[runtime] Replace COMPARE/COMPARE_STRONG with proper Object::Compare.

src/runtime/runtime-strings.cc

Index: src/runtime/runtime-strings.cc
diff --git a/src/runtime/runtime-strings.cc b/src/runtime/runtime-strings.cc
index 0e6bf8308c3bd47ae19acdac9faeead3e4920330..b8ccbc8d93a98b5d1935c35d73165b07082b00b4 100644
--- a/src/runtime/runtime-strings.cc
+++ b/src/runtime/runtime-strings.cc
@@ -419,70 +419,22 @@ RUNTIME_FUNCTION(Runtime_CharFromCode) {
 
 RUNTIME_FUNCTION(Runtime_StringCompare) {
   HandleScope handle_scope(isolate);
-  DCHECK(args.length() == 2);
-
+  DCHECK_EQ(2, args.length());
   CONVERT_ARG_HANDLE_CHECKED(String, x, 0);
   CONVERT_ARG_HANDLE_CHECKED(String, y, 1);
-
   isolate->counters()->string_compare_runtime()->Increment();
-
-  // A few fast case tests before we flatten.
-  if (x.is_identical_to(y)) return Smi::FromInt(EQUAL);
-  if (y->length() == 0) {
-    if (x->length() == 0) return Smi::FromInt(EQUAL);
-    return Smi::FromInt(GREATER);
-  } else if (x->length() == 0) {
-    return Smi::FromInt(LESS);
-  }
-
-  int d = x->Get(0) - y->Get(0);
-  if (d < 0)
-    return Smi::FromInt(LESS);
-  else if (d > 0)
-    return Smi::FromInt(GREATER);
-
-  // Slow case.
-  x = String::Flatten(x);
-  y = String::Flatten(y);
-
-  DisallowHeapAllocation no_gc;
-  Object* equal_prefix_result = Smi::FromInt(EQUAL);
-  int prefix_length = x->length();
-  if (y->length() < prefix_length) {
-    prefix_length = y->length();
-    equal_prefix_result = Smi::FromInt(GREATER);
-  } else if (y->length() > prefix_length) {
-    equal_prefix_result = Smi::FromInt(LESS);
-  }
-  int r;
-  String::FlatContent x_content = x->GetFlatContent();
-  String::FlatContent y_content = y->GetFlatContent();
-  if (x_content.IsOneByte()) {
-    Vector<const uint8_t> x_chars = x_content.ToOneByteVector();
-    if (y_content.IsOneByte()) {
-      Vector<const uint8_t> y_chars = y_content.ToOneByteVector();
-      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
-    } else {
-      Vector<const uc16> y_chars = y_content.ToUC16Vector();
-      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
-    }
-  } else {
-    Vector<const uc16> x_chars = x_content.ToUC16Vector();
-    if (y_content.IsOneByte()) {
-      Vector<const uint8_t> y_chars = y_content.ToOneByteVector();
-      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
-    } else {
-      Vector<const uc16> y_chars = y_content.ToUC16Vector();
-      r = CompareChars(x_chars.start(), y_chars.start(), prefix_length);
-    }
-  }
-  Object* result;
-  if (r == 0) {
-    result = equal_prefix_result;
-  } else {
-    result = (r < 0) ? Smi::FromInt(LESS) : Smi::FromInt(GREATER);
+  switch (String::Compare(x, y)) {
+    case ComparisonResult::kLessThan:
+      return Smi::FromInt(LESS);
+    case ComparisonResult::kEqual:
+      return Smi::FromInt(EQUAL);
+    case ComparisonResult::kGreaterThan:
+      return Smi::FromInt(GREATER);
+    case ComparisonResult::kUndefined:
+      break;
   }
-  return result;
+  UNREACHABLE();
+  return Smi::FromInt(0);
 }