[DAG] Aggressively cleanup dangling node in CombineZExtLogicopShiftLoad.
[DAG] Aggressively cleanup dangling node in CombineZExtLogicopShiftLoad.

While dangling nodes will eventually be pruned when they are
considered, leaving them disables combines requiring single-use.

Reviewers: Carrot, spatel, craig.topper, RKSimon, efriedma

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D57520

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@352784 91177308-0d34-0410-b5e6-96231b3b80d8

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