Request for reviews (S): 7200264: 7192963 changes disabled shift vectors

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7200264/webrev

7192963 changes disabled shift vectors when count is vector. By accident it also 
disable supported shift vectors when count is loop invariant value.

Replaced is_vector_use() call with explicit check for vector shift's count 
(member of some pack).

Also fixed the check in main (first) loop in profitable() method to not check 
for scalar promotion case (inputs are the same) which is already done in 
is_vector_use(). Otherwise cases when input vectors have different size or 
alignment may pass this check  (currently they don't because constructed packs 
have different elements (ideal nodes) - packs are not constructed for the same 
inputs (scalar promotion case)).

Thanks,
Vladimir