Rename String.concat() implementation function.

Rename String::AllocFromStrings() to String::DoConcat() and
rename arguments to h_this and h_arg.

This addresses a comment from
    https://android-review.googlesource.com/1473728 .

Test: testrunner.py --host --optimizing -t 021-string2
Bug: 169674485
Change-Id: I830541b64b51c0170aa5455cbad7cc86f4349f13
diff --git a/runtime/mirror/string.cc b/runtime/mirror/string.cc
index 18ab105..0ce45b8 100644
--- a/runtime/mirror/string.cc
+++ b/runtime/mirror/string.cc
@@ -112,15 +112,13 @@
   return Alloc(self, length_with_flag, allocator_type, visitor);
 }
 
-ObjPtr<String> String::AllocFromStrings(Thread* self,
-                                        Handle<String> string,
-                                        Handle<String> string2) {
-  int32_t length = string->GetLength();
-  int32_t length2 = string2->GetLength();
+ObjPtr<String> String::DoConcat(Thread* self, Handle<String> h_this, Handle<String> h_arg) {
+  int32_t length_this = h_this->GetLength();
+  int32_t length_arg = h_arg->GetLength();
   gc::AllocatorType allocator_type = Runtime::Current()->GetHeap()->GetCurrentAllocator();
-  const bool compressible = kUseStringCompression &&
-      (string->IsCompressed() && string2->IsCompressed());
-  const int32_t length_with_flag = String::GetFlaggedCount(length + length2, compressible);
+  const bool compressible =
+      kUseStringCompression && (h_this->IsCompressed() && h_arg->IsCompressed());
+  const int32_t length_with_flag = String::GetFlaggedCount(length_this + length_arg, compressible);
 
   auto visitor = [=](ObjPtr<Object> obj, size_t usable_size) REQUIRES_SHARED(Locks::mutator_lock_) {
     SetStringCountVisitor set_string_count_visitor(length_with_flag);
@@ -128,25 +126,25 @@
     ObjPtr<String> new_string = obj->AsString();
     if (compressible) {
       uint8_t* new_value = new_string->GetValueCompressed();
-      memcpy(new_value, string->GetValueCompressed(), length * sizeof(uint8_t));
-      memcpy(new_value + length, string2->GetValueCompressed(), length2 * sizeof(uint8_t));
+      memcpy(new_value, h_this->GetValueCompressed(), length_this * sizeof(uint8_t));
+      memcpy(new_value + length_this, h_arg->GetValueCompressed(), length_arg * sizeof(uint8_t));
     } else {
       uint16_t* new_value = new_string->GetValue();
-      if (string->IsCompressed()) {
-        const uint8_t* value = string->GetValueCompressed();
-        for (int i = 0; i < length; ++i) {
-          new_value[i] = value[i];
+      if (h_this->IsCompressed()) {
+        const uint8_t* value_this = h_this->GetValueCompressed();
+        for (int i = 0; i < length_this; ++i) {
+          new_value[i] = value_this[i];
         }
       } else {
-        memcpy(new_value, string->GetValue(), length * sizeof(uint16_t));
+        memcpy(new_value, h_this->GetValue(), length_this * sizeof(uint16_t));
       }
-      if (string2->IsCompressed()) {
-        const uint8_t* value2 = string2->GetValueCompressed();
-        for (int i = 0; i < length2; ++i) {
-          new_value[i+length] = value2[i];
+      if (h_arg->IsCompressed()) {
+        const uint8_t* value_arg = h_arg->GetValueCompressed();
+        for (int i = 0; i < length_arg; ++i) {
+          new_value[i + length_this] = value_arg[i];
         }
       } else {
-        memcpy(new_value + length, string2->GetValue(), length2 * sizeof(uint16_t));
+        memcpy(new_value + length_this, h_arg->GetValue(), length_arg * sizeof(uint16_t));
       }
     }
   };
diff --git a/runtime/mirror/string.h b/runtime/mirror/string.h
index 0e3c500..fd09e54 100644
--- a/runtime/mirror/string.h
+++ b/runtime/mirror/string.h
@@ -148,9 +148,7 @@
                                                        gc::AllocatorType allocator_type)
       REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!Roles::uninterruptible_);
 
-  static ObjPtr<String> AllocFromStrings(Thread* self,
-                                         Handle<String> string,
-                                         Handle<String> string2)
+  static ObjPtr<String> DoConcat(Thread* self, Handle<String> h_this, Handle<String> h_arg)
       REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!Roles::uninterruptible_);
 
   static ObjPtr<String> AllocFromUtf16(Thread* self,
diff --git a/runtime/native/java_lang_String.cc b/runtime/native/java_lang_String.cc
index 7c7c553..86f9329 100644
--- a/runtime/native/java_lang_String.cc
+++ b/runtime/native/java_lang_String.cc
@@ -60,8 +60,7 @@
   int32_t length_this = string_this->GetLength();
   int32_t length_arg = string_arg->GetLength();
   if (length_arg > 0 && length_this > 0) {
-    ObjPtr<mirror::String> result =
-        mirror::String::AllocFromStrings(soa.Self(), string_this, string_arg);
+    ObjPtr<mirror::String> result = mirror::String::DoConcat(soa.Self(), string_this, string_arg);
     return soa.AddLocalReference<jstring>(result);
   }
   jobject string_original = (length_this == 0) ? java_string_arg : java_this;