[es6] Don't disable ES6 tail call elimination when Debugger is on.

src/x64/builtins-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/code-factory.h"
 #include "src/codegen.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 2034 matching lines @@
 // |  f()'s receiver arg
 // |  f()'s caller pc      <- sp
 // ----------------------
 //
 void PrepareForTailCall(MacroAssembler* masm, Register args_reg,
                         Register scratch1, Register scratch2,
                         Register scratch3) {
   DCHECK(!AreAliased(args_reg, scratch1, scratch2, scratch3));
   Comment cmnt(masm, "[ PrepareForTailCall");
 
-  // Prepare for tail call only if the debugger is not active.
-  Label done;
-  ExternalReference debug_is_active =
-      ExternalReference::debug_is_active_address(masm->isolate());
-  __ Move(kScratchRegister, debug_is_active);
-  __ cmpb(Operand(kScratchRegister, 0), Immediate(0));
-  __ j(not_equal, &done);
-
   // Drop possible interpreter handler/stub frame.
   {
     Label no_interpreter_frame;
     __ Cmp(Operand(rbp, CommonFrameConstants::kContextOrFrameTypeOffset),
            Smi::FromInt(StackFrame::STUB));
     __ j(not_equal, &no_interpreter_frame, Label::kNear);
     __ movp(rbp, Operand(rbp, StandardFrameConstants::kCallerFPOffset));
     __ bind(&no_interpreter_frame);
   }
 
@@ skipping 19 matching lines @@
           FieldOperand(scratch1, JSFunction::kSharedFunctionInfoOffset));
   __ LoadSharedFunctionInfoSpecialField(
       caller_args_count_reg, scratch1,
       SharedFunctionInfo::kFormalParameterCountOffset);
 
   __ bind(&formal_parameter_count_loaded);
 
   ParameterCount callee_args_count(args_reg);
   __ PrepareForTailCall(callee_args_count, caller_args_count_reg, scratch2,
                         scratch3, ReturnAddressState::kOnStack);
-  __ bind(&done);
 }
 }  // namespace
 
 // static
 void Builtins::Generate_CallFunction(MacroAssembler* masm,
                                      ConvertReceiverMode mode,
                                      TailCallMode tail_call_mode) {
   // ----------- S t a t e -------------
   //  -- rax : the number of arguments (not including the receiver)
   //  -- rdi : the function to call (checked to be a JSFunction)
@@ skipping 561 matching lines @@
   __ ret(0);
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64