Implement N4295 fold-expressions.

	* cp-tree.def: Add UNARY_LEFT_FOLD_EXPR, UNARY_RIGHT_FOLD_EXPR,
	BINARY_LEFT_FOLD_EXPR, BINARY_RIGHT_FOLD_EXPR.
	* cp-objcp-common.c (cp_common_init_ts): Handle them.
	* cp-tree.h (FOLD_EXPR_CHECK, BINARY_FOLD_EXPR_CHECK, FOLD_EXPR_P)
	(FOLD_EXPR_MODIFY_P, FOLD_EXPR_OP, FOLD_EXPR_PACK, FOLD_EXPR_INIT): New.
	* parser.c (cp_parser_skip_to_closing_parenthesis): Split out...
	(cp_parser_skip_to_closing_parenthesis_1): This function.  Change
	or_comma parameter to or_ttype.
	(cp_parser_fold_operator, cp_parser_fold_expr_p)
	(cp_parser_fold_expression): New.
	(cp_parser_primary_expression): Use them.
	* pt.c (expand_empty_fold, fold_expression, tsubst_fold_expr_pack)
	(tsubst_fold_expr_init, expand_left_fold, tsubst_unary_left_fold)
	(tsubst_binary_left_fold, expand_right_fold)
	(tsubst_unary_right_fold, tsubst_binary_right_fold): New.
	(tsubst_copy): Use them.
	(type_dependent_expression_p): Handle fold-expressions.
	* semantics.c (finish_unary_fold_expr)
	(finish_left_unary_fold_expr, finish_right_unary_fold_expr)
	(finish_binary_fold_expr): New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@227883 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 69 insertions, 0 deletions

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 7215dc672b6..f5bb0c1beb4 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -7763,4 +7763,73 @@ capture_decltype (tree decl)
   return type;
 }
 
+/* Build a unary fold expression of EXPR over OP. If IS_RIGHT is true,
+   this is a right unary fold. Otherwise it is a left unary fold. */
+
+static tree
+finish_unary_fold_expr (tree expr, int op, tree_code dir)
+{
+  // Build a pack expansion (assuming expr has pack type).
+  if (!uses_parameter_packs (expr))
+    {
+      error_at (location_of (expr), "operand of fold expression has no "
+		"unexpanded parameter packs");
+      return error_mark_node;
+    }
+  tree pack = make_pack_expansion (expr);
+
+  // Build the fold expression.
+  tree code = build_int_cstu (integer_type_node, abs (op));
+  tree fold = build_min (dir, unknown_type_node, code, pack);
+  FOLD_EXPR_MODIFY_P (fold) = (op < 0);
+  return fold;
+}
+
+tree
+finish_left_unary_fold_expr (tree expr, int op)
+{
+  return finish_unary_fold_expr (expr, op, UNARY_LEFT_FOLD_EXPR);
+}
+
+tree
+finish_right_unary_fold_expr (tree expr, int op)
+{
+  return finish_unary_fold_expr (expr, op, UNARY_RIGHT_FOLD_EXPR);
+}
+
+/* Build a binary fold expression over EXPR1 and EXPR2. The
+   associativity of the fold is determined by EXPR1 and EXPR2 (whichever
+   has an unexpanded parameter pack). */
+
+tree
+finish_binary_fold_expr (tree pack, tree init, int op, tree_code dir)
+{
+  pack = make_pack_expansion (pack);
+  tree code = build_int_cstu (integer_type_node, abs (op));
+  tree fold = build_min (dir, unknown_type_node, code, pack, init);
+  FOLD_EXPR_MODIFY_P (fold) = (op < 0);
+  return fold;
+}
+
+tree
+finish_binary_fold_expr (tree expr1, tree expr2, int op)
+{
+  // Determine which expr has an unexpanded parameter pack and
+  // set the pack and initial term.
+  bool pack1 = uses_parameter_packs (expr1);
+  bool pack2 = uses_parameter_packs (expr2);
+  if (pack1 && !pack2)
+    return finish_binary_fold_expr (expr1, expr2, op, BINARY_RIGHT_FOLD_EXPR);
+  else if (pack2 && !pack1)
+    return finish_binary_fold_expr (expr2, expr1, op, BINARY_LEFT_FOLD_EXPR);
+  else
+    {
+      if (pack1)
+        error ("both arguments in binary fold have unexpanded parameter packs");
+      else
+        error ("no unexpanded parameter packs in binary fold");
+    }
+  return error_mark_node;
+}
+
 #include "gt-cp-semantics.h"