genmatch.c (struct expr): Add force_single_use flag.

genmatch.c (struct expr): Add force_single_use flag.

2015-07-09  Richard Biener  <rguenther@suse.de>

	* genmatch.c (struct expr): Add force_single_use flag.
	(expr::expr): Add copy constructor.
	(capture_info::walk_match): Gather force_single_use captures.
	(expr::gen_transform): Use possibly NULLified sequence.
	(dt_simplify::gen): Apply single-use restrictions by NULLifying
	seq if any constrained expr is not single-use.
	(parser::parse_expr): Refactor to allow multiple flags.  Handle
	's' flag to force an expression have a single-use if the pattern
	simplifies to more than one statement.
	* match.pd: Convert most single_use conditionals to :s flags.

From-SVN: r225610