* expr.c (expand_expr, case SAVE_EXPR): Set RTX_UNCHANGING_P on
	returned MEM.
	(expand_expr_unaligned, case ARRAY_REF): Check that index is
	a constant before comparing it; use tree_low_cst.
	* tree.c (save_expr): Set TREE_READONLY.
	(substitute_expr): Return inside of NON_LVALUE_EXPR.
	(build, build1): Set TREE_READONLY if all operands are.
	(build_index_type): If upper bound is a negative number, lower
	bound is zero and sizetype is unsigned, use upper bound of one and
	lower of zero.

From-SVN: r36979