* config/rs6000/rs6000.md (cmpmemsi): New define_expand.
	* config/rs6000/rs6000.c (expand_block_compare): New function used by
	cmpmemsi pattern to do builtin expansion of memcmp ().
	(compute_current_alignment): Add helper function for
	expand_block_compare used to compute alignment as the compare proceeds.
	(select_block_compare_mode): Used by expand_block_compare to select
	the mode used for reading the next chunk of bytes in the compare.
	(do_load_for_compare): Used by expand_block_compare to emit the load
	insns for the compare.
	(rs6000_emit_dot_insn): Moved this function to avoid a forward
	reference from expand_block_compare ().
	* config/rs6000/rs6000-protos.h (expand_block_compare): Add a
	prototype for this function.
	* config/rs6000/rs6000.opt (mblock-compare-inline-limit): Add a new
	target option for controlling how much code inline expansion of
	memcmp() will be allowed to generate.

From-SVN: r240455