[DAGCombiner] try to move bitcast after extract_subvector
I noticed that we were failing to narrow an x86 ymm math op in a case similar
to the 'madd' test diff. That is because a bitcast is sitting between the math
and the extract subvector and thwarting our pattern matching for narrowing:
t56: v8i32 = add t59, t58
t68: v4i64 = bitcast t56
t73: v2i64 = extract_subvector t68, Constant:i64<2>
t96: v4i32 = bitcast t73
There are a few wins and neutral diffs in the other tests.
Differential Revision: https://reviews.llvm.org/D61806
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@360541
91177308-0d34-0410-b5e6-
96231b3b80d8