[DAGCombiner] Don't create truncate nodes in (aext (zextload x)) -> (zextload x) and similar folds. NFCI
[DAGCombiner] Don't create truncate nodes in (aext (zextload x)) -> (zextload x) and similar folds. NFCI

The truncate is being used to replace other users of of the load, but we checked that the load only has one use so there are no other uses to replace.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@324567 91177308-0d34-0410-b5e6-96231b3b80d8
(cherry picked from commit d758b76106f97b8bdf4e32cb61ea0454659a65b2)

apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm