Rewrite main normalizer loop to isolate runs of simple clusters

src/hb-ot-shape-normalize.cc

@@ -321,18 +321,32 @@ _hb_ot_shape_normalize (const hb_ot_shape_plan_t *plan,
 
   buffer->clear_output ();
   count = buffer->len;
-  for (buffer->idx = 0; buffer->idx < count && buffer->successful;)
+  buffer->idx = 0;
+  do
   {
     unsigned int end;
     for (end = buffer->idx + 1; end < count; end++)
-      if (likely (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->info[end]))))
+      if (unlikely (HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->info[end]))))
         break;
 
-    if (likely (c.buffer->idx + 1 == end))
+    if (end < count)
+      end--; /* Leave one base for the marks to cluster with. */
+
+    /* From i to end are simple clusters. */
+    while (buffer->idx < end && buffer->successful)
       decompose_current_character (&c, might_short_circuit);
-    else
-      decompose_multi_char_cluster (&c, end, always_short_circuit);
+
+    if (buffer->idx == count || !buffer->successful)
+      break;
+
+    /* Find all the marks now. */
+    for (end = buffer->idx + 1; end < count; end++)
+      if (!HB_UNICODE_GENERAL_CATEGORY_IS_MARK (_hb_glyph_info_get_general_category (&buffer->info[end])))
+        break;
+
+    decompose_multi_char_cluster (&c, end, always_short_circuit);
   }
+  while (buffer->idx < count && buffer->successful);
   buffer->swap_buffers ();