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

src/ppc/builtins-ppc.cc

Index: src/ppc/builtins-ppc.cc
diff --git a/src/ppc/builtins-ppc.cc b/src/ppc/builtins-ppc.cc
index 75f9c7809c0bce4e2f449c1024eb0bd04c82ff5d..884afedb21b78979195f262a8275e753b6b44bcc 100644
--- a/src/ppc/builtins-ppc.cc
+++ b/src/ppc/builtins-ppc.cc
@@ -1987,6 +1987,16 @@ void PrepareForTailCall(MacroAssembler* masm, Register args_reg,
   DCHECK(!AreAliased(args_reg, scratch1, scratch2, scratch3));
   Comment cmnt(masm, "[ PrepareForTailCall");
 
+  // Prepare for tail call only if ES2015 tail call elimination is enabled.
+  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));
+  __ lbz(scratch1, MemOperand(scratch1));
+  __ cmpi(scratch1, Operand::Zero());
+  __ beq(&done);
+
   // Drop possible interpreter handler/stub frame.
   {
     Label no_interpreter_frame;
@@ -2034,6 +2044,7 @@ void PrepareForTailCall(MacroAssembler* masm, Register args_reg,
   ParameterCount callee_args_count(args_reg);
   __ PrepareForTailCall(callee_args_count, caller_args_count_reg, scratch2,
                         scratch3);
+  __ bind(&done);
 }
 }  // namespace