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

include/clang/AST/Expr.h

@@ -1552,6 +1552,10 @@ public:
     /// CK_DerivedToBase - Derived to base class casts.
     CK_DerivedToBase,
 
+    /// CK_UncheckedDerivedToBase - Derived to base class casts that
+    /// assume that the derived pointer is not null.
+    CK_UncheckedDerivedToBase,
+
     /// CK_Dynamic - Dynamic cast.
     CK_Dynamic,
 

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:

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;

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>();

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>();

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;
 }
 

test/CodeGenCXX/member-expressions.cpp

@@ -44,3 +44,43 @@ int f() {
   return A().foo();
 }
 }
+
+namespace test4 {
+  struct A {
+    int x;
+  };
+  struct B {
+    int x;
+    void foo();
+  };
+  struct C : A, B {
+  };
+
+  extern C *c_ptr;
+
+  // CHECK: define i32 @_ZN5test44testEv()
+  int test() {
+    // CHECK: load {{.*}} @_ZN5test45c_ptrE
+    // CHECK-NEXT: bitcast
+    // CHECK-NEXT: getelementptr
+    // CHECK-NEXT: bitcast
+    // CHECK-NEXT: call void @_ZN5test41B3fooEv
+    c_ptr->B::foo();
+
+    // CHECK: load {{.*}} @_ZN5test45c_ptrE
+    // CHECK-NEXT: bitcast
+    // CHECK-NEXT: getelementptr
+    // CHECK-NEXT: bitcast
+    // CHECK-NEXT: getelementptr
+    // CHECK-NEXT: store i32 5
+    c_ptr->B::x = 5;
+
+    // CHECK: load {{.*}} @_ZN5test45c_ptrE
+    // CHECK-NEXT: bitcast
+    // CHECK-NEXT: getelementptr
+    // CHECK-NEXT: bitcast
+    // CHECK-NEXT: getelementptr
+    // CHECK-NEXT: load i32*
+    return c_ptr->B::x;
+  }
+}