Implement support for operator overloading using candidate operator

functions for built-in operators, e.g., the builtin

  bool operator==(int const*, int const*)

can be used for the expression "x1 == x2" given:

  struct X {
    operator int const*();
  } x1, x2;

The scheme for handling these built-in operators is relatively simple:
for each candidate required by the standard, create a special kind of
candidate function for the built-in. If overload resolution picks the
built-in operator, we perform the appropriate conversions on the
arguments and then let the normal built-in operator take care of it. 

There may be some optimization opportunity left: if we can reduce the
number of built-in operator overloads we generate, overload resolution
for these cases will go faster. However, one must be careful when
doing this: GCC generates too few operator overloads in our little
test program, and fails to compile it because none of the overloads it
generates match.

Note that we only support operator overload for non-member binary
operators at the moment. The other operators will follow.

As part of this change, ImplicitCastExpr can now be an lvalue.

llvm-svn: 59148

1 files changed, 14 insertions, 5 deletions

diff --git a/clang/lib/Sema/Sema.h b/clang/lib/Sema/Sema.h
index 7cd507a0aa3..5b66694e045 100644
--- a/clang/lib/Sema/Sema.h
+++ b/clang/lib/Sema/Sema.h
@@ -435,6 +435,12 @@ public:
   void AddConversionCandidate(CXXConversionDecl *Conversion,
                               Expr *From, QualType ToType,
                               OverloadCandidateSet& CandidateSet);
+  void AddBuiltinCandidate(QualType ResultTy, QualType *ParamTys, 
+                           Expr **Args, unsigned NumArgs,
+                           OverloadCandidateSet& CandidateSet);
+  void AddBuiltinBinaryOperatorCandidates(OverloadedOperatorKind Op, 
+                                          Expr **Args, 
+                                          OverloadCandidateSet& CandidateSet);
   void AddOverloadCandidates(const OverloadedFunctionDecl *Ovl, 
                              Expr **Args, unsigned NumArgs,
                              OverloadCandidateSet& CandidateSet,
@@ -1052,16 +1058,13 @@ public:
 
   /// ImpCastExprToType - If Expr is not of type 'Type', insert an implicit
   /// cast.  If there is already an implicit cast, merge into the existing one.
-  void ImpCastExprToType(Expr *&Expr, QualType Type);
+  /// If isLvalue, the result of the cast is an lvalue.
+  void ImpCastExprToType(Expr *&Expr, QualType Type, bool isLvalue = false);
 
   // UsualUnaryConversions - promotes integers (C99 6.3.1.1p2) and converts
   // functions and arrays to their respective pointers (C99 6.3.2.1).
   Expr *UsualUnaryConversions(Expr *&expr); 
 
-  // UsualUnaryConversionType - Same as UsualUnaryConversions, but works
-  // on types instead of expressions
-  QualType UsualUnaryConversionType(QualType Ty); 
-  
   // DefaultFunctionArrayConversion - converts functions and arrays
   // to their respective pointers (C99 6.3.2.1). 
   void DefaultFunctionArrayConversion(Expr *&expr);
@@ -1079,6 +1082,12 @@ public:
   QualType UsualArithmeticConversions(Expr *&lExpr, Expr *&rExpr,
                                       bool isCompAssign = false);
   
+  /// UsualArithmeticConversionsType - handles the various conversions
+  /// that are common to binary operators (C99 6.3.1.8, C++ [expr]p9)
+  /// and returns the result type of that conversion.
+  QualType UsualArithmeticConversionsType(QualType lhs, QualType rhs);
+                                          
+
   /// AssignConvertType - All of the 'assignment' semantic checks return this
   /// enum to indicate whether the assignment was allowed.  These checks are
   /// done for simple assignments, as well as initialization, return from