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

src/mips64/builtins-mips64.cc

Index: src/mips64/builtins-mips64.cc
diff --git a/src/mips64/builtins-mips64.cc b/src/mips64/builtins-mips64.cc
index 2534de5f3d5f141c1328153fc1369c1b54d53a1c..ee156b80afb03923ed90c8e50dbbb5bffb918975 100644
--- a/src/mips64/builtins-mips64.cc
+++ b/src/mips64/builtins-mips64.cc
@@ -1956,6 +1956,15 @@ 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());
+  __ li(at, Operand(is_tail_call_elimination_enabled));
+  __ lb(scratch1, MemOperand(at));
+  __ Branch(&done, eq, scratch1, Operand(zero_reg));
+
   // Drop possible interpreter handler/stub frame.
   {
     Label no_interpreter_frame;
@@ -1998,6 +2007,7 @@ 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