[stubs] Port StringAddStub to TF

src/compiler/code-assembler.cc

 // Copyright 2015 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.
 
 #include "src/compiler/code-assembler.h"
 
 #include <ostream>
 
 #include "src/code-factory.h"
 #include "src/compiler/graph.h"
@@ skipping 130 matching lines @@
 
   return false;
 }
 
 bool CodeAssembler::ToInt64Constant(Node* node, int64_t& out_value) {
   Int64Matcher m(node);
   if (m.HasValue()) out_value = m.Value();
   return m.HasValue();
 }
 
+bool CodeAssembler::ToSmiConstant(Node* node, Smi*& out_value) {
+  if (node->opcode() == IrOpcode::kBitcastWordToTaggedSigned) {
+    node = node->InputAt(0);
+  } else {
+    return false;
+  }
+  IntPtrMatcher m(node);
+  if (m.HasValue()) {
+    out_value = Smi::cast(bit_cast<Object*>(m.Value()));
+    return true;
+  }
+  return false;
+}
+
 bool CodeAssembler::ToIntPtrConstant(Node* node, intptr_t& out_value) {
   IntPtrMatcher m(node);
   if (m.HasValue()) out_value = m.Value();
   return m.HasValue();
 }
 
 Node* CodeAssembler::Parameter(int value) {
   return raw_assembler_->Parameter(value);
 }
 
@@ skipping 956 matching lines @@
       }
     }
   }
 
   bound_ = true;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8