[es6] generate rest parameters correctly for subclass constructors

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index ff42e9e04833e16d8a917b1178a63fa2ef394f3f..64717b979db00d8884583ba4d74060bf1906c5c7 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -232,6 +232,11 @@ void FullCodeGenerator::Generate() {
     }
   }
 
+ArgumentsAccessStub::HasNewTarget has_new_target =
+    IsSubclassConstructor(info->function()->kind())
+        ? ArgumentsAccessStub::HAS_NEW_TARGET
+        : ArgumentsAccessStub::NO_NEW_TARGET;
+
   // Possibly allocate RestParameters
   int rest_index;
   Variable* rest_param = scope()->rest_parameter(&rest_index);
@@ -240,6 +245,11 @@ void FullCodeGenerator::Generate() {
 
     int num_parameters = info->scope()->num_parameters();
     int offset = num_parameters * kPointerSize;
+    if (has_new_target == ArgumentsAccessStub::HAS_NEW_TARGET) {
+      --num_parameters;
+      ++rest_index;
+    }
+
     __ leap(rdx,
             Operand(rbp, StandardFrameConstants::kCallerSPOffset + offset));
     __ Push(rdx);
@@ -275,10 +285,6 @@ void FullCodeGenerator::Generate() {
     // The stub will rewrite receiver and parameter count if the previous
     // stack frame was an arguments adapter frame.
 
-    ArgumentsAccessStub::HasNewTarget has_new_target =
-        IsSubclassConstructor(info->function()->kind())
-            ? ArgumentsAccessStub::HAS_NEW_TARGET
-            : ArgumentsAccessStub::NO_NEW_TARGET;
     ArgumentsAccessStub::Type type;
     if (is_strict(language_mode()) || !is_simple_parameter_list()) {
       type = ArgumentsAccessStub::NEW_STRICT;