[es2015] Precompute the descriptive string for symbols.

src/builtins/mips/builtins-mips.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_MIPS
 
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 280 matching lines @@
     __ SmiTag(t0);
     __ EnterBuiltinFrame(cp, a1, t0);
     __ Call(masm->isolate()->builtins()->ToString(), RelocInfo::CODE_TARGET);
     __ LeaveBuiltinFrame(cp, a1, t0);
     __ SmiUntag(t0);
   }
   __ jmp(&drop_frame_and_ret);
 
   // 3b. Convert symbol in a0 to a string.
   __ bind(&symbol_descriptive_string);
-  {
-    __ Lsa(sp, sp, t0, kPointerSizeLog2);
-    __ Drop(1);
-    __ Push(a0);
-    __ TailCallRuntime(Runtime::kSymbolDescriptiveString);
-  }
+  __ lw(v0, FieldMemOperand(a0, Symbol::kDescriptiveStringOffset));
+  // Fall through.
 
   __ bind(&drop_frame_and_ret);
   {
     __ Lsa(sp, sp, t0, kPointerSizeLog2);
     __ DropAndRet(1);
   }
 }
 
 // static
 void Builtins::Generate_StringConstructor_ConstructStub(MacroAssembler* masm) {
@@ skipping 2795 matching lines @@
   // Now jump to the instructions of the returned code object.
   __ Jump(at, v0, Code::kHeaderSize - kHeapObjectTag);
 }
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS