[x86] try to form broadcast before widening shuffle elements
I noticed that we weren't generating broadcasts as much I thought we would with
D54271, and this is part of the problem.
Widening the shuffle elements means adding bitcasts and hiding the relationship
between a splatted scalar and the vector. If we can form a broadcast, do that
before going through the rest of the shuffle lowering because broadcasts should
be cheap and can often be load-folded.
Differential Revision: https://reviews.llvm.org/D54280
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@346498 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed