Grab-bag of bit-field fixes:

  - References to ObjC bit-field ivars are bit-field lvalues;
    fixes rdar://13794269, which got me started down this.
  - Introduce Expr::refersToBitField, switch a couple users to
    it where semantically important, and comment the difference
    between this and the existing API.
  - Discourage Expr::getBitField by making it a bit longer and
    less general-sounding.
  - Lock down on const_casts of bit-field gl-values until we
    hear back from the committee as to whether they're allowed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181252 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 18 insertions, 5 deletions

diff --git a/include/clang/AST/Expr.h b/include/clang/AST/Expr.h
index 2e66df33ee..4ff1257b7d 100644
--- a/include/clang/AST/Expr.h
+++ b/include/clang/AST/Expr.h
@@ -427,12 +427,24 @@ private:
 
 public:
 
+  /// \brief Returns true if this expression is a gl-value that
+  /// potentially refers to a bit-field.
+  ///
+  /// In C++, whether a gl-value refers to a bitfield is essentially
+  /// an aspect of the value-kind type system.
+  bool refersToBitField() const { return getObjectKind() == OK_BitField; }
+
   /// \brief If this expression refers to a bit-field, retrieve the
   /// declaration of that bit-field.
-  FieldDecl *getBitField();
-
-  const FieldDecl *getBitField() const {
-    return const_cast<Expr*>(this)->getBitField();
+  ///
+  /// Note that this returns a non-null pointer in subtly different
+  /// places than refersToBitField returns true.  In particular, this can
+  /// return a non-null pointer even for r-values loaded from
+  /// bit-fields, but it will return null for a conditional bit-field.
+  FieldDecl *getSourceBitField();
+
+  const FieldDecl *getSourceBitField() const {
+    return const_cast<Expr*>(this)->getSourceBitField();
   }
 
   /// \brief If this expression is an l-value for an Objective C
diff --git a/include/clang/AST/ExprObjC.h b/include/clang/AST/ExprObjC.h
index dfd45279dd..a94c69a115 100644
--- a/include/clang/AST/ExprObjC.h
+++ b/include/clang/AST/ExprObjC.h
@@ -476,7 +476,8 @@ public:
                   SourceLocation l, SourceLocation oploc,
                   Expr *base,
                   bool arrow = false, bool freeIvar = false) :
-    Expr(ObjCIvarRefExprClass, t, VK_LValue, OK_Ordinary,
+    Expr(ObjCIvarRefExprClass, t, VK_LValue,
+         d->isBitField() ? OK_BitField : OK_Ordinary,
          /*TypeDependent=*/false, base->isValueDependent(), 
          base->isInstantiationDependent(),
          base->containsUnexpandedParameterPack()),