[subset/cff1] Don't allocate memory for retaingid holes

40% speedup in BM_subset/subset_glyphs/SourceHanSans-Regular_subset.otf/retaingids/10
benchmark.

src/hb-cff-interp-common.hh

@@ -26,6 +26,8 @@
 #ifndef HB_CFF_INTERP_COMMON_HH
 #define HB_CFF_INTERP_COMMON_HH
 
+extern HB_INTERNAL const unsigned char *endchar_str;
+
 namespace CFF {
 
 using namespace OT;

src/hb-static.cc

@@ -31,6 +31,7 @@
 
 #include "hb-aat-layout-common.hh"
 #include "hb-aat-layout-feat-table.hh"
+#include "hb-cff-interp-common.hh"
 #include "hb-ot-layout-common.hh"
 #include "hb-ot-cmap-table.hh"
 #include "OT/Color/COLR/COLR.hh"
@@ -58,6 +59,8 @@ DEFINE_NULL_NAMESPACE_BYTES (AAT, Lookup) = {0xFF,0xFF};
 /* hb_map_t */
 
 const hb_codepoint_t minus_1 = -1;
+static const unsigned char static_endchar_str[] = {OpCode_endchar};
+const unsigned char *endchar_str = static_endchar_str;
 
 /* hb_face_t */
 

src/hb-subset-cff-common.hh

@@ -809,7 +809,12 @@ struct subr_subsetter_t
 
       if (endchar_op != OpCode_Invalid)
         for (; last < gid; last++)
-	  buffArray.arrayZ[last].push (endchar_op);
+	{
+	  // Hack to point vector to static string.
+	  auto &b = buffArray.arrayZ[last];
+	  b.length = 1;
+	  b.arrayZ = const_cast<unsigned char *>(endchar_str);
+	}
 
       last++; // Skip over gid
       unsigned int  fd = acc.fdSelect->get_fd (old_glyph);
@@ -820,7 +825,12 @@ struct subr_subsetter_t
     }
     if (endchar_op != OpCode_Invalid)
       for (; last < num_glyphs; last++)
-	buffArray.arrayZ[last].push (endchar_op);
+      {
+	// Hack to point vector to static string.
+	auto &b = buffArray.arrayZ[last];
+	b.length = 1;
+	b.arrayZ = const_cast<unsigned char *>(endchar_str);
+      }
 
     return true;
   }

src/hb-vector.hh

@@ -102,8 +102,14 @@ struct hb_vector_t
 
   void fini ()
   {
-    shrink_vector (0);
-    hb_free (arrayZ);
+    /* We allow a hack to make the vector point to a foriegn array
+     * by the user. In that case length/arrayZ are non-zero but
+     * allocated is zero. Don't free anything. */
+    if (!allocated)
+    {
+      shrink_vector (0);
+      hb_free (arrayZ);
+    }
     init ();
   }