporary;
+  case Cl::CL_ArrayTemporary: return LV_ArrayTemporary;
   case Cl::CL_ObjCMessageRValue: return LV_InvalidMessageExpression;
   case Cl::CL_PRValue: return LV_InvalidExpression;
   }
@@ -622,6 +636,7 @@ Expr::isModifiableLvalue(ASTContext &Ctx, SourceLocation *Loc) const {
   case Cl::CL_MemberFunction: return MLV_MemberFunction;
   case Cl::CL_SubObjCPropertySetting: return MLV_SubObjCPropertySetting;
   case Cl::CL_ClassTemporary: return MLV_ClassTemporary;
+  case Cl::CL_ArrayTemporary: return MLV_ArrayTemporary;
   case Cl::CL_ObjCMessageRValue: return MLV_InvalidMessageExpression;
   case Cl::CL_PRValue:
     return VC.getModifiable() == Cl::CM_LValueCast ?