C++ PATCHes for improved template memory use

[Jason Merrill <jason at redhat dot com>]

I've been looking at -fmem-report for a testcase from someone on the
committee, and found a couple of low-hanging fruits.

The first patch doesn't change any allocation, just makes it so
-fmem-report can see who's calling cxx_make_type.

The second patch avoids creating a vector (which we then never freed)
every time we push_to_top_level for doing template instantiation.
This alone improved peak memory use by 30%.

The third patch avoids redundantly creating level-lowered versions of
TEMPLATE_TYPE_PARM, as we had already been doing for non-type
parameters.  This improved peak memory use by another 20%.

Unfortunately, these don't affect the 80290 testcase significantly.

Tested x86_64-pc-linux-gnu, applying to trunk.

commit 472c58fd2b3620b8461c59af58af056e53793d85
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jun 20 15:01:26 2018 -0400

            Let -fmem-report see callers of cxx_make_type.
    
            * lex.c (cxx_make_type): Add MEM_STAT_DECL.
            (make_class_type): Likewise.
            (cxx_make_type_hook): New.
            * cp-objcp-common.h (LANG_HOOKS_MAKE_TYPE): Use cxx_make_type_hook.

diff --git a/gcc/cp/cp-objcp-common.h b/gcc/cp/cp-objcp-common.h
index 18ccc5bb6cf..6f08253f70f 100644
--- a/gcc/cp/cp-objcp-common.h
+++ b/gcc/cp/cp-objcp-common.h
@@ -34,6 +34,7 @@ extern tree cp_unit_size_without_reusable_padding (tree);
 extern tree cp_get_global_decls ();
 extern tree cp_pushdecl (tree);
 extern void cp_register_dumps (gcc::dump_manager *);
+extern tree cxx_make_type_hook			(tree_code);
 
 /* Lang hooks that are shared between C++ and ObjC++ are defined here.  Hooks
    specific to C++ or ObjC++ go in cp/cp-lang.c and objcp/objcp-lang.c,
@@ -126,7 +127,7 @@ extern void cp_register_dumps (gcc::dump_manager *);
 #define LANG_HOOKS_TREE_DUMP_TYPE_QUALS_FN cp_type_quals
 
 #undef LANG_HOOKS_MAKE_TYPE
-#define LANG_HOOKS_MAKE_TYPE cxx_make_type
+#define LANG_HOOKS_MAKE_TYPE cxx_make_type_hook
 #undef LANG_HOOKS_TYPE_FOR_MODE
 #define LANG_HOOKS_TYPE_FOR_MODE c_common_type_for_mode
 #undef LANG_HOOKS_TYPE_FOR_SIZE
diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index ee9242f9313..0994377e5d7 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -6495,8 +6495,8 @@ extern void retrofit_lang_decl			(tree);
 extern void fit_decomposition_lang_decl		(tree, tree);
 extern tree copy_decl				(tree CXX_MEM_STAT_INFO);
 extern tree copy_type				(tree CXX_MEM_STAT_INFO);
-extern tree cxx_make_type			(enum tree_code);
-extern tree make_class_type			(enum tree_code);
+extern tree cxx_make_type			(enum tree_code CXX_MEM_STAT_INFO);
+extern tree make_class_type			(enum tree_code CXX_MEM_STAT_INFO);
 extern const char *get_identifier_kind_name	(tree);
 extern void set_identifier_kind			(tree, cp_identifier_kind);
 extern bool cxx_init				(void);
diff --git a/gcc/cp/lex.c b/gcc/cp/lex.c
index c47ae1dd5a1..bd5d507e97b 100644
--- a/gcc/cp/lex.c
+++ b/gcc/cp/lex.c
@@ -852,9 +852,9 @@ maybe_add_lang_type_raw (tree t)
 }
 
 tree
-cxx_make_type (enum tree_code code)
+cxx_make_type (enum tree_code code MEM_STAT_DECL)
 {
-  tree t = make_node (code);
+  tree t = make_node (code PASS_MEM_STAT);
 
   if (maybe_add_lang_type_raw (t))
     {
@@ -868,10 +868,18 @@ cxx_make_type (enum tree_code code)
   return t;
 }
 
+/* A wrapper without the memory stats for LANG_HOOKS_MAKE_TYPE.  */
+
 tree
-make_class_type (enum tree_code code)
+cxx_make_type_hook (enum tree_code code)
 {
-  tree t = cxx_make_type (code);
+  return cxx_make_type (code);
+}
+
+tree
+make_class_type (enum tree_code code MEM_STAT_DECL)
+{
+  tree t = cxx_make_type (code PASS_MEM_STAT);
   SET_CLASS_TYPE_P (t, 1);
   return t;
 }

commit 0fb3fe86c4e32f8f72976d78f8af5b5229868129
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jun 20 12:05:34 2018 -0400

    Reduce garbage from push_to_top_level.
    
            * name-lookup.c (do_push_to_top_level): Don't allocate
            current_lang_base.
            (do_pop_from_top_level): Release current_lang_base.

diff --git a/gcc/cp/name-lookup.c b/gcc/cp/name-lookup.c
index ec001016d3e..a30c37428ad 100644
--- a/gcc/cp/name-lookup.c
+++ b/gcc/cp/name-lookup.c
@@ -6852,7 +6852,7 @@ do_push_to_top_level (void)
 
   scope_chain = s;
   current_function_decl = NULL_TREE;
-  vec_alloc (current_lang_base, 10);
+  current_lang_base = NULL;
   current_lang_name = lang_name_cplusplus;
   current_namespace = global_namespace;
   push_class_stack ();
@@ -6872,7 +6872,7 @@ do_pop_from_top_level (void)
     invalidate_class_lookup_cache ();
   pop_class_stack ();
 
-  current_lang_base = 0;
+  release_tree_vector (current_lang_base);
 
   scope_chain = s->prev;
   FOR_EACH_VEC_SAFE_ELT (s->old_bindings, i, saved)

commit 93ca12c981968b5d545f1428d7b6d47557f207f7
Author: Jason Merrill <jason@redhat.com>
Date:   Wed Jun 20 12:36:29 2018 -0400

         * pt.c (tsubst) [TEMPLATE_TYPE_PARM]: Use TEMPLATE_PARM_DESCENDANTS.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index c5433dc46ae..69e9479302e 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -14472,6 +14472,15 @@ tsubst (tree t, tree args, tsubst_flags_t complain, tree in_decl)
 		     && !PLACEHOLDER_TYPE_CONSTRAINTS (r))
 	      /* Break infinite recursion when substituting the constraints
 		 of a constrained placeholder.  */;
+	    else if (TREE_CODE (t) == TEMPLATE_TYPE_PARM
+		     && !PLACEHOLDER_TYPE_CONSTRAINTS (t)
+		     && !CLASS_PLACEHOLDER_TEMPLATE (t)
+		     && (arg = TEMPLATE_TYPE_PARM_INDEX (t),
+			 r = TEMPLATE_PARM_DESCENDANTS (arg))
+		     && (TEMPLATE_PARM_LEVEL (r)
+			 == TEMPLATE_PARM_LEVEL (arg) - levels))
+		/* Cache the simple case of lowering a type parameter.  */
+	      r = TREE_TYPE (r);
 	    else
 	      {
 		r = copy_type (t);