DAGCombiner: StoreMerging: Fix bad index calculating when adjusting mismatching vector types

This fixes a case of bad index calculation when merging mismatching
vector types. This changes the existing code to just use the existing
extract_{subvector|element} and a bitcast (instead of bitcast first and
then newly created extract_xxx) so we don't need to adjust any indices
in the first place.

rdar://44584718

Differential Revision: https://reviews.llvm.org/D52681

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@343493 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed