[ast] Inline one DCHECK caller of IsValidReferenceExpressionOrThis()

Also further tighten-up that calling DCHECK in BytecodeGraphBuilder,
and narrow the other caller to IsValidReferenceExpression.

Bug: v8:6092
Change-Id: I432a3d6f5991f2d1adf4f4f86e80d6ed8be5a0e8
Reviewed-on: https://chromium-review.googlesource.com/648196Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47833}

src/ast/ast.cc

@@ -139,11 +139,6 @@ bool Expression::IsValidReferenceExpression() const {
          (IsVariableProxy() && AsVariableProxy()->IsValidReferenceExpression());
 }
 
-bool Expression::IsValidReferenceExpressionOrThis() const {
-  return IsValidReferenceExpression() ||
-         (IsVariableProxy() && AsVariableProxy()->is_this());
-}
-
 bool Expression::IsAnonymousFunctionDefinition() const {
   return (IsFunctionLiteral() &&
           AsFunctionLiteral()->IsAnonymousFunctionDefinition()) ||

src/ast/ast.h

@@ -267,9 +267,6 @@ class Expression : public AstNode {
   // that this also checks for loads of the global "undefined" variable.
   bool IsUndefinedLiteral() const;
 
-  // True iff the expression is a valid target for an assignment.
-  bool IsValidReferenceExpressionOrThis() const;
-
  protected:
   Expression(int pos, NodeType type) : AstNode(pos, type) {}
 

src/interpreter/bytecode-generator.cc

@@ -2464,7 +2464,9 @@ void BytecodeGenerator::BuildVariableAssignment(
 }
 
 void BytecodeGenerator::VisitAssignment(Assignment* expr) {
-  DCHECK(expr->target()->IsValidReferenceExpressionOrThis());
+  DCHECK(expr->target()->IsValidReferenceExpression() ||
+         (expr->op() == Token::INIT && expr->target()->IsVariableProxy() &&
+          expr->target()->AsVariableProxy()->is_this()));
   Register object, key;
   RegisterList super_property_args;
   const AstRawString* name;
@@ -3522,7 +3524,7 @@ void BytecodeGenerator::VisitDelete(UnaryOperation* expr) {
 }
 
 void BytecodeGenerator::VisitCountOperation(CountOperation* expr) {
-  DCHECK(expr->expression()->IsValidReferenceExpressionOrThis());
+  DCHECK(expr->expression()->IsValidReferenceExpression());
 
   // Left-hand side can only be a property, a global or a variable slot.
   Property* property = expr->expression()->AsProperty();