Introduce a new kind of derived-to-base cast which bypasses the need for

null checks, and make sure we elide null checks when accessing base class
members.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@99963 91177308-0d34-0410-b5e6-96231b3b80d8

5 files changed, 12 insertions, 4 deletions

diff --git a/lib/AST/Expr.cpp b/lib/AST/Expr.cpp
index a9b5f36a98..4cb7712e52 100644
--- a/lib/AST/Expr.cpp
+++ b/lib/AST/Expr.cpp
@@ -552,6 +552,8 @@ const char *CastExpr::getCastKindName() const {
     return "BaseToDerived";
   case CastExpr::CK_DerivedToBase:
     return "DerivedToBase";
+  case CastExpr::CK_UncheckedDerivedToBase:
+    return "UncheckedDerivedToBase";
   case CastExpr::CK_Dynamic:
     return "Dynamic";
   case CastExpr::CK_ToUnion:
diff --git a/lib/Checker/GRExprEngine.cpp b/lib/Checker/GRExprEngine.cpp
index 1afe0917f1..04f8cc6142 100644
--- a/lib/Checker/GRExprEngine.cpp
+++ b/lib/Checker/GRExprEngine.cpp
@@ -2306,6 +2306,7 @@ void GRExprEngine::VisitCast(CastExpr *CastE, Expr *Ex, ExplodedNode *Pred,
   case CastExpr::CK_AnyPointerToObjCPointerCast:
   case CastExpr::CK_AnyPointerToBlockPointerCast:
   case CastExpr::CK_DerivedToBase:
+  case CastExpr::CK_UncheckedDerivedToBase:
     // Delegate to SValuator to process.
     for (ExplodedNodeSet::iterator I = S2.begin(), E = S2.end(); I != E; ++I) {
       ExplodedNode* N = *I;
diff --git a/lib/CodeGen/CGExpr.cpp b/lib/CodeGen/CGExpr.cpp
index 2ddc08a4c4..027264f25b 100644
--- a/lib/CodeGen/CGExpr.cpp
+++ b/lib/CodeGen/CGExpr.cpp
@@ -1637,6 +1637,7 @@ LValue CodeGenFunction::EmitCastLValue(const CastExpr *E) {
   case CastExpr::CK_AnyPointerToObjCPointerCast:
     return EmitLValue(E->getSubExpr());
   
+  case CastExpr::CK_UncheckedDerivedToBase:
   case CastExpr::CK_DerivedToBase: {
     const RecordType *DerivedClassTy = 
       E->getSubExpr()->getType()->getAs<RecordType>();
diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index 1ef06ccf6f..42bf68ed52 100644
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -769,6 +769,9 @@ Value *ScalarExprEmitter::VisitInitListExpr(InitListExpr *E) {
 
 static bool ShouldNullCheckClassCastValue(const CastExpr *CE) {
   const Expr *E = CE->getSubExpr();
+
+  if (CE->getCastKind() == CastExpr::CK_UncheckedDerivedToBase)
+    return false;
   
   if (isa<CXXThisExpr>(E)) {
     // We always assume that 'this' is never null.
@@ -826,6 +829,7 @@ Value *ScalarExprEmitter::EmitCastExpr(CastExpr *CE) {
     return CGF.GetAddressOfDerivedClass(Src, BaseClassDecl, DerivedClassDecl, 
                                         NullCheckValue);
   }
+  case CastExpr::CK_UncheckedDerivedToBase:
   case CastExpr::CK_DerivedToBase: {
     const RecordType *DerivedClassTy = 
       E->getType()->getAs<PointerType>()->getPointeeType()->getAs<RecordType>();
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index e232230db7..0980710b3d 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -1461,7 +1461,7 @@ Sema::PerformObjectMemberConversion(Expr *&From,
 
       if (PointerConversions)
         QType = Context.getPointerType(QType);
-      ImpCastExprToType(From, QType, CastExpr::CK_DerivedToBase,
+      ImpCastExprToType(From, QType, CastExpr::CK_UncheckedDerivedToBase,
                         /*isLvalue*/ !PointerConversions);
 
       FromType = QType;
@@ -1497,7 +1497,7 @@ Sema::PerformObjectMemberConversion(Expr *&From,
       QualType UType = URecordType;
       if (PointerConversions)
         UType = Context.getPointerType(UType);
-      ImpCastExprToType(From, UType, CastExpr::CK_DerivedToBase,
+      ImpCastExprToType(From, UType, CastExpr::CK_UncheckedDerivedToBase,
                         /*isLvalue*/ !PointerConversions);
       FromType = UType;
       FromRecordType = URecordType;
@@ -1517,8 +1517,8 @@ Sema::PerformObjectMemberConversion(Expr *&From,
 
   // FIXME: isLvalue should be !PointerConversions here, but codegen
   // does very silly things.
-  ImpCastExprToType(From, DestType, CastExpr::CK_DerivedToBase,
-                    /*isLvalue=*/ true);
+  ImpCastExprToType(From, DestType, CastExpr::CK_UncheckedDerivedToBase,
+                    /*isLvalue=*/ !PointerConversions);
   return false;
 }