CODE STRUCTURE: Refine codes in Vectorizer

CODE STRUCTURE: Refine codes in Vectorizer

Hi, Richard and Richi.

I plan to refine the codes that I recently support for RVV auto-vectorization.
This patch is inspired last review comments from Richard:
https://patchwork.sourceware.org/project/gcc/patch/20230712042124.111818-1-juzhe.zhong@rivai.ai/

Richard said he prefer the the code structure as follows:

Please instead switch the if condition so that the structure is:

   if (...)
     vect_record_loop_mask (...)
   else if (...)
     vect_record_loop_len (...)
   else
     can't use partial vectors

This is his last comments.

So, I come back to refine this piece of codes.

Does it look reasonable ?

This next refine patch is change all names of "LEN_MASK" into "MASK_LEN" but should come after this
patch.

gcc/ChangeLog:

	* tree-vect-stmts.cc (check_load_store_for_partial_vectors):
	Refine code structure.