re PR tree-optimization/63989 (tree-ssa-strlen.c doesn't handle constant pointer plus and array refs if constant offset is smaller than known constant string length)

	PR tree-optimization/63989
	* params.def (PARAM_MAX_TRACKED_STRLENS): Increment default
	from 1000 to 10000.
	* tree-ssa-strlen.c (get_strinfo): Moved earlier.
	(get_stridx): If we don't have a record for certain SSA_NAME,
	but it is POINTER_PLUS_EXPR of some SSA_NAME we do with
	constant offset, call get_stridx_plus_constant.
	(get_stridx_plus_constant): New function.
	(zero_length_string): Don't use get_stridx here.

	* gcc.dg/strlenopt-27.c: New test.

From-SVN: r219362