diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -432,6 +432,7 @@
     'DifferentialChangesSinceLastUpdateField' => 'applications/differential/customfield/DifferentialChangesSinceLastUpdateField.php',
     'DifferentialChangeset' => 'applications/differential/storage/DifferentialChangeset.php',
     'DifferentialChangesetDetailView' => 'applications/differential/view/DifferentialChangesetDetailView.php',
+    'DifferentialChangesetEngine' => 'applications/differential/engine/DifferentialChangesetEngine.php',
     'DifferentialChangesetFileTreeSideNavBuilder' => 'applications/differential/view/DifferentialChangesetFileTreeSideNavBuilder.php',
     'DifferentialChangesetHTMLRenderer' => 'applications/differential/render/DifferentialChangesetHTMLRenderer.php',
     'DifferentialChangesetListController' => 'applications/differential/controller/DifferentialChangesetListController.php',
@@ -2869,6 +2870,7 @@
     'PhabricatorDifferentialExtractWorkflow' => 'applications/differential/management/PhabricatorDifferentialExtractWorkflow.php',
     'PhabricatorDifferentialManagementWorkflow' => 'applications/differential/management/PhabricatorDifferentialManagementWorkflow.php',
     'PhabricatorDifferentialMigrateHunkWorkflow' => 'applications/differential/management/PhabricatorDifferentialMigrateHunkWorkflow.php',
+    'PhabricatorDifferentialRebuildChangesetsWorkflow' => 'applications/differential/management/PhabricatorDifferentialRebuildChangesetsWorkflow.php',
     'PhabricatorDifferentialRevisionTestDataGenerator' => 'applications/differential/lipsum/PhabricatorDifferentialRevisionTestDataGenerator.php',
     'PhabricatorDiffusionApplication' => 'applications/diffusion/application/PhabricatorDiffusionApplication.php',
     'PhabricatorDiffusionBlameSetting' => 'applications/settings/setting/PhabricatorDiffusionBlameSetting.php',
@@ -5729,6 +5731,7 @@
       'PhabricatorDestructibleInterface',
     ),
     'DifferentialChangesetDetailView' => 'AphrontView',
+    'DifferentialChangesetEngine' => 'Phobject',
     'DifferentialChangesetFileTreeSideNavBuilder' => 'Phobject',
     'DifferentialChangesetHTMLRenderer' => 'DifferentialChangesetRenderer',
     'DifferentialChangesetListController' => 'DifferentialController',
@@ -8530,6 +8533,7 @@
     'PhabricatorDifferentialExtractWorkflow' => 'PhabricatorDifferentialManagementWorkflow',
     'PhabricatorDifferentialManagementWorkflow' => 'PhabricatorManagementWorkflow',
     'PhabricatorDifferentialMigrateHunkWorkflow' => 'PhabricatorDifferentialManagementWorkflow',
+    'PhabricatorDifferentialRebuildChangesetsWorkflow' => 'PhabricatorDifferentialManagementWorkflow',
     'PhabricatorDifferentialRevisionTestDataGenerator' => 'PhabricatorTestDataGenerator',
     'PhabricatorDiffusionApplication' => 'PhabricatorApplication',
     'PhabricatorDiffusionBlameSetting' => 'PhabricatorInternalSetting',
diff --git a/src/applications/differential/engine/DifferentialChangesetEngine.php b/src/applications/differential/engine/DifferentialChangesetEngine.php
new file mode 100644
--- /dev/null
+++ b/src/applications/differential/engine/DifferentialChangesetEngine.php
@@ -0,0 +1,223 @@
+<?php
+
+final class DifferentialChangesetEngine extends Phobject {
+
+  public function rebuildChangesets(array $changesets) {
+    assert_instances_of($changesets, 'DifferentialChangeset');
+
+    foreach ($changesets as $changeset) {
+      $this->detectGeneratedCode($changeset);
+    }
+
+    $this->detectCopiedCode($changesets);
+  }
+
+
+/* -(  Generated Code  )----------------------------------------------------- */
+
+
+  private function detectGeneratedCode(DifferentialChangeset $changeset) {
+    $is_generated_trusted = $this->isTrustedGeneratedCode($changeset);
+    if ($is_generated_trusted) {
+      $changeset->setTrustedChangesetAttribute(
+        DifferentialChangeset::ATTRIBUTE_GENERATED,
+        $is_generated_trusted);
+    }
+
+    $is_generated_untrusted = $this->isUntrustedGeneratedCode($changeset);
+    if ($is_generated_untrusted) {
+      $changeset->setUntrustedChangesetAttribute(
+        DifferentialChangeset::ATTRIBUTE_GENERATED,
+        $is_generated_untrusted);
+    }
+  }
+
+  private function isTrustedGeneratedCode(DifferentialChangeset $changeset) {
