[InstCombine] More thoroughly canonicalize the position of zexts

We correctly canonicalized (add (sext x), (sext y)) to (sext (add x, y))
where possible.  However, we didn't perform the same canonicalization
for zexts or for muls.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@290733 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed