[SLP Vectorizer]Generate extract for in-tree uses if the use is scalar operand in vectorized instruction

[Arnold Schwaighofer]

> On Sep 2, 2014, at 1:58 PM, yijiang <yjiang at apple.com> wrote:
> 
> Hi Arnold, 
> 
> Thank you for your comments! Actually this patch will affect the cost estimate. In the loop that we go though all the uses and build ExternalUse list, we will check all in-tree uses in InTreeUserNeedToExtract and add it to the ExternalUse if true. If so, the extra element in the list will add costs when we do cost estimation. 


Ah, okay I missed this.

LGTM.

Thanks!