Surpress the UsualUnaryConversions for compound assignment operators. This change

eliminates the possibility that the left hand expression is an ImplicitCastExpr.
As a result, I removed the check for ImplicitCastExpr in Expr::isLvalue().

This results in the following AST's...

[dylan:~/llvm/tools/clang] admin% cat fix.c

short x; void test4(char c) { 
  x += c; 
  x = x + c;
}
[dylan:~/llvm/tools/clang] admin% ../../Debug/bin/clang fix.c -parse-ast-dump
Read top-level variable decl: 'x'

void test4(char c)
(CompoundStmt 0x2605d30
  (CompoundAssignOperator 0x2605c40 'short' '+='
    (DeclRefExpr 0x2605c00 'short' Decl='x' 0x2605a80)
    (DeclRefExpr 0x2605c20 'char' Decl='c' 0x2605bc0))
  (BinaryOperator 0x2605d10 'short' '='
    (DeclRefExpr 0x2605c60 'short' Decl='x' 0x2605a80)
    (ImplicitCastExpr 0x2605d00 'short'
      (BinaryOperator 0x2605ce0 'int' '+'
        (ImplicitCastExpr 0x2605cc0 'int'
          (DeclRefExpr 0x2605c80 'short' Decl='x' 0x2605a80))
        (ImplicitCastExpr 0x2605cd0 'int'
          (DeclRefExpr 0x2605ca0 'char' Decl='c' 0x2605bc0))))))

llvm-svn: 41404

clang/AST/Expr.cpp

@@ -302,8 +302,6 @@ Expr::isLvalueResult Expr::isLvalue() const {
     if (cast<OCUVectorElementExpr>(this)->containsDuplicateElements())
       return LV_DuplicateVectorComponents;
     return LV_Valid;
-  case ImplicitCastExprClass: // A side-effect of our implementation.
-    return cast<ImplicitCastExpr>(this)->getSubExpr()->isLvalue();
   default:
     break;
   }

clang/Sema/SemaExpr.cpp

@@ -765,9 +765,10 @@ void Sema::UsualUnaryConversions(Expr *&expr) {
 /// responsible for emitting appropriate error diagnostics.
 QualType Sema::UsualArithmeticConversions(Expr *&lhsExpr, Expr *&rhsExpr,
                                           bool isCompAssign) {
-  UsualUnaryConversions(lhsExpr);
-  UsualUnaryConversions(rhsExpr);
-  
+  if (!isCompAssign) {
+    UsualUnaryConversions(lhsExpr);
+    UsualUnaryConversions(rhsExpr);
+  }
   QualType lhs = lhsExpr->getType();
   QualType rhs = rhsExpr->getType();