Summary: Add trimming of unused components of s_buffer_load. For s_buffer_load and unformatted buffer_load also trim unused components at the beginning of vector and update offset accordingly. Subscribers: kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D71785