This patch adds accurate instructions cost. The formula presents two cases(stride 3 and stride 4) and calculates the cost according to the VF and stride. Reviewers: 1. delena 2. Farhana 3. zvi 4. dorit 5. Ayal Differential Revision: https://reviews.llvm.org/D38762 Change-Id: If4cfbd4ac0e63694e8144cb78c7fa34850647ff7 llvm-svn: 316072