+
+    $filename = $changeset->getFilename();
+
+    $paths = PhabricatorEnv::getEnvConfig('differential.generated-paths');
+    foreach ($paths as $regexp) {
+      if (preg_match($regexp, $filename)) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  private function isUntrustedGeneratedCode(DifferentialChangeset $changeset) {
+
+    if ($changeset->getHunks()) {
+      $new_data = $changeset->makeNewFile();
+      if (strpos($new_data, '@'.'generated') !== false) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+
+/* -(  Copied Code  )-------------------------------------------------------- */
+
+
+  private function detectCopiedCode(array $changesets) {
+    $min_width = 30;
+    $min_lines = 3;
+
+    $map = array();
+    $files = array();
+    $types = array();
+    foreach ($changesets as $changeset) {
+      $file = $changeset->getFilename();
+      foreach ($changeset->getHunks() as $hunk) {
+        $lines = $hunk->getStructuredOldFile();
+        foreach ($lines as $line => $info) {
+          $type = $info['type'];
+          if ($type == '\\') {
+            continue;
+          }
+          $types[$file][$line] = $type;
+
+          $text = $info['text'];
+          $text = trim($text);
+          $files[$file][$line] = $text;
+
+          if (strlen($text) >= $min_width) {
+            $map[$text][] = array($file, $line);
+          }
+        }
+      }
+    }
+
+    foreach ($changesets as $changeset) {
+      $copies = array();
+      foreach ($changeset->getHunks() as $hunk) {
+        $added = $hunk->getStructuredNewFile();
+        $atype = array();
+
+        foreach ($added as $line => $info) {
+          $atype[$line] = $info['type'];
+          $added[$line] = trim($info['text']);
+        }
+
+        $skip_lines = 0;
+        foreach ($added as $line => $code) {
+          if ($skip_lines) {
+            // We're skipping lines that we already processed because we
+            // extended a block above them downward to include them.
+            $skip_lines--;
+            continue;
+          }
+
+          if ($atype[$line] !== '+') {
+            // This line hasn't been changed in the new file, so don't try
+            // to figure out where it came from.
+            continue;
+          }
+
+          if (empty($map[$code])) {
+            // This line was too short to trigger copy/move detection.
+            continue;
+          }
+
+          if (count($map[$code]) > 16) {
+            // If there are a large number of identical lines in this diff,
+            // don't try to figure out where this block came from: the analysis
+            // is O(N^2), since we need to compare every line against every
+            // other line. Even if we arrive at a result, it is unlikely to be
+            // meaningful. See T5041.
+            continue;
+          }
+
+          $best_length = 0;
+
+          // Explore all candidates.
+          foreach ($map[$code] as $val) {
+            list($file, $orig_line) = $val;
+            $length = 1;
+
+            // Search backward and forward to find all of the adjacent lines
+            // which match.
+            foreach (array(-1, 1) as $direction) {
+              $offset = $direction;
+              while (true) {
+                if (isset($copies[$line + $offset])) {
+                  // If we run into a block above us which we've already
+                  // attributed to a move or copy from elsewhere, stop
+                  // looking.
+                  break;
+                }
+
+                if (!isset($added[$line + $offset])) {
+                  // If we've run off the beginning or end of the new file,
+                  // stop looking.
+                  break;
+                }
+
+                if (!isset($files[$file][$orig_line + $offset])) {
+                  // If we've run off the beginning or end of the original
+                  // file, we also stop looking.
+                  break;
+                }
+
+                $old = $files[$file][$orig_line + $offset];
+                $new = $added[$line + $offset];
+                if ($old !== $new) {
+                  // If the old line doesn't match the new line, stop
+                  // looking.
