From 810fbedf2717305f99dde0772a10c11380c37325 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Thu, 3 Apr 2025 20:59:23 -0600
Subject: [PATCH] [shape] Use font-data for GDEF varStore cache

Last remaining alloc during shaping is gone!

Fixes https://github.com/harfbuzz/harfbuzz/issues/5237
---
 src/hb-ot-layout-gsubgpos.hh | 18 +++---------------
 src/hb-ot-layout.cc          |  6 +++++-
 src/hb-ot-shape.cc           | 15 +++++++++++----
 3 files changed, 19 insertions(+), 20 deletions(-)

diff --git a/src/hb-ot-layout-gsubgpos.hh b/src/hb-ot-layout-gsubgpos.hh
index 7d49710d1..eab477a8e 100644
--- a/src/hb-ot-layout-gsubgpos.hh
+++ b/src/hb-ot-layout-gsubgpos.hh
@@ -737,7 +737,8 @@ struct hb_ot_apply_context_t :
   hb_ot_apply_context_t (unsigned int table_index_,
 			 hb_font_t *font_,
 			 hb_buffer_t *buffer_,
-			 hb_blob_t *table_blob_) :
+			 hb_blob_t *table_blob_,
+			 ItemVariationStore::cache_t *var_store_cache_ = nullptr) :
 			table_index (table_index_),
 			font (font_), face (font->face), buffer (buffer_),
 			sanitizer (table_blob_),
@@ -756,13 +757,7 @@ struct hb_ot_apply_context_t :
 #endif
 			     ),
 			var_store (gdef.get_var_store ()),
-			var_store_cache (
-#ifndef HB_NO_VAR
-					 table_index == 1 && font->num_coords ? var_store.create_cache () : nullptr
-#else
-					 nullptr
-#endif
-					),
+			var_store_cache (var_store_cache_),
 			direction (buffer_->props.direction),
 			has_glyph_classes (gdef.has_glyph_classes ())
   {
@@ -770,13 +765,6 @@ struct hb_ot_apply_context_t :
     buffer->collect_codepoints (digest);
   }
 
-  ~hb_ot_apply_context_t ()
-  {
-#ifndef HB_NO_VAR
-    ItemVariationStore::destroy_cache (var_store_cache);
-#endif
-  }
-
   void init_iters ()
   {
     iter_input.init (this, false);
diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 3aca40eb7..3c9a0fc5d 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -2015,7 +2015,11 @@ inline void hb_ot_map_t::apply (const Proxy &proxy,
 {
   const unsigned int table_index = proxy.table_index;
   unsigned int i = 0;
-  OT::hb_ot_apply_context_t c (table_index, font, buffer, proxy.accel.get_blob ());
+
+  auto *font_data = font->data.ot.get ();
+  auto *var_store_cache = font_data == HB_SHAPER_DATA_SUCCEEDED ? nullptr : (OT::ItemVariationStore::cache_t *) font_data;
+
+  OT::hb_ot_apply_context_t c (table_index, font, buffer, proxy.accel.get_blob (), var_store_cache);
   c.set_recurse_func (Proxy::Lookup::template dispatch_recurse_func<OT::hb_ot_apply_context_t>);
 
   for (unsigned int stage_index = 0; stage_index < stages[table_index].length; stage_index++)
diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 47db5a0f3..e7a594371 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -46,6 +46,7 @@
 #include "hb-set.hh"
 
 #include "hb-aat-layout.hh"
+#include "hb-ot-layout-gdef-table.hh"
 #include "hb-ot-stat-table.hh"
 
 
@@ -423,17 +424,23 @@ _hb_ot_shaper_face_data_destroy (hb_ot_face_data_t *data)
  * shaper font data
  */
 
-struct hb_ot_font_data_t {};
+struct hb_ot_font_data_t {
+  OT::ItemVariationStore::cache_t unused; // Just for alignment
+};
 
 hb_ot_font_data_t *
-_hb_ot_shaper_font_data_create (hb_font_t *font HB_UNUSED)
+_hb_ot_shaper_font_data_create (hb_font_t *font)
 {
-  return (hb_ot_font_data_t *) HB_SHAPER_DATA_SUCCEEDED;
+  const OT::ItemVariationStore &var_store = font->face->table.GDEF->table->get_var_store ();
+  auto *cache = font->num_coords ? (hb_ot_font_data_t *) var_store.create_cache () : nullptr;
+  return cache ? cache : (hb_ot_font_data_t *) HB_SHAPER_DATA_SUCCEEDED;
 }
 
 void
-_hb_ot_shaper_font_data_destroy (hb_ot_font_data_t *data HB_UNUSED)
+_hb_ot_shaper_font_data_destroy (hb_ot_font_data_t *data)
 {
+  if (data == HB_SHAPER_DATA_SUCCEEDED) return;
+  OT::ItemVariationStore::destroy_cache ((OT::ItemVariationStore::cache_t *) data);
 }