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

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index d7804a0edae0e3e0bc888e6267d0a3ab2e524239..c4b76147f7a2e69c56effb7a27d340275d15ef30 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,11 @@
+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

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 160bf1e0584326a1f58e7e7a8eb70a74c2d0af2f..14ea1194113b8f42d23b708fd0a1930933bbf161 100644 (file)
--- a/gcc/cp/cp-tree.h
+++ b/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)
 

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 30cde0bc678e3cc0276da937272b4898c4730ccb..24ed404adafcabf3a7bba61821741cd3d7a6f00b 100644 (file)
--- a/gcc/cp/parser.c
+++ b/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);

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index b4a5e71b521b5f193afd5f2ee4fac2234959b57c..5868be2e7f257975d3c8f8fdf6783f0112518de7 100644 (file)
--- a/gcc/cp/pt.c
+++ b/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,