PR/20742
	* Makefile.in (tree-chrec.o): Depend on params.h.
	* params.def (PARAM_SCEV_MAX_EXPR_SIZE): New parameter with
	default value 20.
	* tree-chrec.c: Depend on params.h.  Replace build with buildN,
	and fold build with fold_buildN.
	(chrec_fold_plus_1): Fail with a chrec_don_know when the size of
	the expression exceeds PARAM_SCEV_MAX_EXPR_SIZE.
	(tree_contains_chrecs): Compute an estimation of the size of the
	given expression.
	* tree-chrec.h (tree_contains_chrecs): Modify its declaration.
	(tree_does_not_contain_chrecs): Update the use of tree_contains_chrecs.
	* tree-scalar-evolution.c (simple_iv): Ditto.
	* doc/invoke.texi (scev-max-expr-size): Documented.

From-SVN: r98497