[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

apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm