[gcc r13-1046] c++: optimize specialization of templated member functions

[gcc r13-1046] c++: optimize specialization of templated member functions

[Patrick Palka]

https://gcc.gnu.org/g:f9b5a8e58dfd0642bea932d449ad46da9e57396f

commit r13-1046-gf9b5a8e58dfd0642bea932d449ad46da9e57396f
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Jun 10 16:09:58 2022 -0400

    c++: optimize specialization of templated member functions
    
    This applies one of the lookup_template_class optimizations from the
    previous patch to instantiate_template as well.
    
    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 already non-dependent.

Diff:
---
 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 079cadff37c..1f91fc20f7f 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -21714,8 +21714,14 @@ 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);
     }