+                  break;
+                }
+
+                $length++;
+                $offset += $direction;
+              }
+            }
+
+            if ($length < $best_length) {
+              // If we already know of a better source (more matching lines)
+              // for this move/copy, stick with that one. We prefer long
+              // copies/moves which match a lot of context over short ones.
+              continue;
+            }
+
+            if ($length == $best_length) {
+              if (idx($types[$file], $orig_line) != '-') {
+                // If we already know of an equally good source (same number
+                // of matching lines) and this isn't a move, stick with the
+                // other one. We prefer moves over copies.
+                continue;
+              }
+            }
+
+            $best_length = $length;
+            // ($offset - 1) contains number of forward matching lines.
+            $best_offset = $offset - 1;
+            $best_file = $file;
+            $best_line = $orig_line;
+          }
+
+          $file = ($best_file == $changeset->getFilename() ? '' : $best_file);
+          for ($i = $best_length; $i--; ) {
+            $type = idx($types[$best_file], $best_line + $best_offset - $i);
+            $copies[$line + $best_offset - $i] = ($best_length < $min_lines
+              ? array() // Ignore short blocks.
+              : array($file, $best_line + $best_offset - $i, $type));
+          }
+
+          $skip_lines = $best_offset;
+        }
+      }
+
+      $copies = array_filter($copies);
+      if ($copies) {
+        $metadata = $changeset->getMetadata();
+        $metadata['copy:lines'] = $copies;
+        $changeset->setMetadata($metadata);
+      }
+    }
+
+  }
+
+}
diff --git a/src/applications/differential/management/PhabricatorDifferentialRebuildChangesetsWorkflow.php b/src/applications/differential/management/PhabricatorDifferentialRebuildChangesetsWorkflow.php
new file mode 100644
--- /dev/null
+++ b/src/applications/differential/management/PhabricatorDifferentialRebuildChangesetsWorkflow.php
@@ -0,0 +1,92 @@
+<?php
+
+final class PhabricatorDifferentialRebuildChangesetsWorkflow
+  extends PhabricatorDifferentialManagementWorkflow {
+
+  protected function didConstruct() {
+    $this
+      ->setName('rebuild-changesets')
+      ->setExamples('**rebuild-changesets** --revision __revision__')
+      ->setSynopsis(pht('Rebuild changesets for a revision.'))
+      ->setArguments(
+        array(
+          array(
+            'name' => 'revision',
+            'param' => 'revision',
+            'help' => pht('Revision to rebuild changesets for.'),
+          ),
+        ));
+  }
+
+  public function execute(PhutilArgumentParser $args) {
+    $viewer = $this->getViewer();
+
+    $revision_identifier = $args->getArg('revision');
+    if (!$revision_identifier) {
+      throw new PhutilArgumentUsageException(
+        pht('Specify a revision to rebuild changesets for with "--revision".'));
+    }
+
+    $revision = id(new PhabricatorObjectQuery())
+      ->setViewer($viewer)
+      ->withNames(array($revision_identifier))
+      ->executeOne();
+    if ($revision) {
+      if (!($revision instanceof DifferentialRevision)) {
+        throw new PhutilArgumentUsageException(
+          pht(
+            'Object "%s" specified by "--revision" must be a Differential '.
