diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 26ada9c9991..959d15b5041 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2019-08-05  Richard Sandiford  <richard.sandiford@arm.com>
+
+	* tree-core.h (tree_function_decl): Make function_code an
+	independent field.  Group the remaining bitfields into bytes
+	and move decl_type so that it contines to be at a byte boundary.
+	Leave 12 bits for future expansion.
+
 2019-08-05  Richard Sandiford  <richard.sandiford@arm.com>
 
 	* gimple-fold.c (gimple_fold_mask_load_store_mem_ref)
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index 60d8c684171..47195626912 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1857,36 +1857,32 @@ struct GTY(()) tree_function_decl {
   tree vindex;
 
   /* In a FUNCTION_DECL for which DECL_BUILT_IN holds, this is
-     DECL_FUNCTION_CODE.  Otherwise unused.
-     ???  The bitfield needs to be able to hold all target function
-	  codes as well.  */
-  ENUM_BITFIELD(built_in_function) function_code : 12;
-  ENUM_BITFIELD(built_in_class) built_in_class : 2;
+     DECL_FUNCTION_CODE.  Otherwise unused.  */
+  enum built_in_function function_code;
 
+  ENUM_BITFIELD(built_in_class) built_in_class : 2;
   unsigned static_ctor_flag : 1;
   unsigned static_dtor_flag : 1;
-
   unsigned uninlinable : 1;
   unsigned possibly_inlined : 1;
   unsigned novops_flag : 1;
   unsigned returns_twice_flag : 1;
+
   unsigned malloc_flag : 1;
   unsigned declared_inline_flag : 1;
   unsigned no_inline_warning_flag : 1;
-
   unsigned no_instrument_function_entry_exit : 1;
-
-  /* Align the bitfield to boundary of a byte.  */
-  ENUM_BITFIELD(function_decl_type) decl_type: 2;
-
   unsigned no_limit_stack : 1;
   unsigned disregard_inline_limits : 1;
   unsigned pure_flag : 1;
   unsigned looping_const_or_pure_flag : 1;
+
+  /* Align the bitfield to boundary of a byte.  */
+  ENUM_BITFIELD(function_decl_type) decl_type: 2;
   unsigned has_debug_args_flag : 1;
   unsigned versioned_function : 1;
 
-  /* 0 bits left.  */
+  /* 12 bits left for future expansion.  */
 };
 
 struct GTY(()) tree_translation_unit_decl {