[runtime] Remove obsolete %_StringAdd intrinsic.

src/full-codegen/mips/full-codegen-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
 
 // Note on Mips implementation:
 //
 // The result_register() for mips is the 'v0' register, which is defined
 // by the ABI to contain function return values. However, the first
@@ skipping 3830 matching lines @@
   __ jmp(&done);
 
   NopRuntimeCallHelper call_helper;
   generator.GenerateSlow(masm_, NOT_PART_OF_IC_HANDLER, call_helper);
 
   __ bind(&done);
   context()->Plug(result);
 }
 
 
-void FullCodeGenerator::EmitStringAdd(CallRuntime* expr) {
-  ZoneList<Expression*>* args = expr->arguments();
-  DCHECK_EQ(2, args->length());
-  VisitForStackValue(args->at(0));
-  VisitForAccumulatorValue(args->at(1));
-
-  __ pop(a1);
-  __ mov(a0, result_register());  // StringAddStub requires args in a0, a1.
-  StringAddStub stub(isolate(), STRING_ADD_CHECK_BOTH, NOT_TENURED);
-  __ CallStub(&stub);
-  context()->Plug(v0);
-}
-
-
 void FullCodeGenerator::EmitCall(CallRuntime* expr) {
   ZoneList<Expression*>* args = expr->arguments();
   DCHECK_LE(2, args->length());
   // Push target, receiver and arguments onto the stack.
   for (Expression* const arg : *args) {
     VisitForStackValue(arg);
   }
   PrepareForBailoutForId(expr->CallId(), NO_REGISTERS);
   // Move target to a1.
   int const argc = args->length() - 2;
@@ skipping 1200 matching lines @@
          reinterpret_cast<uint32_t>(
              isolate->builtins()->OsrAfterStackCheck()->entry()));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS