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* [PATCH] c++: Micro-optimize most_specialized_partial_spec
@ 2022-08-31 21:15 Patrick Palka
  2022-08-31 21:15 ` Patrick Palka
  2022-09-01 18:40 ` Jason Merrill
  0 siblings, 2 replies; 4+ messages in thread
From: Patrick Palka @ 2022-08-31 21:15 UTC (permalink / raw)
  To: gcc-patches; +Cc: jason, Patrick Palka

This introduces an early exit test to most_specialized_partial_spec for
the common case where we have no partial specializations, which allows
us to avoid some unnecessary work.  In passing, clean the function up a
bit.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?

gcc/cp/ChangeLog:

	* pt.cc (most_specialized_partial_spec): Exit early when
	DECL_TEMPLATE_SPECIALIZATIONS is empty.  Move local variable
	declarations closer to their first use.  Remove redundant
	flag_concepts test.  Remove redundant forward declaration.
---
 gcc/cp/pt.cc | 45 +++++++++++++++++++--------------------------
 1 file changed, 19 insertions(+), 26 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index fe7e809fc2d..497a18ef728 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -187,7 +187,6 @@ static int unify_pack_expansion (tree, tree, tree,
 static tree copy_template_args (tree);
 static tree tsubst_template_parms (tree, tree, tsubst_flags_t);
 static void tsubst_each_template_parm_constraints (tree, tree, tsubst_flags_t);
-tree most_specialized_partial_spec (tree, tsubst_flags_t);
 static tree tsubst_aggr_type (tree, tree, tsubst_flags_t, tree, int);
 static tree tsubst_arg_types (tree, tree, tree, tsubst_flags_t, tree);
 static tree tsubst_function_type (tree, tree, tsubst_flags_t, tree);
@@ -25756,15 +25755,7 @@ most_general_template (tree decl)
 tree
 most_specialized_partial_spec (tree target, tsubst_flags_t complain)
 {
-  tree list = NULL_TREE;
-  tree t;
-  tree champ;
-  int fate;
-  bool ambiguous_p;
-  tree outer_args = NULL_TREE;
-  tree tmpl, args;
-
-  tree decl;
+  tree tmpl, args, decl;
   if (TYPE_P (target))
     {
       tree tinfo = CLASSTYPE_TEMPLATE_INFO (target);
@@ -25788,13 +25779,18 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
   else
     gcc_unreachable ();
 
+  tree main_tmpl = most_general_template (tmpl);
+  tree specs = DECL_TEMPLATE_SPECIALIZATIONS (main_tmpl);
+  if (!specs)
+    /* There are no partial specializations of this template.  */
+    return NULL_TREE;
+
   push_access_scope_guard pas (decl);
   deferring_access_check_sentinel acs (dk_no_deferred);
 
-  tree main_tmpl = most_general_template (tmpl);
-
   /* For determining which partial specialization to use, only the
      innermost args are interesting.  */
+  tree outer_args = NULL_TREE;
   if (TMPL_ARGS_HAVE_MULTIPLE_LEVELS (args))
     {
       outer_args = strip_innermost_template_args (args, 1);
@@ -25806,7 +25802,8 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
      fully resolve everything.  */
   processing_template_decl_sentinel ptds;
 
-  for (t = DECL_TEMPLATE_SPECIALIZATIONS (main_tmpl); t; t = TREE_CHAIN (t))
+  tree list = NULL_TREE;
+  for (tree t = specs; t; t = TREE_CHAIN (t))
     {
       const tree ospec_tmpl = TREE_VALUE (t);
 
@@ -25829,10 +25826,8 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
 	  if (outer_args)
 	    spec_args = add_to_template_args (outer_args, spec_args);
 
-          /* Keep the candidate only if the constraints are satisfied,
-             or if we're not compiling with concepts.  */
-          if (!flag_concepts
-	      || constraints_satisfied_p (ospec_tmpl, spec_args))
+	  /* Keep the candidate only if the constraints are satisfied.  */
+	  if (constraints_satisfied_p (ospec_tmpl, spec_args))
             {
 	      list = tree_cons (spec_args, ospec_tmpl, list);
               TREE_TYPE (list) = TREE_TYPE (t);
@@ -25843,13 +25838,11 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
   if (! list)
     return NULL_TREE;
 
-  ambiguous_p = false;
-  t = list;
-  champ = t;
-  t = TREE_CHAIN (t);
-  for (; t; t = TREE_CHAIN (t))
+  tree champ = list;
+  bool ambiguous_p = false;
+  for (tree t = TREE_CHAIN (list); t; t = TREE_CHAIN (t))
     {
-      fate = more_specialized_partial_spec (tmpl, champ, t);
+      int fate = more_specialized_partial_spec (tmpl, champ, t);
       if (fate == 1)
 	;
       else
@@ -25868,9 +25861,9 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
     }
 
   if (!ambiguous_p)
-    for (t = list; t && t != champ; t = TREE_CHAIN (t))
+    for (tree t = list; t && t != champ; t = TREE_CHAIN (t))
       {
-	fate = more_specialized_partial_spec (tmpl, champ, t);
+	int fate = more_specialized_partial_spec (tmpl, champ, t);
 	if (fate != 1)
 	  {
 	    ambiguous_p = true;
@@ -25889,7 +25882,7 @@ most_specialized_partial_spec (tree target, tsubst_flags_t complain)
       else
 	error ("ambiguous template instantiation for %q#D", target);
       str = ngettext ("candidate is:", "candidates are:", list_length (list));
-      for (t = list; t; t = TREE_CHAIN (t))
+      for (tree t = list; t; t = TREE_CHAIN (t))
         {
 	  tree subst = build_tree_list (TREE_VALUE (t), TREE_PURPOSE (t));
           inform (DECL_SOURCE_LOCATION (TREE_VALUE (t)),
-- 
2.37.2.490.g6c8e4ee870


^ permalink raw reply	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-04-26 19:45 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2022-08-31 21:15 [PATCH] c++: Micro-optimize most_specialized_partial_spec Patrick Palka
2022-08-31 21:15 ` Patrick Palka
2022-09-01 18:40 ` Jason Merrill
2023-04-26 19:45   ` Patrick Palka

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