tree: introduce range adaptor for TREE_VEC

This patch implements a simple tree wrapper, named tree_vec_range, which
lets us idiomatically loop over all the elements of a TREE_VEC using a
C++11 range-based for loop:

  // v is a TREE_VEC
  for (tree e : tree_vec_range (v))
    ...

This is similar to the existing tree-based range adaptors ovl_range and
lkp_range added to the C++ FE in r12-340-g3307b9a07a3c51.

This patch also converts some existing loops over TREE_VEC within the
C++ FE to use tree_vec_range / range-for.

gcc/cp/ChangeLog:

	* constraint.cc (tsubst_parameter_mapping): Convert loop over
	TREE_VEC into a range-based for loop using tree_vec_range.
	* pt.cc (iterative_hash_template_arg): Likewise.
	(template_parms_level_to_args): Likewise.
	(deducible_template_args): Likewise.
	(check_undeduced_parms): Likewise.
	(dependent_type_p_r): Likewise.
	(value_dependent_expression_p) <case NONTYPE_ARGUMENT_PACK>:
	Likewise.
	(dependent_template_arg_p): Likewise.
	* tree.cc (cp_walk_subtrees) <case NONTYPE_ARGUMENT_PACK>:
	Likewise.

gcc/ChangeLog:

	* tree.h (TREE_VEC_BEGIN): Define.
	(TREE_VEC_END): Correct 'length' member access.
	(class tree_vec_range): Define.

1 files changed, 14 insertions, 1 deletions

diff --git a/gcc/tree.h b/gcc/tree.h
index 82eb8ba..5f4b03d 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1107,8 +1107,9 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
 
 /* In a TREE_VEC node.  */
 #define TREE_VEC_LENGTH(NODE) (TREE_VEC_CHECK (NODE)->base.u.length)
+#define TREE_VEC_BEGIN(NODE) (&TREE_VEC_CHECK (NODE)->vec.a[0])
 #define TREE_VEC_END(NODE) \
-  ((void) TREE_VEC_CHECK (NODE), &((NODE)->vec.a[(NODE)->vec.base.u.length]))
+  ((void) TREE_VEC_CHECK (NODE), &((NODE)->vec.a[(NODE)->base.u.length]))
 
 #define TREE_VEC_ELT(NODE,I) TREE_VEC_ELT_CHECK (NODE, I)
 
@@ -4481,6 +4482,18 @@ extern tree make_tree_vec (int CXX_MEM_STAT_INFO);
 
 extern tree grow_tree_vec (tree v, int CXX_MEM_STAT_INFO);
 
+/* Treat a TREE_VEC as a range of trees, e.g.
+   for (tree e : tree_vec_range (v)) { ... }  */
+
+class tree_vec_range
+{
+  tree v;
+public:
+  tree_vec_range(tree v) : v(v) { }
+  tree *begin() { return TREE_VEC_BEGIN (v); }
+  tree *end() { return TREE_VEC_END (v); }
+};
+
 /* Construct various types of nodes.  */
 
 extern tree build_nt (enum tree_code, ...);