+            'revision.'));
+      }
+    } else {
+      $revision = id(new DifferentialRevisionQuery())
+        ->setViewer($viewer)
+        ->withIDs(array($revision_identifier))
+        ->executeOne();
+    }
+
+    if (!$revision) {
+      throw new PhutilArgumentUsageException(
+        pht(
+          'No revision "%s" exists.',
+          $revision_identifier));
+    }
+
+    $diffs = id(new DifferentialDiffQuery())
+      ->setViewer($viewer)
+      ->withRevisionIDs(array($revision->getID()))
+      ->execute();
+
+    $changesets = id(new DifferentialChangesetQuery())
+      ->setViewer($viewer)
+      ->withDiffs($diffs)
+      ->needHunks(true)
+      ->execute();
+
+    $changeset_groups = mgroup($changesets, 'getDiffID');
+
+    foreach ($changeset_groups as $diff_id => $changesets) {
+      echo tsprintf(
+        "%s\n",
+        pht(
+          'Rebuilding %s changeset(s) for diff ID %d.',
+          phutil_count($changesets),
+          $diff_id));
+
+      foreach ($changesets as $changeset) {
+        echo tsprintf(
+          "    %s\n",
+          $changeset->getFilename());
+      }
+
+      id(new DifferentialChangesetEngine())
+        ->rebuildChangesets($changesets);
+
+      echo tsprintf(
+        "%s\n",
+        pht('Done.'));
+    }
+  }
+
+
+}
diff --git a/src/applications/differential/parser/DifferentialChangesetParser.php b/src/applications/differential/parser/DifferentialChangesetParser.php
--- a/src/applications/differential/parser/DifferentialChangesetParser.php
+++ b/src/applications/differential/parser/DifferentialChangesetParser.php
@@ -1419,167 +1419,6 @@
     return sprintf('%d%%', 100 * ($covered / ($covered + $not_covered)));
   }
 
-  public function detectCopiedCode(
-    array $changesets,
-    $min_width = 30,
-    $min_lines = 3) {
-
-    assert_instances_of($changesets, 'DifferentialChangeset');
-
-    $map = array();
-    $files = array();
-    $types = array();
-    foreach ($changesets as $changeset) {
-      $file = $changeset->getFilename();
-      foreach ($changeset->getHunks() as $hunk) {
-        $lines = $hunk->getStructuredOldFile();
-        foreach ($lines as $line => $info) {
-          $type = $info['type'];
-          if ($type == '\\') {
-            continue;
-          }
-          $types[$file][$line] = $type;
-
-          $text = $info['text'];
-          $text = trim($text);
-          $files[$file][$line] = $text;
-
-          if (strlen($text) >= $min_width) {
-            $map[$text][] = array($file, $line);
-          }
-        }
-      }
-    }
-
-    foreach ($changesets as $changeset) {
-      $copies = array();
-      foreach ($changeset->getHunks() as $hunk) {
-        $added = $hunk->getStructuredNewFile();
-        $atype = array();
-
-        foreach ($added as $line => $info) {
-          $atype[$line] = $info['type'];
-          $added[$line] = trim($info['text']);
-        }
-
-        $skip_lines = 0;
-        foreach ($added as $line => $code) {
-          if ($skip_lines) {
-            // We're skipping lines that we already processed because we
-            // extended a block above them downward to include them.
-            $skip_lines--;
-            continue;
-          }
-
-          if ($atype[$line] !== '+') {
-            // This line hasn't been changed in the new file, so don't try
-            // to figure out where it came from.
-            continue;
-          }
-
-          if (empty($map[$code])) {
-            // This line was too short to trigger copy/move detection.
-            continue;
-          }
-
-          if (count($map[$code]) > 16) {
-            // If there are a large number of identical lines in this diff,
-            // don't try to figure out where this block came from: the analysis
-            // is O(N^2), since we need to compare every line against every
-            // other line. Even if we arrive at a result, it is unlikely to be
-            // meaningful. See T5041.
-            continue;
-          }
-
-          $best_length = 0;
-
-          // Explore all candidates.
-          foreach ($map[$code] as $val) {
-            list($file, $orig_line) = $val;
-            $length = 1;
-
-            // Search backward and forward to find all of the adjacent lines
-            // which match.
-            foreach (array(-1, 1) as $direction) {
-              $offset = $direction;
-              while (true) {
-                if (isset($copies[$line + $offset])) {
-                  // If we run into a block above us which we've already
-                  // attributed to a move or copy from elsewhere, stop
-                  // looking.
-                  break;
-                }
-
-                if (!isset($added[$line + $offset])) {
-                  // If we've run off the beginning or end of the new file,
-                  // stop looking.
-                  break;
-                }
-
-                if (!isset($files[$file][$orig_line + $offset])) {
-                  // If we've run off the beginning or end of the original
-                  // file, we also stop looking.
-                  break;
-                }
-
-                $old = $files[$file][$orig_line + $offset];
-                $new = $added[$line + $offset];
-                if ($old !== $new) {
-                  // If the old line doesn't match the new line, stop
-                  // looking.
