Only require segments to merge are inert (and not base) to skip closure.

If all of the things being added to base are inert then we know they don't interact with base so we can skip doing the closure analysis.

Author: garretrieger

ift/encoder/candidate_merge.cc

@@ -612,20 +612,21 @@ StatusOr<std::optional<CandidateMerge>> CandidateMerge::AssessSegmentMerge(
   }
 
   uint32_t new_patch_size = 0;
-  if (!segments_to_merge_and_base_are_inert) {
+  if (!segments_to_merge_are_inert) {
     GlyphSet and_gids, or_gids, exclusive_gids;
     TRYV(merger.Context().AnalyzeSegment(segments_to_merge_with_base, and_gids,
                                          or_gids, exclusive_gids));
     new_patch_size =
         TRY(merger.Context().patch_size_cache->GetPatchSize(exclusive_gids));
   } else {
-    // When the inputs to a merge are all inert then we can assume the merged
-    // patch is just a combination of the glyphs from the input segments. This
-    // saves a closure computation.
+    // When the segments being added to base are all inert then we can assume
+    // the merged patch is just a combination of the glyphs from the base and
+    // the input segments. Since the segments being added are intert we know
+    // that they won't interact with base and will just bring along their own
+    // glyphs.
     GlyphSet merged_glyphs = gid_conditions_to_update;
     merged_glyphs.union_set(
-        merger.Context().glyph_condition_set.GlyphsWithSegment(
-            base_segment_index));
+        merger.Context().glyph_groupings.ExclusiveGlyphs(base_segment_index));
     new_patch_size =
         TRY(merger.Context().patch_size_cache->GetPatchSize(merged_glyphs));
   }