In tsubst_pack_expansion, when we don't have fully instantiated
arguments we try to do a partial instantiation of the pattern if all the
arguments we have are of similar form, for instance if all of them are
pack expansions. In one case with concepts we were failing to do that
and falling back on the PACK_EXPANSION_EXTRA_ARGS mechanism
unnecessarily because we didn't recognize a function parameter pack as
itself a pack expansion, which it properly is because its type is a pack
expansion. This should be an efficiency improvement on the trunk, as well.
Tested x86_64-pc-linux-gnu, applying to trunk.
commit 659af9891dc5046e584e7e0901fd857dc70dddda
Author: Jason Merrill <ja...@redhat.com>
Date: Fri Jul 3 13:49:03 2015 -0400
* pt.c (argument_pack_element_is_expansion_p): A decl pack is an
expansion.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index e819b69..0302de1 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -9838,6 +9838,9 @@ argument_pack_element_is_expansion_p (tree arg_pack, int i)
if (i >= TREE_VEC_LENGTH (vec))
return 0;
tree elt = TREE_VEC_ELT (vec, i);
+ if (DECL_P (elt))
+ /* A decl pack is itself an expansion. */
+ elt = TREE_TYPE (elt);
if (!PACK_EXPANSION_P (elt))
return 0;
if (PACK_EXPANSION_EXTRA_ARGS (elt))
