re PR c++/68422 (compile-time cost of sizeof... is quadratic)

	PR c++/68422

	* cp-tree.h (PACK_EXPANSION_SIZEOF_P): New.
	* parser.c (cp_parser_sizeof_pack): Set it.
	* pt.c 	(tsubst_copy) [SIZEOF_EXPR]: Likewise.
	(tsubst_pack_expansion): Improve T... shortcut for expression packs.

From-SVN: r230629

gcc/cp/ChangeLog

+2015-11-19  Jason Merrill  <jason@redhat.com>
+
+	PR c++/68422
+	* cp-tree.h (PACK_EXPANSION_SIZEOF_P): New.
+	* parser.c (cp_parser_sizeof_pack): Set it.
+	* pt.c 	(tsubst_copy) [SIZEOF_EXPR]: Likewise.
+	(tsubst_pack_expansion): Improve T... shortcut for expression packs.
+
 2015-11-19  Ryan Burn  <contact@rnburn.com>
 
 	PR c++/68396

gcc/cp/cp-tree.h

@@ -98,6 +98,7 @@ c-common.h, not after.
       DECLTYPE_FOR_INIT_CAPTURE (in DECLTYPE_TYPE)
       CONSTRUCTOR_NO_IMPLICIT_ZERO (in CONSTRUCTOR)
       TINFO_USED_TEMPLATE_ID (in TEMPLATE_INFO)
+      PACK_EXPANSION_SIZEOF_P (in *_PACK_EXPANSION)
    2: IDENTIFIER_OPNAME_P (in IDENTIFIER_NODE)
       ICS_THIS_FLAG (in _CONV)
       DECL_INITIALIZED_BY_CONSTANT_EXPRESSION_P (in VAR_DECL)
@@ -3200,6 +3201,9 @@ extern void decl_shadowed_for_var_insert (tree, tree);
 /* True iff this pack expansion is within a function context.  */
 #define PACK_EXPANSION_LOCAL_P(NODE) TREE_LANG_FLAG_0 (NODE)
 
+/* True iff this pack expansion is for sizeof....  */
+#define PACK_EXPANSION_SIZEOF_P(NODE) TREE_LANG_FLAG_1 (NODE)
+
 /* True iff the wildcard can match a template parameter pack.  */
 #define WILDCARD_PACK_P(NODE) TREE_LANG_FLAG_0 (NODE)
 

gcc/cp/parser.c

@@ -25868,6 +25868,7 @@ cp_parser_sizeof_pack (cp_parser *parser)
   else if (TREE_CODE (expr) == CONST_DECL)
     expr = DECL_INITIAL (expr);
   expr = make_pack_expansion (expr);
+  PACK_EXPANSION_SIZEOF_P (expr) = true;
 
   if (paren)
     cp_parser_require (parser, CPP_CLOSE_PAREN, RT_CLOSE_PAREN);

gcc/cp/pt.c

@@ -10868,14 +10868,26 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
 	}
     }
 
-  /* If the expansion is just T..., return the matching argument pack.  */
+  /* If the expansion is just T..., return the matching argument pack, unless
+     we need to call convert_from_reference on all the elements.  This is an
+     important optimization; see c++/68422.  */
   if (!unsubstituted_packs
       && TREE_PURPOSE (packs) == pattern)
     {
       tree args = ARGUMENT_PACK_ARGS (TREE_VALUE (packs));
+      /* Types need no adjustment, nor does sizeof..., and if we still have
+	 some pack expansion args we won't do anything yet.  */
       if (TREE_CODE (t) == TYPE_PACK_EXPANSION
+	  || PACK_EXPANSION_SIZEOF_P (t)
 	  || pack_expansion_args_count (args))
 	return args;
+      /* Also optimize expression pack expansions if we can tell that the
+	 elements won't have reference type.  */
+      tree type = TREE_TYPE (pattern);
+      if (type && TREE_CODE (type) != REFERENCE_TYPE
+	  && !PACK_EXPANSION_P (type)
+	  && !WILDCARD_TYPE_P (type))
+	return args;
       /* Otherwise use the normal path so we get convert_from_reference.  */
     }
 
@@ -13940,7 +13952,6 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
     case SIZEOF_EXPR:
       if (PACK_EXPANSION_P (TREE_OPERAND (t, 0)))
         {
-
           tree expanded, op = TREE_OPERAND (t, 0);
 	  int len = 0;
 
@@ -13966,6 +13977,8 @@ tsubst_copy (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 	    {
 	      if (TREE_CODE (expanded) == TREE_VEC)
 		expanded = TREE_VEC_ELT (expanded, len - 1);
+	      else
+		PACK_EXPANSION_SIZEOF_P (expanded) = true;
 
 	      if (TYPE_P (expanded))
 		return cxx_sizeof_or_alignof_type (expanded, SIZEOF_EXPR,