[es2015] Precompute the descriptive string for symbols.

src/builtins/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/counters.h"
 #include "src/deoptimizer.h"
@@ skipping 1969 matching lines @@
   {
     FrameScope scope(masm, StackFrame::MANUAL);
     __ EnterBuiltinFrame(rsi, rdi, r8);
     __ Call(masm->isolate()->builtins()->ToString(), RelocInfo::CODE_TARGET);
     __ LeaveBuiltinFrame(rsi, rdi, r8);
   }
   __ jmp(&drop_frame_and_ret, Label::kNear);
 
   // 3b. Convert symbol in rax to a string.
   __ bind(&symbol_descriptive_string);
-  {
-    __ PopReturnAddressTo(rcx);
-    __ SmiToInteger32(r8, r8);
-    __ leap(rsp, Operand(rsp, r8, times_pointer_size, kPointerSize));
-    __ Push(rax);
-    __ PushReturnAddressFrom(rcx);
-    __ TailCallRuntime(Runtime::kSymbolDescriptiveString);
-  }
+  __ movp(rax, FieldOperand(rax, Symbol::kDescriptiveStringOffset));
+  // Fall through.
 
   __ bind(&drop_frame_and_ret);
   {
     // Drop all arguments including the receiver.
     __ PopReturnAddressTo(rcx);
     __ SmiToInteger32(r8, r8);
     __ leap(rsp, Operand(rsp, r8, times_pointer_size, kPointerSize));
     __ PushReturnAddressFrom(rcx);
     __ Ret();
   }
@@ skipping 1227 matching lines @@
   // Now jump to the instructions of the returned code object.
   __ jmp(r11);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64