-                  break;
-                }
-
-                $length++;
-                $offset += $direction;
-              }
-            }
-
-            if ($length < $best_length) {
-              // If we already know of a better source (more matching lines)
-              // for this move/copy, stick with that one. We prefer long
-              // copies/moves which match a lot of context over short ones.
-              continue;
-            }
-
-            if ($length == $best_length) {
-              if (idx($types[$file], $orig_line) != '-') {
-                // If we already know of an equally good source (same number
-                // of matching lines) and this isn't a move, stick with the
-                // other one. We prefer moves over copies.
-                continue;
-              }
-            }
-
-            $best_length = $length;
-            // ($offset - 1) contains number of forward matching lines.
-            $best_offset = $offset - 1;
-            $best_file = $file;
-            $best_line = $orig_line;
-          }
-
-          $file = ($best_file == $changeset->getFilename() ? '' : $best_file);
-          for ($i = $best_length; $i--; ) {
-            $type = idx($types[$best_file], $best_line + $best_offset - $i);
-            $copies[$line + $best_offset - $i] = ($best_length < $min_lines
-              ? array() // Ignore short blocks.
-              : array($file, $best_line + $best_offset - $i, $type));
-          }
-
-          $skip_lines = $best_offset;
-        }
-      }
-
-      $copies = array_filter($copies);
-      if ($copies) {
-        $metadata = $changeset->getMetadata();
-        $metadata['copy:lines'] = $copies;
-        $changeset->setMetadata($metadata);
-      }
-    }
-    return $changesets;
-  }
-
   /**
    * Build maps from lines comments appear on to actual lines.
    */
diff --git a/src/applications/differential/storage/DifferentialDiff.php b/src/applications/differential/storage/DifferentialDiff.php
--- a/src/applications/differential/storage/DifferentialDiff.php
+++ b/src/applications/differential/storage/DifferentialDiff.php
@@ -226,23 +226,18 @@
       $changeset->setAddLines($add_lines);
       $changeset->setDelLines($del_lines);
 
-      self::detectGeneratedCode($changeset);
-
       $diff->addUnsavedChangeset($changeset);
     }
     $diff->setLineCount($lines);
 
-    $parser = new DifferentialChangesetParser();
-    $changesets = $parser->detectCopiedCode(
-      $diff->getChangesets(),
-      $min_width = 30,
-      $min_lines = 3);
-    $diff->attachChangesets($changesets);
+    $changesets = $diff->getChangesets();
+
+    id(new DifferentialChangesetEngine())
+      ->rebuildChangesets($changesets);
 
     return $diff;
   }
 
-
   public function getDiffDict() {
     $dict = array(
       'id' => $this->getID(),
@@ -823,50 +818,4 @@
     );
   }
 
-  private static function detectGeneratedCode(
-    DifferentialChangeset $changeset) {
-
-    $is_generated_trusted = self::isTrustedGeneratedCode($changeset);
-    if ($is_generated_trusted) {
-      $changeset->setTrustedChangesetAttribute(
-        DifferentialChangeset::ATTRIBUTE_GENERATED,
-        $is_generated_trusted);
-    }
-
-    $is_generated_untrusted = self::isUntrustedGeneratedCode($changeset);
-    if ($is_generated_untrusted) {
-      $changeset->setUntrustedChangesetAttribute(
-        DifferentialChangeset::ATTRIBUTE_GENERATED,
-        $is_generated_untrusted);
-    }
-  }
-
-  private static function isTrustedGeneratedCode(
-    DifferentialChangeset $changeset) {
-
-    $filename = $changeset->getFilename();
-
-    $paths = PhabricatorEnv::getEnvConfig('differential.generated-paths');
-    foreach ($paths as $regexp) {
-      if (preg_match($regexp, $filename)) {
-        return true;
-      }
-    }
-
-    return false;
-  }
-
-  private static function isUntrustedGeneratedCode(
-    DifferentialChangeset $changeset) {
-
-    if ($changeset->getHunks()) {
-      $new_data = $changeset->makeNewFile();
-      if (strpos($new_data, '@'.'generated') !== false) {
-        return true;
-      }
-    }
-
-    return false;
-  }
-
 }