1 files changed, 32 insertions, 0 deletions
diff --git a/runtime/mirror/class-inl.h b/runtime/mirror/class-inl.h
index 40f119e3c4..373b9b3105 100644
--- a/runtime/mirror/class-inl.h
+++ b/runtime/mirror/class-inl.h
@@ -1356,6 +1356,38 @@ inline ImTable* Class::FindSuperImt(PointerSize pointer_size) {
   return nullptr;
 }
 
+ALWAYS_INLINE FLATTEN inline ArtField* Class::FindDeclaredField(uint32_t dex_field_idx) {
+  size_t num_fields = NumFields();
+  if (num_fields > 0) {
+    // The field array is an ordered list of fields where there may be missing
+    // indices. For example, it could be [40, 42], but in 90% of cases cases we have
+    // [40, 41, 42]. The latter is the case we are optimizing for, where for
+    // example `dex_field_idx` is 41, and we can just substract it with the
+    // first field index (40) and directly access the array with that index (1).
+    uint32_t index = dex_field_idx - GetField(0)->GetDexFieldIndex();
+    if (index < num_fields) {
+      ArtField* field = GetField(index);
+      if (field->GetDexFieldIndex() == dex_field_idx) {
+        return field;
+      }
+    } else {
+      index = num_fields;
+    }
+    // If there is a field, it's down the array. The array is ordered by field
+    // index, so we know we can stop the search if `dex_field_idx` is greater
+    // than the current field's index.
+    for (; index > 0; --index) {
+      ArtField* field = GetField(index - 1);
+      if (field->GetDexFieldIndex() == dex_field_idx) {
+        return field;
+      } else if (field->GetDexFieldIndex() < dex_field_idx) {
+        break;
+      }
+    }
+  }
+  return nullptr;
+}
+
 }  // namespace mirror
 }  // namespace art