[es6] Add a flag to the Isolate that defines whether ES2015 tail call elimination is enabled or not.

src/s390/builtins-s390.cc

 // Copyright 2014 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_S390
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 1931 matching lines @@
 // |  f()'s arg 1
 // |  f()'s receiver arg   <- sp (f()'s caller pc is not on the stack yet!)
 // ----------------------
 //
 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 ES2015 tail call elimination is active.
+  Label done;
+  ExternalReference is_tail_call_elimination_enabled =
+      ExternalReference::is_tail_call_elimination_enabled_address(
+          masm->isolate());
+  __ mov(scratch1, Operand(is_tail_call_elimination_enabled));
+  __ LoadlB(scratch1, MemOperand(scratch1));
+  __ CmpP(scratch1, Operand::Zero());
+  __ beq(&done);
+
   // Drop possible interpreter handler/stub frame.
   {
     Label no_interpreter_frame;
     __ LoadP(scratch3,
              MemOperand(fp, CommonFrameConstants::kContextOrFrameTypeOffset));
     __ CmpSmiLiteral(scratch3, Smi::FromInt(StackFrame::STUB), r0);
     __ bne(&no_interpreter_frame);
     __ LoadP(fp, MemOperand(fp, StandardFrameConstants::kCallerFPOffset));
     __ bind(&no_interpreter_frame);
   }
@@ skipping 26 matching lines @@
                            SharedFunctionInfo::kFormalParameterCountOffset));
 #if !V8_TARGET_ARCH_S390X
   __ SmiUntag(caller_args_count_reg);
 #endif
 
   __ bind(&formal_parameter_count_loaded);
 
   ParameterCount callee_args_count(args_reg);
   __ PrepareForTailCall(callee_args_count, caller_args_count_reg, scratch2,
                         scratch3);
+  __ bind(&done);
 }
 }  // namespace
 
 // static
 void Builtins::Generate_CallFunction(MacroAssembler* masm,
                                      ConvertReceiverMode mode,
                                      TailCallMode tail_call_mode) {
   // ----------- S t a t e -------------
   //  -- r2 : the number of arguments (not including the receiver)
   //  -- r3 : the function to call (checked to be a JSFunction)
@@ skipping 527 matching lines @@
     __ bkpt(0);
   }
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_S390