[PATCH 2/1] c++: optimize specialization of templated member functions

[Patrick Palka <ppalka@redhat.com>]

This performs one of the optimizations added by the previous
patch to lookup_template_class, to instantiate_template as well.
(For the libstdc++ ranges tests this optimization appears to be
effective around 30% of the time, i.e. 30% of the time context of 'tmpl'
is non-dependent while the context of 'gen_tmpl' is dependent.)

gcc/cp/ChangeLog:

	* pt.cc (instantiate_template): Don't substitute the context
	of the most general template if that of the partially
	instantiated template is non-dependent.
---
 gcc/cp/pt.cc | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index e021c254872..208daad298a 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -21661,8 +21661,14 @@ instantiate_template (tree tmpl, tree orig_args, tsubst_flags_t complain)
     ++processing_template_decl;
   if (DECL_CLASS_SCOPE_P (gen_tmpl))
     {
-      tree ctx = tsubst_aggr_type (DECL_CONTEXT (gen_tmpl), targ_ptr,
-				   complain, gen_tmpl, true);
+      tree ctx;
+      if (!uses_template_parms (DECL_CONTEXT (tmpl)))
+	/* If the context of the partially instantiated template is already
+	   non-dependent, then we might as well use it.  */
+	ctx = DECL_CONTEXT (tmpl);
+      else
+	ctx = tsubst_aggr_type (DECL_CONTEXT (gen_tmpl), targ_ptr,
+				complain, gen_tmpl, true);
       push_nested_class (ctx);
     }
 
-- 
2.36.1.363.g9c897eef06